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                 CCl OWeO                                                                047;-3

            HISTORICAL CHANGES AND RELATED COASTAL

                        PROCESSES, GULF AND MAINLAND
                     SHORELINES, MATAGORDA BAY AREA.,

                                                      TEXAS

                                                       property Of CSC Library

                                             J. H. McGowen and J. L. Brewton

                                                     C collecrion

                                                                            DEPARTMENT OF COMMERCE NOA A
                                                                      COASTAL SERVICES CENTER
                                                                      2234 SOUTH HOBSON A VWE
                                                                     CHARLESTON    Sc 29405-2`4

                                           BUREAU OF ECONOMIC GEOLOGY
                                             The University of Texas at Austin
                                                   Austin, Texas 78712
                                                  W. L. Fisher, Director
          (Y                                      IN COOPERATION WITH

                                         THE GENERAL LAND OFFICE OF TEXAS
                                               Bob Armstrong, Commissioner    COASTAL Kilk-
                                                                              INFORMATION CENTER
          Z                                               1975

          @5

                                                             FOREWORD

                         Change, both natural and man induced, is a significant and defining element of the
                   Coastal Zone. Man-induced change, by definition, can be controlled if desired. The work of
                   nature, however, is altered and modified with much more difficulty, if, at all, and attempts
                   to do so commonly lead to unintended results.

                         Prudent use and adequate management of. the Coastal Zone must consider natural
                   changes..These changes.are expressed primarily 'in changes ofnatural boundaries-changes in
                   position of shorelines, changes in position of lines of vegetation, and changes in boundaries
                   of wetlands, among others. These changes assume particular significance when an eroding
                   (and changing) shoreline transgresses coastal structures or when natural boundaries that are
                   also legal boundaries, such as those marking.line of vegetation or boundaries   between fresh
                   and tidal wetlands, change.

                         The best assessment of change is over the long term. In such manner., distinctions can
                  -be made between temporary variations and long-term change. In this report, the technique
                   of historical monitoring has been specifically developed. Through mapping of specific,
                   significant boundaries on vintage photographs and charts, taken at varying periods over the
                   past 125 years, long-term direction, amount, and extent of change are determined. Through
                   comparable historical monitoring or mapping of land use and               land use activities,
                   man-induced changes can be determined and, importantly, distinguished from natural
                   change. A more accurate evaluation of man's impact can be made.

                         In 1971, the Texas General Land Office and the Bureau of Economic Geology, The
                   University of Texas at Austin, initiated on a cooperative basis a comprehensive pilot study
                   of Matagorda Bay and environs. The first phase of that study was an analysis of historical
                   changes and the related coastal processes, herein reported. Techniques of historical
                   monitoring developed in this study have been utilized by the Bureau of Economic Geology
                   to determine long-term changes of the entire Texas Gulf Coast. The second part of the
                   Matagorda pilot study addressed in detail the biologic, physical, and chemical characteristics
                   of sediments in Matagorda Bay.

                         We believe that this project, historical in its orientation, gives us a better ability to
                   make intelligent decisions for the future.

                                                                          Bob Armstrong
                                                                          Commissioner, General Land Office

                                                                          W. L. Fisher-
                                                                          Director, Bureau of Economic Geology

                                                                          CONTENTS

                Abstract                                                      1                  Sand Point area                                 21
                Introduction                                                  2                  Powderhorn Lake                                 21
                Acknowledgments                                               2            Lavaca Bay North Area                                 21
                General Setting                                               3                  West shoreline- Lavaca Bay                      22
                Geologic History of the Matagorda Bay Area                    6                  North shoreline- Lavaca Bay                     22
                      Pleistocene history                                     9                  East shoreline-Lavaca Bay                       22
                      Holocene history                                        9                  Cox Bay                                         22
                      Modern history                                        10             Carancahua Bay Area                                   22
                             Prehistoric development                        10                   North shore-Matagorda Bay                       22
                             Historic development                           10                   Carancahua Bay shoreline                        23
                Historical Shoreline Monitoring: General Methods                                 Keller Bay shoreline                            23
                   and Procedures Used by the Bureau of Economic                                 Salt Lake and Redfish Lake                      23
                   Geology                                                  11             Tres Palacios Bay Area                                23
                      Definition                                            11                   Palacios Point-Oliver Point                     23
                      Sources of data                                       11                   Oliver Point-Tres Palacios Creek                23
                      Procedure                                             11                   Tres Palacios Creek-Turtle Point                24
                      Factors affecting accuracy of data                    11                   Turtle Point-Turtle Creek                       24
                             Original data                                  12                   Turtle Creek-Sartwelle Lakes                    24
                                   Topographic surveys                      12                   Oyster Lake                                     24
                                   Aerial photographs                       12             Summary                                               24
                             Interpretation of photographs                  12       Marsh Distribution, 1856-1957                               25
                             Cartographic procedure                         13             General wetland trends                                25
                                   Topographic charts                       13             Marsh changes re  sulting from natural processes      25
                                   Aerial photographs                       13             Marsh changes resulting from man's activities         26
                             Measurements. and calculated rates             13       Coastal Processes and Short-Term Shoreline Changes          26
                      Justification of methods and limitations              14             Coastal processes                                     26
                Vintage Cartographic /Photographic Materials Used in                       Short-term shoreline changes, 1957-1972               26
                   the Matagorda Bay Area Study                             15                   Open Gulf shorelines                            27
                Presentation of Data in Map Form                            15                   Bay shorelines                                  33
                Effect of Astronomical Tide on Mapping Waterlines                                       Cliffed shorelines                       33
                   on Vintage Aerial Photographs                            15                          Shorelines characterized by shell
                Gulf and Mainland Shoreline Changes, 1856-1957              16                             beaches and berms                     35
                      Brown Cedar Cut Area                                  16                          River-influenced shorelines              40
                             Gulf shoreline                                 16                          Shoreline segments dominated by
                             Bay shoreline of Matagorda Peninsula           16                             salt marsh                            42
                             Mainland shoreline                             18                          Shorelines dominated by spoil
                      Colorado River Area                                   18                             outwash                               43
                             Gulf shoreline                                 19       Stability of Shorelines                                     44
                             Bay shoreline of Matagorda Peninsula           19             Sediment availability                                 44
                             Mainland shoreline                             19             Subsidence                                            45
                             Deltaic shoreline                              19             Shoreline orientation                                 45
                      Shell Island Reef Area                                19             Direction of sediment transport                       45
                             Gulf shoreline                                 19       Distinction Between Natural and Man-Induced Shore-
                             Bay shoreline of Matagorda Peninsula           19          line Changes                                             46
                             Mainland shoreline                             19             Natural shoreline changes                             46
                             Oyster Lake                                    20             Man-induced shoreline changes                         46
                      Pass Cavallo Area                                     20       Conclusions                                                 53
                             Gulf shoreline                                 20             Shoreline Change                                      53
                             Bay shoreline-Matagorda Peninsula and                         Marsh Area Change                                     54
                                Matagorda Island                            20             Future Studies                                        55
                             Mainland shoreline                             20       References                                                  56
                             Marsh islands                                  21       Appendix A: Changes in Shoreline for the Period
                      Lavaca Bay South Area                                 21          1856-1957                                                58
                             West Matagorda Bay                             21       Appendix B:    Changes in Marsh Area for the Period
                             West Lavaca Bay                                21          1856-1957                                                59
                             Cox Bay                                        21       Appendix C:    Profiles of Gulf and Mainland Beaches        61

                        iv

                                                                                 ILLUSTRATIONS

                       Figures--

                          1.  Locality map of the Matagorda Bay area                      4       16.   Locations of trenches dug into shell beaches,
                          2.  Geologic map, Matagorda Bay area                            5             berms, and spits                                         37
                          3.  Slope of the lower 20 miles of coastal plain                6       17.   Distribution of shell beaches, berms, and spits
                          4.  Temperature and rainfall distribution for        Bay                      in the Magnolia Beach-Indianola area,                    38
                              City, Port Lavaca, Palacios, and Port O'Connor              7       18.   Wave refraction at Arena Cove, California                40
                          5.  Location of weather stations in the Matagorda                       19.   Map of the growth of the Colorado delta during
                              Bay area                                                    7             the period 1908-1941                                     41
                          6.  Percentage frequency of surface wind direction
                                                                                                  20.   Area increase of the Colorado delta, in acres,
                              (annual)                                                    7
                          7.  Sea-level changes related.to glacial and inter-                           for the period 100.8-1953                                42
                              glacial stages                                              8       21.   Net annual longshore drift                               45
                          8.  Slopes of Gulf and mainland beaches                       17        22.   Locations of jetties in the   Port O'Connor area,
                          9.  Index of shoreline change and marsh distribu-                             and changes in the shoreline and nearshore sand
                              tion maps                                                 18              distribution during the interval 1934-1956               48
                         10.  Shoreline types of the Matagorda Bay area                 28        23.   Distribution of bay-margin sand north of the
                         11.  Short-term erosional and accretionary shore-                              jetties at Port O'Connor                                 49
                              lines of the Matagorda Bay area                           29        24.   Accretion and erosion associated with Mata-
                         12.  Effects of Hurricane Carla, 1961., on a segment                           gorda .Ship Channel jetties                              49
                              of Matagorda Peninsula beginning about 1.5                          25.   Shoreface profiles in the area of the north jetty,
                              miles west of theColorado River                           31              Matagorda Ship Channel                                   50
                         13., Relationship between direction of wave                              26.   Shoreface profiles in the area of the south jetty,
                              approach and longshore drift                              32              Matagorda Ship Channel                                   51
                         14., Postulated sequence of events leading. to the                       27.   Dredging of Dog Island Reef for oyster shell             52
                              development of an 'erosional unconformity on
                              Matagorda Island                                          34
                         15.  Cuspate shell beaches, oyster reefs,. and, spoil                    Plate-
                              outwash along the north shore of Matagorda
                              Bay, w est of the Colorado delta                          36          1.  Gulf and mainland beach profiles.                In pocket

                                                                                          MAPS

                          1.  Matagorda Bay System: Gulf and mainland shorelines                    2.  Matagorda Bay System: marsh distribution

                              Brown Cedar Cut Area                             In pocket                Brown Cedar Cut Area                             In pocket
                              Colorado River Area                              In pocket                Colorado. River Area                             In pocket
                              Shell Island Reef Area                           In pocket                Shell Island Reef Area                           In pocket
                              Pass cavallo Area                                In pocket                Pass Cavallo Area                                In pocket
                              Lavaca Bay South Area                            In pocket                Lavaca Bay South Area                            In pocket
                              Lavaca Bay North Area                            In pocket                Lavaca Bay North Area                            In pocket
                              C Iarancabua Bay Area                            In pocket                Carancahua Bay Area                              In pocket
                              Tres Palacios Bay Area                           In pocket                Tres Palacios Bay Area                           In pocket

                                                                                        TABLES

                        Tables--

                          1.  Pleistocene glacial and interglaciaI episodes               6         3. Comparison of changes along bay-shore shell
                          2.  Comparison of erosional, rates of.cliffed shore-                          beaches; filed field measurements (1957-1972)
                              lines determined from field measurements                                  and historical monitoring (1856-1957)                    39
                              (1957-1.972) and from historical monitoring                           4.  Erosional and accretionary rates (1957-1972)
                              (1856-1957)                                               33              and physiographic units associated with marshes          43

                                 HISTORICAL CHANGES AND RELATED COASTAL PROCESSES,
                                                GULF AND MAINLAND SHORELINES,
                                                  MATAGORDA BAY AREA, TEXAS

                                                   J. H. McGowen and J. L. Brewton'

                                                               ABSTRACT

                  Most of the Gulf and bay shorelines of the                  Shoreline stability (accretion, equilibrium, or
              Aatagorda Bay area are in an erosional state.              erosion) is a function of the interplay among
              Historical shoreline monitoring, during the interval       several geological processes such as wind, waves,.
              1856-1957, and field measurements, made in                 tides, the kinds and volumes of sediment con-
              1971-1972, document direction and rate of shore-           tributed to bays and the Gulf of Mexico, storm
              line change for a 116-year interval. Average               frequency, and compactional subsidence, and
              erosional rates of 16 and 22 feet per year occur at        slump which is restricted to the cliffed shoreline
              Brown Cedar Cut and along the northeastern part            segments. Erosion dominates the coastal scene
              of Matagorda Island, respectively. Erosional rates
              along bay shorelines range from less than 1, foot          primarily because of a deficit of sand supplied to
              per year to 15 feet per year.                              the area. In general, the shores of large bays are
                                                                         eroded more rapidly than those of small bays; the
                  All shoreline segments are not erosional. Parts        fetch of large bays is great and waves tend to be
              of central and western Matagorda Peninsula were            large. Also, bay shores that face into the prevailing
              either in equilibrium or in an accretionary phase          wind erode rapidly. Shoreline erosion is relatively
              during 1856-1957, as was Matagorda Island near             slow along high cliffed shorelines that lie in the lee
              the western limit of the area of investigation. Field      of prevailing southeast winds. Northers are gen-
              measurements made in 1971-1972 indicated that              erally accompanied by high-velocity, short-
              most of the Matagorda Peninsula shoreline was              duration winds. These winds generate rather large
              erosional. Several bay shoreline segments exhibited        waves, which erode north-facing shorelines.
              net land gain for the 116-year interval. Such areas
              as bayhead deltas, spits which developed down-                  Exceptionally high tides and large waves are
              current from erosional headlands, and bay shores
              that are adjacent to spoil-disposal sites are cur-         produced by hurricanes. Storm surge (storm tides)
              rently accreting.                                          and large waves severely erode coastal barriers and
                                                                         peninsulas. Hurricane Carla J1961) eroded the
                  Marshes generally decreased in area during the         shoreline of Matagorda Peninsula as much as 800
              period 1856-1957. Known causes of marsh decline            feet in a few hours. Low-relief barrier islands and
              are shoreline erosion which occurs under normal            peninsulas, such as Matagorda Peninsula, are easily
              sea and storm conditions, inundation by sediments          breached by storm surge, and large volumes of
              related to storm washovers, and burial of wetlands         sediment eroded from the shoreface and beach are
              beneath dredge spoil. A few marshes have increased
              in size; the most notable expansion is the marsh           transported into the bays. This volume of sediment
              associated with the Colorado delta. Most of the            is effectively removed from the sediment transport
              Colorado delta, which is some 7,000 acres in area,         system operating in the nearshore zone of the Gulf
              was constructed between 1929 and 1936.                     of Mexico and is stored in the Matagorda Bay
                                                                         system. Erosion of the shoreline of the Modern
              Continental Oil Company, Ponca City, Oklahoma.             Matagorda Peninsula by storms is irreparable.

                                                                    INTRODUCTION

                          The Texas Gulf Coast consists of erosional             expand with larger oil imports and a shift from
                    deltaic headlands and of peninsulas and barrier              fossil fuel to nuclear-powered generating plants.
                    islands, which separate bays and lagoons from the
                    Gulf of Mexico. There are about 367 miles of Gulf                 The objectives of this study were: (1) to
                    shoreline and about 1,425 miles of lagoon, bay,              document the direction and magnitude of shoreline
                    and estuary shoreline in Texas. Climate of the               change; (2) to present some possible causes of
                    Texas Coastal Zone is mild with average annual               change; and (3) to make this information available
                    temperature ranging from 69'F in the east to 74'F            to those who might be interested in shoreline
                    in the south. A mild climate, coupled with access            stability as it will affect man-made structures.
                    to relatively wide sand beaches, fishing, and other          Man's activities in the Coastal Zone have grown
                    water-related sports, makes the Texas7 Coast a               without an adequate knowledge of shoreline
                    prime tourist attraction. Natural resources within           stability. About 60 percent of the Texas Gulf
                    the coastal plain and the relative ease of trans-            shoreline is now erosional, with rates up to 80 feet
                    porting raw materials and finished products via              per year locally. Principal causes of erosion are
                    intracoastal waterways have attracted industry to            natural, but certain of man's activities may have
                    the region.                                                  increased erosional rates. Natural causes of shore-
                                                                                 line retreat, such as sand deficiency and relative
                          In recent years the Texas Coastal Zone has             rise in sea level, pose problems that cannot be
                    experienced a rather dramatic change. Approxi-               readily solved. It is imperative, therefore, that rates
                    mately one-fourth of the State's population now              and directions of shoreline change be measured and
                    resides in the region, and population is steadily            that man's Coastal Zone activities proceed in
                    increasing. Consequently, shoreline property is in           concert with this natural change.
                    exceeding demand for construction of permanent
                    homes, second homes, condominiums, hotels and                     The Matagorda Bay area was chosen for study
                    motels, and for recreational use. Similarly,, indus-         because it is one of the segments of the Texas
                    trial development is also expanding significantly.           Coast that has been least affected by man's
                                                                                 activities. A two-phase study of the Matagorda Bay
                          Added to an increasing population and indus-           area was undertaken to determine shoreline
                    trial expansion within the region are a decrease in          stability of Gulf and bay shorelines and changes in
                    supply of domestic oil and gas and a greater                 marsh area for the period 1856 through 1972, and
                    reliance on foreign oil imports to fulfill energy            to map the distribution of sediment types, total
                    requirements. Deepwater ports or offshore mono-              organic carbon, trace elements, and molluscs. This
                    buoy systems will be required to handle super-               report presents the results of the first phase of the
                    tankers. Increased use of nuclear power for                  Matagorda Bay investigation by the Bureau of
                    meeting energy needs will require a number of sites          Economic Geology and the General Land Office,
                    in the Coastal Zone. Construction in the region will         undertaken between October 1971 and May 1972.

                                                                 ACKNOWLEDGMENTS

                          Many individuals and organizations con-                     L. E. Garner, Bureau of Economic Geology,
                    tributed to this project. The project was funded in          B. H. Wilkinson, C. V. Proctor, Jr., and A. W.
                    part by the General Land Office of Texas. Funds              Erxleben, former employees of the Bureau of
                    to help defray some of the costs of printing the             Economic Geology, and Scooter Cheatham and
                    shoreline maps were contributed by the Sea Grant             Lee McKibben, General Land Office, assisted with
                    Program, Texas A&M University, through a grant               the field work. R. W. Nordquist participated in'the
                    from the National Oceanic and Atmospheric                    field work and mapping shorelines on sequential
                    Administration, U. S. Department of Commerce.                aerial photographs. Virgil Townley, Harry Smith,,
                    Boats were provided by E. Gus Fruh, Department
                    of Civil Engineering, The University of Texas at             W. F. Green, and Bruce Kay granted access to their
                    Austin, and by the Marine Science Institute of The           properties and/or provided information concerning
                    University of Texas at Port Aransas.                         history of local areas.

                                                                                                                                    3

                   Special thanks are extended to the following             of molluscan shell and wood collected on Mata-
             people for enlightening discussions concerningthe              gorda Peninsula and from Cedar Lake and Cow
             problems. associated with shoreline stability: B. H.           Trap Lakes.
             Wilkinson, University of Michigan; L. F. Brown,
             Jr., W. L. Fisher, L. E. Garner, and R. A. Morton,                  The manuscript was reviewed by W. L. Fisher,
             Bureau of Economic Geology; K. 0. Emery, Woods                 L. F. Brown, Jr., E. G. Wermund, and J. R. Byrne,
             Hole Oceanographic Institution; J. R. Byrne and                Bureau of Economic Geology, and W. D. (Red)
             Walter Leeper, Department of Geological Sciences,              Oliver, Peggy Harwood,'and Rose Ann Rowlet,
             The University of Texas at Austin; Peggy Harwood,              General Land Office. Cartographic preparation was
             the General Land Office; and Wayne Ahr and Barry               by D.F. Scranton under the supervision of J. W.
             Sullivan, Texas A&M University.                                Macon, who also supervised drafting of the illustra-
                                                                            tions. Elizabeth T. Moore edited and typed the
                   Sam Valastro, Research          Scientist, Radio-        manuscripts;  final editing was by Kelley Kennedy.
             carbon Laboratory, The University of Texas at                  The paper was composed by Fannie Mae
             Austin, provided, radiocarbon age determinations               Sellingsloh.

                                                             GENERAL SETTING

                   The Matagorda Bay study area consists of                 relatively. flat. Maximum elevation is about 50 feet
             deltaic headlands, peninsulas and barrier islands,             in the northwest comer of the, area. The. slope of
             large bays and estuaries, and gently seaward-sloping           the upland surface is shown on figure 3. Areas of
             uplands that form the mainland shoreline.                      lowest slope are near, Caney 'Creek and Port
             Matagorda Bay system and environs        .are situated in      O'Connor. Small drainage systems are, in part,
             parts of Matagorda, Calhoun, Victoria, and Jackson             affected by the degree and direction of the slope of
             Counties (fig. 1). Size of the area is approximately           the land surface.
             2,000 square miles, consisting of: (1) 1,470 square
             miles of uplands; (2) 455 square miles of bays and                  Several rivers and creeks discharge water and
             estuaries; and (3) 75 square miles of.peninsulas,              sediment into the Matagorda Bay system. The
             barrier islands, and tidal deltas.                             larger streams, such as the Colorado and.Lavaca
                                                                            Rivers and Garcitas Creek have constructed bay-
                   Gulf beaches in the area     are about 65 miles          head deltas along   Ithe bay margins. The largest of
             long. They range in composition and texture from               these deltas, the Colorado, has prograded. Com-
             terrigenous fine. sand to shell and rock fragment              pletely across Matagorda Bay.
             gravel. The bay shoreline, consisting of wetlands,
             deltas, sand and shell beaches, and, almost vertical                Climate of the Matagorda Bay area is humid
             Cliffs, is approximately 235 miles.long.                       subtropical (U. S. Dep      .artment of - Commerce,
                   Three general physiographic elements charac-             1958-1969). Rainfall and te'niperature.data (fig. 4)
             terize the study area., These are: (1) Matagorda               are almost identical for, four weather stations in the
             Peninsula and Matagorda Island; (2) the Pleistocene            vicinity of Matagorda Bay (fig. 5). Rainfall distri-
             uplands; and (3) rivers and small streams that                 bution graphs show two peaks, one, in June and the
             dissect the uplands. Matagorda Peninsula ranges in             other in September, which coincide with thunder-
             width from 0.75 to 1.0 mile, and has an average                storm and hurricane occurrences, respectively.
             elevation of about 7 feet. Dunes are rare on the
                                                                                 Wind data from the Victoria Weather Station
             peninsula, but. some isolated dunes attain heights
             of - 25 feet. Only the eastern 7.5 miles of Matagorda          records indicate that surface winds are chiefly
             Island occurs in the study area. The islan   Id ranges in      onshore (fig. 6). Prevailing winds for the period
             width from 1.25. to 1.5 miles. Foremisland dunes up            1951-1960 were from the south-southeast, whereas
                                                                            strongest winds during the same period were from
             to 30   feet high (Wilkinson, 1973) are well devel-            the northwest.
             oped on Matagorda Island.

                   Pleistocene uplands, which are underlain by                   Hurricanes and tropical storms are naturally
             fluvial-deltaic and strandplain deposits (fig. 2), are         occurring phenomena of the Atlantic, Caribbe          an,

                     4

                                                     NAVIO

                      GARCI rAS
                        DEL TA                      A VA CA
                                                   DELrA

                                                SWAN
                                               LAKE

                         PORT                                                                                    BAY CITY
                         LAVACA           POINT
                                         COMFORT

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                                                          POINT
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                              LAKE                        PALACIOS          LAKE
                                   PORT                     POINT                                  MATAGORDA
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                     E-SPIRITU SANro BAY                                                          EAsr AfATAGORDA
                                                             D MATAGORDA                                            BAY                 SARGENT
                                               :__::@GRE_'EENS BAYOU                                                                     EACH
                     7MA @TA G 0 @RD A I @S                                                                           BROWN CEOA R
                                                                                                                          CUT
                                                                                                     GULF OF MEXICO

                                                                    0     4             1.2
                                                                            MILES

                                                           Figure 1. Locality map of the Matagorda Bay area.

                     and Gulf Coast areas. Hurricanes are storms of                  each tidal day). Tidal range is low. The mean
                     tropical origin with cyclonic circulation of 74 mph             diurnal range at Freeport Harbor is 1.7 feet and 1.4
                     or higher (Dunn and Miller, 1960). During the                   feet at Pass Cavallo (U. S. Department of Com-
                     period 1900-1963, the Texas Coast was struck by                 merce, 1973). Tidal currents are an important
                     42 tropical cyclones, a frequency of one storm                  sand-transporting mechanism in tidal pass areas;
                     every 1.5 years (Hayes, 1965, 1967). Hurricanes                 elsewhere waves and longshore currents are the
                     occur most commonly during the months August                    principal sediment-transporting mechanisms.
                     and September. The effects of hurricanes on the
                     Coastal Zone are: (1) shoreline erosion; (2) breach-                 The Texas Coast is a wave-dominated coast
                     ing of barrier islands and peninsulas; (3) salt-water
                     flooding by storm surge; (4) damage to man-made                 (Hayes, 1965). Since prevailing wind in the
                     structures by flooding and wind; and (5) flooding               Matagorda Bay area is from the southeast quad-
                     resulting from aftermath rains.                                 rant, most waves approach the shoreline from that
                                                                                     direction, strike the shoreline at an angle, and set
                          Tides in the northern Gulf of Mexico are                   up longshore currents that move sediment to the
                     chiefly diurnal (one high and one low water level               southwest.

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                                                                                                                                                                                                                                                                                     ov..,
                                                                                                                                                                                                         MODERN-HOLOCENE DEPOSITS
                                                                                                                                                                                                                                                                         BARRIER ISLAND PENINSULA
                                                                                                                                                                                        11.VIAL-DEITAI.
                                                                                                                                                                                                                                                                                     B-h:
                                                     0         2       4       6                                                                                                                                                                                                        P.I. .. W..-d. 1,
                                                                                                                                                                                                                     --I.m by bb-       Ild Ild -1-1,

                                                                 SCALE IN       MILES                                                                                                                                                                                                Sh.11 -i,             bl

                                                                                                                                                                                                                                                                                     -d lid.1 ft..; I. with

                                                                                                                                                                                                   MW-               -11- by W- b., - -d! -,bl@k ,tbdi                               S@It -,tt. .d..d @ddy

                                                                                                                                                                                                  MI 11 d1IIl        111"dll         I'd - ,It 1"d 1,111,11
                                                                                                                                                                                                  _d

                                                                                                                                                                                                  Mbd@         pl,!,, d,,i ... ld! by  I-        -11h; IW,

                                                                                                                                           GEOLOGIC MAP, MATAGORDA BAY AREA

                                                                                                                                                       Figure 2. Geologic map, Matagorda Bay area.

                                                 GEOLOGIC HISTORY OF THE MATAGORDA BAY AREA

                            Pleistocene, Holocene, and Modem deposits                    tinental glaciers. Glaciation began to affect the
                      constitute the uplands, bay margins, and Gulf                      North American continent approximately three
                      shoreline features (fig. 2). Water bodies, including               million years B.P. (Cooke, 1973, table 3, p. 215).
                      bays, estuaries, and their associated fluvial systems,             The sequence of Pleistocene glacial events is shown
                      are Holocene and Modem features. Uplands are                       in table I and figure 7.
                      underlain by deltaic sediments which were
                      deposited during the Sangamon Interglacial Stage                         Table 1. Pleistocene glacial and interglacial episodes
                      and a strandplain sand that accumulated during a                   (after Kummel, 1961).
                      Wisconsin Interstadial Stage. Shorelines of the
                      Matagorda Bay area began developing their present
                      configuration at sea-level stillstand, about 3,000 to              Glacial                                      Interglacial
                      2,500 years B.P. (before present). The term still-                 (Low Sea-Level Stand)                 (High Sea-Level Stand)
                      stand implies a halt in the rise of sea level. The
                      dates given for stillstand are those reported by                                                                        Holocene
                      Curray (1960), Nelson and Bray (1970), and                         Wisconsinan
                      Frazier (1974).                                                    Illinoian                                           Sangamon
                           Depositional and erosional features of the                    Kansan                                              Yarmouth
                      Texas Gulf Coast were created, indirectly, by                                                                            Aftonian
                      alternate growth and reduction in size of con-                     Nebraskan

                                                                 4e 11
                                          @7,

                      3.6' per mile       Della
                                                      Lavaca
                                                       06/to                                                     0        5        10 rnde@
                                                                       0                                                Scale
                                                          4.4' per mile

                                      Lavaca 8ay
                                                                                    2. 8' per mile

                               Pori
                              L-c a                                                             A

                                                                                                2.0' per mile
                          1.7' per mile
                                                                              Pdoci.@*                                              .1.8'per mile

                                                                                                            Colorado
                                                                                                             Dell,
                                                                                                       ...........
                                                    Molag-do Bay                                                            Lake
                                                                                                                           A'SI'n

                                          Pori
                                        O'Connor

                                                                                                              EaV N010�701dl Bly
                       E5.0"d, SaNo 80y"=ZZ,

                                                             Gulf of mexlco

                           Figure 3. Slope of the lower 20 miles of coastal plain. Slope gradient and direction are shown for six areas along the
                      Sangamon delta plain and Wisconsin strandplain. Slope directions converge. along the axis of Lavaca Bay.

                                                                                                                                                                                               7

                         100-

                         90-

                         80-                                                                                      5-
                     0-  70-
                                                                                                                  4-
                     @i  60-
                     E
                         50
                                                                                                              &
                         40-
                                                                                                                  2
                         30

                               Jan.  Feb.  Mar.  Apr.  May 'June  July   Aug.' Sept. Oct.  Nov. I Dec.                                    4pr. 1 May 1 June 1 July Aug.' Sept. Oct. Nov.  Dec.
                                              say City                      19 year average                                           Bay City - 19 year average
                                          Port Lavaca                       22 year average                                       Port Lavaca   - - - - - - - - -    22 year average
                                             Polocios   ............................ 2 1 year average                                Palocios   .......................... 28 year average
                                        Port dConnor    - - - - - -    - 22yearaverage                                          Port dConnor    - - - - - -     - 2 2 year average

                            Figure 4. Temperature and rainfall distribution. for Bay City, Port Lavaca, Palacios, and Port O'Connor. (A) Mean
                     monthly temperature. (B) Mean monthly precipitation. Data from U. S. Dept. Commerce, Climatological summary, Bay City,
                     1943-1961, andfrom Env. Sci. Serv. Adm., U. S. Dept. Commerce, Palacios 1941-1968, Port Lavaca 1947-1968, and Port
                     O'Connor, 1948-1969.

                                                                         Ba*YCity

                     Port                                  P locios                                                                          Wind co           nditions calm
                         vaca                                                                                                                6% of the time

                                                                            N
                             Port O'Connor 0                  %GO                                                                                                                   N
                                                     Of
                                                                                                                                0-%                               20%

                         Figure 5. Location of weather stations in the Matagorda                                     Figure 6. Percentage frequency of surface wind direction
               Bay area.                                                                                     (annual). Data from Victoria weather station (U. 9. Depart-
                                                                                                             ment of Commerce, Local Climatological Data, Victoria,
                                                                                                             Texas, 1958-1969).

                                                                                                THOUSANDS OF YEARS BEFORE            PRESENT
                                                                  0               200                400               600              Boo                    1000         1200

                                                                                             wP
                                                                                             _j                                   P
                                                                  SEE FIG. 5B  DEPOSITION                 DEPOSITION                        DEPOSITION         VALLEY CUTTING

                                                                                                      @WA LEVEL

                                                                                                            OUITH                      AFTONIAN
                                                                            SANGAM                   IN E   LACIAL                    INTERGLACIAL
                                                                               INTER-                         E                          STAGE
                                                                              GLACIAL
                                                                               STAGE                                       KANSAN                     NEBRASKAN
                                                                  WISCONSIN            ILUNOIAN                        GLACIATION                     GLACIATION
                                                                  GLACIATION           GLACIATION                                After Fisk (1944) and Berna

                                                                                                                      A

                                                                                                THOUSANDS OF YEARS BEFORE PRESENT
                                                                  0                          50                            too                           156

                                                                                             VALLEY
                                                                  SEE FIG. 5C DEMSITIONI CUTTING            DEPOSITION                VALLEY CUTTING              DEPOSITION

                                                                  t                    LATE                                EARLY
                                                                                  WISCONSIN                            WISCONSIN
                                                                                 GLACIATION                           GLACIATION                 SEA LEVEL'
                                                                                                        PEORIAN                                       SANGAMON
                                                                  MODERN-                            INTERGLACIAL                                   INTERGLACIAL
                                                                  HOLOCENE                              STAGE                                            STAGE

                                                                                                                                 After Fisk (1944) and Bernard & LeBlanc (19652

                                                                                                                      B

                                                                                                         YEARS BEFORE PRESENT (B.P)
                                                                  TODAY                5,000                  10,000                  15,000                   20,000 ......

                                                                                                                                                               LATE
                                                      w
                                                      w     50       MODERN                                                HOLOCENE                      PLEISTOCENE
                                                                                                                                                               (WISCONSIN
                                                      _j                                                                                                       GLACIATION)
                                                      w
                                                      U,   too-

                                                      w
                                                      Z                                W                                                                 N     EXTENDS TO
                                                      <                                w                                                                 0
                                                      uJ   150                         0                                                                 0 APPROXIMATELY
                                                                                       0                                                                 0     1.2 MILUON
                                                                                                                                                         CL
                                                                                                                                                         T     YEARS B.P.
                                                      Z
                                                      w
                                                      U)
                                                      w
                                                      cr
                                                      Q_   200

                                                                                Proposed Sea Levels:
                                                                                _       Frazier-in press
                                                           250                  -       Curray-1960
                                                      w                                 Nelson 8 Bray-1970

                                                                                                                       C

                                                                               Figure 7. Sea-level changes related to glacial and inter-
                                                                      glacial stages.. (A) Generalized Pleistocene sea-level variations
                                                                      and associated erosional and depositional episodes. (B)
                                                                                                                      1@@ @@N                     <A  LEVEL
                                                                                                     @TE@                                           IN   NGAMO IN
                                                                                                                           @A
                                                                                                        PEORIAN                                       rERG A AL
                                                                  or     N                           IN RGLACIAL                                               LC
                                                                    LZ@E                                STAGE                                            STAGE

                                                                                                                                                  and '..'     a
                                                                                                                                    er @1,60941)@d@.. @0961)

                                                                      Generalized sea-level changes during Late Wisconsin glaciation.
                                                                      (C) Proposed sea-level changes during the last 20,000 years
                                                                      (after Fisher and others, 1973).

                                                                                                                                  9

                               Pleistocene History                         characterized by several advances and retreats of
                                                                           the continental ice sheet and fluctuations in sea
                   Alternate deposition and erosion occurred.,             level. During one of the advances and associated
             along the coastal plain in. response to waxing and            lowering of sea level, a soil was developed on the
             waning of continental glaciers (fig. 7). With the             Sangamon delta plain. The following         Irise in sea
             growth of glaciers, there was a lowering of sea               level flooded part of the area covered by this soil.
             level, and streams were entrenched across the                 During subsequent stillstand, sand delivered to the
             coastal plain and continental shelf. Melting glaciers         Gulf of Mexico by several local streams con-
             returned water to the sea creating.a rise in sea level        structed a. strandplain in the area of Port O'Connor
             and renewed sedimentation in the area of the                  (McGowen and others, 1972; Wilkinson, 1974;
             present outer coastal plain (outer coastal plain is           Wilkinson and others, in press). Where observed in
             the general area extending inland from the      Gulf of       outcrop and by subsurface methods, the strand-
             -Mexico a distance of 50 miles). The sediments                plain sand rests on the soil horizon.
             ,exposed within the outer coastal plain were
             deposited during one Pleistocene interglacial stage                During the late Wisconsin, sea level was
             and one interstadial stage, probably during the               lowered approximately 390 feet (Curray, 1960) to
             Sangamon Interglacial Stage and a Wisconsin Inter-            450 feet (LeBlanc and Hodgson, 1959). According
             stadial Stage.                                                to Curray, shoreline position at that time was at or
                                                                           near the edge of the continental shelf. Streams
                   During the Sangamon high stand of sea level,            entrenched their courses across the coastal plain
             most of the outer coastal plain, extending from the           and continental shelf in response to a changing
             bay shore inland, was constructed by sediment                 base level.
             delivered to the area by the ancestral Brazos-                                  Holocene History
             Colorado and   'San Antonio-Guadalupe Rivers. The
             coastal plain was built seaward into the Gulf of                   Sea level began to rise approximately 18,000
             Mexico by prograding. deltas. The Pleistocene delta           years B.P. (fig. 7). This rise marks the beginning of
             lyingto the east.of the Modem Lavaca River.was
                                                                           the Holocene Epoch. Several temporary stillstands
             constructed by the ancestral . Brazos-Colorado                during Holocene sea-level rise produced barrier
             Rivers, and the delta to the west -is the Pleistocene
                                                                           islands and lagoons on the continental shelf similar
             San Antonio-Guadalupe delta. The. slope of the
                                                                           to Modem barriers and lagoons of the Texas Coast
             coastal plain surface (fig. 3) reflects the overlap of        (Frazier, 1974). The sea reworked these deposits as
             these two major deltaic systems.
                                                                           it resumed. its landward migration with rising sea
                   Sangamon deposits consist of fluvial and                level. River valleys were filled with sediment during
                                                                           this Holocene transgression across the continental
             distributary gravel and sand, interdistributary and           shelf.
             overbank mud, and bay-estuarine mud and shell. In
             some outcrops along the shores of the Matagorda                    Erosion associated with Wisconsin low stand
             Bay system, red to brown bay mud containing                   of sea level produced numerous valleys in the
             oyster reefs is overlain by thin progradational               Matagorda 'Bay area. The largest of these valleys
             deltaic sequences. Deltaic muds and sands are                 was scoured by the Lavaca-Navidad fluvial system.
             chiefly red or brown. Commonly, both mud and                  Smaller systems, such as Tres Palacio's and
             sand have been extensively calichified. Distributary          Carancahua Creeks, were probably tributary to the
             channel filt is coarse-grained silt and very fine-            Lavaca-Navidad Rivers. Data from subbottom
             grained sand. Channel-fill fluvial sand and gravel            profiling and coring indicate that the depth     .of the
             were recognized in only one bay-shore outcrop. It             Lavaca-Navidad valley ranged from about 100 feet
             consists of a lower granule to small pebble gravel            near the head of the Modem Lavaca Bay to at least
             unit (containing abundant vertebrate remains)                 125 feet in the vicinity of Port O'Connor. Water
             which grades upward into fine-grained sand. Sedi-@            from the Gulf of Mexico first invaded the Lavaca-
             mentary structures are well preserved in the fluvial          Navidad estuary 11,000 to 10,500 years B.P. These
             deposit, but structures have been obliterated in              dates were derived from Frazier's (1974) sea-level
             adjacent Pleistocene units.by     caliche replacement.        data.

                   The Wisconsin     Glacial   Stage which began                A relict shorelne at 45 to 60 feet below sea
             about 130,000 years B.P.         (Cooke, 1973) was            level was reported by Frazier (1974) to have

                     10

                     developed between 10,000 and 7,500 years B.P.                  Rivers was put into the longshore drift system; at
                     During this time interval, water from the Gulf of              this time Matagorda Peninsula began to develop.
                     Me xico probably exerted an influence on the                   The Brazos and Colorado bayhead deltas were
                     Lavaca-Navidad estuary as far north as the present             characterized by distributary sands and inter-
                     head of Lavaca Bay.                                            distributary muds, but deltas constructed by these
                                                                                    same rivers in the open Gulf of Mexico were similar
                          Transgression was resumed at          about 7,500         to the present Brazos delta; they were high-
                     years B.P. Sea level reached its present position              destructional, wave-dominated deltas (Scott and
                     between 3,000 and 2,500 years B.P. (Curray, 1960;              Fisher, 1969, p. 11-29).
                     Nelson and Bray, 1970; Frazier, 1974). During the
                     latter phases of Holocene transgression, estuaries                   While the Brazos and Colorado Rivers were
                     were being filled by a sequence of fluvial and                 filling their estuary, the north and west shores of
                     estuarine sediments, and parts of the Pleistocene              Matagorda Bay were probably open to the Gulf of
                     strandplain sand were being reworked and trans-                Mexico. At this time,. mudflats and marshes were
                     ported landward to form nuclei for Matagorda                   .developing in the area of Lake Austin and shell
                     Island (Wilkinson, 1973).                                      beaches were being constructed along most of the
                                                                                    remaining shoreline. West of Pass Cavallo, incipient
                                        Modem History                               islands had coalesced to form Matagorda Island.

                          Modem history of the Matagorda Bay area
                     dates from stillstand, 3,000 to 2,500 years B.P., to                 Subsequent to the filling of the Brazos-
                     the present. Development of the Modem shoreline                Colorado estuary, sand was transported toward the
                     may be divided into prehistoric and historic cate-             southwest by persistent longshore drift. Matagorda
                     gories. Prehistoric development is based chiefly on            Peninsula was constructed by spit accretion across
                     interpretation of field data, and documentation, of            the . bay and estuarine muds. Growth of the
                                                                                    peninsula eventually separated Matagorda Bay
                     historic development is from both published                    from the Gulf of Mexico. Since Matagorda Penin-
                     records and field observations.                                sula has been erosional throughout much of its
                                                                                    history, it does not display its original accretionary
                                     Prehistoric Development                        grain.
                          Following stillstand, rivers. began to.fill their
                     estuaries by progradation of bayhead deltas. Sedi-                   Approximately 1,000 years ago, the lower
                     ment derived from several major fluvial systems                part of the Colorado River, known today as Caney
                     directly influenced the   I development of shoreline           Creek, was captured in the area between Wharton
                     features in the Matagorda Bay area. Among these                and Columbus by a headward-eroding stream.
                     are the Brazos, Colorado, and Lavaca-Navidad                   After its capture, the Colorado began discharging
                     Rivers, and Garcitas Creek.                                    into Matagorda Bay in the vicinity of the small
                                                                                    town of Matagorda.
                          At stillstand, the Brazos and Colorado Rivers
                     weredischarging into a common estuary which had                                  Historic Development
                     an estimated average depth of 25 feet, a width of
                     30 miles, and a length (measured from the Gulf                       Configuration of Gulf and mainland shore-
                     shoreline to bayhead) of 22 miles. With the use of             lines has not changed significantly since the first
                     sediment volume data for theBrazos and Colorado                reliable coastal charts were produced in
                     Rivers published mi the Nineteenth Report. of                  185.6-1859. Some local changes have resulted from
                     Texas Board of Water Engineers (1950, p. 161), it              man's activities. Accretion of the north shore of
                     is apparent that the Brazos. and Colorado Rivers               Matagorda Bay (between Lake Austin and Oyster
                     could have filled their estuary in 1,200 years. While          Lake) and the north shore of Espiritu        Santo Bay
                     these rivers were filling their estuary, and before            resulted from dredging the Intracoastal Canal.
                     Matagorda Peninsula was constructed, much of the               Construction of Matagorda Ship Channel jetties has
                     suspension load delivered to the Gulf of Mexico by             produced changes along the Gulf shoreline. Sand
                     these streams was transported into Matagorda and               that is transported to the southwest by longshore
                     Lavaca Bays. Upon reaching the Gulf of Mexico,                 currents is trapped along the north jetty, thereby
                     bed-load material from the Brazos and Colorado                 accreting the shoreline. Since most of the sand is

             trapped by the north jetty, the Gulf shoreline lying       the town of Matagorda. A large volume of sedi-
             between the south jetty and Pass Cavallo conse-            ment had accumulated in the river because of the
             quently is eroding.                                        greatly reduced flow. Upon release of the logjam,
                                                                        sediment was rapidly transported to the bay
                   Perhaps the    most obvious change in the            creating a delta that prograded completely across
             Matagorda Bay area was the growth of the                   Matagorda Bay. In 1936, a channel was dredged
             Colorado delta, during 1929-1935, from a small             through Matagorda Peninsula, and the Colorado
             45-acre delta to a complex delta of almost 5,000           River began to discharge into the Gulf of Mexico.
             acres. Rapid deltation resulted from removal of a          Tiger Island Channel was dredged from the river to
             log jam from the river in 1929 (Wadsworth, 1941,           west Matagorda Bay in the early 1950's. Since then
             1966). The log jam extended inland 46 miles from           a small delta lobe has developed in Matagorda Bay.

                                              HISTORICAL SHORELINE MONITORING

                                     GENERAL METHODS AND PROCEDURES USED BY THE
                                                 BUREAU OF ECONOMIC GEOLOGY

                                  Definition                            (1:24,000 or 1 inch     2,000 feet) are used for this
                                                                        purpose. Topographic charts and aerial photo-
                   Historical Shoreline Monitoring is the docu-         graphs are either enlarged or reduced to the precise
             mentation of direction and magnitude of shoreline          scale of the topographic maps. Shorelines shown
             change through specific time periods using accurate        on topographic charts and sediment.-water interface
             vintage charts, maps, and aerial photographs.              mapped directly on sequential aerial photographs
                                                                        are transferred from the topographic charts and
                                Sources of Data                         aerial photographs onto the common base map
                                                                        mechanically with a reducing pantograph or opti-
                   Basic data used to determine changes in              cally with a Saltzman projector. Lines transferred
             shoreline position are near-vertical aerial photo-         to the common base map are compared directly
             graphs and mosaics       .and topographic charts.          and measurements are made to quantify any
             Accurate topographic charts dating       from 1850,        changes in position with time.
             available through the Department of Commerce,
             National Oceanic and Atmospheric Administration                    Factors Affecting Accuracy of Data
             (NOAA), were mapped by the U. S. Coast Survey
             using plane table procedures. Reproductions of                  Documentation of long-term changes from
             originals are used to establish shoreline position         available records, referred to in this report as
             (rnean high water) prior to the early 1930's. Aerial       historical monitoring, involves repetitive sequential
             photography supplemented and later replaced                mapping of shoreline position using coastal charts
             regional topographic surveys in the early 1930's;          (topographic surveys) and aerial photographs. This
             therefore, subsequent shoreline positions are              is in contrast to short-term monitoring which
             mapped on individual stereographic photographs             employs beach profile measurements and/or the
             and aerial photographic mosaics representing a             mapping of shoreline position on recent aerial
             diversity of scales and vintages. These photographs        photographs only. There are advantages and disad-
             show shoreline position based on the sediment-             vantages inherent in both techniques.
             water interface at the time the photographs were
             taken.                                                          Long-term historical monitoring reveals trends
                                                                        which provide the basis for projection of future
                                   Procedure                            changes, but the incorporation of coastal charts
                                                                        dating from the 1850's introduces some uncer-
                   The key to comparison of various data needed         tainty as to the precision of the data. In contrast,
             to monitor shoreline variations is agreement in            short-term monitoring can be extremely precise.
             scale and adjustment of the data to'the projection         However, the inability to recognize and differ-
             of the selected map base; U. S. Geological Survey          entiate long-term trends from short-term changes is
             7.5-minute quadrangle topographic maps                     a decided disadvantage. Short-term monitoring also

                     12

                     requires a . network of stationary, permanent                     tant variations in mapping precision. The sediment-
                     markers which are periodically reoccupied because                 water interface can be mapped with greater preci-
                     they serve as a common point from which future                    sion on larger scale photographs, whereas the same
                     beach profiles are made. Such a network of                        boundary cqn be delineated with less precision on
                     permanent markers and measurements has not                        smaller scale photographs. Stated another way, the.
                     been established along the Texas Coast and even if                line delineating the sediment-water interface repre-
                     a network was established, it would take consider-                sents less horizontal distance on larger scale photo-
                     able time (20 to 30 years) before sufficient data                 graphs than a line of equal width delineating the
                     were available for determination of long-term                     same boundary on smaller scale photographs.
                     trends.                                                           Aerial photographs of a scale less than that of the
                                                                                       topographic base map used for compilation create
                           Because the purpose of shoreline monitoring                 an added problem of imprecision because the
                     is to document past changes in shoreline position                 mapped line increases in width when a photograph
                     and to provide basis for the projection of future                 is enlarged optically to match the scale of the base
                     changes, the method of long-term historical moni-                 map. In contrast, the mapped line decreases in
                     toring is preferred.                                              width when a photograph is reduced optically to
                                                                                       match the scale of the base map. Furthermore,
                                            Original Data                              shorelines mechanically adjusted by pantograph
                                                                                       methods to match the scale of the base map do not
                           Topographic surveys.-Some inherent error                    change in width. Fortunately, photographs with a
                     probably exists in the original topographic surveys               scale equal to or larger than the topographic map
                     conducted by the U. S. Coast Survey [U. S. Coast                  base can generally be utilized.
                     and Geodetic Survey, now called National Ocean
                     Survey]. Shalowitz (1964, p. 81) states ". . . the                     Optical aberration causes the margins of
                     degree of accuracy of the early surveys depends on                photographs to be somewhat distorted and shore-
                     many factors, among which are the purpose of the                  lines mapped on photographic margins may be a
                     survey, the scale and date of the survey, the                     source of error in determining shoreline position.
                     standards for survey work then in use, the relative               However, only the central portion of the photo-
                     importance of the area surveyed, and the ability                  graphs are used for mapping purposes, and
                     and care which-the individual surveyor brought to                 distances between fixed points are adjusted to the
                     his , task." Although it is neither possible nor                  7.5-minute topographic base.
                     practical.to comment on all of these factors, much
                     less attempt to quantify the error they represent,                     Meteorological conditions prior to and at the
                     in general the accuracy of a particular survey is                 time of photography also have a bearing on the
                     related to its date; recent surveys are more accurate             accuracy of the documented shoreline changes. For
                     than older surveys. Error can also be introduced by               example, deviations from normal astronomical
                     physical changes in material on which the original                tides caused by barometric pressure, wind velocity
                     data appear. Distortions, such as scale changes                   and direction, and attendant wave activity may
                     from expansion and contraction of the base                        introduce errors, the significance of which depends
                     material, caused by reproduction and changes in                   on the, magnitude of the measured change. Most
                     atmospheric conditions, can be corrected by                       photographic flights -are executed during calm
                     cartographic techniques. Location of mean high                    weather conditions, thus eliminating most of the
                     water is also subject to error. Shalowitz, (1964,                 effect of abnormal meteorological conditions.
                     p. 175) states ". . . location of the high-water line
                     on the early surveys is within a maximum error of                               Interpretation of Photographs
                     10 meters and may possibly be much more
                     accurate than this."                                                   Another factor that may contribute to error
                                                                                       in determining rates of shoreline change is the
                           Aerial photographs.-Error introduced by use                 ability of the scientist to interpret correctly what
                     of aerial photographs is related to variation in scale            he sees on the photographs. The most qualified
                     and resolution, and to optical aberrations.                       aerial photograph mappers . are those who have
                                                                                       made the most observations on the ground. Some
                           Use, of aerial photographs of various scales                older aerial photographs may. be of poor quality,
                     introduces variations in resolution with concomi-                 especially along the shorelines. On a few photo-

              graphs, both the beach and swash zone are bright                    Aerial photographs.-Accuracy of aerial pho-
              white (albedo effect) and cannot be precisely                 tograph mosaics is similar to topographic charts in
              differentiated; the shoreline is projected through            that quality is related to vintage; more recent
              these areas, and therefore, some error may be                 mosaics are more accurate. Photograph negative
              introduced. In general, these difficulties are                quality, optical resolution, and techniques of com-
              resolved through an understanding of coastal                  piling controlled mosaics have improved with time;
              processes and a thorough knowledge of factors that            thus, more adjustments are necessary when work-
              may affect the appearance of shorelines on                    ing with older photographs.
              photographs.
                                                                                  Cartographic procedures may introduce minor
                    Use of mean high-water line on topographic              errors associated with, the transfer of shoreline
              charts and the sediment-water interface on aerial             position from aerial photographs and topographic
              photographs to define the same boundary is                    charts to the base map. Cartographic procedures do
              inconsistent because normally the sediment-water              not increase the accuracy of mapping; however,
              interface falls somewhere between high and low                they tend to correct the photogrammetric errors
              tide. Horizontal displacement of the shoreline                inherent in the original materials such as distor-
              mapped using the sediment-water interface is                  tions and optical aberrations.
              almost always seaward of the mean high-water line.
              This displacement is dependent on the tide cycle,                        Measurements and Calculated Rates
              slope of the beach, and wind direction when the
              photograph was taken. The combination of factors                    Actual measurements of linear distances on
              on the Gulf shoreline which yield the greatest                maps can be made to one-hundredth of an inch
              horizontal displacement of the sediment-water                 which corresponds to 20 feet on maps with a scale
              interface from mean high water are low tide                   of 1 inch = 2,000 feet (1:24,000). This is more
              conditions, low beach profile, and strong northerly           precise than the significance of the data warrants.
              winds. Field measurements indicate that along the             However, problems do arise when rates of change
              Texas Gulf Coast, maximum horizontal displace-                are calculated because: (1) time intervals between
              ment of a photographed shoreline from mean                    photographic coverage are not equal; (2) erosion or
              high-water level is approximately 125 feet under              accretion is assumed constant over the entire time
                                                                                                               2
              these same conditions. Because the displacement of            period; and (3) multiple rates (--'@-Fn, where n repre-
              the photographed shoreline is almost always                   sents the number of mapped shorelines) can be
              seaward of mean high water, shoreline changes                 obtained at any given point using various combina-
              determined from comparison of mean high-water                 tions of lines.
              line and sediment-water interface will slightly
              underestimate rates of erosion or slightly over-                    The beach area is dynamic and changes of
              estimate rates of accretion.                                  varying magnitude occur continuously. Each
                                                                            photograph represents a sample in the continuum
                               Cartographic Procedure                       of shoreline changes and it follows that measure-
                                                                            ments of shoreline changes taken over short time
                    Topographic charts.-The topographic charts              intervals would more closely approximate the
              are replete with a 1-minute-interval grid; transfer of        continuum of changes because the procedure
              the shoreline position from topographic charts to             would approach continuous monitoring. Thus, the
              the base map is accomplished by construction of a             problems listed above are interrelated, and solu-
              1-minute-interval grid on the 7.5-minute topo-                tions require the averaging of rates of change for
              graphic base map and projection of the chart onto             discrete intervals. Numerical ranges and graphic
              the base map. Routine adjustments are made across             displays are used to present the calculated rates of
              the map with the aid of the 1-minute-interval                 shoreline change.
              latitude and longitude cells. This is necessary
              because: (1) chart scale is larger than base map                    Where possible, dates when individual photo-
              scale; (2) distortions. (expansion and contraction)           graphs actually were taken are used to determine
              in the medium (paper or cloth) of the original                the time interval needed to calculate rates, rather
              survey and reproduced chart, previously discussed,            than the general date printed on the mosaic.
              require adjustment; and (3) paucity of culture                Particular attention is also paid to the month, as
              along the shore provides limited horizontal control.          well 'as year of photography; this eliminates an

                     14

                     apparent age difference of one year between                             cally all based on a geodetic network which
                     photographs taken in December and January of the                        minimized the possibility of large errors being
                     following year.                                                         introduced. They therefore represent the best
                                                                                             evidence available of the condition of our
                           Justification of Method and Limitations                           coastline a hundred or more years ago, and the
                                                                                             courts have repeatedly recognized their com-
                           The methods used in long-term historical                          petency in this respect . . .
                     monitoring carry a degree of imprecision, and
                     trends and rates of shoreline changes determined                        Because of the importance of documenting
                     from these techniques have limitations. Rates of                  changes over a long time interval, topographic
                     change are to some degree subordinate in accuracy                 charts and aerial photographs have been used to
                     to trends or direction of change; however, there is               study beach erosion in other areas. For example,
                     no doubt about the significance of the trends of                  Morgan and Larimore (1957), Harris and Jones
                     shoreline change documented over more than 100                    (1964), El-Ashry and Wanless (1968), Bryant and
                     years. An important factor in evaluating shoreline                McCann (1973), and Stapor (1973) have success-
                     changes is the total length of time represented by                fully used techniques similar to those employed
                     observational data. Observations over a short                     herein. Previous'articles describing determinations
                     period of time may produce erroneous conclusions                  of beach changes from aerial photographs were
                     about the long-term change in.coastal morphology.                 reviewed by Stafford (1971) and Stafford and
                     For example, it is well established that landward                 others (1973).
                     re treat of the shoreline during a storm is accom-
                     panied by sediment removal; the sediment is                             Simply stated, the method of using topo-
                     eroded, transported, and temporarily stored off-                  graphic charts and aerial photographs, though not
                     shore. Shortly after storm passage, the normal                    absolutely precise, represents the best method
                     beach processes again become operative and some                   available for investigating long-term trends in
                     of the sediment is returned to the beach. If the                  shoreline changes.
                     shoreline is monitored during this recovery period,
                     data would indicate beach accretion; however, if
                     the beach does not accrete to its prestorm position,                    Limitations of the method require that
                     then net effect of the storm is beach erosion.                    emphasis be placed first on trend of shoreline
                     Therefore, long-term trends are superior to short-                changes with rates of change being secondary.
                     term observations. Establishment of long-term                     Although rates of change from map measurements
                     trends based on changes in shoreline position                     can be calculated to a precision well beyond the
                     necessitates the use of older and less precise                    limits of accuracy of the procedure, they are most
                     topographic surveys. The applicability of topo-                   important as relative values-, that is, do the data
                     graphic surveys for these purposes is discussed by                indicate that erosion is occurring at a few feet per
                     Shalowitz (1964, p. 79) who stated:                               year or at significantly higher rates. Because
                                                                                       sequential shoreline positions are seldom exactly
                                "There is probably little doubt but that               parallel, in some instances it is best to provide a
                           the earliest records of changes in our coastline            range of values such as 10 to 15 feet per year. As
                           that are on a large enough scale and in                     long as users realize and understand the limitations
                           sufficient detail to justify their use for quanti-          of the method of historical monitoring, results of
                           tative study are those made by the Coast
                           Survey. These surveys were executed by com-                 sequential. shoreline mapping are significant and
                           petent and careful engineers and were practi-               useful in coastal zone planning and development.

                              VINTAGE MATERIALS USED IN THE MATAGORDA BAY AREA STUDY

                    Two types of data were collected to docu-             approximately 1:24,000. Other data used were
              ment direction and rates of shoreline change: (1)           U. S. Geological Survey topographic maps
              historical data from charts, maps, and aerial photo-        (1946-1947) and two vintages of Tobin aerial
              graphs; and (2) field data. Historical monitoring           photomosaics (1934-1937 and 1956-1957), also at
              was accomplished for the years 1856-1859,                   a scale of 1:24,000. A set of U. S. Department of
              1934-1937, 1946-1947, 1952-1953, and                        Agriculture stereophoto graphic pairs (1952-1953),
              1956-1957, specifically to document long-term               at a scale of 1:10,000, completes the list of vintage,
              changes. Field observations and measurements                materials used for compiling the Matagorda Bay
              were made to document changes that occurred                 shoreline change map. All charts, maps, and
              between 1957 and 1971-72.
                                                                          photos, with exception of the stereophotos, were
                    Baseline data for this  study are U. S. Coast         at approximately the same scale. The base on
              Survey charts for the years    1856-59. These charts        which the vintage data were compiled was at a
              were reproduced photographically to a scale of              scale of 1:24,000.

                                               PRESENTATION OF DATA IN MAP FORM

                    Each of the five vintages of Gulf and main-           have an overall erosional trend, it may display
              land shorelines is color coded and presented on a           short-term accretionary trends; these trends will be
              series of accurate base maps. Measurements of               depicted by the graphs.
              distances between the oldest and youngest shore-                 Long-term erosional and accretionary shore-
              lines are adequate to show long-term shoreline              lines are highlighted on the maps by color, red for
              trends. Intermediate shorelines may not all show            erosion and green for accretion. Width of the color
              the same trend (erosion or accretion). To aid in            bands are indicative of the amount of erosion or
              reading the shoreline map, graphs were prepared at          accretion experienced by a particular shoreline
              selected intervals along the shoreline. The                 segment. The 100-year shoreline change can be
              1856-1859 shoreline serves as the      'base line for       determined by measuring distances between the
              these graphs. Although a shoreline segment may              color-coded, vintage shorelines.

                                EFFECT OF ASTRONOMICAL TIDE ON POSITION OF WATERLINES
                                                 ON VINTAGE AERIAL PHOTOGRAPHS

                    In general, differences in position of mean           degrees and shell beaches 3.9 degrees. Slopes of
              high-water line, as shown on topographic charts,            Gulf beaches are roughly bimodal with 44 percent
              and waterline, as mapped on aerial photographs,             occurring in the 2- to 3-degree range and 47
              were discussed in the section on Interpretation of          percent in the 4- to 5-degree range. There are three
              Photographs. Slopes of Gulf and mainland beaches            types of mainland beaches: (1) terrigenous sand;
              were measured in the Matagorda Bay area for the             (2) shell gravel; and (3) caliche and shell gravel
              purpose of showing the effect of tides on historical        veneer over Pleistocene mud. Slopes of mainland
              monitoring.                                                 beaches range from less than 1 degree to 11 degrees
                                                                          (fig. 8B). Sand beaches average 5.25 degrees, shell
                    Slopes  of Gulf and mainland beaches were             beaches 6.3 degrees, and caliche and shell gravel
                                                                          beaches have average slopes of 5.4 degrees. Main-
              measured and the horizontal distance between                land beaches are steeper than Gulf beaches; 37
              flood and ebb tide was determined. Gulf beaches             percent of the mainland beaches occur in the 3- to
              consist of sand and shell with slopes of 1.5 to 6.0         5-degree range and 50 percent range from 6 to 7.5
              degrees (fig. 8A). Sand beaches average 2.75                degrees.

                   16

                         Assuming a 2-foot mean tidal range along the            slopes, and associated horizontal distances between
                   Gulf shoreline, the horizontal distance between               ebb and flood tide positions are 3- to 5-degree
                   flood and ebb tide along the 2- to 3-degree beaches           beaches and 6- to 7.5-degree beaches. Horizontal
                   would be 60 and 40 feet, respectively, and the                distance between ebb and flood tide is 8 and 7
                   horizontal distance along, the 4- to 5-degree                 feet, respectively. These differences would not be
                   beaches would be 30 and 23 feet, respectively.                detected on aerial photographs.
                   Accuracy of measurement at the 1:24,000 scale
                   used in the historical monitoring program is on the                 Parts of the mainland shoreline are almost
                   order of �40 feet. The difference between ebb and             vertical cliffs. Here the horizontal difference be-
                   flood tide would have an effect on waterline                  tween flood and ebb tide is insignificant. Low-lying
                   position, indicated on aerial photos, where beaches           areas, such as marshes, are inundated by astro-
                   slope 2 degrees or less, but the difference probably          nomical and wind tides. Extent of inundation may
                   would not be detected on beaches with higher                  not be discernible on conventional black-and-white
                   slopes.                                                       aerial photographs because marsh plants tend to
                                                                                 obscure the tidal waters. Regardless of whether the
                         Range of astronomical tide in Matagorda Bay             tidal cycle is ebb or flood, however, the bay margin
                   is on the order of 0.5 to 0.7 foot. A 1-foot tidal            of the salt marsh is commonly defined by Spartina
                   range was used for determination of the horizontal            alterniflora. Height of S. alterniflora is greater than
                   distances between ebb and flood tide along main-              the tidal range and is not inundated by the flood
                   land beaches. Two dominant beach classes, their               tide.

                                           GULF AND MAINLAND SHORELINE CHANGES, 1856-1957

                         The purpose of this section on historical                                    Gulf Shoreline
                   monitoring is to document the direction and rate
                   of long-term shoreline change and to present some                   The Gulf shoreline has been chiefly erosional
                   of the probable causes of change. Elaboration on              since 1856. Minor accretion occurred between
                   the interaction of coastal processes and shoreline            1946 and 1956, and between 1952 and 195,6 (see
                   stability is deferred, however, until short-term              fluctuation graphs for stations 1 through 6).
                   shoreline changes are considered.                             Maximum erosion (1856-1956) of 1,580 feet was
                                                                                 recorded at station 3. Least amount of erosion was
                         Long-term trends of Gulf and mainland shore-            880 feet at station 6. Yearly erosional average was
                   lines are presented on eight maps, each at a scale of         about 11 feet, with total land loss for this 100-year
                   1:24,000 (in pocket). Four of the maps display                period being about 1,575 acres. This is the most
                   only the mainland shoreline. These are-Lavaca                 rapidly eroding shoreline segment in the study
                   Bay South, Lavaca Bay North, Carancahua Bay,                  *area. Several factors contribute to rapid shoreline
                   and Tres Palacios Bay areas (fig. 9). Both Gulf and           retreat. These are: (1) Matagorda Peninsula is a
                   mainland shorelines occur on the remaining maps--             thin sand body; (2) there is a sand deficit; (3)
                   Brown Cedar Cut, Colorado River, Shell Island                 waves approach the shoreline at a high angle; (4)
                   Reef, and Pass Cavallo areas. In the following                eustatic rise of sea level has increased over the past
                   discussion, shoreline trends are presented for each           50 years (K. 0. Emery, personal communication);
                   map area.                                                     (5) the low peninsula is frequently washed over
                                                                                 during storms; and (6) there is compactional
                                   Brown Cedar Cut Area                          subsidence of underlying deltaic muds.

                         Salient features of this area are: (1) Mata-                      Bay Shoreline of Matagorda Peninsula
                   gorda Peninsula, which is tied at its.east end to a
                   deltaic headland; (2) an inactive tidal delta (near                 With the exception of the two tidal pass areas,
                   station 13); (3) an active tidal delta (Brown Cedar           the bay shoreline has been chiefly erosional. Land
                   Cut); and (4) east Matagorda Bay.                             area accreted to this shoreline amounts to about

                                                                                                                                                                                                                         17

                           20-

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                                                                                         Slopes         of Mainland                Beaches          (in   degrees)
                                                                                                                                 B

                                 Figure 8. Slopes of Gulf and mainland beaches. Measurements are representative of slopes lying between the lower berm
                      and the toe of the forebeach.

                    18

                                   JACKSON CC)
                      VICTORIa CO

                      CALHOUN CO

                     Lavaca Bay North
                           Area                 JACKSON CO

                                              Cor'anca UG
                                                   oy Area

                     Lavaca Bay SoutN,@
                           Area                              V

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                                                      QP
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                      Pass Covallo    Area
                                                   MAT,4GOR,94
                                                     SAY

                                                       Shell Island Reef                   Colorado Riv
                                                                          Area                          er Area

                                                                                                                   Brown Cedar Cut Area

                                                                                      0

                                                                                 01-

                                                   Figure 9. Index of shoreline change and marsh distribution maps.

                    424 acres, whereas land loss was about 298 acres.             trend since 1934. Accretion ranged from a maxi-
                    Most of the accretion, 337 acres, occurred in the             mum of 400 feet at station 14 to a minimum of 80
                    tidal pass areas. West of Brown Cedar Cut, approxi-           feet at station 21. Maximum erosion of 760 feet
                    mately 210 acres of land were lost through erosion.           was measured at.station 19, and least erosion was
                    Maximum erosion of 600 feet was recorded at                   recorded at station 22. In 1856, Dressing Point was
                    station 8, and least erosion, 240 feet, occurred in           tied to the mainland. Net land loss of about 501
                    the area of station 12.                                       acres occurred along the mainland shoreline.

                          Erosion of Matagorda Peninsula bay shore                                 Colorado River Area
                    results from waves generated by north winds.
                                                                                        Gulf and   bay shorelines of Matagorda Penin-
                                       Mainland Shoreline                         sula have been   chiefly erosional since 1856. Main-
                                                                                  land shoreline was mostly erosional until a logjam
                          Mainland shoreline, the area between stations           was removed from the Colorado River and the
                    14 and 22, was primarily erosional during the                 Intracoastal Canal was dredged. Following the
                    interval 1856-1957. Shoreline fluctuation graphs              removal of the log jam in 1929, a delta rapidly
                    indicate short-term accretionary periods since                prograded across Matagorda Bay. To the east of the
                    1934.   Accretion resulted from spoil outwash.                delta, the mainland shoreline accreted by spoil
                                                "J"cKsON0
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                    Stations 14, 18, and 21 all display an accretionary           outwash.

                                                                                                                                        19

                                     Gulf Shoreline                            (12.5 square miles).. Except for the Tiger Island
                    Gulf shoreline erosion decreases westward.                 Channel area, the delta is depositionally inactive.
              This shoreline segment experienced short-term                                    Shell Island Reef Area
              accretion (sections 2-6). Station 1 has shown
              overall net accretion for the 100-year period.                         Both Matagorda Bay and Matagorda Peninsula
              Maximum shoreline retreat of 300 feet was                        widen somewhat to the west. Long oyster reefs
              recorded at station 4, and the minimum of 80 feet                extendat right angles from the mainland shoreline
              was recorded, at station 2. Net land loss of 245                 into west Matagorda Bay. Matagorda. Peninsula is
              acres was recorded for this shoreline segment.                   divided -into two sections on this map; these are
                                                                               treated as a single unit in the following discussion.
                    The westward decrease in erosion and            slight
              accretion between Spring Bayou and the mouth of                                        Gulf Shoreline
              the Colorado River result in. part from low,
              continuous, fore-island dunes that prevent sand                        During the period 1856-1957, the shoreline
              transport across the peninsula into Matagorda Bay.               east of . Greens Bayou was mostly erosional,'where-
                                                                               as to the west of Greens Bayou,, the shoreline was
                         Bay Shoreline of Matagorda Peninsula                  accretionary. Maximum accretion of 260 feet was
                    The bay shoreline was erosional during the                 recorded at, station 4, and minimum accretion of
              historical monitoring period. Three stations (9, 10,             40 feet occurred at station 3. Maximum erosion of
                                                                               500 feet occurred atstation 11, and the minimum
              and 11) show insignificant short-term accretion.
                                                                               of 150 feet was recorded at station 13. Net land
              Accretion. near TigerIsland and Greek Island is                  gain.of  121, acres   Io.ccu.rred to the west of. Greens
              related to Colorado River deltation. Maximum                     T
              erosion of about 560 feet was recorded at station 7              Bayou,    and land loss of about 652 acres was
              and a minimum of 120 feet at station 11.                         calculated for the shoreline between stations 3 and
                                                                               11.
                    Minor accretion was shown as small beaches                           Bay Shoreline of Matagorda Peninsula
              in embayed areas and as spits downcurrent from
              erosional segments. Net land loss was about 532
                                                                                     Erosion exceeded accretion along the. bay
              acres.
                                                                               shoreline during the 1 00-year period. Land loss was
                                  Mainland Shoreline                           approximately 1,807 acres.
                    With the exception of the area of station,16,                    The bay shoreline between stations 8 and 21
              the mainland shoreline is accretionary. The                      is highly irregular. The serrated bay shoreline
              shoreline segment bounded by stations 13 and 16                  results from. the scouring of storm channels. Storm
              is regarded as, mainland shoreline;.the I      .arge accre-      breaching is common east of Greens Bayou, but is
              tionary area. to the west is the Colorado delta. All             uncommon west of Greens Bayou because of the
              of the mainland shoreli      InIe, except the station 16         continuous fore-island dunes.
              area, is accretionary.                                                 Bay-shore accretion. occurs during hurricanes.
                    Most of. the accretion occurred after 1934.                Sediment . is transported across the peninsula
              Accretion values range from 1,050 feet at station                through storm channels; it accumulates in the bay
              15 to 1,680 feet at station 13. Spoil outwash is the             as small islands (station 21). Extremeerosion takes
              cause of accretion.                                              place during storms,, at which time the peninsula
                                                                               may -be segmented. At station 20, about 2,520 feet
                    Net land gain was about 675 acres. Part of the             of the peninsula was eroded by storms. Minimum
              sediment which accreted this shoreline was derived               erosion of 120 feet (1856-1957) was recorded at
              from the Co   lorado. River.                                     station 6.

                                   Deltaic Shoreline                                              Mainland Shoreline

                    In 1957, the subaerial. Colorado delta, which                    The mainland shoreline has been accreting
              was chiefly marsh, covered an area of 8,000 acres                since 1934. West of station 27, the shoreline,

                    20

                    consisting chiefly of shell beaches and berms, was                    Matagorda Island was erosional between sta-
                    erosional. Shell beaches and berms also form the                tions 2 and 6, and accretionary west of station 2.
                    shoreline east of station 27. Prior to removal of the           Maximum erosion of 2,200 feet was recorded at
                    Colorado River log jam and dredging of the                      station 3, and maximum accretion of 620 feet at
                    Intracoastal Canal, shell beaches also existed west             station 1. Net land loss between stations 2 and 6
                    of station 27. Now the shoreline west of station 27             was about 816 acres, and net land gain in the area
                    is composed of spoil outwash.                                   of station 1 was about 47 acres.

                          Accretion began after 1934 (fluctuation                    Bay Shoreline-Matagorda Peninsula and Matagorda Island
                    graphs 22, 23, 24, and 25); rates of accretion
                    increase from west to east. Land gain from spoil                      The bay shoreline of Matagorda Peninsula
                    outwash was about 1,079 acres. Land loss of about               begins at Decros Point and extends to the east map
                    80 acres occurred in the area of stations 26 and 28.            limit, and the bay shoreline for Matagorda Island
                    A net. gain of about 1,000 acres was experienced                lies between the south bank of Saluria Bayou and
                    by the mainland shoreline during the interval                   the west map limit.
                    1886-1957.
                          Approximately 2,200 feet of accretion was                       There are a few local accretion areas along the
                    recorded at station 22, and minimum accretion of                bay   shore of Matagorda Peninsula, but principal
                                                                                    direction of change has been erosional. Net land
                    150 feet occurred at station 25. Maximum erosion                loss was about 501 acres.
                    of 330 feet occurred in the area of station 26; the
                    minimum was 160 feet at station 28.                                   Areas of erosion alternate with accretion
                                           Oyster Lake                              along the bay shore of Matagorda Island with
                                                                                    erosion occurring in the area of stations 12 and 13,
                          Only the southern accretionary shore Of                   and accretion occurring between Lighthouse Cove
                    Oyster Lake is shown on this map. Here, spoil                   an .d Saluria Bayou. The tidal delta was the
                    outwash has created about 97 acres of new land.                 pnncipal site of sedimentation. Net land gain was
                                                                                    about 123 acres.
                                       Pass Cavallo Area                                                Mainland Shoreline
                          Pass Cavallo, a major tidal pass, separates the                 There are two mainland shoreline segments on
                    erosional Matagorda Peninsula from Matagorda                    this  map. One is sit  .uated along the west shore of
                    Island. This is the only major pass on the Texas                Matagorda Bay between Saluria Bayou and the
                    Coast that has not been physically altered by man.              northwest map limit. The other is along the north
                    A ship channel was dredged through Matagorda                    shore of Espiritu Santo Bay between Port
                    Peninsula in 1965, and since then Pass Cavallo has
                    begun to shoal. The vintage shorelines displayed on             O'Connor and the west map boundary.
                    the Pass Cavallo area map all predate dredging of                   . The west shoreline of Matagorda Bay was
                    the ship channel.                                               dominated by erosion. Maximum erosion of 1,200
                                          Gulf Shoreline                            feet and a minimum of 370 feet were measured at
                                                                                    stations 7 and 10, respectively. Net land loss was
                          The Gulf shoreline is defined by the areas                about 770 acres. Rapid erosion was documented
                    lying between' station 23 and Decros Point, and                 between Port O'Connor and the north map bound-
                    Saluria Bayou and station 1. Erosion exceeded                   ary. Here, relatively nonresistant Pleistocene sand
                    accretion during the period of historical moni-                 is subjected to wave erosion. Erosion of the
                    toring, and local changes in shoreline stability were           shoreline south of Port O'Connor has also been
                    effected by the Matagorda Ship Channel jetties..                rapid. Here, almost pure sand beaches are attacked
                                                                                    by unimpeded waves which approach the area from
                          The Gulf shoreline of Matagorda Peninsula at              the northeast and southeast.
                    station 23 was in equilibrium from 1856 to 1957.
                    Shoreline retreat of approximately 1,460 feet was                     The north shoreline of Espiritu Santo Bay is
                    recorded at station 25. Net land loss was calculated            erosional along    Dewberry and Blackberry Islands;
                    to be about 289 acres.                                          net land loss was 113 acres. Shoreline accretion

                                                                                                                                      21

               ranging from 140 to 190 feet was measured                            The overall direction of change has been
               adjacent to the Intracoastal Canal; net land gain              erosional. Indian Point (station 12) exhibited the
               was approximately 633 acres.                                   maximum accretion of 360 feet, whereas 200 feet
                                                                              of shoreline recession was measured at station 17.
                                     Marsh Islands                            Net land loss for this area was about 49 acres.

                     Farwell, Grass, and Bayucos Islands are emer-                                     Cox Bay
               gent parts of Pass Cavallo tidal delta. The islands
               which are bounded by Big Bayou and Barroom Bay                       The bay shore between stations 18 and 22 is
               are also part of the tidal delta. Most of the islands          chiefly low-relief vertical cliffs with a few marsh
               are vegetated with salt-tolerant plants. Land loss in          areas such as the head of Huisache Cove. In this
               the areas of Bayucos, Grass, and Farwell Islands               area, accretion (58 acres) and erosion (59 acres)
               amounted to about 188 acres. Net land gain in the              were virtually equal. Between 1856 and 1957, the
               Big Bayou--Barroom Bay area was about 81 acres.                trend in shoreline change was to erode promon-
                                                                              tories and deposit sediment in the small reentrants.
                              Lavaca Bay South Area
                                                                                    This shoreline segment lies in the lee of the
                     The amount of physical energy (waves, tidal              prevailing southeast wind. North wind, however,
               and longshore currents) expended along the bay                 generates waves that break. on the south shore of
               shoreline varies from place to place depending                 Cox Bay.
               upon (1) shoreline orientation, (2) width of the
               bay, and (3) the extent of bay segmentation                                         Sand Point Area
               resulting from spoil islands adjacent to dredged
               channels. Wave energy appears to be more intense                     Erosion dominates this shoreline segment.
               along the north and west shores of Matagorda Bay               Maximum land loss (116 acres) occurred between
               and the west shore of Lavaca Bay. Smaller waves                Sand Point and the northeast map limit. Accretion
               attack the shores of small, enclosed water bodies              was measured in marsh areas along the south shore
               such as Powderhorn Lake, Chocolate Bay, and                    of Keller Bay.
               Keller Bay.
                                                                                    A maximum of 500 and a minimum of 20
                     For convenience of discussion, the shoreline             feet of shoreline retreat were recorded at stations
               has been divided into five segments: (1) west                  25 and 23, respectively. Net land loss was approxi-
               Matagorda Bay; (2) west Lavaca Bay; (3) Cox Bay;               mately 130 acres.
               (4) Sand Point area; and (5) Powderhorn Lake.
                                                                                                  Powderhorn Lake
                                  West Matagorda Bay
                                                                                    Powderhorn Lake is a water body with its
                     This  part  of the bay shoreline lies between            longest dimension oriented transverse to the pre-
               station 1   and   Indian Point; it is predominantly            vailing southeast wind. Because of its orientation,
               erosional. The shoreline at stations 2 and 10                  small waves from the southeast do not significantly
               accreted between 1856 and 1934. An equilibrium                 erode the north shore; sedimentation exceeds
               shoreline existed in the area of station 10. Approx-           erosion. The opposite is true for the south shore.
               imately 580 feet of shoreline retreat occurred at              High-velocity, short-duration north winds generate
               station 1. Net land loss was approximately 162                 waves that erode the south shoreline. Net.land loss
               acres.                                                         was approximately 49 acres.

                                   West Lavaca Bay                                            Lavaca Bay North Area

                     From Indian Point to the north map limit, the                  The north bay shore receives sed       iment from
               bay   shore is diversified. It is made up of shell             Garcitas Creek and Lavaca River. At Port Lavaca
               beaches and berms, almost vertical bluffs, shell               and in the Mitchell Point area, some shoreline
               spits, and marshes. This shoreline segment has not             changes have resulted, from man's activities. Many
               experienced the dramatic changes that characterize             of the man-made changes are directly related to
               some of the previously described areas.                        dredging activities. For this discussion, the shore-

                    22

                    line was divided into four sections based on                   Calculations made for the shoreline segment south
                    shoreline orientation: (1) west, shoreline of Lavaca           of State Highway 35 indicate that at least 95 acres.
                    Bay from the map boundary northward to Placedo                 of bay bottom were covered with spoil.
                    Creek; (2) north shoreline of Lavaca Bay from
                    Placedo Creek eastward to station 8; (3) east                                           Cox Bay
                    shoreline of Lavaca Bay from station 8 to Mitchell
                    Point; and (4) Cox Bay shoreline from Mitchell                        Historical shoreline data for the period
                    Point to the southeast map boundary.                           1856-1957 document a net land gain of about 39
                                                                                   acres. Field observations made in the winter of
                                   West Shoreline, Lavaca Bay
                                                                                   1971   and spring of 1972, however, revealed that
                          Erosion exceeded sedimentation, and net land             the shoreline was in an erosional state. Net gain
                    loss was approximately 162 acres. Noble Point and              and loss of land for the period 1856-1972 were
                    station 13 experienced the most erosion, 1,200 and             approximately equal.
                    600 feet, respectively. Noble Point was a large
                    marsh area; loss of wetland area was about 128                                  Carancahua Bay Area
                    acres.
                                                                                          Within this map area there are: (1) large water
                          The principal areas of accretion were stations           bodies characterized by large waves generated by
                    14 and 16. Spoil dredged from boat basins, in the              prevailing southeast winds; (2) enclosed bays that
                    vicinity of station 16, created about 24 acres of              are elongate transverse to the prevailing wind; and
                    new land. At least two factors contributed to                  (3) small, shallow, enclosed water bodies charac-
                    sedimentation near station 14. These are: (1) a                terized by small waves.
                    concave shoreline; and (2) sediment discharged
                    into the bay through drainage ditches.                                For convenience of discussion, the shoreline
                                   North Shoreline, Lavaca Bay                     was    divided into four segments. Grouping of
                                                                                   shoreline segments was made on the basis of
                          There was a net land gain of about 34 acres              relative wave intensity, shoreline orientation, and
                    along the north shore. Shoreline accretion is                  degree of enclosure. The segments are (1) the north
                    attributed to sediment delivered to the bay by                 shore of Matagorda Bay, including part of Turtle
                    Placedo Creek, Garcitas Creek, and the Lavaca                  Bay, (2) Carancahua Bay, (3) Keller Bay, and (4)
                    River. Erosion is restricted to cliffed shorelines in          Salt Lake and Redfish Lake.
                    the stations 10-12 area. The amount of shoreline
                    retreat was 720 and 580 feet at stations 12 and 10,                           North Shore, Matagorda Bay
                    respectively.
                          Land loss in these two areas amounts            . to            The shoreline was erosional during
                                                                                   1856-1957, except for two small accretionary
                    approximately 138 acres. Approximately 137 acres               areag--a shell spit at Well Point, and a salt marsh
                    of new marsh in Garcitas Cove resulted from                    between station. 2 and Carancahua Pass.
                    sedimentation at the mouth of Garcitas Creek.
                                   East Shoreline, Lavaca Bay                             The banks of Carancahua Pass were highly
                                                                                   erosional. At station 3, shoreline retreat was about
                          The Lavaca River strongly influences shore-              1,540 feet and about 1,480 feet at station 15.
                    line stability north of State Highway 35. South of             Beaches and berms in the Carancahua Pass area are
                    the highway, man dominates shoreline activities.               composed of 80 to 90 percent shell, and erosion is
                    There has been a net gain of about 103 acres along             attributed to a decrease in shell production within
                    the east shore. Sediment for shoreline accretion               the bay.
                    was derived from the Lavaca River and from
                    material dredged from the bay bottom for a                            This part of the bay shore is fronted by a
                    turning basin.                                                 wide bay and is, therefore, subjected to the forces
                                                                                   of breaking waves generated by southeast winds.
                          Deltation at the mouth of the Lavaca River               Land loss resulting largely from wave activity was
                    created approximately 96 acres of new land.                    about 342 acres.

                                                                                                                                    23

                               Caraneahua Bay Shoreline                      derived from Pleistocene uplands and from
                                                                             Carancahua Bay.
                    The east shore is. in the lee of the southeast
               wind, but is open to waves approaching from the                               Tres Palacios Bay Area
               north. The opposite is true for the west shoreline.
                                                                                   Most of the Tres Palacios Bay shore is
                    Erosion has dominated the east shore since               relatively protected from waves approaching from
               1856. Maximum erosion of 280 feet was recorded                the southeast. The orientation of spits, which
               at station 6; at station 11, directly across the bay,         occur between Palacios Point and Oliver Point,
               420 feet of shoreline retreat.was measured during             indicates that southeast waves generate longshore
               the same penod. Small areas of spit and marsh                 currents which transport sediment northward.
               accretion occur between sections 5 and 6. Net land            Depositional 'grain preserved as beach ridges along
               loss amounts to about 83 acres.                               the same point suggests that net longshore drift
                                                                             was to the south in 1856.
                    The west shore has undergone almost equal
               amounts of accretion and erosion; there was a net                   The shoreline, was divided into the following
               land loss of about 29 acres., Accretion occurs                segments based upon shoreline orientation and
               downdrift. from erosional cliffs (see, section 8) and         degree of enclosure of water bodies: (1) Palacios
               along concave shoreline segments (between sec-                Point to Oliver Point; (2) Oliver Point to the
               tions 9 and 11 and 11 and 12). Shoreline.con-                 mouth of Tres Palacios Creek; (3) mouth of Tres
               -figuration is continually - changing in the area             Palacios Creek to Turtle Point; (4) Turtle Point to
               between sections 12 and 14. Here, shell spits                 the mouth of Turtle Creek; (5) mouth of Turtle
               accrete across entrances to Salt Lake and Redfish             Creek to Sartwelle Lakes; and (6) Oyster Lake.
               Lake; spits are breached during storms.
                                                                                             Palacios Point-Oliver Point
                                 Keller Bay Shoreline
                                                                                   Between Palacios Point and Oliver Point, the
                    Both the east and west shores of Keller Bay,             shoreline trend was erosional. All. shoreline changes
               which are modified by processes identical, to those           were natural exc   ept for the area just north of the
               operating in Carancahua Bay, are chiefly erosional.           dredged channel. Sediment accumulated as spits
                                                                             downcurrent from erosional headlands. Successive
                    Net land loss along. the east shore was about            changes in.size, shape, and orientation of spits. are
               47 acres. Up to 260 feet of shoreline retreat was             illustrated at Palacios Point and at.stations 2 and 3.,
               recorded at station 20, which is near the bayhead.            In the winter of 1972, the spit at Palacios Point
               Bluffs that front the bay are up to 10 feet high and          was attached to the headland at both. its upcurrent
               slumping is probably the dominant cause of shore-             and downcurrent ends.
               line retreat. Sedimentation occurred along two
               concave shoreline segments at stations 17 and 19.                   Approximately 1,040 feet of erosion was
                                                                             recorded at station 2. Material eroded from station
                    Approximately 61 acres of land were eroded               2 was moved downcurrent and was deposited at
               from the west shore of Keller Bay. In the area of             station 3, accreting the shoreline about 520 feet.
               station 22, where maximum erosion of 370 feet                 Although the shoreline between Palacios Bayou
               was recorded, there is evidence that.erosion was              and Oliver Point is concave, it was also eroded. The
               prevalent prior to 1856.                                      shoreline was erosional because waves approaching
                                                                             from the north struck the area at a high angle. Net
                              Salt Lake and Redfish Lake                     land loss was about 199 acres.

                    Salt and Redfish Lakes were initially parts.of                        Oliver Point-Tres Palacios Creek
               Carancahua Bay. They were cut off from the main
               body of water by the accretion of spits. The                        This segment of the bay.shore lies in the lee
               shoreline of Salt Lake accreted approximately 8               of the prevailing southeast wind and, -therefore, it
               acres since 1856, but there was a loss of about 28            is not significantly affected by waves generated by
               acres along the Redfish Lake. shore. The long-term            the southeast winds. However, waves approaching
               trend has been for the lakes to fill with sediment            from the north do erode the shoreline.

                     24

                           Several accretionary pockets are present along             the dominant process along this part of the bay
                     this predominantly erosional bay shore, e.g., the                shore. Deposition was recorded in local reentrants
                     southeast shore of Coon Island Bay and a small                   and to the west of Buttermilk Slough where shell
                     area lying between stations 11 and 12. Accre-                    beaches and berms are common.
                     tionary areas are protected by oyster reefs (Coon
                     Island) and shell spits.                                               Deposition and erosion were approximately
                                                                                      the same between 1856 and 1957. There was a net
                           Approximately 350 to        440 feet of shoreline          land loss of approximately 23 acres.
                     retreat were recorded at         stations 12 and 13,
                     respectively. Each of these areas is a promontory,                                       Oyster Lake
                     upon which wave energy is focused. Net land loss
                     was ap Iproximately 73 acres.                                          Oyster Lake is a small, shallow, tidally influ-
                                                                                      enced water body that is connected to Matagorda
                                  Tres Palacios Creek-Turtle Point                    Bay through Palacios Bayou and the Intracoastal
                                                                                      Canal.
                           Shoreline accretion prevailed between the                        Most of the south shore is accretionary.
                     mouth of Tres Palacios Creek and Grassy Point,                   Erosion dominates the other shoreline segments.
                     whereas erosion dominates the shoreline between                  Erosion amounting to 150 feet was recorded at
                     Grassy Point and Turtle Point. Sediment is                       station 7. Spoil outwash has accreted the south.
                     supplied to the north shore by river flooding and                shore 1,040 to 1,480 feet at stations 5 and 4,
                     by wind tides produced by the southeast wind.                    respectively. There was a net land gain of about
                     Erosion in the Grassy Point-Turtle Point areas                   220 acres.
                     results from a paucity of sand-size sediment
                     supplied to the area and from relatively large waves                                     Summary
                     from the southeast. Net land gain for the shoreline
                     segment between the mouth of Tres Palacios Creek                       Most of the Gulf and mainland shorelines of
                     and Grassy Point was about 78 acres.
                                                                                      the Matagorda Bay area were in an erosional phase
                                                                                      from 1856 through 1957. The erosional shoreline
                           Only one significant accretionary area occurs              trend was established prior to any major activities
                     between Grassy Point and Turtle Point. This is a                 of man which could have caused a change in
                     spoil area created by dredging boat harbors at                   shoreline stability.
                     Palacios; 'accretion amounts to about 9 acres. Net
                     land loss for the Grassy Point-Turtle Point shore-                     Man's activities tend to accelerate Gulf shore
                     line was about 91 acres.                                         erosion by depleting the sand supply. Sedimenta-
                                                                                      tion has been localized by jetties that trap sand on
                                     Turtle Point-Turtle Creek                        their upcurrent sides. Erosion is initiated or accel-
                                                                                      erated on- the downcurrent sides of jetties. The
                           Waves that approach from the north affect                  principal effect of man's activities in the bay area
                     this shoreline segment more than waves produced                  was shoreline accretion.
                     by southeast wind. This is demonstrated by the
                     fact that erosion exceeds accretion, and that the                      Natural accretion of the Gulf shoreline was to
                     rate of erosion increases as Turtle Bay widens                   the southwest of Greens Bayou and Pass Cavallo.
                     westward. Shoreline retreat of 320 feet was                      Accretion to bay shores occurred at the heads of
                     recorded at station 20. Net land loss was about 45               bays as bayhead deltas, at the terminus of tidal
                     acres.                                                           channels as flood deltas, and on the back side of
                                                                                      Matagorda Peninsula as washover deposits.
                                    Turtle Creek-Sartwelle Lakes
                                                                                            Appendix A summarizes the shoreline changes
                           Depositional and erosional shoreline segments              (1856-1957) of the Matagorda Bay area in terms of
                     alternate in this area. Waves from the southeast are             acres of land acereted or eroded.

                                                      MARSH DISTRIBUTION, 1856-1957

                    Marshes were mapped on the same, charts,                  tion, and relative sea-level change.. River diversion
               maps, andaerial photographs that were utilized for             and impoundment, construction of dams across
               shoreline mapping. Five vintages of marsh distribu-            tidal creeks, dredging of channels, and creation of
               tion could not,be displayed on a single set of maps,           spoil mounds are some of man's activities that
               and, therefore, long-term changes in marsh area                produce change in marsh area.
               were determined by comparing the oldest coastal
               charts and the youngest aerial photographs.                      Marsh Change Resulting From Natural Processes
                    The 19.56-1957 marsh distribution was                           A decrease in marsh area was recorded along
               mapped on Tobin photomosaics (scale .1: 24,000).               the bay shore of Matagorda Peninsula. The
               Field work (winter 1971 through spring .1972)
               verified the photo interpretation and also docu-               1856-1859 marsh was widely distributed, whereas
                                                                              the 1956-1957     marsh was more restricted in area.
               mented the fact that certain marsh areas had been
               filled or dammed by man in the interim period of               Between 1856 and 1957,. themarsh area decreased
                                                                              through erosion and deposition. The Gulf shore         line
               1957-1972. Wetlands were mapped by the U. S.
               Coast Survey in 1856-1859. The distinction was                 was eroded and marsh . deposits were locally
               not made                                                       exposed,in the swash zone.. Burial of marsh by
                         . however, between salt marsh and fresh-
               water marsh. The 1856-1859 marsh boundaries                    washover deposits and erosion along the.bay shore
                                                                              further reduces marsh area.
               were determined      by comparing the 1934-1937,
               1952-.1953,. and    1956-1957 photomapping with
               the U. S. Coast Survey charts.                                       Erosion and deposition have decreased the
                                                                              marsh area of the Pass Cavallo flood delta. Marsh
                    A set of eight maps at       a scale of 1:48,000          has been destroyed by erosion as Pass Cavallo
               shows the distribution of marshes during                       migrates westward, and burial of marsh by wash-
               1856-1859 and 1956-1957. Marshes are color                     over deposits has also reduced marsh area.
               coded. The 1856-1859 marsh is represented by
               diagonal red lines and the 1956-1957 marsh is                        Much of the bay, shore is composed of marsh.
               shown in solid green.. An overlap of colors depicts            Marsh is commonly eroded by waves approaching
               the persistence.of the marsh for at least 100 years.           from the. south or north. C     Ionstruction of beaches
               Extinct marshes are shown in red only, and a single
                                                                              and   beims at the     bay margin is coincident with
               green color indicates areas of marsh expansion.                marsh erosion.

                    Marsh maps have the. same designation as
               shoreline change maps--Brown Cedar Cut,                              Small, enclosed water bodies, such as Powder-
               Colorado River, Shell Island Reef, Pass Cavallo,               horn Lake, Chocolate Bay, Salt Lake, and Redfish
                                                                              Lake, are less affected by wave erosion than are the
               Lavaca Bay South, Lavaca Bay North, Carancahua
               Bay, and Palacios Bay areas (fig. 9).                          larger water bodies. Marshes associated with the
                                                                              small enclosed water bodies, however, also
                              General Wetland Trends                          decreased in size. Sediment was washed into the
                                                                              marsh from adjacent slopes.
                    Many of the marshes in. the Matagorda Bay
               area decreased in size from 1856 to 1957. Some of                    Marsh area increased. where streams discharge
               the 18564859 maps, however, did not extend far                 directly into the bays, for example: (1) at the head
               enough up some of the bays and their associated                of Lavaca Bay (Placedo Creek, Garcitas Creek, and
               creeks and rivers for a  .vAlid.comparison to be made          Lavaca River).; (2) at the head of Carancahua Bay
               between the oldest and youngest marshes.                       (Carancahua Creek); and (3) at the head of Tres
                                                                              Palacios Bay (Tres Palacios Creek). Marshes asso-
                    Significant marsh changes occurred on                     ciated with the Holocene Brazos-Colorado delta
               Matagorda Peninsula, in the Lake Austin area, and              (Lake Austin area). increased in size . during
               on the Colorado delta. Changes in marsh area result            1856-1957. A probable cause.of marsh expansion
               from both natural. processes and man's activities.             was compactional subsidence of formerly surficial
               Natural causes are shoreline erosion, sedimenta-               deltaic deposits.

                   26

                         Three areas on the bayside of Matagorda               large marsh areas. This kind of activity converts
                   Peninsula exhibited an increase in marsh area.              marshes into fresh-water lakes. Examples of
                   These are marsh islands associated with active and          marshes that were dammed are: (1) Blind Bayou
                   inactive tidal channels. Two of these tidal channels        area (Lavaca Bay South area); (2) Huisache Cove
                   occur on the Brown Cedar Cut area map.. The                 (Lavaca Bay North area); (3) Piper Lakes and a
                   western channel, Brown Cedar Cut, is active; the
                   ot .her channel, no .w closed, lies at the east end of      marsh along the    'north shore of Carancahua Bay
                   east Matagorda Bay. A third tidal pass area, Greens         near the Jackson-Calhoun County line (Carancahua
                   Bayouj is also closed (Shell Island, Reef area map).        Bay area); and (4) Buttermilk Slough. (Palacios Bay
                                                                               area).
                      Marsh Change Resulting From Man's Activities
                                                                                    A large marsh has developed on the Colorado
                         Man's activities may either destroy or create         delta. Within the next few years, the course of the
                   conditions that promote marsh growth. Some                  Colorado River will be diverted, and it will
                   marshes were buried by spoil along the bay margin;          discharge into Matagorda Bay between Culver Cut
                   see the mainland shoreline on the Brown Cedar
                   Cut, Colorado. River, Shell Island Reef, and Pass           and Middle Channel (Colorado River area map). A
                   Cavallo, maps. Spoil outwash has created conditions         new delta will be constructed in this area and there
                   favorable for marsh growth in the vicinity of               should be an increase in salt marsh in that area.
                   McNabb Lake (Colorado River area) and Fresh-
                   water Lake (Shell Island Reef area).                             Expansion and/or decrease in marsh area is
                                                                               summarized in appendix B. Net loss or gain for the
                         Several dams have been constructed across             period 1856-1859 through 1956-1957 is expressed
                   tidal creeks and between the      bays and relatively       as. acres.

                                       COASTAL PROCESSES AND SHORT-TERM SHORELINE CHANGES

                         Observations of coastal processes operating on             Gulf and mainland shorelines may be dras-
                   Gulf . shorelines of Matagorda Peninsula and                tically altered during the approach, landfall, and
                   Matagorda Island began in the winter of 1970 and            inland passage of hurricanes (Hayes, 1967; Scott
                   continued through the fall of 1973. Similar obser-          and others,. 1969; Shepard,, 19,73). Storm-surge
                   vations were made along the mainland shoreline              flood and attendant , breaking waves erode Gulf
                   during the winter of 1971 and spring of 1972.               shorelines a few tens to a few hundreds of feet.
                   Short-term shoreline.changes were measured in the           Washovers along barriers and peninsulas are com-
                   field, and an attempt was made to correlate these           mon, and salt-water flooding may be extensive
                   changes with coastal processes.                             along mainland shorelines.
                                     Coastal Processes                              Rivers and small streams normally flood in
                         Processes that constructed and that are               the spring and early fall. Flooding corresponds
                   presently. modifying shorelines. in the M    .atagorda.     with spring thunderstorm activity and the
                   Bay area are astronomical and wind tides,. long-            hurricane season. Rivers may flood as a result of
                   shore currents, normal. wind and waves, hurricanes,         regional rainfall, but the smaller streams may be
                   river flooding, and slump along cliffed shorelines.         activated only by. local thunderstorms. Effects of
                                                                               river flooding are: (1) overbanking into floodbasins
                         In the Gulf Coast region, astronomical tides          and onto delta plains; (2) progradation of bayhead
                   are low, ranging from a maximum of about 2 feet             and oceanic deltas; and (3) flushing of bays and
                   along the Gulf shoreline to about 0.5 foot in the           estuaries.
                   bays.. Wind regime greatly influences coastal
                   processes by raising or lowering water level along              Short-Term Shoreline Changes, 1957-1972
                   both Gulf and mainland shorelines, and by gen-
                   erating waves and. longshore currents, (Price, 1954;             The direction and rate of shoreline change for
                   Hayes, 1965; Watson, 1968; Watson and Behrens,              the  period 1856-1957 were determined by using
                   1970).                                                      vintage charts, maps, and aerial photographs. A

                                                                                                                           27

             field study was conducted from October 1971                     Beaches composed of shell and rock frag-
             through May 1972,, for the purpose of docu-                ments characterize the rapidly eroding shorelines.
             menting shoreline changes which occurred after             Shell and rock fragments are derived primarily
             1957. Profiles were measured with alidade and              from Pleistocene and Holocene deposits which are
             stadia rod along Gulf and mainland shorelines.             being eroded from the shoreface and inner conti-
                                                                        nental shelf. These materials are direct evidence
                  Beach profiles were - measured in 1971-72             that the volume of terrigenous sand is low. The
             from the waterline to a known geographic point,            relative abundance of shells of shelf and bay
             which distance could be compared to the distance           species indicate that relict paralic deposits are the
             between the 1957 waterline and the same geo-               chief sources of coarse sediment that compose
             graphic point. At each profiling station, physio-          beaches and ramps of Matagorda Peninsula.
             graphic setting and sediment composition were
             described. Normally, the profiles were extended                 Beaches between Caney Creek and Pass
             into the bays and Gulf of Mexico to water depths           Cavallo have a high      shell and rock fragment
             from 1 to 3 feet. Sediment characteristics, fauna          content (fig. 10). Shell material consists of both
             and/or flora were determined for. the shallow,             bay. and Gulf species, with bay species being more
             nearshore parts of. the profiles. Also, marsh and          abundant. East of the mouth of the Colorado
             upland flora were described wherever a profile             River, Crassost.rea virginica and Rangia,sp. are the
             crossed these communities. Observations of coastal         most common species.. Radiocarbon ages for
             processes were made at. each profiling station;            Crassostrea virginica shell collected from this beach
             observations were. also made at selected intervals         segment range from 860 to 37,000 years B.P.,
             between profile stations.                                  indicating that offshore Pleistocene and Holocene
                  Within the Matagorda Bay area, there are two          deposits are sources of oyster shell. West of the
             broad classes of shorelines: (1) open Gulf shoreline       mouth of the Colorado River, three bay species
             which extends from the vicinity. of Caney Creek on         (Crassostrea virginica_ Y-ereenaria campechiensis
             the northeast to about 4.5. miles west of Pass             texana, and Rangia cuneata) are more common
             Cavallo (fig. 1); and (2) mainland shoreline. A wide       than Gulf species. Locally, one, of these bay species
             range of variation in sediment types and physio-           may be more abundant than the, other two, but
             graphic features was encountered within the                throughout this segment of, beach, Rangia cuneata
             Matagorda Bay region. These variations reflect past        is the dominant species. Rock fragments are
                                                                        common between Caney Creek and Pass Cavallo;
             geologic history , of the area, coastal processes
             currently - operating on the shoreline, sediment           they occur most frequently between Caney Creek
             availability, and, to a certain degree, man's              and.the Colorado River. Rock fragments range in
             activities.                                                size from granule-size gravel. to boulders up to
                                                                        2-foot-maximum diameter. Small rock fragments
                  Characteristics of Gulf and mainland shore-           are compact, and, large fragments are - platy to
             lines, based upon field observations, are presented        bladed (clast morphology, after Sneed and Folk,
             in the following sections on           "Open Gulf          1958). Pleistocene distributary sand, beach rock,
             Shorelines" and "Bay Shorelines."                          reef flank sediments, and carbonate lacustrine
                                                                        deposits are the sources of rock fragments.
                              Open Gulf Shorelines
                                                                             Profiles of the Gulf beaches (figs. 10, 11, and
                  In general, Matagorda Peninsula beaches are           pl. I) show that shell beaches are narrower and
             characterized by a mixture of terrigenous sand,            steeper than sand beaches. Evidence.that most shell
             shell, and rock fragments. Matagorda Island, on the        beaches are erosional is the common occurrence of
             other hand, has beaches composed of terrigenous            marsh deposits in the swash.zone. An exception to
             sand (Wilkinson, 1973). Composition of beach               the erosional nature of shell beaches is shown at
             sediment is a good indication of sand availability         profiles 10, 11, and 12 (fig. 11). Terrigenous sand
             and stability of a particular shoreline segment            content of these shell beaches, is higher than those
             (McGowen and Garner, 1972; McGowen and                     to the east. This segment of Matagorda Peninsula is
             others, 1972). Most of @Matagorda Peninsula has            slightly convex seaward; it lies along the axis of a
             been in an erosional condition for at least 118            buried Pleistocene fluvial sand body (fig. 2). The
             years, whereas Matagorda Island has just recently          shoreline convexity, short-term, accretionary trend,
             shifted from an equilibrium to an erosional phase.         and increase in terrigenous sand are probably

                   28

                                                                          Cliffed shoreline with Pleistocene deposits exposed
                                                                            in the swash zone

                                                                          Shell and rock fragment beaches

                                                                          Terrigenous sand beaches

                                                                          Marsh-dominated strondline

                                                                          Shoreline altered by man's activities

                        Port
                       Lovaco

                                                                               9@1 @O

                                         Keller
                                                                    WOOS

                                                                710 P,10,io

                                         MArAGORDA BAK
                                                                   ke
                                                                                             MotogordG             Austin
                           Port O'Connor

                    ESPIRIrU SAWO
                      84),                                                                  rAsr mAr46oRDA aA),
                                     rj

                                                       S111f of AASWO

                                                                                  0
                                                                                                     12

                                                      Figure 10. Shoreline types of the Matagorda Bay area.

                   related to the Pleistocene sand source, which              9 to 25 feet, occur along segments of Matagorda
                   underlies the shoreface in the vicinity of profiles        Peninsula that have broad sandy beaches.
                   10, 11, and 12.
                                                                                   Some of the principal questions about Gulf
                        The distribution of sand and shell beaches is         shorelines in the area involve the location of sand
                   shown on figure 10, erosional and accretionary             and shell beaches and the factors which cause
                   rates are shown. on figure 11, and beach profiles are      shoreline erosion. Sand and shell beaches are the
                   shown on plate I. Profiles of sand beaches on plate        products of sediment availability and coastal
                   I are represented by numbers 4, 5, 13, 14, 15, 16,         processes that are operating in the area. Sediment
                   28, 30, 31, and 32 (appendix C, profiles. 23 and           sources are the Brazos and Colorado Rivers, the
                   30). The occurrences of fore-island dunes and              Holocene Brazos-Colorado delta, and the inner
                   beaches consisting of shell and rock fragments are         continental shelf and shoreface. The principal
                   mutually exclusive. Coppice mounds and low,                coastal processes responsible for sediment trans-
                   discontinuous sand dunes are associated with shell         port and deposition are wind, waves and attendant
                   beaches. Fore-island dunes, ranging in height from         longshore drift, and hurricane storm surge.

                                                                                                                                   O'er                            Gulf and mainland beach profiles run in
                                                                                                                                                                                               compared with shoreline position

                                                                                                                                                                                                12
                                                                                                                                                                                                         Location of profiles

                                                                                                                                                                                                         Average yearly erosional rate (25
                                                                                                                                                                                                14
                                                                                                                                                                                                         Average yearly accretion rate (25
                                                                         52
                                                             51        +2              53         Swan Lake                                                                                   0          Stable shoreline segment
                                                                                     -1                                            Caan C 10
                                                PORT                                       54                                                                                                                                                                                              /V
                                              LAVACA

                                                                                                                                   -2
                                                             10
                                                        50 +-2
                                                             'q8      -7                   55                    59
                                                               47 -20                        N-6                        Q
                                                               46                           Keller               -5                                                              66
                                                                    45                      190Y -                                                                            6@          .2
                                                                    44      -5                         57 58                                                   64*            -1.4 67
                                                                                                56                                 1 652  63                       6                                                                                                     4                 8
                                                                 @
                                                                      3                              A          A-                 V 4      0                  -2             PALACIOS
                                                                    51   1,+ 1                       -0.                    0.5 -4 _6                                      -3
                                                                      42 _4                                                                                          69 68                                                                                                    Miles

                                                               Powderhorn
                                                                    0*8                             Adatagoroa BGy                            -3t,             Oyster
                                                                                                                                                       71          ake
                                                                               41     -32                                                                   73
                                                                    PORT                                                                                                                                                           42   MATAGORDA
                                                               O'CONNOR 4            4-10                                                                                                                                                               74                                 -2
                                                                                                                                                                                                                                                      IN                .75         77
                                                                                                                                   Greens 80YOU                                                                                                   -13               +                  076
                                      ESPIrdu Santo Bay                                            -2           -3                 +12                                                                                                                                           -44
                                                                                         -2          35         30       0 -2            2726 25 24            23 4_1 el        20       19 1                                      East lwalworda           Bay
                                                                                       3 3    34                1                  6 39 4           6 A          6 A 0             A                           A
                                                                      C:Z>               A3            -                           -12 -0+4 -11 -10 -12        -4-8               -2    - 10      11 411  161           13
                                                                                                                                                                                                         u
                                                                                           -16                                                                                                +4  _,        T                                                   10
                                                                                                                                                                                                    .2                0                                                         9 8,
                                                                                                                                                                                                           +7
                                                                                                                                                  Go// of                         Ivexice                                                       15 +3        +;                  -9        +8

                                                 Figure 11. Short-term erosional and accretionary shorelines of the Matagorda Bay area. At each profile, which was run in I
                                      measured from the waterline to a known geographic point. These distances were then compared with the 1956-57 distances from the w,

                   30

                         Modem rivers are not providing a significant         energy events, the entire peninsula migrates bay-
                   volume of sand to. the longshore drift system. The         ward. Major hurricanes scour storm channels
                   Brazos River discharges its sediment load about 17         through the peninsula and build lobate sand bodies
                   miles east of the study area. The Brazos transports        that project into the bay. At this.time, coarse shell
                   a large volume of sand and mud to the Gulf, but            and rock fragments accumulate in.the interchannel
                   beaches only five miles west of the river mouth Are        areas as shell ramps. Storms that raise the water
                   retreating at rates of 25 to 40 feet per year. The         level less than 5 feet activate a few storm channels,
                   Brazos carries a large suspension load, approxi-           and sand -is transported through these channels
                   mately 993 x 106 cubic feet per year. The                  toward the bay area, building small washover fans.
                   morphology of the present Brazos delta (con-               Most of the present beach of Matagorda Peninsula
                   structed since 1929, Nienaber, 1963) and the               west of the mouth of the Colorado River postdates
                   direction of wave approach and wave, refraction            Hurricane Carla.
                   limit the volume of sand that will be contributed
                   to the beaches of Matagorda Peninsula.                           Under normal wind and tide conditions,
                                                                              sediment is moved onshore and alongshore to the
                         Promontories, such asthe Brazos delta, cause         southwest. Erosion is not as severe under normal
                   waves , to refract. Sometimes wave refraction              sea conditions as during storms, but steep, short-
                   creates currents that flow counter to the dominant         period waves are especially erosive in the area of
                   direction of southwest longshore drift. Hayes and          the Holocene deltaic headland. There is selective
                   others (1970), in their discussion of offset inlets,       sorting of terrigenous sand, shell, and rock frag-
                   explain the mechanism of countercurrent genera-            ments. Turbulence of. breaking waves tends to keep
                   tion by wave refraction. The Brazos delta, by              the fine- to very fine-grained terrigenous sand in
                   causing wave refraction, creates a local drift system      suspension, making it readily available. for long-
                   that is directed eastward along its western periph-        shore transport. The large, heavy shell and rock
                   ery. This countercurrent system is possibly one of         fragments travel at a slower rate than sand, thereby
                   the mechanisms that retards westward sand trans-           forming a lag in the upcurrent areas; terrigenous
                   port along Matagorda. Peninsula.                           sand tends to be concentrated.in the downdrift
                                                                              direction (figs. 11 and 13).
                         The Colorado River contributes about 250 x
                   106 cubic feet of suspension load to Matagorda                   Two other factors are involved in sand and
                   Bay and the Gulf of Mexico annually. Annual sand           shell distribution. First, .. the Pleistocene and
                   contribution is estimated to be about 20 x 10'             Holocene sedimentary sources have a high mud/
                   cubic feet. Sediment and water discharge is divided        sand ratio. Secondly,.tidal passes are areas in which
                   between west Matagorda Bay and the Gulf of                 sand is concentrated. In the areas where
                   Mexico; the sediment volume delivered to each has          Pleistocene and Holocene deposits are bemig
                   not been determined. Sand delivered to the Gulf            eroded, the longshore current system is sand
                   by. the Colorado River, however, causes accretion.         deficient; erosion occurs because the longshore
                   of the shoreline for a distance of about 1 mile west       current has the capacity to. transport a greater
                   of the river mouth. Beyond. that point, the                sediment load. Since the shoreline is eroded
                   shoreline is mostly erosional.                             throughout most of its length from Caney Creek to
                                                                              Pass Cavallo and because drift is to the west, sand
                         In 1957, Matagorda Peninsula had a well-             load tends to increase in the direction of longshore
                   developed beach, shell ramp, and wind,tidal flat           drift. This, in part, explains local development of
                   (fig. 12). Hurricane Carla (1961) breached, the            sand beaches. The volume of sand within the
                   peninsula in many places (fig. 12). Field measure-         longshore drift . system also increases, in areas
                   ments made in the spring of 1971 (fig. 12, and pl.         underlain by.Pleistocene fluvial sand.
                   I, profiles 19 and 23). indicate that during
                   Hurricane Carla the shoreline. was eroded 450 to                 Sand is stored in the bays within flood deltas.
                   600 feet. Shepard (1973) reported that as much as          Sand also accumulates on the barrier islands
                   800 feet of shoreline erosion occurred west of the         immediately downdrift from tidal inlets; this
                   Colorado River. In addition to eroding the beach           downdrift accumulation of sand produces a Gulf-
                   area, hurricanes and tropical storms transport             ward offset of barrier islands adjacent , to tidal
                   sediment onto the back.side of barrier islands and         channels. Downdrift offset is another indication of
                   into the adjacent bay. Through these brief but high        a sand deficient system (Seelig . and - Sorensen,

                                                                                                                                          31
                                         MA U GORDA           48AY

                                                                    A

                                      A                  GUL F      OF    MEXICO

                                                                             /V

                                                                                                              q

                                  U

                                             0                                                  2

                                                                      MILES
                                Wind-fidal flat and marsh      Shell romp and vegetated flat     Beach          Bare sand
                                                                      B

                     A                                SHELL RAMP
                                   BEACH
                   6                                                                     VEGETATED FLAT
                                           --,Erosional                                     JD-TIDAL FLAT
                   4                            Escarpment
                                                                                                                           BAY MARGIN
                   2
                   OL@
               U.

                           co          I/
                   4                               0                  1,000            2,0 0
                                                    I,--
                                                                      FEET                                                 &E.G
                                                                      C

                    Figure 12. Effects of Hurricane Carla, 1961, on a segment of Matagorda Peninsula beginning about 1. 5 miles west of the
              Colorado River. (A) Matagorda Peninsula as it appeared in 1957. (B) Matagorda Peninsula shortly after the passage of
              Hurricane Carla. This shoreline segment was eroded.as much as 800 feet. (C) Profile across Matagorda Peninsula (May 1971);
              parts of the shoreline had accreted 500 feet.

                   32

                                                                                                Z

                                    - -- - ----------
                                                                            17)

                                                          'eN @w
                                                                                                    oo

                                                        MATAGORDA BAY AREA
                                                                                    0

                                              0 100 200 300

                                         Figure 13. Relationship between direction of wave approach and longshore drift.
                                    Waves generated by prevailing southeast wind strike the shoreline at an angle. The
                                    northeast segment of the wave begins to feel bottom before the southwest segment,
                                    thereby generating currents that move alongshore toward the southwest.

                                                                                                                                                      33

               1973). Tidal channels along Matagorda Peninsula                         shorelines; (2) shorelines characterized by shell
               have opened and closed several times. For example,                      beaches and berms; (3) river-influenced shorelines;
               Greens Bayou was openedby hurricanes in 1943,                           (4) shoreline segments dominated by salt                  marsh;
               1961, and 1967, and closed shortly after passage of                     and (5) shorelines dominated by spoil outwash.
               the storms. Pass Cavallo was closed at least once.
               With the closing of a tidal pass, the shoreline is                             Cliffed shore lines.-The. distribution of cliffed
               straightened when sediment -is eroded from the                          shorelines is shown on figure 10. Cliffed shoreline
               downcurrent island (fig.. 14). Sediment eroded                          profiles are shown on figure 11. A comparison of
               from Matagorda Island moved to the southwest by                         these profiles (pl. 1, profiles 37, 41, 46, 47, 51, 55,
               longshore currents where it accumulated causing                         59, 62, 63, 65, 66, 71; appendix C, profiles 37, 41,
               accretion of a shoreline segment without any                            47, 51, 55, 59, and 62) with figure 11 indicates
               significant increase in the overall sand budget.                        that cliffed shorelines are erosional. Cliffed shore-
                                                                                       lines increase in height, toward the heads of Lavaca,.
                                        Bay Shorelines                                 Keller, Carancahua, and Tre.s.Palacios Bays (fig..1).
                                                                                       Commonly, as cliff heights increase, erosional rates
                      There are a variety of overlapping bay shore-                    decrease.
               line types (fig. 10) in Matagorda Bay. Most of the
               bay shoreline is eroding; rates of erosion (for the                            Field measurements and historical monitoring
               interval 1957-1972) range from 1 foot. to. 25 feet                      both indicate that cliffed shorelines., have been
               per year. Equilibrium and accretionary shorelines                       erosional for at least the past 116 years (from 1856
               are rare; accretionary -rates range from 0.5 foot to                    to 1972). A comparison of erosional rates for the
               3.0 feet per year.                                                      interval 1856-1957 with                field measurements
                                                                                       (1957-1972) indicates that             there has been an
                      Five types       of shorelines characterize the                  increase, in erosional rates            for most of these
               Matagorda Bay system. Shorelines are classified on                      shoreline segments. (table 2).
               the basis of elevation and gradient, composition
               and caliber of materials constituting beaches, dom-                            The height of cliffed shorelines, in Matagorda
               inance of vegetation,and degree of alteration by                        Bay    generally 'increases northward; erosional rates
               man's activities. The shoreline types are: (1) cliffed                  consequently decrease northward. Lowest cliffs are

                                                Table 2. Comparison of erosional rates of cliffed shorelines
                                          determined from field measurements (1957-1972) and from historical
                                          monitoring. (1856-1967).

                                            Field Measurements (1957-1972)          Historical Monitoring (1856-1957)
                                          Station            Erosional Rate            Station             Erosional Rate
                                                              ,(yearly av.)                                  (yearly av.)

                                          41                       -32  feet           41                        - 7  feet
                                          46                       -20                 46                        -1.4
                                          47                       - 7                 47                        -0.6
                                          51                       -1.5                51                        .5.2 t
                                          57                       -0.4                57                        -2.5 *
                                          58                       .9.0                58                        -3.8 *
                                          62                       -4.0                62                        -1.7 *
                                          63                       -6.0                63                        -1.5 *

                                          tThis segment is near the head of Lavaca Bay. A decrease inerosional rate
                                          m ay result from increased sediment delivery. through Lavaca-Navidad
                                          Rivers and Garcitas Creek as a result of increase in area of.cultivation.

                                          *This area is adjacent to that part of Matagorda Bay that is being dredged
                                          for oyster shell. Increased erosional rates may result from destruction of
                                          marine grassflats and decrease.in numberof Orassostrea virginica clumps
                                          (personal communication, Mr. H. C. Smith, Dec. 20, 1971).

                      34

                       &CLOSING OF TIDAL PASS
                       B.TIDAL PASS CLOSED, DELTA
                              BECOMES A WASHOVER,
                               BEACH EROSION
                       C. TIDAL PASS OPENED, TIDAL DELTA
                               ERODED, BEACH ACCRETION

                       A.

                                                                                                    ................    ...
                                                                       ...             . . ....... .

                       B.
                                                                             . . . . . . . . . . . . .

                       C.

                           Figure 14. Postulated sequence of events leading to, the development of an erosional unconformity on Matagorda
                     Island. Sequence C is the pres;Ient confieuration of Matagorda Peninsula and Matagorda Island in the vicinity of Pass Cavallo.

                                                                                                                                     35

              about 4 to 5 feet, and the highest cliffs stand. about         area. to the swash zone where they form beaches
              20 feet above bay level. The most rapid erosional              along small reentrants, or a gravel veneer over the
              rates occur along shoreline segments,that face into            Pleistocene.
              the southeast wind (pl. 1, profiles 41, 46, 55, 59,
              62, and 63; appendix C, profiles 41, 55.1 59, and                     Shorelines at Gallinipper Point (appendix C,
              62). Each of these shoreline segments, except the              profile 47), north of Port Lavaca (appendix C,
              area of profile 41, is eroded into Pleistocene deltaic         profile 51) and along the south shore of smaller
              deposits (distributary sand, interdistribu.tary mud).          bays (pl. I, profiles 65, 66, 71) erode less rapidly
              The cliffed shoreline at profile 41 is eroded into a           than other cliffed . shorelines because they are
              lower, muddy, deltaic sand, and an upper, clean,               either in the lee of southeast winds or they are near
              incoherent strandplain sand. Since this shoreline              the heads , of bays where rivers discharge their
              segment is situated near Pass Cavallo, it is affected          sediment load. Profile 47 (appendix C) istypical of
              by both tidal currents and waves. Th       e bay margin        Pleistocene deposits exposed along Alamo Beach-
              in, the vicinity of profile 41 is, characterized by a          Gallinipper Point. This shoreline segment erodes
              broad sandflat with marine grass and oyster                    more rapidly in the winter when winds are from
              clumps.                                                        the north., Cliffs are 17 to 20, feet high in the area
                                                                             of profile 51. Pleistocene distributary sands and
                   The shoreline in the area of profiles 55 and 59           interdistributary muds are exposed in cliff faces.
              faces into the southeast wind. Cliffs have. been               Shoreline recession. results from wave erosion and
              eroded into Pleistocene muds that accumulated                  slumping (profile 51, appendix C).. In the imme-
              along the distal. end of abandoned Sangamon                    diate area of.. this. shoreline segment, the bay is,
              deltas. Erosional rates here are less. than those.             floored by Pleistocene mud.
              along, the western shoreline of Matagorda and
              Lavaca Bays because fetch is relatively short across                  Parts of the Matagorda Peninsula bay shore-
              Keller and Carancahua Bays and Pleistocene muds                line   are characterized by low cliffs. Erosional
              offer more resistance to wave erosion than sandy               escarpments have been cut into barrier-flat sands
              deposits. The bay bottom immediately offshore                  and marsh deposits consisting of muddy sand.
              from profiles 55 and 59consists of Pleistocene                 Escarpments are about 1 to 4 feet, high, and,
              mud...Beaches are virtually nonexistent in these               erosional rates are 2 to 3 feet per year. Erosion is
              areas, but there is generally a veneer of caliche     and      greatest during the winter when winds are from- the
              shell gravel over the eroded Pleistocene surface.              north.
              Most of, the shell is derived from Crassostrea
              virginica. During exceptionally high wave condi-                      Cliffed shorelines have developed primarily
              tions, gravel composed of caliche and oyster shell is          from lateral cutting of Pleistocene, de        posits by
              deposited upon these erosional escarpments                     wind@-generated wa    ves. They are developed, to a
              forming a thin berm.                                           lesser. degree, on      th e b.ayside of barriers and
                                                                             peninsulas. Shorelines    'of bays having a.large fetch
                   Erosional rates along the north shore of                  erode rapidly, particularly in areas where cliff
              Matagorda Bay (profiles 62 and 63) are inter-                  height is low and. where cliffs consist of incoherent
              mediate between... those of the west shore of                  sand. Along most of these shorelines, the only
              Matagorda and Lavaca Bays and the northeast                    coarse sediment (sand size or greater) available to
              shore of Keller and Carancahua Bays. Cliffs are cut            the, wave and longshore - drift. system is derived
              into Pleistocene muds, and, like the shorelines of             from the cliffs and from molluscs living in the
              Keller and Carancahua Bays, beaches are rare; there            adjacent, shallow, bay-margin areas. Where oyster
              are shell beaches to the east and west of, this area           clumps are abundant, they provide coarse material
              (Carancahua Pass and Well.Point). To the south of              that may be deposited at the base. of cliffs, thereby
              the Carancahua Pass-Well Point area, there is a                retarding wave erosion.
              relatively broad shoal up. to 0.25 mile wide
              developed on eroded Pleistocene sediments. A sand                     Shorelines characterized by shell beaches and
              veneer overlies the Pleistocene for a distance of              berms.-Parts of Matagorda Bay and Lavaca Bay
              about 200 feet -from the cliff; this 200-foot zone is          shorelines are characterized by shell beaches (fig.
              characterized by bare Pleistocene mud with some                10). Prominent shell beaches occur along the north
              caliche clasts, burrows, and oyster clumps. Oysters            and west shores of Matagorda Bay and the west
              and caliche fragments are transported from this                and south shores of Lavaca Bay. Prior to excava-

                     36

                     tion of the Intracoastal Canal, shell beaches were                     Composition of shell beaches is variable. At
                     continuous between the West Branch of the                        Dog Island, whole and fragmented oyster shell
                     Colorado River and Palacios Point. This shoreline                makes up most of the deposit. In the Shell Lakes
                     segment was, cuspate, and oyster reefs were. off-                area, the ridges consist almost entirely of frag-
                     shore from each salient. Shell Island Reef and Mad               mented shell ranging in size from coarse sand to
                     Island, Reef appear to be bayward extensions of                  pebbles. Oyster shell is the most abundant con-
                     these salients (fig. 15).                                        stituent; however, shelf species are common. One,
                                                                                      of the highest shell ridges lies just to the east of
                           Numerous shell beach segments were profiled                Carancahua. Pass. The ridge is fronted by.
                     (fig. 11, profiles 42, 43, 44, 45, 48, 49, 50, 56, 57,           1,250-1,3,00 feet of salt marsh, which is underlain
                     58, 68, 70, .72, and 73; pl. I). Generally, salt                 by shell, suggesting that the shell ridge has
                     marshes lie between shell beaches and Pleistocene                remained virtually unchanged since it was
                     uplands. A few shell deposits are spits that are tied            deposited. The ridge at Carancahua Pass consists of
                     to Pleistocene headlands; others have accumulated                shell debris, with oyster shell being. the most
                     upon gently sloping, eroded, Pleistocene deposits.               abundant type. Caliche fragments constitute about
                     Heights of shell beaches and berms range from 1.0                5 percent of the deposit. Bay species, other than
                     foot to 9.5 feet and widths from 80.to.900 feet.                 oysters, and Gulf species were present; among Gulf
                     Thicknesses of shell beaches and berms were                      species identified was the "surf clam," Donax.
                     determined at Dog Island, Shell Lakes, Carancahua
                     Pass, Indianola, and Magnolia Beach (figs. 10 and                      In the Magnolia Beach-Indianola area (fig.
                     16); thicknesses range from 1 foot to 8 feet. Only               17),  there are two prominent beach ridges and
                     two trenches      completely penetrated the shell                several older shell berms that were deposited upon
                     deposits; both      were in the Indianola-Magnolia               escarpments cut into. the Pleistocene. Thickness of
                     Beach area.                                                      these deposits is   3 to 8 feet.  There is a wide range

                         M-r.Sh                                                                            .......... ...

                                                                                                                         Crob Lo

                                                              .. ..... ...
                                 Loke
                                                                                                                                        A H--
                      Mcd
                                                                                           MA
                                                                                                                                            - r---n

                         S e I i'd

                                                                                      SPOIL OUTWASH

                                                                                 1956 SHORELINE

                                       MATAGORDA                                 B A Y

                                                                                                              0     1/4   1/2          1 mile
                                                                                                                        SCALE

                           Figtire 15. Cuspate shell beaches, oyster reefs, and spoil outwash along the north shore of Matagorda Bay, west of the
                     Colorado delta. The shell beach marks the position of the 1856 shoreline. Mad Island and Shell Island reefs appear to have
                     been attached to cusps of the shell.beach. The 1956 shoreline lies some 1,100 to 2,500 feet bayward of the shell beach. The
                     shoreline accreted from spoil outwash.

                                                                                                                                      37

                               Bay
                     Port
                      Lavaca

                                                       CCARANCC HU  Palocios
              MAGNO    EACH-                           PASS
                   L'A 8'
              INDIANOLA AREA
                              U
                              0 0
                                         malagorda Bay
                                                                          SHELL       DOG
                                                                          LAKES        ISLAN  Matagorda
                                                                                             A

                                Port
                               O'Connor.                                                         Eas  A-fotGg0rdC
                                                                                                     say

                                                             GUL F_        OF       MEXICO

                                                                 0      4            12

                                                                          MILES

                                           Figure 16. Locations of trenches dug into shell beaches, berms, and spits.

              in texture and composition of materials composing               characterized by steep foresets that dip in the
              the shell. ridges. Some deposits, e.g. in the area of           direction of channel migration, horizontal bedding,
              the 3-foot trench, consist mostly of oyster shell               and a few poorly developed soil zones. Oyster shell
              with a few rock -fragments. Others, such as in the              is the most abundant component; however, there
              area of. the 4-foot trench south of Blind Bayou,                are many shelf- and inlet-related. species in this
              consist almost entirely of shell debris from coarse.            deposit (Parker, 1960.; Andrews, 1971), such as
              sand to pebble size. Shell was derived from both                Macrocallista nimbosa, Eonitia ponderosa,
              bay and Gulf species.                                           D-achycardium muricatum, Polinices duplicatas,
                                                                              Busycon contrarium, and R spiratum plagosus.
                    A large shell ridge extending from Blind                  This shell deposit accumulated as a northward
              Bayou to Old Town Lake (fig. 17) is up to 8 feet                migrating spit across a tributary of Matagorda Bay.
              thick; it is separated. from the Pleistocene uplands            A second . spit is represented by the present
              and Modem beach by salt marsh. This ridge has                   beach-berm system (fig. 17). With. the exception of
              been mined for road metal. Faces of some of the                 shell removed for road material, the older spit has
              shell pits display graded bedding, channel fill                 remained virtuallyintact since it was deposited.

                      38

                                                                     45

                                                                                                44

                                                               'x

                                                                                                         'T>

                                                                                                                            N

                            EXPLANATION

                               Modern shell beach
                                  and berm

                               Holocene beaches
                                  and spits
                               Salt marsh

                               Ponds
                     =45       Beach profile
                               Trench locality
                        8.0    Total thickness in
                                  feet
                        5.7+   Thickness from sur-
                                  face to water tabl
                                  in feet

                                                                                                                                77 7.
                                                                                                                                      0+
                                                                                                                         \3Q
                                                                                                                                        ..................

                                                                                                            -PLEIS
                                                                                                                      TOCENE..
                      0                     112                   1
                                                                                                                       UPLAND
                                          MILE

                                                                                                                                              A\

                             Figure  17.  Distribution of  shell beaches, berms,   and spits in the  Magnolia Beach-Indianola area. See figure 16 for
                       location.

                                                                                                                                                       39

                      A comparison of field measurements and                            beaches in the areas of profiles 57 and 73 are
                historical monitoring (table 3) indicates that most                     backed      by Pleistocene and older Holocene
                of the shell beaches were erosional during the                          deposits; during storms these deposits build
                period 1856-1972. Three segments, defined.by                            upward.     In the area of, profile 58, the low shell
                profiles 42-45, profile 48, and profiles 56-58,                         beach is    backed by wind-tidal flat, marsh, and a
                experienced an overall increase in rate of erosion                      water   body. During. storms, shell from the beach
                for the period 195,7-1972. Each of these shoreline                      washes into the marsh and lake. Erosional rates in
                segments is fronted by relatively wide bays on                          these three areas are controlled by height of the
                which large waves are generated by southeast or                         beach-berm system and the physiography of the
                north winds. Remaining shell beach areas display a                      adjacent area.
                decrease in rate of erosion. With exception of
                profile 73, each of these beaches is associated with                          Shell beaches that form parts of southern bay
                somewhat. le     ss expansive water bodies. Shell                       shorelines are depicted by profiles 48, 56, and 68
                beaches have an average yearly erosional rate that                      (pl. I and appendix C). These shoreline segments
                is significantly less than cliffed shorelines (shell                    erode at rates of 2 to 3 feet per year. Waves
                beaches, 2.6 feet; cliffed shorelines, 10 feet).                        generated. by northers, . are the . chief erosional
                                                                                        agents. The beach and berm in the vicinity of
                      Based on direction of prevailing wind alone,                      profile 48 is 9 to 10 feet high. It consists chiefly of
                the north and west shorelines should erode. the                         oyster shell; live Crass.ostrea virginica were found
                most rapidly. Profiles 42-45 are along. the west                        offshore in water about 3 feet deep. North of
                shoreline. Two of these areas (42 and 44) are                           profile 48, fetch is greater than in the other areas.
                erosional; one is, accretionary (43) and one is, in                     It is unlikely, however, that winter storms ever
                equilibrium (45). Shoreline configuration in this                       generate waves sufficiently large to construct, a
                area probably localizes erosion or accretion. Profile                   10-foot-high berm.. Large waves, associated with.
                45 is typical of the Modem shell beach, berm, and                       hurricane storm-surge ebb, probably constructed
                marshes of the Magnolia Beach area (appendix C).                        this beach and berm couple. Parts of this berm
                                                                                        have. been removed. for road material. The shell
                      Most of the shell beaches along the north                         berm in the area of profile 56 is about 2.5 feet
                shore of Matagorda Bay are erosional. At profiles                       high;.it consists of subequal amounts of caliche
                57 (appendix C) and 73, erosional rates are 0.4 and                     gravel and oyster shell. Live oyster clumps were
                1.0 foot per year, whereas at profile 58, the                           found along the shallow bay margin in water I to 2
                erosional rate is 9 feet per year. Shell berms and                      feet deep. A relatively wide salt marsh lies behind

                                                Table 3. Comparison of changes along bay-shore shell beaches, field
                                          measurements (1957-1972) and historical monitoring (1856-1957).

                                              Field Measurements (1957-1972)             Historical Monitoring (1856-1957)
                                          Station      Erosion or Accretion Rate        Station      Erosion or Accretion Rate
                                                               (yearly av.)                                  (yearly av.)

                                          42                       - 4.0 feet           42                         4.5 feet
                                          43                       + 1.0                43                         0.0
                                          44                         5.0                44                         2.8
                                          45                         0.0                45                      +3.6
                                          48                         2.0                48
                                          49                       + 6.0                49
                                          50                       +10.0                50
                                          56                       - 3.0                56                      +0.8
                                          57                         0.4                57                      - 2.5
                                          58                         9.0                58                         3.5
                                          68                         3.0                68                         0.4
                                          70                         1.2                70                         6.4
                                          72                         3.0                72                      -10.3
                                          73                         1.0                73                      - 1.5

                    40

                    the berm, and marsh deposits were exposed in the                River-influenced shorelines.-Where a river
                    swash zone. Winter storms are responsible for              discharges into a bay, its velocity decreases and its
                    development of this berm.                                  sediment load is . deposited forming a bayhead
                                                                               delta. The Trinity, Colorado, and Guadalupe bay-
                         Profiles 70 and 72 (fig. 11 and appendix C)           head deltas have been studied extensively
                    are typical of shell beaches that occur along east         (Wadsworth, 1941, 1966; McEwen, 1963; Kanes,
                    bay shores. Erosional ratesat profiles. 70 and 72          @1965, 1970; Bounia and.Bryant, 1969; Donaldson
                    are 1.2 and 3 feet per year, respectively. The shell       and others, 1970; Manka and Steinmetz, 1971). To
                    beach in the area of profile 70 is backed by a wide        date, there are no data on the Lavaca and Garcitas
                    salt marsh. Oyster reefs which lie offshore from           bayhead deltas which are building into Lavaca Bay
                    profiles 70 and 72 are effective in damping waves          (fig., 1). The Garcitas delta has not prograded
                    and reducing erosional rates.                              significantly beyond the head. of Lavaca Bay,
                                                                               whereas. the Lavaca delta has prograded about 2.7
                         Shell beaches erode less rapidly than       other     miles into the bay. For the most part, deltas are
                    bay shoreline types because shell material remains         accretionary features. However, because of the
                    in the swash zone, whereas, very fine-grained sand         lateral shifts in sites of sediment input, one deltaic
                    and silt are kept in suspension in the swash and           segment may be accretionary, whereas another
                    breaker zones, and subsequently come to rest in            segment may be undergoing erosion. The two
                    water 1 to 2 feet deep. The most rapidly eroding           deltas at. the head of Lavaca Bay are experiencing
                    shell beaches are those which face into, the south-        growth primarily in the immediate vicinity of the
                    east wind and those that.are backed by marsh or            river mouths. The Colorado River builtits delta
                    shallow water bodies. Configuration of shorelines          across Matagorda Bay, a distance of about 4 miles,
                    determines, in part, whether a particular segment          between 1929 and 1935 (Wadsworth, 1966).
                    will  be erosional or , accretionary. Waves are            Figures 19 and 20 show t  he growth.of the delta; by
                    normally   focused on promontories (fig. 18),              1941, the delta had almost completed its growth.
                    thereby accelerating erosion. Orthogonals diverge
                    along concave shorelines, waves decrease in.height,             In. the area of. Tiger Island Channel, the
                    physical energy decre         ases,   and. sediment        Colorado delta is prograding about 28 feet per
                    accumulates.                                               year; elsewhere it is in a destructive phase. A delta

                                                                                                            0    10,000

                                                                                                              Fe et

                                                                                             DIVERGENCE      OF ORTHOGONALS
                                                                                             PRODUCES LOW WAVES IN
                                                                                             THIS AREA      (EMBAYMENT)

                                  -A,

                                                                                      CONVERGENCE OF        ORTHOGONALS
                                                                                      PRODUCESHIGH WAVES IN
                                                                                      THIS AREA (PROMONTORY)

                         Figure 18. Wave refraction at Arena Cove, California (after Wiegel, 1964; reprinted by permission of Prentice-Hall, Inc.,
                    Englewood Cliffs, New Jersey).

                                                                                                                                  41

                                                                                 Garcitas Creek delta is protected by
                                                                            Pleistocene headlands from waves approaching
                         N
                                                                            from the southeast. Within the estuary, the deltaic
                                                                            shoreline is relative ly stable. Some sediment has
                                                                            accreted to marsh islands at the mouth of Garcitas
                  Miles
                                                                            Creek. Sedimentation rates, thickness of deltaic
                                                                            deposits, the ratio of mud to sand, and rates of
                                                                            compactional subsidence are not known.
                    ,.,RACO'
                                                            0A
                                                          GOP                    The Lavaca delta is undergoing erosion along
                                                       ATA
                                              K@
                                                         DAY                most of its perimeter. The area between the Lavaca
                                                                            River and Venado Lakes was once the site of
                                                                            deltation. This shoreline segment, which is now
                                                                            straight, was cut back by wave and current activity.
                             6 AY                                           Since 1934, parts of this shoreline have eroded
                         p0A
                    MATAGO                                                  from 1 to 5 feet per year, whereas other parts show
                                                                            no change. While the abandoned delta was under-
                                            W
                                                                            going erosion, the active delta prograded about 2.7
                                       . . .. .                             miles into Lavaca Bay.. Shoreline accretion is now
                                            Delta 0@d Shorelire 1908 (45 acres) - -limited to the immediate area of the moutli of the
                          U__               D
                                            elta 1930 (1780 acres) N=
                                            Delta 1936 (4890 acres)=
                                                                            Lavaca River. Accretion rates near the river mouth
                                            Delta 1941 (7100 acres) C=
                                                                            were about 4 feet per year for the interval from
                                            (After Wadsworth, 1966)
                                                                            1957-1972. The western margin of the delta was in
                                                                            equilibrium over the.same time period. Thickness
                    Figure 19. Map of the growth of the Colorado delta      of the delta, sand and mud ratio, frequency of
              during the period 1908-1941 (after Wadsworth, 1966;           overbank flooding, and compactional subsidence
              reprmted by permission of the author).                        are not known for Lavaca delta.

                                                                                 The largest marsh areas in the Matagorda Bay
              is destroyed by erosion and compactional subsi-               system are associated with, deltas. These include
              dence (Scruton, 1960). Compactional subsidence is             the active Colorado, Lavaca, and Garcitas deltas
              rapid where prodelta mud is thick, where sedimen-             and the inactive Holocene Brazos-Colorado delta.
              tation rates were rapid prior to abandonment, and             Delta plains of the active deltas are covered with
              where deposits are young. The Colorado delta                  salt marsh, brackish marsh, and fresh-water marsh.
              prograded rapidly as a consequence of a large                 The Holocene Brazos-Colorado delta (most of this
              sediment volume and a shallow receiving basin;                delta lies to the east of the Matagorda Bay area) is
              maximum depth of the basin was about 6 feet                   characterized by marshes that are broken by tidal
              (Kanes, 1970). Total thickness of the delta is .8 to          channels, lakes, and ponds. Expansion of lakes and
              10 feet, and maximum thickness of the prodelta is             ponds indicates that the area is subsiding (Kolband
              4 to 5. feet (Manka and Steinmetz, 1971). The thin            Van Lopik, 1966).
              prodelta mud precludes excessive compactional
              subsidence. Bay muds that are 10 to 14 feet thick                  In order for marshes to propagate, there must
              and estuarine deposits up to 80 feet thick underlie           be a rather constant relationship between the delta
              the delta.                                                    plain and sea level. If there is excessive vertical,
                                                                            accretion, marsh vegetation is replaced by gras      ses,
                    The Colorado delta is eroding 6 to 8 feet per           shrubs, and trees. If, on the other hand, the marsh
              year along its eastern margin, but the western delta          surface subsides rapidly, the plants drown, and
              margin has remained relatively stable during the              waves and currents erode the area.
              interval 1957-1972. Subsequent to diverting river
              discharge into the Gulf of Mexico, oysters had                     At the present, marsh surface-water level
              begun to colonize the offshore . area of east                 relationships of Garcitas, Lavaca, and Colorado
              Matagorda Bay. Shell berms and beaches now                    deltas are stable. Apparently subsidence and sedi-
              accentuate parts of the deltaic shoreline of east             mentation rates are balanced. Delta-plain and
              Matagorda Bay.                                                marsh deposits are derived from rivers and bays.

                    42

                                                                                                            1953
                                                                                       7098.22 ACRES       7200-00 AC. EST
                                   7000

                                   6000

                                   5000
                                                                                             4889.88 ACRES

                                   4000
                                  Cr
                                                                                          1933
                                                                                         3470 ACRES

                                   3000

                                   2000
                                                                                    1930
                                    1000                                            1780.46 ACRES

                                        1908
                                        45.8 ACRES
                                     0
                                            19b8 10      15      20       25     30      35     40      45      50      55
                                                                      Y E A R S

                                     Figure 20. Area increase of the Colorado delta, in, acres, for the period 1908-1953 (after
                                Wadsworth, 1966; reprinted by permission of the author).

                    When the streams overflow their banks, fine                  along the back sides of shell berms that tie
                    sediment is added to the delta plain. Southeast              Pleistocene headlands together (the south shore of
                    winds create wind tides that inundate parts of the           Keller Bay), at bay margins of spoil outwash, and
                    bayhead deltas. These wind-driven waters transport           along the mainland shoreline between the Colorado
                    fine sediment onto the delta plain.                          River and Oyster Lake.

                         The normal succession of marsh types from                    Most of the marsh areas are undergoing
                    bayward inland is salt marsh, brackish marsh, and            erosion. Table 4 shows the erosion or accretion
                    fresh-water marsh. Some marsh areas on the Lavaca            rate for the marsh areas measured in the field and
                    delta do not exhibit the normal floral succession            their associated physiographic features.
                    (figs. 10 and 11; appendix C,  profile 54).
                                                                                      Several profiles were measured across marshes
                         Shoreline segments dominated by salt                    that face into the southeast wind. Cliffs occur
                    marsh.-The most extensive marshes are associated             landward of three of the marsh areas (fig. 10; pl. 1,
                    with deltas (figs. 1 and 2). Salt marsh is also              profiles 52, 61@ 64; appendix C, profiles 52 and
                    associated with barrier islands and peninsulas; salt         61). Two of the marshes are accretionary; the
                    marsh of this type is situated between Brown                 other is erosional. The remaining two profiles are
                    Cedar Cut and the Colorado delta. Other marshes              representative of marshes associated with spoil
                    occuron the flood-tidal delta at Pass Cavallo, along         outwash (fig. 10; pl. I, profiles 74 and 75;
                                              CRES,_-@

                    minor reentrants and mouths of lesser streams,               appendix C, profile 75); one of these marshes is

                                                                                                                             43

                   Table 4. Erosional, and accretionary rates                 Marshes that are not associated with deltas
              (1957-1972) and physiographic units associated with        receive sediment from the adjacent bay and from
              marshes.                                                   the erosion of headlands. Under normal wind and
                                                                         wave conditions, the marsh at profile 56 is supplied
                                                 Nature of Associated    sediment from Keller Bay. Storm washovers from
              Station   Accretion    Erosion*    Physiographic Unit      Matagorda Bay transport sand and shell into the
                                                                         marsh. The equilibrium marsh at profile 67 is
               52           +2                     Cliffed shoreline     affected by waves generated by both north and
               56                      -3            Shell berm          south winds. Measurements made along profile 67
               60                       -2         Cliffed shoreline
               61         +0.5                     Cliffed shoreline     during a norther indicated that water level was 1.5
               64                       -2         Cliffed shoreline     feet below normal bay level. Spartina alterniflora
               67           0           0          Cliffed shoreline     marsh was completely emergent and the high salt
               68                       -3           Shell berm          marsh extended 3 feet above bay level. South or
               70                      -1.2          Shell berm          we Ist winds inundate the marsh and a poorly
               74                      -13          Spoil outwash
               75           +3                      Spoil outwash        defined, wind-tidal flat occurs at about 1.5 feet
                                                                         above mean high water.
              *Erosion and  accretion rates are yearly averages for the
              time interval 1957-1972.                                        Two profiles were measured across marshes
                                                                         that form parts of the eastern shorelines of
              erosional, the other - accretionary. Accretionary          Carancahua and Matagorda Bays (figs. 10 and 11;
              marshes, which are backed by cliffs, lie downdrift         appendix C, profiles 60, 70). Both marshes were
              from eroding headlands. Other marshes (e.g.,               being eroded, but the rate was slightly less at
              profile 64) associated with cliffed shorelines occur       profile 70 where oyster reefs lie offshore. Each
              in concave shoreline areas.                                marsh is rather broad, and under normal condi-
                                                                         tions, they are inundated by about 0.5 foot of
                   In east Matagorda Bay, marshes that front the         water. Water levels were measured along profiles 60
              southeast wind are developed upon spoil outwash.           and 70 during a norther. Water level at profile 60
              The marsh at profile 75 is accretionary and receives       was 0.75 foot below normal and 1.5 feet below
              its sediment from the erosional shoreline to the           normal at profile 70. A wind-tidal flat is developed
              east and   from reworked spoil adjacent to         the     1.5 feet above normal bay level at profile 60, and
              Intracoastal Canal. The spoil area. that supplies          at about the same elevation to the north of profile
              sediment to the, marsh at profile 75 has about 5           70. Low and high marsh are well developed in the
              feet of relief and is 600 to 950 feet from the     bay     area of profile 60; Distichlis spicata dominates the
              margin. The erosional marsh at profile 74 received         high marsh. There is no low marsh at profile 70;
              sediment from a spoil area having about 7 feet of          the high marsh is characterized by three floral
              relief; the spoil was 1,200 to 1,450 feet from the         zones (appendix C, profile 70).
              bay mar gin. Marshes that face the southeast wind
              are flooded by wind tides which have a range of a               Shorelines dominated by spoil outwash.-Bay
              few inches to approximately 2 feet.                        shorelines adjacent to the Intracoastal Waterway
                                                                         have been significantly altered. The areas that have
                   Marshes mostly affected by waves that                 been affected the most lie between Caney Creek
              approach from the north were also profiled (figs.          and the town of Matagorda, between the Colorado
              10 and 11; pl. I, profiles 56, 679 68; appendix C,         delta and Oys   .ter Lake, and to the west of P O'rt
              profile 56). Two ofthe marshes (profiles 56 and            O'Connor (figs. 1 and 10). Approximately 40 miles
              68) areeroding at rates of about 3 feet per year.          of canal were dredged through marshes and shell
              The other marsh area (profile 67) has been in              beaches which bordered Matagorda and Espiritu
              equilibrium since 1957.                                    Santo Bays. The canal was initially 12 feet deep
                                                                         and 200 feet wide.
                   The marsh at profile 56 is about 1,000 feet
              wide and is a rather uniform 0.75 foot above bay                With the completion of the Intracoastal
              level; it increases to 1.5 feet above bay level where      Waterway, approximately 500,544,000 cubic feet
              salt-marsh vegetation gives way to Spartina                of spoil were placed adjacent to the bay margin.
              spartinae (sacahuista) and Tamarix gallica (salt           Depth measurements made in the Intracoastal
              cedar).                                                    Waterway in the spring of 1973 indicated that the

                    44

                    canal had been deepened about 6 feet, thereby                 periods, when the volume of spoil is low and when
                    increasing the spoil volume to approximately                  dense vegetation inhibits transport of sediment by
                    750,800,000 cubic feet.                                       sheetwash.

                          Results of dredging and spoil disposal adja-                   Profile s 75 and 76 (figs. 10 and 11; appendix
                    cent to bay margins are destruction of certain                C, profiles 75, 76) are characteristic of bay
                    physiographic and environmental units, and filling            shorelines that have been affected by dredging and
                    of the bays through shoreline accretion (fig. 15).            spoil outwash. The shoreline at profile 76 was
                    Accretion from spoil outwash is not a continuous              experiencing erosion when. this study was termi-
                    process. Accretion occurs during dredging opera-              nated. The shoreline was. eroding because the
                    tions and during heavy rains when sheetwash                   volume of spoil was relatively low. At the same
                    transports sediment from spoil mounds into the                time, the shoreline at profile 75 was accreting. The
                    bay. Bay shorelines that have accreted as a result of         volume of spoil was great, and the distal part of the
                    dredging operations also go. through periods of               spoil outwash was densely vegetated by marsh
                    erosion. Erosion occurs during extended dry                   Plants.

                                                              STABILITY OF SHORELINES

                          The term stability refers to the accretionary,          uplands, and from molluscs that live along the bay
                    equilibrium, or erosional condition of a particular           margin. . Sources of sediment for Matagorda Penin-
                    shoreline segment. The specific, condition may                sula and Matagorda Island are the Brazos and
                    result from long-term, annual, or short-term                  Colorado Rivers, as well as erosion of Holocene
                    processes (Wiegel, 1964). Short-term stabil       'ity, as    Brazos-Colorado delta, and erosion of Pleistocene
                    used in this report, refers to shoreline changes that         deposits exposed on the inner continental shelf.
                    occur during a time interval of months or a few
                    years. Long-term stability reflects shoreline                       Most of the shorelines associated with the
                    changes over a period of a few decades on up to a             Matagorda Bay system        Iare eroding, a fact    which
                    century or more. 'Shorelines that have a long-term
                    erosional history may accrete under certain short-            indicates that the sediment volume. supplied to
                    term wave conditions, and similarly shorelines with           Gulf and b   .ay shorelines is insufficient to balance
                    a long-term accretionary trend may be erosional               the amount of sediment removed by waves and
                    under certain short-term wave conditions (Wiegel,             longshore drift. The nature of beaches in the
                    1964).                                                        Matagorda Bay area is a good indicator of the
                          Over the short term, the beach may be                   condition of shoreline stability. There are very few
                                                                                  pure sand beaches along the mainland shoreline.
                    erosional, accretionary, or in equilibrium, de-               Sediments of mainland beaches are a mixture of
                    pending upon wave conditions at the time the
                    observations were made. Steep waves that develop              sand, shell, and rock fragments; shell and rock
                                                                                  fragments are the most common constituents.
                    in deep'water affect erosion or accretion at a
                    moment in time. Steep waves tend to erode the                 Beaches composed of shell and rock fragments
                    beach, whereas flat waves have the opposite effect.           indicate that virtually no sand is supplied currently
                                                                                  to these beaches by fluvial systems. Accretionary
                          Long-term shoreline trends are controlled by            mainland shorelines generally coincide with river
                    sediment availability, subsidence,, shoreline orienta-        mouths.
                    tion, existence - of promontories, and direction of
                    sediment transport. In general, the long-term trend                 There are two contrasting areas along the Gulf
                    of Matagorda Peninsula has been erosional, and the            shoreline: (1) the area from Pass Cavallo westward
                    .trend of Matagorda Island has been accretionary or           (Matagorda Island); and (2) the area from Pass
                    in equilibrium. Mainland shorelines have been                 Cavallo eastward to the boundary of the study area
                    chiefly erosional during the same time interval.              (Matagorda Peninsula).      Composition of materials
                                                                                  making up these two areas is different. Matagorda
                                    Sediment Availability                         Island is composed chiefly of terrigenous sand,
                                                                                  whereas shell and rock fragments compose a
                          Sediment supplied to the mainland shore is              significant part of Matagorda Peninsula. The rate of
                    derived from rivers, from erosion of Pleistocene              delivery of terrigenous sand to Matagorda Penin-

                                                                                                                                       45

               sula is now, and probably was in the past, slower                             97*            916.          96.          30-
               than the delivery rate to Matagorda, Island. Among
               the more obvious lines of evidence are the follow-                                           111
               ing: (1) Matagorda Peninsula has a long erosional
               history, whereas Matagorda Island is just entering                                                      Golvesto.n
               an erosional phase; (2) accretionary grain through-
               out Matagorda Island indica       tes rapid sand accu-                                                                  29'
               mulation, whereas Matagorda Peninsula only
               exhibits accretion near Decros Point; (3) the two
               areas have cont   rasting widths, with a broad, barrier
               sand body indicating an excess of terrigenous sand
                                                                                           <5
               and a narrow island suggesting the opposite; and                                                               _,@1_28o
                                                                                 -Corpus                                   N  11\
               (4) there is a contrasting sediment composition in                Christil
               the two areas.                                                                         GULF OF                  @aAR SEPT
                                                                                                                               4P
                                      Subsidence                                                                                  k41-

                                                                                                   ZONE OF
                    In some      areas of the Texas Coastal Zone,                                CONVERGENCE
               subsidence is     a major cause of shoreline retreat.
               There has been some subsidence in the northeast                                 0
               part of the study area as a consequence of
               dewatering of Holocene         Brazos-Colorado deltaic                                                                  26*
               deposits. Transgression in the area from Caney                                                      0     2    50.iles
               Creek to about halfway          to the mouth of the                                                      SCALE
               Colorado River probably resulted from a low sand
               supply and compactional subsidence. Subsidence                        Figure 21. Net annual longshore drift (after Watson,
               changes the relative position of sea level and would             1968).
               by itself be sufficient to cause shoreline retreat.

                                 Shoreline Orientation                               In the Matagorda Bay area, waves approaching
                                                                                from the east, east-southeast, and southeast
                    Interaction between the direction of wave                   generate southwestward-flowing longshore cur-
               approach and shoreline orientation determines the                rents. Rate of longshore drift is greatest when wave
               direction of longshore drift (fig. 21). Prevailing               approach is from the east, because the angle
               wind and, hence, the direction of wave approach, is              between wave approach and the shoreline is at a
               from the southeast. Near. the shore, the shallow                 maximum. Waves approaching from the south and
               bottom begins to exert a drag (friction) on waves;               south-southeast create longshore drift and sedi-
               it is in this shallow water zone that shoreline                  ment transport to the northeast.
               orientation begins to exert its influence on break-
                                                                                          Direction of Sediment Transport
               ing waves and nearshore currents. The Texas Gulf
               shoreline is concave to the southeast, According to                   The dominant sediment. transport direction,
               Watson (1968):                                                   as indicated by natural tracers, is both onshore
                                                                                (from the inner shelf and shoreface) arid along-
                         "An onshore wind blowing onto a concave                shore. to the southwest. Natural tracers are frag-
                    shoreline will produce wave fronts normal to
                    the wind direction. These wave fronts move                  ments of lacustrine limestone, calcite-cemented
                    shoreward and  . are incompletely refracted. As             sandstone blocks, plates of beach rock, caliche
                    they break, the waves generate a longshore                  nodules, and vertebrate 'and invertebrate fossils.
                    current due to their oblique approach to the                During hurricanes, these material's are eroded from
                    shoreline. This current is strongest at, the                Pleistocene.and Holocene deposits exposed on the
                    greatest distance from the central point where
                    the waves approach the shore at the greatest                shoreface and inner continental shelf and trans-
                    angle. The current decreases in magnitude                   ported to barriers and peninsulas.
                    toward the center where. it diminishes to zero
                    because the waves     Iapproach parallel to the                  Morphological     features of barrier islands and
                    shoreline at the point where the wind direction             peninsulas indicate   that dominant sediment trans-
                    is normal to the shoreline and no current. is
                    generated."                                                 port is southwestward. Ridges and swales at Decros

                   46

                   Point indicate that Matagorda Peninsula grew to              west where part of it accumulates on beaches.
                   the southwest by spit accretion.                             Coarse shell and rock fragments remain behind to
                                                                                be transported onshore by a storm surge.
                         Rock fragments and shell,     which are derived
                   from bay species, occur on beaches throughout the                 Coarse materials are probably more abundant
                   extent of Matagorda Peninsula. The greatest con-             in relict sediment in the nearshore zone adjacent to
                   centration of shell and rock fragments is on the             eastern Matagorda Peninsula than to the west.
                   eastern two-thirds of the peninsula. The day-to-day          Onshore winds contribute to the concentration of
                   process of breaking waves and longshore currents             coarse materials by selectively removing sand-size
                   selectively transports terrigenous sand to the south-        particles fromback-beach areas.

                                                     DISTINCTION BETWEEN NATURAL. AND
                                                      MAN-INDUCED SHORELINE CHANGES

                         Natural changes in the Coastal Zone are those          cent to shallow bay margins which are inhabited by
                   changes that would occur even in the absence of              clumps of Crassostrea virginica.
                   man. Such natural changes result from, the inter-
                   play among the various coastal processes an      .d the           Marsh areas, particularly those associated with
                   interaction of these processes with sediments that           theJarger fluvial systems, are least likely to erode.
                   are available for. construction and maintenance of           Erosion is retarded by the ability of plant roots to
                   shoreline features. Man's role   Iin producing shore-        trap and bind sediment particles. Some marshes are
                   line changes generally'has been to bring about a             undergoing erosion; these are situated on aban-
                   state of natural disequilibrium by interrupting the          doned delta lobes and along bay margins of barriers
                   progression of natural coastal processes and by              and peninsulas.
                   decreasing the sediment budget.                                   Bay shorelines also erode because of -a sedi-
                                                                                ment deficit. Maximum sediment input is localized
                                Natural Shoreline Changes                       at the mouths of Garcitas Creek, Lavaca and
                                                                                Colorado Rivers. The Matagorda Bay system con-
                         Historical monitoring and field studies have,          stitutes a large water body which is conducive to
                   shown that most of the shoreline changes in the              generation of rather large waves. Waves strike much
                   Matagorda Bay area are the result of natural                 of the bay shoreline at an angle and are refracted,
                   processes. During the past 116 years, the dominant           thereby setting up longshore drift. The north
                   trend of Gulf and bay shorelines has been                    shorel ine of Matagorda Bay is at the present a
                   erosional.                                                   relatively straight segment, which results from
                                                                                wave erosion and longshore drift (the area between
                         The Gulf shoreline of the Matagorda Bay area           Well Point and Sand Point is an example). Waves
                   is -erosional because there is a.deficit of sand-size        erode the Pleistocene headlands, and longshore
                   sediment. Based upon calculations of Volumes I of            currents transport granular materials to the west
                   sand eroded from the inner shelf and shoreface,              where they accumulate in spits (Turtle Point, Sand
                   sand volume delivered to the Gulf by the Brazos              Point, and Rhodes Point).
                   and Colorado Rivers, and the volume of sand
                   trapped by the north jetty of. the. Matagorda Ship                The natural trend is for the bay shorelines to
                   Channel, it is concluded that materials derived              retreat, thereby increasing the bay area. Matagorda
                   froin shelf and shoreface erosion constitute over 60         Peninsula is also retreating; the peninsula will
                   percent of the current sand budget for this                  ultimately migrate across Matagorda Bay and
                   shoreline segment.                                           attach itself to the bay-shore segment that lies
                                                                                between Chinquapin and Palacios Point.
                         Bay shorelines are mostly erosional. Shoreline
                   segments that face into the predominant southeast                      Man-Induced Shoreline Changes
                   wind or face the north and that are adjacent to
                   water bodies with significant fetch tend to erode                 A few areas of shoreline change are definitely
                   rapidly. Erosion is retarded along shorelines adia-          related to man's activities in the Coastal Zone.

                                                                                                                           47

              Some of man's activities that affect shorelines, or       shoreline erosion and accretion adjacent to Mata-
              that have the potential of affecting shorelines are:      gorda Ship Channel jetties was determined from
              (1) construction of dams across major fluvial             data (1964 through 1971) provided by the
              systems; (2) river diversion; (3) land use in major       Galveston Office, U. S. Army Corps of Engineers.
              drainage basins; (4) construction of bulkheads,           Twelve profiles (figs. 25 and 26) were constructed
              groins, and jetties; (5) mining beach materials; (6)      from the Corps data. The volume of sand that
              shell dredging; (7) dredging canals; and (8) dune         accumulated adjacent to the north jetty over the
              alteration. A few of these are ongoing activities in      seven-year period was about 45,000,000 cubic feet
              the Matagorda Bay area, and others have been              (about 6,400,000 cubic feet per year). The shore-
              conducted in the past.                                    line adjacent to the south jetty has undergone
                                                                        erosion during the 1964-1971 interval (fig. 24);
                   Consequences of three of man's activities have       approximately 51,500,000 cubic feet of sand was
              been documented in the Matagorda Bay area. The            removed from the beach and shoreface during the
              rapid shoreline accretion which followed dredging         period 1964-1971 (fig. 26).
              of the Intracoastal Waterway, and progradation of
              the Colorado delta across Matagorda Bay are                    Activities of man' in the drainage basins of
              examples of shoreline changes produced by man's           major streams that discharge into bays and the
              activities. jetties cause changes in shoreline sta-       Gulf of Mexico also affect shorelines. In most areas
              bility by trapping sand transported by, longshore         of the Texas Coastal Zone, the magnitude            of
              currents. There are two jetty systems in the              shoreline changes resulting from altering, major
              Matagorda Bay area that are currentl   y being used,      fluvial systems has not been determined. Increase
              one at Port O'Connor and the other on the Gulf            in agricultural activity in drainage basins increases
              side of Matagorda Peninsula.                              sediment yield, and dams constructed across major
                   Data on the jetties at    Port O'Connor have         streams impound water and sediment. Suspension
              been derived from 1934 and 1956 photomosaics,             load volumes have been calculated for the major
              1969 NASA photographs, and data supplied by the           streams, but at this time the volume of bed load
              Galveston Office, U. S. Army Corps of Engineers.          carried. by these streams is not known. Other
              There are two sets of jetties at Port O'Connor. The       unknowh factors are lag time between, man's
              oldest jetties (fig. 22, area 1), shown on 1934           activities (increased sedimentation or reservoir con-
              photographs, have been abandoned; a second set of         struction) in the drainage basin and shoreline
              jetties (fig. 22, area 2) was constructed in 1939 and     changes related to these activities. Examples of
              improved in 1965. Pleistocene strandplain sand in         stream alteration are: (1) the diversion of the
              the Port O'Connor area yields sediment that is            Brazos River in the Freeport area; and (2) removal
              transported southward by tidal and longshore              of the log jam on the Colorado River. Diversion of
              currents. Jetties at Port O'Connor prevent south-         the Brazos River has caused: (1) destruction of the
              ward movement of this sand. These jetties are n    ot     old Brazos delta (Seelig and Sorensen, 1973); (2)
              the cause of downdrift. erosion because the trend         construction of a new delta at the river mouth
              during 1856-1957 also had been erosional. The             (Odem, 1953; Nienaber, 1963; Seelig and
              jetties trap sand that would normally move south-         Sorensen, 1973); and (3) development of a
              ward to an area already experiencing erosion. By          trapping mechanism (local reversal of longshore
              1969, sand had accreted to a point where it began         currents) for most of the sand transported to the
              to bypass the jetties and move into the Intracoastal      Gulf of Mexico by the Brazos River. Rivers have
              Waterway (fig. 23). Sand dredged from the, canal is       not been intensively studied with respect to the
              placed south of the jetties where it is picked up by      role they play in shoreline'stability.
              the current system and transported toward the
              Gulf of Mexico.                                                Bulkheads have been constructed to retard
                                                                        erosion of. cliffed shorelines in several areas along
                   Matagorda   Ship Channel (fig. 24) was com-          the mainland shore. Such areas are: (1) Port
              pleted in 1965.  Initially,.the north jetty extended      O'Connor along the west shoreline of Matagorda
              approximately 5,000 feet beyond the shoreline             Bay; (2) Olivia along the north shore of Keller Bay;
              into about 4 fathoms of water. Since 1964, the            (3) near the mouth of Keller Creek; and (4) along
              shoreline has accreted from 100 to 950 feet updrift       the east shore of Carancahua Bay west of the
              from the north jetty (fig. 24). The nature of             mouth of Fivemile Branch.

                     48                     EXPLANATION
                              FED     Pleistocene subaerial sand

                                      Modern subaerial flood delta

                                      Modern subaqueous sand

                                      Mainland shoreline 1934

                               ......... Mainland shoreline 1956

                                      Erosion 1934-1956

                                      Accretion 1934-1956

                                      Seaward limit of subaqueous sand 1934

                                      Seaward limit of subaqueous sand 1956

                              L.      Erosion 1934-1956
                                      Accretion 1934-1956                                      PORT O'CONNOR

                                 I    Pre-1934 jetty system
                                2     1939 Jetty system

                                                                                                                                   2
                                                                                      0011,

                                                                                     956

                                                                                934

                                                                                                                        MILES

                                                                                      IV
                                                                                     N/

                                                              1956
                                                                         qY,

                                                       1934

                Figure 22. Locations of jetties in the Port O'Connor area, and changes in the shoreline and nearshore sand distribution during the interva.
          1934-1956.

                                                                                                                                   49

                                                                           Bay-Margin
                                                                  Port        Sand
                                                              Ocorn 0,1                        Ord'
                                                                                       MOO 00Y

                                                                      Sand Bar
                                                                                        43poil Island,

                                                                                                       Matagorda Peninsula
                                                                                    s     s                                  rs
                                                                     Vegetate        P    P1  Flat

                                                     Breaker                0         16         32
              Matagorda Island                                                         I          I
                                                                             Thousands   of Feet

                                                                       GUL F OF MEXI CO

                   Figure 23. Distribution of bay-margin sand north of the jetties at Port O'Connor. The map was derived from 1969
              NASA photography. Between 1956 and 1969, the bay-margin sand had accreted at least as far as the bayward extent of the
              north jetty.

                                                           MA TA GORDA               B A K

                  Z
                 @J                        MATAGORDA                                                PENINSULA

               Co
                                               1                                         1) 12 13  1  15  16  IT Is  19 20
                                                      'o     -o  _o

                                                                                    Q,

                                     0 5
                             0
                                              Miles
                                                                                              NORTH  JETTY

                                                                                GULF OF MEXICO

                   Figure 24. Accretion and erosion associated with Matagorda Ship Channel jetties. Accretion occurs adjacent to the
              upcurrent (north) jetty; erosion occurs downcurrent from the south jetty.

                                     50

                                     SE                                                                                                                                                                                                                     NWO

                                                                                                                           ----------                                                                                 Accretion
                                                                                     1964                                                               1971                                                                                                          5

                                                                                                                                                                                                                                                                      0

                                                                                                                                                   13                                                                                                                 2

                                                                                                                                                                               --------------
                                                                                                                                                                ----------                                                    ccretion                                4
                                                                                                                             ------               ------------

                                                                                    1971         1964

                                                                                                                                                         Erosion

                                                                                                                                                   15

                                                                                                                                                                                                                                                                      3
                                                                                                                                                                     ---- ----------                                      Accretion                                   4

                                                                                                                                                                                                                                                                      W
                                                                            1967             -T6-6-9-:r                                                                                                                                                               52
                                                                                                                                                                Erosion

                                                                                                                                                   17                                                                                                                 2

                                                                                                                                                                                                                         Accretion                                    4
                                                                                                                                                 ---------------         1971
                                                         - - - - - -                    F9 @72
                                                                                                                                                                                                                                                                      5
                                                                                                        1964
                                                                                                                                                                E,osion

                                                                                                                                                                                                                                                                      0

                                                                                                                                                   19

                                                                                                                                                                                                                                                                      3
                                                                                                                                                                               -------                                   Accretion
                                                                                                    1967-1  - - - - - ----- - - --- ----- ------------------------
                                                                                                                                                                                                                                                                      5

                                                                                                                                                                                                                                                                      0

                                                                                                                                                                                                                                                                      I
                                                                                                                                                  20                                            1971                                                                  2

                                                                                                                                                                                                                                                                      3
                                                                                                                                                   1964                                                                    ccretion
                                                                                                                                                                                                                                                                      4
                                                                                                                                       ----------------
                                                                                                                               I 9@;                                                                                                                                  5

                                     10                    9                     8                     7                     6                      5                    4                     3                     2                      1                     0
                                                                                                                               THOUSANDS OF FEET

                                               Figure 25. Shoreface profiles in                            the area of the north jetty, Matagorda Ship Channel. The upper set of profiles at each
                                     station includes profiles for 1960, 1964, 1967, 1969, and 1972. Accretion or erosion was determined for each profile by
                                     comparing the oldest and youngest data. See figure 24 for profile locations.

                                                                                                                                                                                                                                                                            51

                         SE                                                                                                                                                                                                                                                 0

                                                                                                                                                                                                                                     1964
                                                                                                                                                                                                                      ----- -----------            191,
                                                                                                                                                                                                                                                                            3

                                                                                                                             ----------                                                                                                                                     4
                                                                                          -0-

                                                                                                                                                                                                                                                                            0

                                                                                                                                                                                                           - - - -----------                       1971

                                                                                                                                                                                                                                                                            4
                                                                              -----------

                                                                                                                                                                                                                                                                            0

                                                                                                                                                                                                                                                                            I
                                                                                                                                                 4
                                                                                                                                                                                                                       -----------                 197
                                                                                                                                                                          ------------------------     ----- -
                                                                                                                                                                                                                                                                            4

                                                                                                                                                                                                                                                                            0

                                                                                                                                                                                                                              1964                 197,

                                                                                                                                                                      -------------
                                                                                                                       6                                                         969                                                                                        4
                                                                              ----------  I--
                                                                                    @960@

                                                                                                                                                                                                                                                      711
                                                                                                                                                                                                                                                                            2
                                                                                                                                                                                                                              1964

                                                                                                                                                                                 969
                                                                --------------- -- ----------------------                                                                                                                                                                   4
                         ----------------------------                         - --------  I----------------------                                                                                                                                                           5
                                                                                     960J

                                                                                                                                                 10                                                    1971

                                                                                                                                                                                           ----------
                                                                                                                     1967@  ------------    W(I@ --------------    ---- -- ---                                                    A-tw
                                                                                                                             --------------------
                                                                                                                                ........ ..
                                                                                                -----------
                                                                                                                                             9691

                       11               14             11               12                11            1.              1                               1                                               4                                                                   0
                                                                                                                                  THOUSANDS OF          FEET

                                    Figure 26. Shoreface profiles in the area of the south jetty, Matagorda Ship Channel. The upper set of profiles at each
                        station includes profiles for 1960, 1964, 1967, 1969, and 1971. Accretion or erosion was determined for each profile by
                        comparing the oldest and youngest data. See figure -24 for profile locations.

                                   52

                                                                                                                                                                                    V,

                                                                                                                                                                                                                                          a,

                                                                                                                                          K

                                                                                                                                                                                                                                                   1 "'K

                                                                                                                                                                  m

                                                                       p p
                                                      7x-        ME     a E&                     6ORK-
                                                                     , km

                                                                              3                 v-1
                                                                      "N

                                                                IF
                                                           . ..... .F    0                                IN,
                                                                                  ""4
                                                                                                                 @@v
                                                        '01                         NIZIM

                                                            OL

                                                                                                                         V

                                                                                    Scale
                                                    0,                                0.5                                   1.0

                                                                                     Mile

                                               Figure 27. Dredging of Dog Island Reef for oyster shell (USDA photos, 1953). Dog Island Reef is situated west of the
                                    Colorado delta.

                                                                                                                                       53

                    Shell dredging has in the past and is presently            along the older Holocene deposits. A few shell pits
               being conducted in the Matagorda Bay system.                    were operated on the marsh side of Modern shell
               Dredging in the early 1950's destroyed Dog Island               beaches. Holocene beach ridges, which are up to 10
               Reef (fig. 27). Dredging operations,,are proceeding             feet high, provide protection for man-made struc-
               near the north shore of Matagorda Bay in the                    tures during storms. Mining of shell from these
               general area between Carancahua Pass and Sand                   ridges created gaps that can be easily breached
               Point. The effects of shell dredging,on shoreline               during storms. Shell removed from Modern beaches
               stability are not definitely known.                             has not destroyed these features, but continued
                    In the past, Holoceneand Modem beach and                   mining could bring about serious erosional prob-
               spit deposits were mined in the Indianola-Magnolia              lems, particularly during hurricanes or tropical
               Beach area. Most of the mining operations were                  storms.

                                                                   CONCLUSIONS

                    Historical shoreline monitoring (for the                   Matagorda Island eroded at a rate of about 11 feet
               period 1856-1957) and field measurements                        per year; combined land loss in these two areas was
               (1971-1972) demonstrate that erosion is an impor-               about 1,050 acres.
               tant natural process along both Gulf and bay
               shorelines of the Matagorda Bay area. Erosion is a                    During the 100-year period, the bay shore-
               long-term trend. These trends were established at               lines, of Matagorda Peninsula and Matagorda Island.
               least 118 years ago prior to any significant modifi-            (including the bay margin of the tidal delta
               cation of the coastal environment by man. Ero-                  associated with Pass Cavallo) were in an erosional
               sional shoreline trends will probably continue and              state, although there were areas of local accretion.
               may accelerate in the future as some of man's                   Average rate of erosion along Matagorda Peninsula
               activities interrupt the normal movement of sand                was approximately 4 feet per year; approximately
               in the natural sediment dispersal system.                       2,650 acres of land were lost. The bay shoreline of
                                                                               Matagorda Island retreated at an average rate of
                                  Shoreline Change                             about 2.0 feet per year with a land loss of about 41
                                                                               acres.
                    For the 100-year period of         historical mon-
               itoring (1856-1957), approximately 8,450 acres of                     Most of the remaining shoreline segments of
               land were lost by natural erosion of Gulf and bay               the   Matagorda Bay system experienced erosion
               shorelines. During this same period, approximately              during the 100-year period. Shorelines of Powder-
               615 acres of land was gained through natural                    horn Lake and Carancahua Bay retreated at ave         rage
               accretion. Natural accretion occurred at the                    rates of 0..2 and 0.7 foot per year, respectively. The
               mouths of Garcitas Creek and Lavaca River, along                west shorelines of Matagorda and Lavaca Bays
               the Gulf shore of Matagorda Island near the west                eroded at about 2.6 feet per year, and the north
               limit of the study area, and at ephemeral tidal                 shore of Matagorda Bay between Sand Point and
               passes such as Brown Cedar Cut and Greens Bayou.                Well Point eroded at an average rate of about 2.4
               Since 1929, certain of man's activities have caused             feet per year. Other shoreline segments retreated at
               local accretion. Through man-induced accretion, a               rates between the maximum displayed by west
               total of 9,600 acres has been gained at the mouth               Matagorda-Lavaca Bay and the minimum displayed
               of the Colorado River, along segments of the north              by Powderhom Lake and Carancahua Bay. Total
               shore of Matagorda and Espiritu Santo Bays, and in              land loss from these areas was approximately 2,200
               the Port Lavaca-Point Comfort area.                             acres.

                    Gulf shorelines have experienced the greatest                    Waves are the dominant erosive mechanism
               amount of erosion. Matagorda Peninsula eroded at                acting on both Gulf and bay shorelines. Prevailing
               a rate of about 5 feet per year during the 100-year             southeast winds generate waves that erode south-
               period; approximately 2,600 acres of land were                  and east-facing shoreline segments. Northers gen-
               lost. The shoreline along Pass Cavallo retreated at a           erate rather large waves which erode north- and
               rate of about 33 feet per year, and parts of                    west-facing shoreline segments. Huge waves

                    54

                    generated by hurricanes erode both Gulf and bay            stored within the river was available for transport
                    shorelines. Erosion of several hundred feet of Gulf        to the bay; rapid deltation ensued. Initial rates of
                    beaches, dunes, and shell ramps occurs when                shoreline accretion were about 1 mile per year.
                    hurricanes such as Carla, 1961, make landfall in the
                    Matagorda Bay area.                                              Parts of the Gulf Intracoastal Waterway were
                                                                               dredged across coastal lands adjacent to the north
                         Natural accretion in the Matagorda Bay area           shores of Matagorda and Espiritu Santo Bays.
                    was local and relatively insignificant when com-           Sediment dredged from the canal was deposited as
                    pared with the widespread erosion. Accretion               spoil banks upon marshes along the bay margins
                    occurred in a protected bay at the mouth of                and within the bays. Spoil, deposited directly in
                    Garcitas Creek where over the 100-year period              the bays by the dredging process, or subsequently
                    there were approximately 132 acres of land gain.           washed into the bays by sheetwash, has filled
                    Although Lavaca River is larger than Garcitas              approximately 1,560 acres of the subaqueous bay
                    Creek, only 55 acres of new land was constructed           margin. Spoil mounds and spoil outwash have
                    during the same time interval; the Lavaca delta has        created approximately 1,560 acres of new land by
                    prograded into Lavaca Bay and is subject to wave           shoreline accretion.
                    erosion.
                                                                                     Dredging of boat basins and turning basins in
                         Approximately 380 acres of land have                  the Port Lavaca and Point Comfort areas created
                    accreted to the bayside of Matagorda Peninsula in          approximately 110 acres of new land.
                    the form of emergent segments of tidal deltas.
                    These areas occur at the extreme eastern part of                 Approximately 9,600 acres of new land ac-
                    east Matagorda Bay, at Brown Cedar Cut, and at             creted to bay shorelines as a result of man's
                    Greens Bayou. Each of these areas is representative        activities. Or, stated differently, 9,600 acres of bay
                    of ephemeral tidal passes, each created when a             bottom have been filled by these activities.
                    hurricane scoured a channel through Matagorda
                    Peninsula. Brown Cedar Cut is the only one of                               Marsh Area Change
                    these passes that is presently active.. Most of the
                    sediment comprising these emergent tidal deltas                  Marshes were historically monitored during
                    was transported into the bay during hurrican    es or      the same time interval (1856-1957) as the mon-
                    tropical storms.                                           itoring of shoreline changes. Comparison of the
                                                                               distribution of marshes during the period from
                         The westernmost part of the Gulf shoreline of         1856-1957 indicates that there has been a decrease
                    Matagorda Island was accretionary during the               in wetland areas of approximately 5,000 acres (an
                    100-year period of historical monitoring; approxi-         average loss of 50 wetland acres per year). For the
                    mately 47 acres of land was added to this area.            period 1856-59, there were approximately 46,000
                    Sand that accreted this shoreline segment was              acres of wetlands, and in 1956-57 there were about
                    derived from the erosional segments of Matagorda           41,000 acres.
                    Peninsula, from along the west bank of Pass
                    Cavallo, and from the northeast end of Matagorda                 Locally there was a natural increase in wet-
                    Island; the sand was transported southwestward by          lands during the 100-year period; for example,
                    longshore currents.                                        wetlands formed at the mouths of Garcitas' Creek
                                                                               and Lavaca River, in the Lake Austin area, and at
                         Large and small areas of shoreline accretion          active and inactive tidal passes through Matagorda
                    have resulted from man's activities. The largest           Peninsula. Most of the wetlands experienced a loss
                    single area, amounting to approximately 7,900              in areal extent, and generally the magnitude of the
                    acres of new land, is the Colorado delta which             loss increased from the heads of bays toward the
                    prograded completely across Matagorda Bay be-              barriers and peninsulas; maximum loss occurred
                    tween 1929 and 1936. The delta owes its existence          along the bayside of Matagorda Peninsula.
                    to removal of a log jam which retarded water and
                    sediment movement into Matagorda Bay. The log                    Natural changes in wetland areas are brought
                    jam extended from the town of Matagorda up the             about through shoreline erosion or accretion, and
                    Colorado River a distance of about 46 miles. With          land-surface subsidence, and by burial beneath
                    removal of the log jam, sediment that had been             sediment and burial loss during droughts. Man-

                                                                                                                            55

              induced changes in wetland areas have occurred as         were possibly destroyed by drought. Expansion of
              a result of construction of earthen dams across           marsh in the Lake Austin area has resulted
              marshes and tidal creeks, burial of wetlands              primarily from subsidence of the Brazos-Colorado
              beneath spoil or creation of new wetland areas by         delta. Subsidence in the vicinity of Lake Austin has
              spoil outwash, and by changing a river regime so          been on the order of 0.2 to 1.0 foot during the
              that there is an increase or decrease in the volume       past 3 or 4 decades (Brown and others, 1975).
              of fresh water and sediment delivered to bay-
              margin areas.                                                  Man has contributed directly to reduction of
                                                                        marsh area. Principal activities resulting in marsh
                   Approximately 5,800 acres of wetlands were           loss were construction of dams across marshes and
              lost along the bayside of Matagorda Peninsula             tidal creeks and piling of spoil in marshes adjacent
              between 1856 and 1957 (a rate of about 58 acres           to dredge channels and boat basins. A total of
              per year). During this time, approximately 2,650          1,307 acres of marsh was dammed between 1856
              acres of land were lost by erosion along the bayside      and 1972. These areas are (1) the Blind Bayou area
              of Matagorda Peninsula. Erosion accounts for              between Indianola and Magnolia Beach (about 315
              almost half of the loss of marsh area; marsh area         acres); (2) Huisache Creek (approximately 200
              was reduced at a rate of about 26 acres per year          acres); (3) Piper Lakes (301 acres); (4) the marsh
              through shoreline erosion. Burial beneath washover        northwest of, Piper Lakes (114 acres); and (5)
              deposits, possibly in conjunction with the drought        Buttermilk Slough (379 acres). A total of 1,987
              of the 1950's, accounts for about 3,150 acres of          acres of marsh was destroyed when buried by
              marsh reduction.                                          dredge spoil. The three principal areas are (1) south
                                                                        of Oyster Lake along the north shore of Matagorda
                   There was    a decrease in marsh area from           Bay (560 acres); (2) west of Port O'Connor along
              about 4,175 acres to about 2,250 acres on the Pass        the north shore of Espiritu Santo Bay (1,323
              Cavallo tidal delta and along the bayside of              acres); and (3) the Point Comfort area along the
              Matagorda Island; this was a natural change of            east shore of Lavaca Bay (104 acres).
              about 1,925 acres (19 acres per year). Approxi-
              mately 475 acres of marsh were destroyed by                    Environments favorable for marsh develop-
              erosion along Pass Cavallo, and approximately             ment have also been created directly and indirectly
              1,450 acres were destroyed by burial beneath              by man's activities. The removal of some 46 miles
              sediment and perhaps by drought conditions.               of log jam along the lower Colorado River (be-
                                                                        tween Matagorda and Wharton) changed the river
                   Marshes have expanded through natural                regime and transported a large volume of sediment
              processes in three general areas. There was an            to Matagorda Bay. Rapid deltation resulted in
              increase in wetland area of about 130 acres at the        creation of a delta plain covering an area of about
              mouth of Garcitas Creek; this is an increase of           7,910 acres of which about 4,000 acres are
              about 1.3 acres per year. At the mouth of the             inhabited by marsh plants. Outwash from spoil
              Lavaca River, marsh area increased by. 55 acres           mounds created environments favorable for marsh
              (about 0.5 acres per year); marshes expanded as           plants. Two areas of spoil outwash along the north
              new sediment was deposited at the river mouth.            shore of Matagorda Bay are now inhabited by
              Flood-tidal deltas were constructed at the extreme        marsh plants. These areas are (1) east of the
              east end of east Matagorda Bay, at Brown Cedar            Colorado delta and south of McNabb Lake (about
              Cut, and at Greens Bayou. Emergent and intertidal         316 acres); and (2) west of the Colorado delta and
              segments of these deltas were the sites of marsh          south of Freshwater Lake (about 267 acres).
              expansion; total marsh area related to these tidal
              deltas in 1957 was about 380 acres (an average                               Future Studies
              increase of about 3.8 acres per year). The Lake
              Austin area has experienced an increase in wetland             The study of the Gulf and bay shorelines of
              area of about 835 acres; rate of increase was about       the Matagorda Bay area has documented the rates
              8 acres per year. Within this area (bounded on the        and directions of shoreline changes and changes in
              east by Caney Creek and extending to the north-           marsh area. Field observations of coastal prpcesses
              west boundary of the Brown Cedar Cut Area map),           were made in the winter of 1971 and spring of
              there were some large patches of marsh which did          1972, and an attempt was made to explain
              not appear on the 1957 photomosaies; these areas          shoreline changes in terms of these processes.

                       56

                             This study does not answer the question-                         present). Bay area is increased, in part, by shoreline
                       Why are Texas Gulf and bay shorelines eroding9 It                      erosion.
                       does, nevertheless, suggest that a major cause is a
                       deficit in the volume of sand being supplied to                              Any future program intended to mitigate the
                       Gulf shorelines. It also suggests that, with the                       effect of shoreline erosion and loss of wetlands
                       exception of a few local areas such as bayhead                         along the Texas Gulf Coast will depend upon a
                       deltas, the bays have been increasing in area at least                 thorough understanding of the sediment budget
                       since stillstand (some 3,000 to 2,500 years before                     and sediment dispersal systems.

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                             and London, Univ. Texas Press, 298 p.                                  Groat, C. G., 1973, Environmental geologic atlas of
                       Bernard, H. A., and LeBlanc, R. J., 1965, Resume of the                      the Texas Coastal Zone-Beaumont-Port Arthur area:
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                       Curray, J. R., 1960, Sediments and history of Holocene                       coastal inlets, in Proceedings of 12th Coastal Engi-
                             transgression, continental, shelf, northwest Gulf of                   neering Conference, Washington, D. C., p. 1187-1200.
                             Mexico, in Shepard, F. P., Phleger, F. B., and van               Kanes, W. H., 1965, Facies and development of the delta of
                             Andel, T. H., eds., Recent sediments, northwest Gulf                   the Colorado River, Texas: Morgantown, West
                             of Mexico: Tulsa, Okla., Am. Assoc. Petroleum                          Virginia, Univ. West Virginia, Ph.D. dissert., 106 p.
                             Geologists, p. 221-266.                                                    1970, Facies and development of the Colorado
                       Donaldson, A. C., Martin, R. H., and Kanes, W. H., 1970,                     River delta in Texas, in Deltaic sedimentation,
                             Holocene Guadalupe Delta of Texas Gulf Coast, in                       modern and ancient: Soc. Econ. Paleontologists and
                             Deltaic sedimentation, modern and ancient: Soc.                        Mineralogists Spec. Pub. No. 15, p. 78-106.
                       -     Econ. Paleontologists and Mineralogists Spec. Pub.               Kolb, C. R., and Van Lopik, J. R., 1966, Depositional
                             No. 15, p. 107-137.                                                    environments of the Mississippi River deltaic plain7-
                       Dunn, G. E., and Miller, B. 1., 1960, Atlantic hurricanes:                   southeastern Louisiana, in Shirley, M. L., and
                             Baton Rouge, La., Louisiana State Univ. Press, 377 p.                  Rogedale, J. A., eds., Deltas in their geologic frame-
                       El-Ashry, M. T., and Wanless, H. R., 1968, Photo interpre-                   work: Houston, Tex., Houston Geol. Soc., p. 19-61.
                             tation of shoreline changes between Capes Hatteras               Kummel, B., 1961, History of the earth-An introduction
                             and Fear (North Carolina): Marine Geology, v. 6,                       to historical geology: San Francisco, Calif., W. H.
                             p. 347-379.                                                            Freeman & Co., 610 p.
                       Environmental Science Services Administration,                         LeBlanc, R. J., and Hodgson, W. D., 1959, Origin and
                             1941-1968,    Climatological summary (revised March                    development of the Texas shoreline: Gulf Coast
                             1970), Station Palacios, Texas: U. S. Dept. Com-                       Assoc. Geol. Socs. Trans., v. 9, p. 197-220.
                             merce, Weather Bureau.                                           Manka, L. L., and Steinmetz, R., 1971, Sediments and
                       - 1947-1968, Climatological summary, Station Port                            depositional history of the southeast lobe of the
                             Lavaca, Texas: U. S. Dept. Commerce, Weather                           Colorado River delta, Texas: Gulf Coast Assoc. Geol.
                             Bureau.                                                                Socs. Trans., v. 21, p. 309-323.
                       - 1948-1969, Climatological summary, Station Port                      McEwen, M. C., 1963, Sedimentary facies of the Trinity
                             O'Connor, Texas: U. S. Dept. Commerce, Weather                         River delta, Texas: Houston, Tex., Rice Univ., Ph.D.
                             Bureau.                                                                dissert., 113 p.

                                                                                                                                                             57

                McGowen, J. H., and Garner, L, E         1972, Relation between            Shepard, F. P., 1973, Submarine geology: New York,
                       Texas barrier islands and late Pleistocene depositional                    Harper and Row, 517 p.
                       history (abst.): Am. Assoc. Petroleum Geologists                    Sneed, E. D., and Folk, R. L., 1958, Pebbles in the lower
                       Bull., v. 56, no. 3, p. 638-639.                                           Colorado River, Texas-a study in particle morpho-
                         I Garner, I. E., find Wilkinson, B. H., 1972, The                        genesis: Jour. Geology, v. 66, no. 2, p. 114-150.
                       significance of changes in shoreline features along the             Stafford, D. B., 1971, An aerial photographic technique for
                       Texas Gulf coast (abst.): -Gulf Coast Assoc. Geol.                         beach erosion surveys in North Carolina: U. S. Army
                       Socs. Trans., v. 22, p. 240.                                               Corps Engineers, Coastal Eng. Research Center Tech.
                Morgan, J. P., And Larimore, P. B., 1957, Changes in the                          Memo. 36,115 p.
                       Louisiana shoreline: Gulf Coast Assoc. Geol. Socs.                  -1 and Bruno, R. 0., and Goldstein, 11 M., 1973, An
                       Trans., v. 71 p. 303-310.                                                  annotated bibliography of aerial remote sensing in
                Nelson, H. F., and Bray, E. E., 1970, Stratigraphy and                            coastal engineering: U. S. Army Corps Engineers,
                       history of the Holocene sediments in the Sabine-High                       Coastal Eng. Research Misc. Paper 2-73, 122 p.
                       Island area, Gulf of Mexico, in Morgan, J. P., and                  Stapor, F., 1973, History and sand budgets of the barrier
                       Shaver, R. H., eds., Deltaic sedimentation, modern                         island system in the Panama City, Florida, region:
                       and ancient: Soc. Econ. Paleontologists and Mineral-                       Marine Geology, v. 14, p. 277-286.
                       ogists Spec. Pub. No. 15, p. 48-77.                                 Texas Board Water Engineers, 1950, Nineteenth report for
                Nienaber, J. I-L, 1963, Shallow marine sediments offshore                         the State of Texas covering biennium September 1,
                       from the Brazos River, Texas: Univ. Texas, Port                            1948 to August 31, 1950 inclusive: Texas Bd. Water
                       Aransas, Marine Science Institute Pub., v. 9,                              Engineers, 186 p.
                       p. 311-372.                                                         U. S. Dept. Commerce,         1943-1961, Climatological sum-
                Odem, W. L, 1953, The delta of the diverted Brazos River                          mary, Station Bay City, Texas: U. S. Dept.
                       of Texas: Univ. Kansas, Lawrence, Master's thesis,                         Commerce.
                       112 p.                                                       -      - 1941-1968, Climatological summary, Station
                Parker, R. H., 1960, Ecology and distributional patterns of                       Palacios, Texas: U. S. Dept. Commerce.
                       marine macro-invertebrates, northern Gulf of Mexico,                - 1947-1968, Climatological summary, Station Port
                       in Shepard, F. P., Phleger, F. B., And van Andel,                          Lavaca, Texas: U. S. Dept. Commerce.
                       T. H., eds., Recent sediments, northwest Gulf of                    - 1948-1969, Climatological summary, Station Port
                       Mexico: Tulsa, Okla., Am. Assoc. Petroleum                                 O'Connor, Texas: U. S. Dept. Commerce.
                                                                                           - 1958-1969, Local climatological data, Victoria,
                       Geologists, p. 302-337.                                                    Texas: U. S. Dept. Commerce, Weather Bureau,
                Price, W. A., 1954, Dynamic environments: reconnaissance                          Environmental Data Service.
                       mapping, geologic and geomorphic, of continental                    - 1973, Tide tables, east coast of North and South
                       shelf of Gulf of Mexico: Gulf Coast Assoc. Geol.                           America: U. S. Dept. Commerce, Natl. Oceanic and
                       Socs. Trans., v. 4, p. 75-107.                                             Atmospheric Adm., 388 p.
                Scott, A. J., and Fisher, W. L, 1969, Delta systems and                    Wadsworth, A. H., Jr., 1941, The lower Colorado River,
                       deltaic, deposition, in Delta systems in the exploration                   Texas: Univ. Texas (Austin), Master's thesis, 61 p.
                       for oil and gas: Univ. Texas, Austin, Bur. Econ.                               1966, Historical deltation of the Colorado River,
                       Geology Syllabus for Delta Colloquium, p. 10-29.                           Texas, in Shirley, M. L., and Rogedale, J. A., eds.,
                         I Hoover, R. A., and McGowen, J. H., 1969, Effects                       Deltas in their geologic framework: Houston, Tex.,
                       of Hurricane Beulah, 1967, on coastal lagoons and                          Houston Geol. Soc., p. 99-195.
                       barriers, in CastaR-ares, A. A@, and Phleger, F. B., eds.,          Watson, R. 1., 1968, Origin of shell beaches, Padre Island,
                       Lagunas Costeras, Un Simposio: Mexico City, Univer-                        Texas: Univ. Texas, Austin, Master's thesis, 12 1 p.
                       sidad Nacional Autonoma de Mexico, UNAM-                            -1 and Behrens, E. W., 1970, Nearshore surface
                       UNESCO, Mem. Simp. Internatl. Lagunas Costeras,                            currents, southeastern Texas Gulf coast: Univ. Texas,
                       p. 221-236.                                                                Port Aransas, Marine Science Institute, Contr. in
                Scruton, P. C  *, 1960, Delta building and the delta sequence,                    Marine Sci., v. 15, p. 133-143.
                       in Shepard, F. P., and others, Recent sediments,                    Wiegel, R. L., 1964, Oceanographical Engineering:
                       northwest Gulf of Mexico: Tulsa, Okla., Am. Assoc.                         Englewood Cliffs, N. J., Prentice-Hall, Inc., 532 p.
                       Petroleum Geologists, p. 82-102.                                    Wilkinson, B. H., 1973, Matagorda Island-The evolution of
                Seelig, W. N., And Sorensen, R. M., 1973, Investigation of                        a Gulf coast barrier complex: Univ. Texas, Austin,
                       shoreline changes at Sargent Beach, Texas: College                         Ph.D. dissert., 178 p.
                       Station, Tex., Texas A&M Univ., Sea Grant Pub. No.                  -, McGowen, J. H., and Lewis, C. R., in press,
                       TAMU-SG-72-212,153 p.                                                      Ingleside strandplain sand of the central Texas coast:
                Shalowitz, A., 1964, Shore and sea boundaries: U. S. Dept.                        Tulsa, Okla., Am. Assoc. Petroleum Geologists
                       Commerce Pub. 10-1, v. 2, 749 p.                                           Bulletin.

                                                                                   APPENDIX A

                                                     CHANGES IN SHORELINE FOR THE PERIOD 1856-1957

                             Shoreline changes for the Matagorda Bay area are                  whereas only one shoreline group may occur in other map
                       summarized in this appendix. Shorelines have been divided               areas.
                       into three groups: (1) Gulf shoreline, (2) the bay shorelines                  .Map areas are referred to by number in the following
                       of Matagorda Peninsula and Matagorda Island, and (3)                    table: (1) Brown Cedar Cut Area, (2) Colorado River Area,
                       mainland shoreline. Erosion or accretion associated with a              (3) Shell Island Reef Area, (4) Pass Cavallo Area, (5) Lavaca
                       particular shoreline group is shown for each map area. All              Bay South Area, (6) Lavaca Bay North Area, (7)
                       three shoreline groups may occur in some map areas,                     Carancahua Bay Area, and (8) Tres Palacios Bay Area.

                       Map                                                       Bay Shoreline, Barriers, and
                       Area                Gulf Shoreline                                 Peninsulas                               Mainland Shoreline
                                                             Net Loss                                     Net Loss                                      Net Loss
                                Erosion       Accretion       or Gain      Erosion       Accretion         or Gain         Erosion      Accretion       or Gain

                         1      -1,574.87       -            -1,574.87        297.51      +424.29         + 126.78          546.37      +     44.99     - 501.38
                         2         256.19     + 11.02           245.17        585.56      + 53.53         - 532.03             21.11    +8,674.98       +8,653.87
                         3         651.98     +121.21           530.77     -1,998.99      +191.75         -1,807.24            83.55    +1,179.28       +1,095.73
                         4      -1,118.44     + 59.68        -1,058.76    - 328.74        +294.76              33.98     -1,056.93      +  894.37         162.56
                         5                                                                                                  649.33      +  263 7          387.63
                         6                                                                                                  498.66      +  513.0        +   14.34
                         7                                                                                                  771.29      +  197.43         579.86
                         8                                                                                                  634.62      +  363.65         270.97

                         For. the period 1856-1957, there              For the period 1856-1957, there               When the         Colorado delta is
                         was a loss of 3,409.57 acres of land          was a loss of 2,246.47 acres of land          included in shoreline change, there
                         along the Gulf shoreline of                   along the bay shore of Matagorda              has been 7,861.54 acres of land
                         Matagorda Peninsula and Matagorda             Peninsula and Matagorda Island.               accreted to mainland shorelines. If
                         Island.                                                                                     the Colorado delta is excluded,
                                                                                                                     then there has been a loss of 138.45
                                                                                                                     acres of land along the mainland
                                                                                                                     shoreline.

                                                                            APPENDIX B

                                             CHANGES IN MARSH AREA FOR THE PERIOD 1856-1957

                      Areas of marsh expansion or diminution are sum-                   SHELL ISLAND REEF AREA (3)
                marized in this appendix. Marsheson the Brown Cedar Cut,
                Colorado River, Shell Island Reef, and Pass Cavallo area                       Matagorda Peninsula
                maps have been divided into two groups based upon (1)                                1856 marsh-4,255.68 acres
                whether they occur on the bayside of Matagorda Peninsula                             1957 marsh-926.64 acres
                and Matagorda Island, or (2) whether they are associated                       Mainland
                with the Pass Cavallo flood-tidal delta, or (3) whether they                         1856 marsh-2,738.74 acres
                are situated along the mainland shoreline. Marsh associated                          1957 marsh-2,100.38 acres
                with the Colorado delta developed since 1930 and is                                       -
                considered as a separate category.                                             There was a decrease of 3,329.04 acres of marsh on
                                                                                               Matagorda Peninsula for the period 1856-1957.
                BROWN CEDAR CUT AREA (1)                                                       Causes of decreases are the same as for Map Area 1.
                                                                                               For the same period (1856-1957), there was a loss of
                      Matagorda Peninsula (Caney Creek to west limit of                        638.36 acres of marsh along the mainland shoreline.
                      the map)                                                                 Change in area resulted from slopewash and dredging
                             1856 marsh-2,031.74 acres                                         of the Intracoastal Waterway.
                             1957 marsh-1,404.83 acres
                      Marsh on Matagorda Peninsula was larger in 1856                   PASS CAVALLO AREA (4)
                      than in 1957. Loss in area was 626.91 acres for the
                      100-year period. Loss in marsh area resulted from                        Matagorda Peninsula
                      erosion along the bay margin, and burial of marsh by                           Only 1856 marsh recorded-251.68 acres
                      washover deposits. Marsh area along the mainland                         Matagorda Island
                      increased during 1856-1957 by about 835.12 acres.                              1856 marsh-205.92 acres
                      This area is representative of delta plain and mudflats                        1957 marsh-18.30 acres
                      associated with the Holocene Brazos-Colorado delta                       Flood Tidal Delta
                      prior to construction of Matagorda Peninsula. Marsh                            1856 marsh-4,173.31 acres
                      area is expanding as the area is undergoing subsidence                         1957 marsh-2,244.53 acres
                      and is also experiencing a rise in sea level.                            Mainland (includes Espiritu Santo and Matagorda Bay
                                                                                               shorelines)
                COLORADO RIVER AREA (2)                                                              1856 marsh-1,671.38 acres
                                                                                                     1957 marsh-800.8 acres
                      Matagorda Peninsula
                             1856 marsh-4,752.18 acres                                         Matagorda Peninsula had virtually no marsh for the
                             1957 marsh-2,795.94 acres                                         period 1957. There was a loss of 251.68 acres of
                      Mainland (east boundary of the         map to Colorado                   marsh between 1856 and 1957. Matagorda Island
                      delta plain)                                                             (this includes the island proper, which is the area
                             1856 marsh-5,193.76 acres                                         lying to the south of a line through Fish Pond and
                             1957 marsh-2,951.52 acres                                         Lighthouse Cove). There has been a decrease in marsh
                      Colorado Delta Plain                                                     area amounting to 187.62 acres for the 100-year
                             Marsh     in    this   area     developed since                   period. Some of the loss is attributed to filling of
                             1930-3,628.77 acres                                               swales on the island (this is fresh-water marsh) and
                      Causes of loss of marsh area on Matagorda Peninsula                      part to erosion along the bay margin.
                      amounting to 1,956.24 acres are the same as for Map
                      Area 1.                                                                  Flood-tidal delta (from the Fish Pond-Lighthouse
                                                                                               Cove area northward to the Barroom Bay area). There
                      Between 1856-1957, there was a loss of marsh on the                      was a loss of marsh for the period 1856-1957 of
                      mainland of about 2,242.24 acres. Two natural                            about 1,928.78 acres. Two . factors, both natural,
                      processes and one man-made structure effected reduc-                     appear to, be the, cause of change in marsh area. First,
                      tion in marsh area. Slopewash along some of the                          erosionalong the right @bank of Pass Cavallo removed
                      Pleistocene cliffs and transportation of this material                   considerable marsh. Secondly, deposition on the
                      to marshes reduced marsh area. Vertical accretion and                    marsh islands covered a large part of the marsh and
                      progradation of the Colorado delta reduced marsh                         raised the surface of the islands sufficiently to
                      area, particularly to the west of the town of                            prevent inundation by tides.
                      Matagorda. Dredging of the Intracoastal Waterway
                      reduced marsh area by burial of marsh with spoil.                        Mainland marsh shows a decrease in area amounting
                      Since 1930, 3,628.77 acres of new marsh developed                        to 870.58 acres for the 100-year period. Marsh has
                      on the Colorado delta plain. This marsh was in-                          been lost through the natural process of erosion and
                      directly created by man's activities (a log jam was                      through man's activities. Man's activities, dredging of
                      removed in late 1929-early 1930).                                        the Intracoastal Waterway, resulted in burial of marsh

                      60

                             by spoil and by creation of a barrier (spoil mounds)                  There has been a decrease in marsh area for the
                             between marshand the bay.                                             100-year period amounting to approximately 253.96
                                                                                                   acres (the loss would be even more if the 1957 marsh
                      LAVACA BAY SOUTH AREA (5)                                                    at the head of Tres Palacios Bay were not included in
                                                                                                   the calculations). Most of the 1856 marsh south of
                             Mainland shoreline                                                    Palacios and east of Turtle Point has been removed.
                                   1856 marsh-3,759.18 acres                                       At Turtle Point, the marsh was destroyed by dredging
                                   1957 marsh-4,164.16 acres                                       shell from the Turtle Point spit. East of Turtle Point,
                                                                                                   much of the 1856 marsh was at least 5 feet above bay
                             For the 100-year period, there has been an increase in                water level; most of this was probably fresh-water
                             marsh area of approximately 404.98 acres. Most of                     marsh.
                             this gain has been in the area of Powderhorn Lake
                             and in the area lying between Powderhorn Bayou and                                        Summary
                             Indian Point Powerhorn La       ke   area was not com-
                             pletely mapped in 1856. New marsh areas were                          During the mid 1800's, there was a large area of salt
                             created between Powderhorn Bayou and Indian Point               in arsh on the bay side of Matagorda Peninsula and on the
                             by partial filling of shallow water bodies with                 flood-tidal delti. associated with Pass Cavallo. Total area of
                             sediment during storms and by spit accretion.                   the 1856 salt marsh was 15,670.51 acres. In 1957, the salt
                                                                                             marsh acreage was only 7,390.24. There was a decrease in
                      LAVACA BAY NORTH AREA (6)                                              marsh area amounting to approximately 8,280.27 acres (a
                                                                                             reduction in area of about 53. percent).
                             Change in marsh area for the period 1856-1957 is not
                             accurate for this area because mapping in 1856 was                    Total marsh area for the mainland shoreline in
                             incomplete along Chocolate Bayou, Placedo Creek,                1856-1859 amounted to 30,600.85 acres. Total marsh area
                             Agula Creek, and the Lavaca delta.                              for the mainland shoreline 1956-1957 amounted to
                                   1856 marsh-3,134.56 acres                                 29,927.03 acres. There was a loss in marsh area for the
                                   1957 marsh-4,296.86 acres                                 100-year interval of approximately 673.82          acres (or a
                                                                                             reduction in area of only 2 percent).
                             According to the calculations of acreages,for the two
                             vintages of marsh, there has been a net gain of about                 Several areas of marsh were not mapped in 1856.
                             1,162 acres. Accretion    of 137.73. acres occurred on          Marsh areas mapped on the 1956-1957 photos but not on
                             the Garcitas delta; this is new marsh land. Accretion           18N-1859. charts are: (1) along Placedo Creek-648.27
                             of 95.51 acres occurred at the mouth of the Lavaca              acres; (2) along Garcitas Creek-549.88 acres; (3) along
                             River; this is new marsh land. At Noble Point, 127.64           Keller Creek-97.62 acres; (4) at the head of Carancahua
                             acres of marsh have been lost by erosion during.the             Bay-551.41 acres; and (5) at the head of Tres Palacios
                             period 1856-1957.                                               Bay-453.02 acres. This is a total of 2,302.18 acres. In
                                                                                             order for the 1856 and 1957 comparison of marsh areas to
                      CARANCAHUA BAY AREA (7)                                                be valid, the. above marsh areas must be deleted from the
                                                                                             1956-1957 marsh area calculations. The new value is
                             Complete data are not..available for this map since             27,624.85 , acres. Using this value, there was a loss of
                             1856 marsh mapping did not extend up Keller Creek               approximately 2,976 acres of marsh for the period
                             and Carancahua Creek.                                           1856-1957. Reduction in marsh acreage results primarily
                                   185.6 marsh-3,310.74 acres                                from natural causes.
                                   1957 marsh-4,239.66 acres
                                                                                                   Several marsh areas have been dammed in order to
                             There was an increase of 928.92      acres in marsh area        create fresh- to brackish-water ponds. Salt marsh areas that
                             for the period 1856-1957.                                       have been dammed are: (1) Blind Bayou area-312.69 acres;
                                                                                             (2) northwest of Carancahua Pass and northeast and across
                      TRES PALACIOS BAY AREA (8)                                             the bay from Port Alto-75.5 acres; (3) Piper Lakes
                                                                                             area7-237.95 acres; and (4) Buttermilk Slough-379.04
                             With exception of the small. delta at the head of Tres          acres. This is,a total of 1,005.18 acres. Total marsh area lost
                             Palacios Bay, the 1856 marsh mapping was complete.              by natural processes and man's activities is 3,981.18 acres.
                                   1856 marsh-3,793.50 acres                                 Man's activities are responsible for at least 2.5 percent of the
                                   1957 marsh-3,539..54 acres                                reduction in marsh area.

                                                                 APPENDIX C

                        CHARACTERISTIC PROFILES OF GULF AND MAINLAND SHORELINE FEATURES

                    Details of Gulf and mainland shorelines are exhibited by the following 21 profiles. The profile numbers correspond to
              those shown on figure 11. Characteristics of the five shoreline types, as shown on figure 10, are depicted by these
              representative profiles.

                                                               BACKBEACH                                         BARRIER FLAT-
                                                               Shell romp                    Coppice mounds

                          xx                                     Salt ceda
                                                                                                               /@@elnsline
                                                 Whole shell, shell frogments,and rock fragments Shell sand     Terrigenous sand
                                        Spring tide                                                             and shell fragments
                                        debris line
               SL

                          5

                               5d

                                                                    Profile 23

                                                                                      FORE-ISLAND DUNES

                                                                                            Dune field

                                             Deflation
                                             zone

                                                        Spring tide debris line                                Debris line Hurricane Corla
              SL
                                            Whole shell, shell
                      Terrigenous sand      fragments and        Terrigenous sand, some shell debris in swales
                      and shell fragments   terrigenous sand
                5

                     5d

                                                                     Profile 30

                            62

                                                                                                                                     Barrier f lot

                            SL                         N.                                        Terrigenous sand and shell fragments
                                    Whole shell,            S@e I I
                                     fragments, and
                             5'      terrigenous sand

                                          50'

                                                                                                               Profile 37

                                                                                                                                                                                    Shell berm (Holocene)
                                                                                                                                                            Wave-\                  - - - - - - - - - -- -
                                                                                                                                                              cut             Str   Indploin sand
                                                                                                                                                             Cliff                  c
                                                                   Bay margin                                                                      Swash   e                  (Pleistocene)

                                                                                                                                                                         with plant roots (Pleistocene)
                                                                                                                                                                        Mottled red and gray muddy sand

                             5L
                                                                                                                                       9,Sflchlis
                                                                                                                         Bare sand
                                                "er                                                                                               I    Red and brown muddy sand
                                               lumps   WrIgNII       Oyster clumps      (cottered oyster clumps
                                                                        (dead)          both alive and dead)                                           (Pleistocene)
                              5-7y                             Terrigenous, sand with whole and fragmented shell
                                      50'

                                                                                                               Profile 41
                                                                                                                                                               At.

                                                                                                                                                                                    ------ ---- --
                                                                                                                                                                 ej@
                                                                                                                                                            vvov                    ndp
                                                                                                                                                                              Str.    l-'n s-nYd
                                                                                                                                                        Sh      utf           (PI   escen.)
                                                                                                                                                             cl f
                                                                                                                                                          ne             Matti ed red and  gr.    muddy  sand
                                                                                                                                                                           th plant roots (Pie  'stocene)

                                                                                                                                                        63

                                                                                        BEACH RIDGES

                                                   Seowo I I
                                   Shell                                 Shell ramp                         Salt morsh
                     4013   \
                         Swash     ramp        Tropical sto-
                          zone                 debris It
                                                                                 Po,
                                   Whole shell,                                     Anae
                                   shen fragments                                           :Sporfinasparflnod@: Halo- i 60VO sp/colo UCO :richia
                                     and rock frog-    Oyster shell                         :8arrich1qAsM7hAs1 plyra,5:        bu-S,      I Halophytes :Sparllm
                                                                                            soicalo, and Uco                                (dornlmNly :01tem-
                          Terri,enous son1l, ents                                           burrows                                         succulents) flara
                          with whole and                                        Predominantly shell frogments, some whole shel I            Muddy frogmented
                          fragmented shell
                      5                                                                                                                     shell

                            50'

                                                                                 Profile 45

                                                                                             Form Road 2717

                                                                                   Soil zone
                                                   4:p -
                                                     4                     CrGSSOSf1_6o and Rcngic
                                                     ,:S"-               Dark gray mud, caliche nodules. (Pleistocene)
                                                 Ci                  CcIficnassO burrows common.
                                                                  Alternating, red, very fine sand, silt, and mud.
                                                          Ripple cross-lomince and parallel laminae
                                                                                                                                          S.
                                                       characterize sand and silt; mud is homogeneou
                                   4
                                                       Some injection, features and cut-outs. Bedding
                         C-5    IV                     o/   1 --,_,@-4 inches thick. (Pleistocene)
                           S'L                     n roc       n     r gmentid-
                                                                  r                     OYster sheT/
                                             Re                           ents.
                                                                                    (Recent)

                                                                           ene)
                              5

                                         50

                                                                                Profile 47

                     64

                                                       Shell romp                                                                      zone

                                                                                  Salt marsh             Gross -
                                                                                                                                 Gray mud
                                                                                                           land
                                           Berm-                                                                               with coliche
                                 Z        swo I e                                                                                 nodu I es
                                                                                                                             (Pleistocene)
                                            zone

                                              Whole and fragmented                   Holop                          es
                                                                                          hytes         Prairie gross
                                                                  she[ I
                      SL                Well-rounded
                                        Shell debris

                           Oyster clumps
                            Muddy sand and
                            sandy mud with shell

                     5

                             50'

                                                                              Profile 48
                                                                                                             ras                        So
                                                                                                                S'
                                                                                                          I @and
                                                                                                                x

                                                                                                                                   65

                                                                                   (prairie grosses)

                                                                                 Soil zone

                                                                              Mottled gray and
                                                                            brown mud with
                                                            C)              caliche nodules

                                                                           ------------

                                                                     Mottled red and brown
                                              65                     mud and brown, very
                                                                     fine sand (Pleistocene)

                                                ,5L
                                                               Granule caliche gravel

                                                      Red mud and
                                                51    very f ine sand
                                                       (Pleistocene)

                                                   I
                                                           50  1

                                                                      Profile 51

                          66

                                                                                                                                                                        Prairie grosses

                                                                                                                                                                          Dark gray soil

                                                                                                                                                                          Reddish brown,
                                                                                                                                                                          slightly muddy,
                                                                                                                       dc@                                                very fine sand
                                                                                                                              'e                                          and coarse silt;
                                                                                                                       91C@                                               caliche nodules
                                                                                                                                                                          common; no
                                                                                                                                                                          stratif ication.
                                                                                                                                                                          Pleistocene
                                                                                                                 C:x)II

                               Bay margin                                 Salt marsh                                                        Prairie grosses and
                                                                                                                                            mesquite trees

                                                                                                                            Tropical storm
                                                                                                                            debris line

                                                                                                               --Uco burrows
                            SL                                                         DIsfichlis and
                                                                                       Sorrichic
                                                        Sporlino     allernIflora                                         Granule - bearing,
                                          Muddy, very fine sand                                                           very f ine sand
                                5                                                                                         and muddy sand

                                            50

                                                                                                        Profile 52

                                                                                                                                                             67

                                                                                                                                       Densely vegetated wor,
                                                                                                                                       brush and grosses
                              Shell IFresh-water marsh                         Salt-water marsh              CP                        Pleistocene
                cotfth          berm
                 50YOU

                              \Whole ",@ Sporflno spGrlmoe and                Distichlis splcolo and HGlophyles
                             Oyster\and       ",,, Juncus (clay)
                          ,@_Ic lumps  agmentedl-I                                             Sandy mud                             5
                        Oyster            shell                                  Clay               and          I113arren
                         reef                                                                                      sand
                                                                                                muddy sand
                                                                                                                                             50'

                                                                                   Profile 54
                                 Who  le

                                 r
                       ;@tue        and
                             c, r s f

                     68

                                                                                         @O Grassland

                                                                             4
                                                                             ,ZI
                                                                           -0
                                                                          c;:
                                                                                            Soil zone
                                                           Bay                            _r a-y -m t Td - -
                                                            margin'\\                      (Pleistocene)
                                                    SL                                Veneer of calliche
                                                                                      frogments ond
                                                                                      oyster shel I
                                                               DIPIGntherc
                                                                 Wrl_01711.i

                                                     5         Mud

                                                                 50'

                                                                                 Profile 5&

                                       Shell berm                                       Salt marsh

                                                                                                                                                    U
                        Bay N
                        margin                                                                                 f                                    I
                     SL                                                       U                                  U AEII
                                                                   MonGl7thochloe lltto@alts, SGlicornia, perennis, some blue-green algae, and UCG burrows Pure stand
                         Oyster flat with                                                                                                  of D151'Clyfis
                         green algae  Marsh mud with plants@                                  Sandy mud                                    sp/Co/0
                          Muddy       in growth position,
                         terrigenous  overlain by shell and
                          sand and    rock fragment gravel               5
                         shell debris

                                                                                                                                       Solt cedar
                                      Z                                                                                                 matte
                                                                                50,

                                                                                U
                                 ,5L_
                                                                                                     Pure stand of Mononihochloe Nforolis, Sorrio@io f,,ut-
                                                                                                     sparl(no      escens, Limonium, Sporlina, SpGrIln0e,
                                                                                                     sportmoe      and 7omorix gaffica
                                                          Sandy mud
                                                                                                                      Sandy mud
                                                                         ccj
                                                             a                            G
                                                        Lmayr

                                                                                                                                       Sol, cedar
                                                                                                                                        matte

                                                                                                     V

                                                                                 Profile 56

                                                                                                                                                                                                                 69

                                    Storm                 Short prairie gross Ies                 Shell romp                                                    Salt marsh                          Fresh-water
                                     @ierms                                                                                           Short prairie                                                     marsh
                                                                                                                                      grosses            Nononlhoclo& liftorobs with
                              w a S;\h@                                                                                               and shrubs         some Schcormo perenrils                   Spoltino sportinae
                     Bo y                                                               Coarse sand to                                                                  'W
                       O\Y& zone                                                                                                             Mu
                   margin                       aliche and                              granule-size caliche                                   Clay                        Mud with some shell gravel
                                                     _@phell gravel                     fragments and shell debris                           shel I
                           15-L\                                                                                                         /gravel
                                     @Terrigenous sand ar@
                    Pleistoce e        granule-pebble size
                             mud        caliche fragments                          5
                                          nd shelf debris                            .1
                                                                                             50'

                                                                                                              Profile 57

                                                               Public                           Extensively developed area at Port Alto
                                                    T.il parking
                                               @q   0
                                                                 a rea
                                                                                                                                   Soil zone

                                   0
                   Bay      ""<       (9 \              - -                                                                     Pleistocene muds
                   margin                             Coarse sand to pebble-size caliche,
                                                       siderite, and shell debris                                                                                                                  - ---- -
                                             Pleistocene m

                    5

                                 5,0

                                                                                                              Profile 59

                                                                                                                                                              Erosional escarpment

                                                                                                                                                                                                        @o
                                                                                                                                                                                                             @O
                                                                                                                                                                                                              0.

                                                                                                                                                      Wind-tidal
                   Boy margin Sporflho                                                                                                                    flat
                   alternifloro marsh                              Solt marsh

                                                                                                                                                       chloe
                         C,11,- .,d                                                                                                    nd                        'ao                 5'
                         b"'_'                                                                                                        hl@-14
                             Fine sand         MAdy,fihe sand              Red, moddy fine 5and and mud                               Red, sandy mud
                                                                                                                                                                                           50'

                                                                                                              Profile 60

                   70

                                                                                                               Top of
                                                                                                             escarpment
                                                                                        OS04                          Oyster shel I
                                                                                                                      veneer
                                                                                                                 Prairie grosses and
                        Bay margin                                                                               chaparral
                            SPCI-11@7G                                                    Debris
                                                    Salt marsh                           /line           Oyster shel I
                        Gllel-nlflolv
                             Marsh                                       Debris\                         veneer
                                                                          line               spGrt1nae
                                                                              I           /a  and short
                   5L                                                            Ifrulescens  prairie gr  @s
                          0                  Sparfina clterniflorq, Bclis mGri-
                           Yster C/UMPS      fimq, DIsI10711s splcatq, Uca bur- 15parfinG
                         Sand and mud-       rows, Litfol-Ina Irrorato            sparfinoe
                     5   dy sand                      Sandy mud

                              50'

                                                                       Profile 61

                                                                                       f
                                                         &

                                                                Prairie grosses, shrubs, OpunlIc
                                                              Soil zone

                                                            Light brown mud with callche nodules
                                           Swash
                                 Bay                        (Pleistocene)
                                             zone
                               margin                 Veneer of granule and pebble-size callche and
                                                      oyster she I I

                                               Mottled red and green
                                               mud with collche nodules
                                               (Pleistocene)

                                                 50'
                                           @ICJO  ell"

                                                                      Profile 62

                                                                                                                                                                                                                       71

                                                                                                                                                      Oyster
                                                                                                                                                                                                                          _j
                                                                                            Bay margin                                         \shel                                  Salt marsh                          T

                                                                               5L
                                                                                       Oyster reef            Son    ive oyster clumps              Wholp and           Sdtls marill-, 01511chlIs SPICOIC, Ond
                                                                                                                                                      rogmented         patches of 5,oorliao olternIflora; UCG
                                                                                                              Shell flat, muddy shell               ySter she    "      burrows
                                                                                                              and rock     frogmen    t         /arld    caj@'  he                       Mud
                                              5'j                                                             gravel                               rag ment    gr'_@
                                                                                                                                                  vel

                                                       50
                     Lu                                                                                                                                                                     Drainage /Oyster
                     Z                                                                                                                                                                                         shell
                     _j
                                                                                           Salt marsh                                                                                           ditch          road

                             Predominantly DI@71iclVls spicatc, some Sallcorn1c, peremns and BG115 MGri&nG                             Predominantly Bcli@ marlfl@no with some
                                                                                                                                       Distlcl7M5 soicara, Uco burrows

                                                                      Mud                                                                     Mud and sandy mud

                                                                                                                 Profile, 70

                                                                                                                                                                                                    'r. co@9
                                                                                                                                                                                                         w9e
                                                                                                                                                                                       0S
                                                                                                                                                                                              '@PP9
                     Bay               Storm berms                             Fresh-water                       Erosional surface, gentle slope
                   margin         i@                                               marsh

                                                                                                                                                             Chaparral, short grisses, some mesquile
                                    CD     Broad, upper berm vegetated
                                             ith Opunlid, short grosses,       sparllnc sportince
                                           shrubs and sell cedar               .1uncus, short grosses
                          SL        /                                          and shrubs                        Coarse sand to granule-size shell debris                                 Pleistocene mud
                                 01 0,.   Coarse sand to pebble-
                                    ,.   - size shell and caliche              Shell and rock
                     5                            fragments, swales            fragment gravel
                                                      are finer grained
                                                          than ridges

                                                                                                                 Profile 72
                                                    erms

                                           Coarse   sand
                                               sze  she 11
                                                  fragm@
                                                      are

                                     72

                                           Low salt marsh                     High                 Wind-fidol                             High salt marsh                                                          Wash from spoil                                         Z
                                                                              salt
                                                                                                   f lot
                                                                               marsh

                                   5L
                                             "3@1_11n' allmifloric,           Bat's          Desiccation    rocks,           D'shchlis, Bobs, Soficornio; abundant Llco                      S'oamnc sporlince,         SpartIna polens, some Heliotrpoatm,
                                              Baf,s, Dsfchhs                                 a few UcG burrows               bu rrows                                                        prairie grosses
                                           Sand withi Mud with                    Sand with mud drape                        Sand and muddy sand washed from                                 Surface sediment is sand and muddy sand
                                           ripple-bedl rippled                                                               spoil
                                           for             sand

                                                                                                                                             Spoil mound

                                                           Z                                 50'                                                                                                               Intracoastal canal
                                                                                                                                                                                                               315' wide
                                                                       '@Iil Ali
                                                               First appearance of                 Sporfmc sportince, Prosopis, shrubs, Indian gross,                           No veget it
                                                               sorqhostrum exottit
                                                      SL    --and shrubs

                                                                         Surface sediment is sand, shell,                                    Gravel-size slabs of mud and sand.,
                                                                         sandstone and coliche fragments                                     shell of bay species abundant

                                                                                                                                                Profile 7 5

                                                                                                                                                          Spoil mound                Wash from
                                                                                                                                                                                     si@olr mound
                                                                                                                                                        5-1,"--        1        .__ _      -, @.11   - rtt,    Salt marsh (wash from spoil mound)                     Pond
                                                                                               Intracoastal canal                  \Sw.h zon
                                      Boy @Berm Salt                                                                                                                                         Uca :U ..... .
                                    margin            marsh                                                                                                  Su                                             I
                                                                                                                                                               frface veneer
                                                              st-1- pi-, "o                                                                                  o terrige, .1                                1 1
                                                              u-                                                                                             sand no coliche\                                              ly-
                                           Mixed sand and mud                                                                                   /Vereer of coich-e--                              Surface sediment is sand
                                                                  n                                                                               gravel over spoil
                                           bay, rock frogmen's  a'no         5
                                           sheti on the berm, salt
                                           marsh underlain by spoil
                                                                                    50

                                                                                                                                                Profile 76
                                                                                                                                                           ound
                                                                             aorsn

                                                                                    L                                                        Spoil
                                                                                             5  -                                                                                                         I

                                                                                                                                                            gross,
                                                                                                                                         @IrbslndM.@.                           No @@,e,.r.
                                                                                  "of              lpo,',n,

                                                                                                             DATE DUE

                                                                                           GAYLORD No. 2333                              PRINTED M U SA

                                                                                                   36668 1