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                     )EPAR TMENT OF GEOGRAPHY AND ENVIROMENTAL ENGINEERING



















                                         US Department of Commerce
                                    NOAA Coastal Services Center Library
                                           2234 South Hobson Avenue
                                           Charlston, SC 29405-2413


                                  Calvert Cliffs Slope Erosion Project
                                           Phase I Final Report


                                         Processes and Controls
                                         of Coastal Slope Erosion


                                                January 31, 1992


                                                  Submitted by


                                        Peter R. Wilcock and David S. Miller
                              Department of Geography and Environmental Engineering
                                           The Johns Hopkins University
                                              Baltimore, MD 21218


                                                      and


                                                Randall T. Kerhin
                                            Maryland Geological Survey
                                               2300 St. Paul Street
                                              Baltimore, MD 21218



                        Funding for this project was provided by the Coastal Resources Division,
                     Tidewater Administration, Maryland Department of Natural Resources through a
                        CZM Program Implementation Grant from the Office of Ocean and Coastal
                                           Resource Management, NOAA.
 










                                                    Table of ContentS


                  List of Figures												3                                                                                                          


                 	List of Tables												4                                                                                                           



                  Executive Summary												5                                                                                                        


                  Acknowledgements												8                                                                                                        



                  1.   Introduction  											9                                                                                                     

                  1.1  Background											     	9	                                                                                                          
                  1.2  Overview of the Calvert Cliffs Slope Erosion Project				     10	                                                                    10
                  1.3  Overview of Phase I -CCSEP								     11	                                                                                            


                  2.   Site Selection 										     12                                                                                                     

                  2.1  Controlling factors of coastal slope erosion					     12                                                                                 
                  2.2 Selection of study sites									     13                                                                                            
                  2.3  Field experiments										     13                                                                                                  


                  3. Description of the Study Sites								     15                                                                                        

                  3.1 Survey Methods										     15                                                                                                      
                       Slope Profile Surveys - all sites							     16                                                                                   
                       Field Observation and Photo Stations							     16                                                                                
                  3.2  Geotechnical Methods 									     17                                                                                               
                       Stratigraphic Description, Well Logging, and Sample Collection		     17                                                      
                       Laboratory Analysis									     17                                                                                                 
                  3.3  Description of Erosion Mechanisms							     18		                                                                                   
                  3.4  Naval Research Laboratory								     20                                                                                              
                       General Site Description									     20	                                                                                            
                       Geotechnical Properties 									     21                                                                                            
                       Erosion Mechanism										     22                                                                                                   
                  3.5  Scientists Cliffs										     23                                                                                                   
                       General Site Description									     23                                                                                            
                       Geotechnical Properties 									     24                                                                                            
                       Erosion Mechanism										     25                                                                                                   







							    1	










                 3.5  Calvert Cliffs State									28                                                                                           
                      General Site Description									28                                                                                       
                      Geotechnical Properties									28                                                                                        
                      Erosion Mechanisms										29                                                                                             
                 3.7  Chesapeake Ranch Estates									33                                                                                       
                      Gneral Site Description									33                                                                                        
                      Geotechnical Properties									34                                                                                        
                      Erosion Mechanism										34                                                                                              


                 4.   Mechanisms and controls of coastal slope failure 					38                                                              

                 4.1 Wave undercutting and its relation to other controlling factors of coastal slope erosion.	     38                          
                 4.2 Groups of slope erosion mechanisms: Classification of the Calvert Cliffs slopes			     38	                                    
                 4.3 Environmental factors controlling the recession of each slope type.					     42                                                 
                 4.4 Field Experiments													     44	                                                                                                
                      Material Strength                                                                                              
                      Slope Height 														     45                                                                                                  
                      Wave Undercutting 													     45                                                                                             

                 5.0 Comparison with Historical Erosion Rates									     46                                                                        


                 6.0 Extrapolation of Observations to Other Portions of the Chesapeake Bay Shoreline			     50                               


                 7.0 References												53	                                                                                                   



                 Report Tables											      54                                                                                                      


                 Appendix: Laboratory Data for Geotechnical Samples


                 Report Figures


                 Photographic Plates








							   2	










                                                                    Lost of Figures




                  2.1       Study Site Locations: Calvert Cliffs Slope Erosion Project

                  3.1       Study Site NRL: Naval Research Laboratory

                  3.2a      Randle Cliffs North Slope Profile

                  3.2b      Randle Cliffs South Slope Profile

                  3.2c      Naval Research Laboratory Slope Profile

                  3.3       Naval Research Laboratory Geotechnical. Profile

                  3.4       Study Site SC: Scientists' Cliffs

                  3.5a      Parkers Creek Slope Profile

                  3.5b      Scientists' Cliffs North Slope Profile

                  3.5c      Scientists' Cliffs South Slope Profile

                  3.5d      Governor's Run Slope Profile

                  3.6       Scientists' Cliffs Geotechnical Profile


                  3.7       Study Site CCSP: Calvert Cliffs State Park

                  3.8       Gray's Creek South Slope Profile

                  3.9       Calvert Cliffs State Park Gootechnical Profile


                  3.10      Study Site CRE: Chesapeake Ranch Estates

                  3.11a     Little Cove Point Slope Profile

                  3.1 lb    Laramie Lane Slope Profile

                  3.12      Chesapeake Ranch Estates Geotechnical Profile

                  4.1       Classification of coastal slopes by undercutting rate and characteristic groups of erosion mechanisms

                  6.1       Distribution of Coastal Plain Sediments Around the Chesapeake Bay

                  6.2       Conceptual Model for extending CCSEP results to predict coastal slope erosion along the Chesapeake Bay













                                                               List of Tables


                Table I - Characteristics of CCSEP Sites and Subsites                                                       54


                Table 2 - CCSEP Experiments                                                                                 55


                Table 3 - Summary of slope types                                                                            42


                Table 4 - Summary of Historical Erosion Rates                                                               49





                                                                Lost of Plates


                Plate 1 - Naval Research Laboratory, Type I vs. Type IV slopes


                Plate 2 - Scientists' Cliffs and Chesapeake Ranch Estates, Type II slopes

                Plate 3 - Calvert Cliffs State Park, Type III slopes


                Plate 4 - Calvert Cliffs State Park and Naval Research Laboratory, Type IV slopes

                Plate 5 - Scientists' Cliffs and Chesapeake Ranch Estates, Type IV slopes

                Plate 6 - Calvert Cliffs State Park, example of spalling event












                  Executive Summary

                  More than one-half of the shoreline of Calvert County, Maryland consists of steep, actively eroding slopes 10 m to
                  35 m high. 'Ibis slope erosion presents numerous environmental, safety, and economic problems. A particular
                  concern is the response of the cliffs to a rise in sea level, which would accelerate cliff recession by allowing wave
                  erosion and slope undercutting to work at higher locations on the cliffs. An adequate prediction of the cliff response
                  to sea level rise requires an understanding of the mechanisms by which the cliffs erode and the critical environmental
                  factors that determine the type and rate of slope erosion.

                  This report presents the results of the first year of the Calvert Cliffs Slope Erosion Project (CCSEP), a three-year
                  collaborative effort between the Maryland Geological Survey and the Department of Geography and Environmental
                  Engineering at the Johns Hopkins University. The overall goal of the Calvert Cliffs Slope Erosion Project
                  (CCSEP) is to develop a quantitative understanding of slope erosion that can be used to predict past or future slope
                  failures, The goal of the first year of the project is to to characterize the slope materials and types of slope failures
                  presently occurring along the tall coastal cliffs of Calvert County. This information provides the basis for
                  quantitative modeling of slope failures and recession in the latter two years of the project. In the second year, the
                  individual factors contributing to slope erosion-wave undercutting, groundwater flux, surficial erosion, and slope
                  stability will be modelled. In the final phase of the project, these models will be integrated to provide quantitative
                  guidelines concerning the response of slope erosion to changes in external factors, particularly sea level change.

                  Four sites have been selected for detailed study. These sites are representative of the slope materials and erosion
                  along the Calvert Cliffs. Each site has been further subdivided into several subsites so that a larger range of slope
                  conditions could examined in an efficient manner. A summary of the geotechnical properties of the cliff materials
                  has been prepared based on field observations, the logging of 22 groundwater observations wells, and the laboratory
                  testing of samples taken from the four cliff study sections. The types and rates of slope erosion were measured using
                  repetitive field observations and surveys of slope profiles at multiple sites for each of the four study sections. The
                  heart of the report is Section Three, which characterizes the slope materials and types of slope failures along the
                  Calvert Cliffs using a detailed description of the slope geometry, groundwater, geotechnical properties, and observed
                  erosion at each study site.

                  A wide variety of slope erosion processes operate simultaneously on these steep, rapidly eroding slopes. These
                  include direct wave removal of material at the slope toe, block falls along tension cracks, undercutting by
                  groundwater seepage, surficial erosion by seepage discharge and surface wash, simple falling of material from near-
                  vertical slopes, flow of saturated material during freeze/thaw cycles, shallow sliding of saturated surface material, and
                  deep-seated rotational slides. Because of the number and complexity of these processes, we have developed a
                  classification system for the cliff slopes based on the typical groups of erosion mechanisms and rates and their
                  associated slope profiles. The classification system provides a basis for organizing a highly complex physical
                  situation and serves to organize field experiments in the latter years of CCSEP. These experiments are designed to


                                                                               5










                  determine the critical values of environmental factors determining the different types and rates of slope erosion.
                  Because the classification system is based on the erosion mechanisms that occur on individual slopes, it also
                  provides the basis for designing and evaluating erosion mitigation projects and predicting slope response to changes
                  in sea level and wave activity.

                  The slope classification system is based on two observations. First, a permanent seepage zone is found to occur on
                  all cliffs in the range of 2 in to 15 in above beach level. Second, the geotechnical properties and resistance to
                  erosion of the material above and below the seepage zone are found to be generally different. Below the seepage
                  zone, the materials tend to be permanently moist, dark-colored, and massive in structure. These materials tend to be
                  more resistant to surficial erosion than the overlying materials and fail primarily by direct falling from slopes
                  oversteepened by direct wave activity. Within and above the seepage zone, the materials tends to be more granular in
                  structure and more susceptible to surface erosion. These materials fail by a variety of mechanisms, but only
                  occasionally' by fracturing and falling driven directly by wave steepening of the slope. The slope classification
                  system is organized according to the relative recession rates of the lower and midslope sections. Four slope types are
                  recognized:

                                     Zero or minimal slope toe recession, allowing slope debris to build a depositional and vegetated
                                     lower slope. The lower slope stands at a smaller angle than the upper portions of the slope.

                           (11)      Wave erosion removes accumulations of slope debris at the toe, but produces little, if any erosion
                                     of intact slope material. These slopes tend to be relatively straight, with minor slope variations
                                     appearing at boundaries between different stratigraphic materials.

                            (M)      Wave erosion removes both toe debris and intact material at a rate sufficient to cause
                                     oversteepening of the lower slope and erosion by direct falling of the lower slope material.
                                     Despite the accelerated rate of lower slope recession relative to Type (1) and (II) slopes, midslope
                                     erosion driven by seepage discharge, surface wash, or gullying causes recession of the midslope to
                                     proceed even more rapidly than the lower slope, producing a characteristic decrease in slope angle at
                                     the boundary between lower and midslopes.

                                     Wave-driven recession of the lower slope proceeds sufficiently rapidly that the midslope also
                                     becomes oversteepened and fails by spalling and shallow sliding. Deep-seated rotational slips can
                                     occur on slopes with sufficient height above a weak zone that is susceptible to elevated pore
                                     pressures. Type IV slopes tend to be relatively straight and much steeper than those of other

                                     types.

                  All categories of slope type are found within our study sites. In general, individual slopes can be readily placed
                  within the slope classification system based on the characteristic slope geometry associated with each slope type.
                  The slope measurements we have made to date indicate that the slope angles characteristic of the four basic slope
                  types fall into distinct, nonoverlapping groups. This is a potentially important and useful result. Our slope


                                                                              6










                 classification is based on observations of groups of erosion processes and rates that typically occur together, and on
                 the slope geometry developed by these groups of processes. If the type of slope can be determined based on the
                 overall slope angle, the classification of individual slopes can be done quite readily. Once classified into a particular
                 type, the erosion mechanisms acting on that slope, and the environmental factors controlling that erosion, can be
                 estimated. Classifying slope type by angle can also provide the opportunity to make classifications from aerial
                 photographs or detailed maps.

                 Type III slopes are the most common along unprotected sections of tall cliffs in Calvert County. Because recession
                 of the middle and upper portion of Type III slopes is driven by hydrologic erosion processes related to seepage
                 discharge and surface flow, it is clear that environmental factors other than wave undercutting can determine the type
                 and rates of slope erosion acting at any one location. This point is particularly evident at two of our study sites,
                 where direct wave undercutting has been prevented by man-made structures. At both sites, active erosion of the
                 middle and upper slopes continues, despite the fact that toe erosion has been prevented for decades. An understanding
                 of slope erosion along tall cliffs, such as those in Calvert County, clearly must include the erosion driven by
                 seepage discharge and overland flow.

                 A summary of erosion rates measured over the last 140 years is provided in this report and compared to the short
                 term processes investigated here. The distribution of sediments with similar properties along other portions of the
                 Maryland Chesapeake Bay shoreline is given to provide a basis for extrapolating the erosion mechanisms and slope
                 types observed in Calvert County.











                  Acknowled-ements

                  Funding for this project was provided by the Coastal Resources Division, Tidewater Administration, Maryland
                  Department of Natural Resources through a CZM Program Implementation Grant from the Office of Ocean and
                  Coastal Resource Management, NOAA.

                  We are indebted to Jack Pomeroy for introducing us to the sites along the Calvert Cliffs and the erosion mechanisms
                  operating there, and to Peter Vogt for his perspectives on the erosion processes and stratigraphy of the cliffs. Our
                  thanks are extended to Commanders Jones and Kummer and Mr. Tracy Erwin of the Naval Research Laboratory,
                  Chesapeake Bay Division for their cooperation in establishing a study site there; to the Honorable David Bonior, the
                  Walter Lippold farn  ily, and Ms. Ruth Shinn for granting us permission to install and monitor groundwater wells on
                  their property; and to Mr. John Westerfield for his assistance in establishing a study site at the Calvert Cliffs State
                  Park. Thanks are also in order to Mr. Dick Mulford and Ms. Carole Yatchum of the Scientists'Cliffs Association

                  and Property Owners Association of Chesapeake Ranch Estates, respectively, for facilitating our activities at our
                  study sites.

                  A special debt of gratitude is owed to our field assistants Rachel Zimmerman, Jennifer Isoldi, Margaret Carruthers,
                  Jamie Berry, Amir Erez, Brian McArdell, Alan Barta, and Betsy Killer who, undaunted, braved bees, snakes,
                  jellyfish, cold, waves, wind, and crab feasts to make our field work a success. We would also like to thank our
                   transportation specialists" Danielle de Clercq, our pilot, and Rick Younger, our skipper, without whom we would

                  be lost.


                  And finally, we thank Darwin Feheley, Mark Filar, Dave Montgomery, and Dave Vodak, the drill crew and technical
                  experts from the Technical Services Branch of the Maryland Department of Natural Resources for their invaluable
                  contribution to this project. Rachel Zimmerman ably'prepared many of the figures.






















                                                                              8













                  1. Introduction


                  1.1 Background

                  The open shoreline of Calvert County, Maryland extends 45 krn along the western side of the Chesapeake Bay. Of
                  this shoreline, 65% consists of steep slopes 10 m to 35 m high. Most of these slopes, well-known as the
                  fossiliferous Calvert Cliffs, are actively eroding. Slope recession rates greater than 2.5 m/yr over a 96 year period
                  have been measured along the Calvert Cliffs (Slaughter, 1949). This slope erosion presents numerous
                  environmental, safety, and economic problems. Sediments eroded from the cliffs contributes to increased
                  sedimentation and turbidity in the bay. Pollution from septic leachate is a growing problem where slope recession
                  approaches septic fields. Direct undercutting of homes and civil structures incurs large personal and social costs.
                  Shore erosion control measures designed to protect slopes from undercutting and farther recession are very expensive
                  and difficult to finance by private or community funds. Slope failures also create a personal safety problem in areas
                  of public accpess, such as the Calvert Cliffs State Park. Adequate safety guidelines, development plans, and
                  remediation programs all require a reliable understanding of the type, timing, and rate of slope erosion and of the
                  environmental factors which control slope instability.

                  Population growth in Calvert County and nearby metropolitan areas has maintained a continued pressure for
                  development of property along the Calvert Cliffs. At the same time, interest in protecting the Chesapeake Bay and
                  its shorelines as a natural resource has resulted in the passage of the Chesapeake Bay Critical Areas Act, which
                  implements strict guidelines limiting development of land within 1,000 feet of tidal water and tidal wetlands and
                  requires the maintenance of a 100 foot intact buffer. Reasonable application of these guidelines in planning future
                  development, particularly at the case-by-case level, as well as protection of existing development, requires reliable
                  information concerning the rates, timing, and type of shoreline erosion and the environmental factors which control

                  it.

                  One driving mechanism for the slope recession observed over the past 150 years is a slow rise in sea level, causing
                  wave erosion and slope undercutting to work at progressively higher locations on the cliffs. The change in sea level
                  in the Calvert County area over the past 150 years is not precisely known, but appears to fall within the rates of 1.5
                  to 4 cm/decade (Emery and Aubrey, 1991). It is clear that future increases in sea level would compound the existing
                  erosion problem and accelerate the long-term recession rate.

                  Estimates of slope recession over a period of 100 years have been prepared from an analysis of historical maps and
                  modem aerial photographs (Slaughter, 1949). These efforts are currently being updated and extended over an
                  additional 45 years by the Maryland Geological Survey. Because the the type and rate of slope erosion can vary
                  locally, and because slope erosion can be cyclic, with periods of little erosion followed by periods of intense
                  erosion,(Quigley et al., 1977), it is difficult to apply the regional, historical slope recession rates to short-term
                  planning, safety guidelines, or remediation plans for specific sites. It is also difficult to use past erosion rates to



                                                                           9









                 predict future slope recession if the basic driving forres-the bay water level and wave activity--change in the future.
                 The goals of the Calvert Cliffs Slope Erosion Project are to develop an understanding of the slope erosion
                 mechanisms and rates based on the local slope and shoreline characteristics, and to determine the environmental
                 factors that control slope erosion on a site-specific basis. Because local cliff properties control the response of
                 individual slopes to undercutting, the information collected in this project, and the slope erosion models developed
                 from that information, should be valuable for local planning and remediation. Because the results of this project
                 incorporate the mechanics of the slope erosion, we can address how the slopes will respond to conditions that differ
                 from those acting during the three year project@ or over the past 150 years. The local, mechanics-based approach
                 followed here, and the regional, historical approach work well together. The first provides explanation, local
                 application, and predictive capabilities to the second, while the second provides measured limits to the short-term
                 processes involved in the first.

                 1.2 Overview of the Calvert Cliffs &= Erosion Projec

                 The overall goal of the Calvert Cliffs Slope Erosion Project (CCSEP) is to develop a quantitative understanding of
                 slope erosion that can be used to predict past or future slope failures. Ibis understanding will be developed in a
                 three-step process. First, the erosion mechanisms occurring at each study site must be identified. Second, the
                 environmental factors controlling these particular erosion processes must be determined, based on our understanding
                 of the erosion mechanics, the gootechnical properties of the soil and slope, the pore pressure regime of the slope, and
                 the wave and precipitation driving forces of the erosion. Third, critical values of the environmental factors
                 controlling slope erosion determine the types of erosion and their relative importance at each site and will be
                 quantified through the development and testing of quantitative models of the slope erosion for each study site.

                 These models will tested in two ways, one absolute and one relative. First, predictions of types and rates of slope
                 erosion may be directly compared with field observations. These tests are direct and useful, but limited by the fact
                 that coastal slope erosion typically occurs over periods of time much longer than this study, and by the amount of
                 error inherent in predicting the rates of complex physical processes. The first problem is partially addressed by
                 extrapolating our predicted results over a much longer time frame and comparing the result with historical
                 observations of slope recession over the past 150 years. The second test is a relative one and is based on comparing
                 predicted results between individual sites by means of field experiments. We define field experiments as a pair of
                 slopes between which there is a significant variation in one environmental factor of slope erosion and a much
                 smaller variation in the other controlling factors. Our ability to predict differences in behavior between two sites is
                 often better than our ability to predict the absolute rates at an individual site. By examining and modelling pairs of
                 sites where there is a significant variation in only one slope erosion factor, we can test our modeling by comparing
                 prediction vs. observation of the contrast in slope erosion between the pair. For cliffs that are actively eroding, such
                 as at Calvert Cliffs, this second test allows us to identify critical values of the factors that control slope erosion.
                 These models, together with an understanding of critical values of erosion controlling factors, allow us to estimate
                 slope erosion types, rates, and timing at each study sites.


                                                                            10










                  The goals of Phase I of CCSEP are to accomplish the first two tasks. We have identified the the suite of erosion
                  processes currently occurring along the cliffs. We have developed a data base of geotechnical and slope geometry
                  information. These data are then used, together with a mechanical description of each erosion process, to identify the
                  controlling factors of coastal slope erosion in Calvert County. An important factor limits our ability to completely
                  characterize the slope erosion controlling factors at each study site. Funding restrictions prevent a study of the wave
                  energy distribution in front of the cliffs to the level necessary to identify wave energy flux and undercutting rates
                  driving the slope erosion at each study site. Our description of the effect of undercutting on slope erosion focuses
                  more on protected vs unprotected slopes and, for unprotected slopes, uses the elevation of the beach and slope toe and
                  the cliff orientation as a surrogate for wave erosion energy.

                  Information on slope materials, groundwater flow, and wave conditions will be combined with the slope erosion
                  observations to develop a slope erosion model that can be used to predict the response of slopes to future changes in
                  sea level. Because the model will operate a site-specific level, and because it will be based on the mechanisms and
                  controlling factors of coastal slope erosion, it will also provide a basis for designing and evaluating shore erosion
                  hazard mitigation projects.

                  1.3 Overview of Phase I - CCSE


                  This report describes the mechanisms, rates, timing, and environmental controlling factors of cliff erosion in Calvert
                  County. These are the results of the first phase of the Calvert Cliffs Slope Erosion Project (CCSEP). The
                  objective of Phase I of CCSEP is to characterize the slope materials and types of slope failures presently occurring
                  along the tall coastal cliffs of Calvert County. Four sites have been selected for detailed study. These sites are
                  representative of the slope materials and erosion along the Calvert Cliffs. A summary of the geotechnical properties
                  of the cliff materials has been prepared based on field observations, the logging of 22 groundwater observations
                  wells, and the laboratory testing of samples taken from the four cliff study sections. The types and rates of slope
                  erosion were measured using repetitive field observations and surveys of slope profiles at multiple sites for each of
                  the four study sections. From these data, we have developed a summary of the types, timing, and magnitude of
                  slope failures. The slope profile and geotechnical data are used to summarize the influence of geotechnical properties
                  on slope erosion. The distribution of geotechnical properties and slope failures at the Calvert Cliffs are used to
                  extrapolate the observed effects of geotechnical properties on slope failure to other regions in the Calvert Cliffs and
                  to other parts of the Chesapeake Bay coastline where the same types of sediments are found.














                  2. Site Selection


                  2.1 Controllina factors of coastal sloM erosion

                  A basic objective of this project is to identify the slope erosion mechanisms and the critical values of the
                  environmental factors that control the types and rates of the slope erosion. By knowing how the slopes erode and
                  what controls the erosion at individual locations, we can begin to predict how the slopes will respond to future
                  changes in the basic driving forces. This section briefly outlines the environmental controlling factors of slope
                  erosion and explains how we will use field experiments to identify the critical values of these controlling factors at
                  particular locations.

                  Ile environmental factors controlling coastal slope erosion may be organized into four basic categories: slope
                  geometry, hydrology, material properties, and basal undercutting.

                        1. Slope geometry - The stability of a slope depends in part on its spatial dimensions, particularly slope
                        height, and the geometric shape of the slope. The geometry controls the total stresses developed in the
                        slope and, in conjunction with the pore pressures generated by groundwater flow, controls the shear strength
                        that can be mobilized within the slope. Slope geometry also controls the gradients of runoff over the slope
                        surface, and therefore the erosive force supplied by surface water. The pattem of groundwater flow within
                        the slopes is also partially controlled by slope geometry.

                        2. Hydrology - Slope erosion produced by both surface runoff and groundwater seepage has been observed
                        along the Calvert Cliffs (Leatherman, 1984). Surface runoff generated by precipitation on the slopes can
                        directly erode material. Surface runoff can also saturate and weaken near-surface materials and contribute to
                        shallow sliding. Erosion from surface runoff can also be generated by groundwater seepage on the slopes.
                        Seepage may occur along a strata, which we call sapping, or at concentrated points, called piping. In both
                        cases, sediment may be directly eroded at seepage outlets, which results in undercutting and erosion of
                        overlying strata. The effective strength of materials against deep-seated slope failures in the slopes depends
                        in part on pore pressures related to groundwater flow within the slope.

                        3. Material properties - Material strength and resistance to erosion depend on properties such as grain size
                        and sorting, cohesive strength, and material internal friction. The Calvert Cliffs are composed of
                        interbedded fossiliferous sands, gravelly sands, silts, and clays. Ironstone, a particularly strong type of rock
                        that occurs in the sediments composing the Calvert Cliffs, forms in laterally discontinuous patches and is
                        the hardest material present in the slope materials. Due to the variety of materials, there are large contrasts
                        of material strength between stratigraphic units. Because these units dip gently along the shoreline, there
                        are also contrasts in material strength along the cliffs.




                                                                               12










                        4. Undercutting by waves - Waves actively cut into the intact slope, material at the cliff base and also
                        remove eroded debris from the slope toe. Wave action is controlled by several factors, including shoreline
                        orientation, elevation of the slope toe, near-shore bathymetric configuration (including offshore sand bars),
                        variations in water level, shoreline protection, and wind speed, duration and fetch (fetch is the water surface
                        area available to the wind on which waves can be formed).

                    2.2 Selection of study sites

                    The following criteria were used in the site selection process:

                        1. Taken together, the sites must represent the range of hydrology, material type, wave climate, cliff
                        geometry, and modes of failure found at Calvert Cliffs.

                        2. 'Me sites must be accessible and property owners must be amenable to the requirements of all proposed

                        activities.

                        3. The properties of individual sites must permit between-site comparisons in which a large variation in
                        one factor of slope instability is observed along with only minor variation in all of the other controlling
                        factors. Each such comparison comprises a field experiment that will help us define the critical values of
                        the environmental factors controlling slope instability along the Calvert Cliffs.

                    Four study sites were selected along the Calvert County shoreline. Each site was divided into several subsites so
                    that the number and diversity of field experiments could be as large as possible. Each site is named after a feature
                    near its geographic center. Some slope controlling factors are common to all of the subsites within each site. For
                    instance, stratigraphic horizons maintain a nearly uniform material composition across each study site. The sites are
                    shown on Figure 2.1. Listed from north to south their names and acronyms are:

                        1. The Naval Research Lab                               GqRL)
                        2. Scientists! Cliffs                                    (SC)
                        3. Calvert Cliffs State Park                          (CCSP)
                        4. Chesapeake Ranch Estates                             (CRE)

                    2.3 Field expgLnments

                    Each study site represents a particular combination of the factors controlling slope erosion. Some of these factors
                    may not remain constant in time. Three of these controlling factors (slope height, material properties, and wave
                    undercutting) are suitable for defining our field experiments because they may be reasonably considered to be
                    independent variables in the slope erosion problem. That is, they may be considered as given for a particular cliff
                    section, allowing us to reliably compare two sections between which only one of these controlling factors differs. In
                    order to determine the critical values of these controlling factors, our site selection process was designed to identify
                    pairs of sites for which there is a significant variation in only one factor. 'Me fourth factor, slope hydrology, has an
                    important influence on slope erosion, but the variation in hydrologic input (snow and rain) over the Calvert Cliffs


                                                                                13










                 area is negligible, so that field experiments in which the hydrologic input varies cannot be defined. Instead, we must
                 carefully monitor precipitation, runoff, and groundwater flow at each site in order to measure the effect of slope
                 hydrology on erosion. Other controlling factors of slope erosion, such as slope shape, may be considered dependent
                 variables. Although slope shape influences the slope stability at any particular time, the shape itself depends on the
                 combination of slope height, material properties, wave undercutting, and precipitation that have existed at that site

                 over time.


                 The field experiments we have been able to define to date are listed in section 4.4 of this report, following detailed
                 descriptions of the study sites, the ongoing erosion mechanisms, and their environmental controlling factors.














































                                                                            14













                  3.  Description of the Study Sites
                  3.1 Surva Methods                                  Slope Surveys

                  Surveying instruments used during the course of Phase I included:

                  1) Lietz/Sokkisha SET3 - electronic total station (serial # 84121)

                                                       Vertical Accuracy          511

                                                       Horizontal Accuracy        2-f

                                                       EDM Accuracy               ï¿½ (5mm + @ppm x distance (m))

                  2) Lietz/Sokkisha DT20E Theodolite - electronic digital theodolite (serial # 60619)

                                                       Vertical Accuracy          20-

                                                       Horizontal Accuracy        20"

                  3) Topcon AT-176 Auto Level (serial # X60457)

                                    Accuracy in I Km in double run leveling       ï¿½2.0 mm

                  Elevation Surveys

                  All elevations were established relative to the 1929 National Geodetic Vertical Datum. The double run leveling
                  method was used to perform all elevation transects. Elevations were established for the well heads and surveying
                  reference stations using the Topcon level and a level rod. Elevations for slope survey instrument stations were
                  established from surveying reference stations using the SET3 total station distance ranging feature.

                  U.S. Coast and Geodetic Survey benchmarks were used directly for all of the elevation transects except the transect at
                  the Chesapeake Ranch Estate site. There, the elevation of a public water supply well head at well site No. 3 was
                  used. The elevation at this well head was established in reference to 1929 NGVD by the Maryland Department of
                  Natural Resources, Technical Services Division and designated "Ca-Fe 18". A list of the benchmarks used to

                  establish elevation at each site follows.




                                            Six                                                     Benchmark

                                    Naval Research Lab                                           Navy (reset 1971)

                                      Scientists' Clfffs                                         U133 (reset 1971)



                                                                            15
















                        Calvert Cliffs State Park                                        Cove B.M.


                       Chesapeake Ranch Estates                                           Ca-Fe 18




         Horizontal control

         Horizontal control was not referenced to a general horizontal network. instead, it was maintained locally at each
         study site, typically referenced to a unique, obvious, and permanent feature.



                                                   Slope Profile Surveys - all sites

         Open traverses were used to establish baselines along the shoreline for the horizontal control used in slope surveys,
         Accurate and efficient closed traverses were virtually impossible to complete due to the nature of the slope
         topography. Except for slope survey instrument stations on protected slope toes, instrument stations could only be
         temporarily established due to washover by high tides. Therefore, baselines had to be established each time a survey

         was made.


         A typical slope survey was performed using both the SET3 total station and the DT20E theodolite. The instruments
         were set up two to three meters apart. Both instruments sighted on identical points along a slope profile.
         Triangulation was used to establish the horizontal and vertical position of individual points on the slope. Ile
         distance ranging feature of the total station was not used because safe access for positioning the reflector was
         restricted to the slope too and bluff top region. One instrument was located along a profile line and the horizontal
         angle was set for that machine so that it was perpendicular to the slope toe. This angle remained unchanged during
         the course of the survey. Points along the slope surface and on this profile line were selected and the angles to each
         point from both machines were recorded.

                                                Field Observations and Photo Stations

         In addition to repetitive slope surveys, regular site visits am made to observe changes in the slope geometry, seepage
         condition, and shoreline configuration. During each slope survey and when visual inspection indicates significant
         changes have taken place, the slopes are photographed from fixed stations established during the initial baseline

         surveys.
















                                                                   16














                 3.2 Geotechnical Methods


                                           Stratigraphic Description, Well Logging, and Sarnple Collection

                 Prior to establishing groundwater monitoring wells, a preliminary survey of the slope profile adjacent to each well
                 site was conducted. A detailed stratigraphic description was then made at the cliff face along the surveyed profile.
                 For those stratigraphic units buried by debris or located in the inaccessible upper cliff, descriptions were made of the
                 same unit as close as possible to the surveyed profile. The stratigraphic description of each unit included
                 information on the strength, color, thickness, grain size, moisture content, hydrology, paleontology, sedimentary
                 structures, and vegetative surface cover. All elevations are referenced to the 1929 National Geodetic Vertical Datum
                 and elevations associated with stratigraphic intervals are given where they occur in the sampled borehole at each site.

                 A total of twenty-two groundwater monitoring wells were drilled over the period from 6 December 1990 to 1
                 February 1991; six at the NRL, five at SC, six at the CCSP, and five at the CRE. They were drilled using a rotary
                 drill rig owned and operated by the State of Maryland, Department of Natural Resources, Water Resources
                 Administration, Technical Services office. The drilling was done using a hollow stemmed auger through which a
                 standard penetration test (SPT) was performed and a split-spoon sample obtained, each at five foot intervals. The
                 penetration tests and sampling were done in the first (and deepest) well drilled at each site.

                 The SPT is a reliable, widely used method for estimating the relative variations of in-situ, undrained shear strength
                 of subsurface cohesionless materials. For strongly cohesive materials it provides a somewhat less reliable, but
                 useful, estimate of the stiffness (cohesive strength) of the unit. The results of the SPT are reported as the number of
                 blow counts required to drive the split-spoon sampler the final twelve inches of each sampling interval. The blow
                 count is corrected for overburden pressure as specified in the procedure for the SPT. The SPT data is presented
                 graphically on the geotechnical diagram for each site. These diagrams permit an immediate evaluation of the relative
                 strength of each stratigraphic unit at each site.

                 Split-spoon samplers are driven 1.5 feet vertically downward, ahead of the auger bit. Upon retrieval, each sample is
                 described and a representative portion or portions is obtained for laboratory analysis. The field description includes
                 information on the color, grain-size, fossil content, and moisture content.

                                                                  Laboratory Analysis

                 A grain size analysis was performed at the Maryland Geological Survey's sediment laboratory on 70 samples taken
                 from the spHt-spoon. For split-spoon samples which spanned more than one stratigraphic unit, each unit was
                 analyzed. The information is graphically presented on the geotechnical diagram for each site as percentages of gravel,
                 sand, silt and clay. A tabular presentation of the grain size analysis is provided in Appendix A.





                                                                           17












                 A summary of the procedure used by the Maryland Geological Survey for grain size analysis follows:

                      1. Approximately thirty grams of the material are mixed with 300 mL of 10% hydrochloric acid (HCI).

                      The HCI is allowed to remain in contact with the material for 24 hours to dissolve the calcium carbonate

                      contained in the sample. The sample is then rinsed with deionized water.

                      2. Approximately 300 mL of 15% hydrogen peroxide (H202) is added to the sample to remove organic
                      material. The sample is allowed to react with the H202 for twelve hours and then it is heated at 1000 C
                      until the reaction is observed to be negligible. Ile sample is then rinsed with deionized water.

                      3. 0.3% sodium hexametaphosphate, a dispersant, is added to deflocculate the silt and clay particles. After
                      twelve hours each sample is passed through a 63 micron sieve to separate the sand and gravel from the silts
                      and clays. The portion which passes through the sieve is transferred to a graduated cylinder and deionized
                      water is added to the 1,000 mL mark. The mixture is agitated thoroughly and two samples are taken to
                      determine the amount of silt and clay respectively. The first sample is taken at 20 cm depth after 20
                      seconds and the second at 5 cm depth after approximately one hour. The "act time interval between
                      samples depends on the temperature of the suspension.

                      4. The samples and the sand and gravel remaining on the 63 micron sieve are dried and weighed. The
                      gravel is separated from the sand by passing it through a 2 mm sieve, and the total weight fractions of each
                      of the gravel, sand, silt and clay are determined.

                 Laboratory analysis determined that most of the sample weight loss occurred during the HCI digestion and was due to
                 the dissolution of calcium carbonate shells and shell fragments. Therefore, the weight loss provides a good
                 indication of the presence of shell beds and is included on the geotechnical diagrams for each site.

                 3.3 Description of Erosion Mechanisms

                 Because particular groups of erosion processes tend to occur together at different elevations on the slopes, we have
                 found it useful to organize these mechanisms and their controlling factors according to three cliff sections: lower,
                 middle and upper. Along the length of the Calvert Cliffs, two conditions exist in the toe zone: the intact slope
                 material may be exposed to direct wave activity or may be covered with debris eroded from the slope above.
                 Regardless of the two conditions, a feature common to all slopes is that the intact material comprising the lower
                 zone of the slope is moist or saturated and distinctly darker colored than the slope above. The upper boundary of this
                 zone is defined by a seepage layer that seeps year-round or continuously during wetter periods. On slopes where
                 debris has accumulated in the toe zone, the dark, wet material of the lower slope is often completely covered. The
                 erosion mechanisms acting on the lower slope are directly related to wave activity and, in many cases, are different
                 from the erosion mechanisms acting on the middle section of the slopes. The latter are often controlled by local
                 surface water and groundwater, slope geometry, and material strength. Similarly, the types of erosion types acting


                                                                             18










                  on the n-dddle portions of the slope generally differ from those acting on the upper portions of the slope. In the upper
                  slope root mats, soil development, and weathering act to strengthen the slope, which often stands at a very steep
                  angle, and erodes by debris falls in response to direct undercutting.

                  The wave dominated lower slopes erode by

                           (a) surficial erosion (direct wave action; freeze/thaw; surface wash) or

                           (b) spalling (intact blocks of material separate from the slope along nearly vertical cracks and eventually fall
                               as a block onto the beach below) in direct response to undercutting

                  Hydrologic processes tend to dominate in the mid-slopes. Erosion caused by hydrologic processes occurs by

                           (a) slumps along deep-seated failure zones. Typically, slumps are found above the perennial seep in tall
                           cliffs (> 25 rn). They are often rotational and result when groundwater pore pressures cause materials to
                           weaken to critical levels. Important slope parameters include slope height, slope angle, and pore pressure.

                           (b) removal of surface material by overland flow. The source of water may be

                               (1) seepage, which may occur in

                                    relatively continuous sapping zones, which tend to produce a more uniform lateral topography
                                    below the seep, or as piping outlets, which produce a more concentrated flow and contribute to
                                    mid-slope gullying

                               (2)  direct surface runoff of precipitation, which tends to produce gullying beginning at the top of the
                               slope.

                           (c) undercutting by seepage erosion and failure of the overlying layers.

                  Mthough erosion of the midslope is most commonly accomplished by hydrologically driven processes, at some
                  locations (Randle Cliffs, Parker Creek), the rate of wave-driven recession of the lower slope may exceed that due to
                  hydrologically driven erosion of the midslope, causing oversteepening of the mid-slope, which results in spalling of
                  relatively fte-grained materials, or shallow sliding in coarser units.

                  Gravity driven failures along desiccation cracks and root channels tend to dominate in the upper mid-slope through
                  the bluff top. Failures characteristic of this type of slope recession are

                           (a) collapse of soil fragments from near vertical slopes

                           (b) columnar fracturing and toppling

                           (c) collapse of overhung root mats






                                                                            19












                 The upper slopes often stand close to vertical because of increased cohesion due to clay deposition in the root zone
                 and binding by roots. Ile root mat may even create an overhang at the slope top. Because slope recession is driven
                 from below, the recession of the upper slope ultimately depends on the erosion rates of the lower and middle slopes.
                 'Me slope angle at which the upper slope can stand, the period of time at which it may stand close to vertical, and
                 the degree of overhang the soil and roots can maintain, are all limited. If the lower slope and midslope recedes, the
                 upper slope will eventually fail. Local factors controlling erosion of the upper slope cannot prevent recession of the
                 slope top, although they tend to make the recession episodic.

                 3.4 Naval Research LaboraIM

                                                       General Site Description (Figures 3.1, 3.2)

                 The site encompasses the shoreline and cliffs from Randle Cliffs to Holiday Beach. The subsites are Randle Cliffs
                 (RC), Naval Research Lab North (NRLN), Naval Research Lab South (NRLS), and Holiday Beach (HB).

                 The cliffs are uniformly oriented east-northeast along strike, except at Randle Cliffs where they face due east. Shore
                 protection exists in the form of a seawall in front of the Naval Research Laboratory (subsites NRLN and NRLS).
                 The shoreline is unprotected at the northern and southern ends of the site (subsites RC and HB). A series of sub-
                 parallel longshore sand bars is present at both the northern and southern ends of the site (subsites RC and HB), but
                 the bars are not evident along the portion of shoreline protected by the seawall.

                 The cliffs vary gradually between 18 and 27 meters in height along the Randle Cliffs subsite and have steep slope
                 angles approaching 90 degrees. At NRL-North, the cliffs vary between 18 and 34 meters in height and the slope
                 angle near the toe is shallow at 30 degrees, but increases to nearly vertical about five meters from the cliff top.
                 Along NRL-South, the cliff height is consistent at 31 meters and the slope angles are similar to NRLN. At Holiday
                 Beach, cliff height varies gradually from 20 to 34 meters and the slope angle maintains a uniform 70 degrees from

                 toe to top.

                 The site lies entirely within the Mocene Calvert Formation. All stratigraphic units dip gently to the southeast.
                 Stratigraphic units located near the cliff top at the north end of the site gradually descend toward beach level at the
                 southern end. At Randle Cliffs, a heavily diatomaceous clayey-silt layer occurs in the tidal zone and gradually dips
                 below beach level at NRL-North. Very little beach is present along the Randle Cliffs subsite with the cliff face
                 extending below high water level in most places. Where the slope base is once again exposed to tidal action near
                 Holiday Beach, there is beach present under most tide conditions. The cliff base is composed of a greenish-gray
                 sandy clay known as marl. Across the entire site, the upper stratigraphic horizons of the cliffs are composed
                 principally of a grayish-green sandy clay interrupted vertically by layers of somewhat sandier fossiliferous horizons.
                 On the highest cliffs, a brown clayey sand is present.




                                                                            20











                  At the Randle Cliffs and NRL-North subsites, surface water drains toward the cliffs over an area extending almost
                  one krn we,t of the cliff top. NRL-South and Holiday Beach subsites are located on hilltops which cause the surface
                  water to drain in all directions. Across the entire site, groundwater seeps from the cliff face at the interface between a
                  sandy shell bed overlying a sandy clay unit. 'Mere appears to be a greater volume of seepage where topographic lows

                  intersect the cliff face.


                                                         Geotechnical Properties (Figure 33)

                  Ile cliffs at NRL are 12 to 34 in high and the materials which compose them may be divided into four major
                  groups: a fine grained root zone with well developed soil horizons, and two extensive cliff segments composed
                  primarily of sands separated by a 4.3 rn thick series of silts and clays.

                  The soil horizons and the majority of the root zone extend from the cliff top, which at the well site is at 27.9 rn in
                  elevation, into a silty, sandy clay which is 1.5 m thick. From 26.5 rn to 17.6 rn the cliffs are composed primarily
                  of moist, light brown to tan, leached and oxidized sands with increasing amounts of silt and clay with depth. The
                  SPT indicates that the materials reach a minimum in undrained shear strength at an elevation of approximately 20.5

                  In .


                  At 17.6 rn a change of grain size takes place from materials dominated by sands to a section approximately 4.3 in
                  thick dominated by drier, greenish-gray to gray silts and clays. An intermittent seepage zone is evident at the base of
                  the sandy units, because the fine grained silts and clays act as a barrier to the downward movement of water. The
                  materials reach a peak strength in the silt and clay materials; however, it should be noted that the materials were dry
                  when tested and are composed of cohesive materials which may behave very differently when saturated. The two clay
                  units "tending between 13.3 in and 16.8 in in elevation form columnar pillars which either topple or disintegrate
                  into angular fragments.

                  Below the silty-clayey material at 13.3 rn in elevation, fies a gray, saturated, sandy shell bed which is approximately
                  1.5 rn thick. At the base of the shell bed is a seepage zone, which has been observed to be constantly seeping over
                  the past 10 months.

                  Beginning at an elevation of 11.3 rn and extending below the cliff base, the materials are composed of gray-green to
                  green, dry to moist, sandy sediments that contain increasing amounts of fine-grained material with depth. During
                  field mapping, the unit located between the elevations of 4.2 rn and 11.3 in, composed of a gray-green, silty, clayey
                  sand, was observed to be strongly jointed. The joint surfaces were visibly wet, acting as preferential flow paths for
                  groundwater and creating planes along which block spalling takes place. Where this unit is exposed, it has been
                  observed to spaU year-round, although the frequency of spalling increases during freeze-thaw periods. Ile spalling
                  tends to terminate near the contact of this unit with the shell bed above causing the shell bed to form an overhang in
                  many places.





                                                                           21






                  Site/Subsite: Navy Research Lab/Holiday Beach  Erosion Mechanisnu

                  Lower SloW. Most of the toe zone is covered with a light mantle of unconsolidated upper slope debris generated on
                  the upper slopes which forms laterally continuous, wedge-shaped deposits or larger triangular debris fans. Sparse,
                  herbaceous vegetation has become established on the unconsolidated debris along most of the toe zone. Physical and
                  chemical weathering result in disintegration of the silty, clayey, very fine sand which comprises the intact slope
                  material along the toe zone. Daily waves and tides do not remove toe zone debris at this site. However, wave action
                  due to strong winds and storms periodically removes the unconsolidated debris and erodes the intact slope.

                  MidsloM A nearly uniform, fairly gentle incline occurs from the base of the debris fans at the toe to the base of the
                  root zone. A perennial seepage zone occurs at approximately 5 m above the beach where a shell bed with a gray,
                  medium to fine sand overlies a gray-green clayey, silty, very fine sand. At locations where the topographic surface
                  behind the cliffs is low, groundwater seepage tends to be stronger and keeps the slope face below moist. Below the
                  seepage zone, the face is covered with a thin veneer of weathered debris which presents a uniform planar surface when
                  viewed from a distance but, although closer inspection reveals that it is slightly rilled, indicating some erosion by
                  overland flow. Above the shell bed seepage zone is a drier face composed of a gray, silty, sandy clay which coarsens
                  upward to become a clayey, sandy, silt and is prone to fragmental disintegration primarily due to desiccation.
                  Continuing upslope an ephemeral seepage zone is encountered where the clayey, sandy, silt meets a silty, clayey,
                  fme sand. This seep periodically supplies water to the slope face below and when active, undercuts the bluff top by
                  sapping erosion. (Sapping erosion is the erosion of slope materials by groundwater flow along a laterally
                  continuous seepage zone).

                  JIpI&r Slg=. The bluff top is nearly vertical along this site with very little undercutting. The bluff top retreats by

                  surficial erosion of weathered sediments and some root mass failures.


                  Site/Subsite: Naval Research Lab/ NRL North and South

                  Lower SloM The entire length of the shoreline along the Navy property has been protected by a bulkhead for a
                  period of 60 years. The slope toe is completely protected. The result is that toe debris has been allowed to
                  accumulate a, an angles of less than 11 degrees and become vegetwed'

                  Midslo . Typically, the middle portion of cliffs along the Navy property is vegetated and inclined at a gentle angle
                  composed primarily of unconsolidated upper slope debris. At the top of the mid-slope incline is an ephemeral
                  seepage zone where a densely fossiliferous shell bed with a fine sand matrix overlies a green-gray, clayey, silty, very
                  fine sand. Here, sapping erosion is prevalent. This erosion undercuts overlying units, causing them to fall. Field
                  inspection of this seepage zone indicates that it is subject to both piping and sapping erosion when the seepage is
                  active. Field strength tests indicate the shear strength of the materials comprising the cliffs to be at a minimum at


                                                                           22










                 the seepage interface. Seepage from the shell bed produces surficial erosion of weathered material from the slopes
                 below. In this way, bluff top recession continues despite significant toe protection.

                 UpMr SloM The slope break between the midslope and upper slope is defined by an intermittent seepage zone.
                     bluff top recedes by an undercutting due to seepage, surficial erosion of weathered materials, and toppling of
                 columns of material that separate from the slope along vertical stress-relief fractures.

                 Site/S ubsite: Naval Research Lab/ Randle Cliffs

                 Lower SIoM. The toe zone is composed of a green-gray clayey SilL The elevation of the toe zone is below mean
                 low water and the toe zone is subjected to nearly continuous wave undercutting which results in spalling of large
                 blocks from the nearly vertical lower slope. Removal of the slope debris is generally quite rapid; only debris from
                 the largest slope failure, remains on the beach for periods longer than several weeks to a month. Approximately half
                 of the toe zone is devoid of slide debris at any time.

                 M[iid@Tle active wave undercutting and retreat of the lower slope tends to steepen the midslope sections, which
                 initiates further spalling and shallow sliding in the midslope zone. This process of failures in the lower slope
                 triggering additional failures in the overlying material, leading to a series of retrogressive failures at higher elevations
                 has been described for other coastal slopes (Edil and Vallejo, 1977; Quigley et al., 1977). Typically, spalls work
                 their way up the steep slope face to the perennial seepage zone where the lower sandy shell bed is located. Some
                 spalls are sufficiently large that they extend from beach level to the perennial seep approximately 10 in above the
                 beach. Undercutting and spalling tend to keep the slope face straight and nearly vertical. Above the seep, columnar
                 slope sections separate from the face along tensional fractures and topple or fall to the beach. The columnar joints
                 form in response to stress relief in the, rapidly retreating slopes, as well as to the swelling and shrinkage associated
                 with the wetting and drying of the material comprising the columns. Columns topple and fall when undercut by
                 failure and retreat of the slope below them.

                 Jh2Mr Sl= Weathered and leached materials near the bluff top tend to fail in undercut slunips that bury earlier
                 spalled material beneath. Undercut root zones eventually collapse in cantilever type failures.
                 3.5 Scienfists Cliffs                General Site Description (Figures 3.4, 3.5)

                 Ile site encompasses the shoreline and cliffs from Parkers Creek to Governors Run. The subsites are Parkers Creek
                 South (PCS), Scientists' Cliffs North (SCN), Scientists Cliffs South (SCS), and Governors Run (GR).

                 17he cliffs are uniformly oriented east-northeast along the entire site. Beach protection exists in the form of
                 uniformly spaced gabion groins in front of the Scientists Cliffs Community (SCN and SCS). Ilese groins have
                 produced a beach up to one meter higher than found at the subsites to the immediate north and south (PCS and GR).
                 'Me beach at Scientists Cliffs appears to offer a significant degree of slope toe protection. The cliffs to the north and
                 south of Scientists Cliffs (PCS and GR) have little or no beach at their too, are generally devoid of vegetation, and


                                                                           23









                 are actively e'roding,. Tle slopes are relatively steep along the Parkers Creek South subsite, standing at angles
                 between 70 and 80 degrees. Slope height varies between 15 and 30 meters. The subsite at Governors Run has slope
                 angles of 65 to 80 degrees and cliff heights between 18 and 36 meters. At both the Scientists' Cliffs North and
                 South subsites, the slopes are thickly vegetated and slope angles vary between 45 and 60 degrees. However, the
                 cliffs are generally taller at the southern subsite, ranging from 20 to 29 meters, while at the northern subsite, they
                 range from 15-25 meters.

                 The sediments of this site consist of interbedded clays, silts, and sandy fossiliferous units of Mocene age. The
                 Calvert Formation is found in the lower portions of the slopes and the Choptank Formation in the upper portions.
                 All stratigraphic units dip to the southeast, although individual stratigraphic thicknesses are less uniform than
                 elsewhere in the Calvert Cliffs. Spalling occurs near the cliff base at the Parkers Creek South subsite in a thick
                 blue-gray silty clay unit. Stratigraphic horizons in the upper sections of the cliff tend to be leached and less cohesive

                 than those below.


                 The surface topography of the site is characterized by a highly dissected drainage consisting of a series of hilltops
                 separated by drainage channels. Groundwater seepage is evident along exposed cliff faces and tends to occur at the
                 base of a sandy fossiliferous stratigraphic unit. Seepage volumes tend to be higher where topographically low

                 surface areas intersect the cliff face.


                                                         Geotechnical Properties (Figure 3.6)

                 The cliffs at Scientists'Cliffs range between 15 in and 36 m in height. The stratigraphic profile consists of five
                 material groups at this site. The root zone and soils are developed in a silty, very fine sand. A weathered clay
                 separates the sandy soils above from another thick sequence of sands containing shell beds below. About mid-slope
                 the sands are interrupted by a thick, clayey, sandy silt. Beneath the silt lies another shell bed and series of fine to
                 very fine sand units. This sequence continues uninterrupted to the cliff base and below.

                 The surface elevation at the well head is 26.9 m. The matrix in the soil horizons and root zone is composed of an
                 orange, very fine sand. The amount of silt and clay increases with depth to an elevation of 23.4 in where a unit
                 composed predominantly of clay is present. It consists of a series of tan and gray clays and extends to 21.7 in where
                 a sandy shell bed is encountered. The 4.2 rn thick shell bed is quite porous and permeable. SPT blow counts
                 indicate that it has the highest strength of all the stratigraphic units in the entire Scientists' Cliffs profile. At its
                 base the shell bed grades into a non-fossiliferrous, brown, medium sand, approximately I in thick.

                 The base of the brown sand lies at an elevation of 17 in on a noticeably finer grained, dry, gray, silty sand creating a
                 permeability contrast which gives rise to intermittent seepage on the cliff face. Erosion due to seepage in this
                 material is responsible for undercutting the bluff top, causing it to fail under its own weight. The brown sand and
                 the underlying gray silty sand are the weakest units in the profile as indicated by the SFr.





                                                                           U










                  From the base of the medium brown sand, the silt and clay contents increase for approximately 6 meters reaching a
                  maximum in a gray, clayey, sandy silt which extends to an elevation of I I in.

                  The lower shell bed occurs below the gray clayey, sandy, silt and is 2.4 in thick. It is composed of numerous shells
                  in a brown, medium to fine sand matrix. This unit is indicated to be relatively strong by the SPIT. The shell bed
                  grades into a gray green, medium to fine sand at 8.6 meters which extends to an elevation of 5 in exhibiting
                  decreasing strength and increasing water content with depth. The gray-green, medium to fine sand reaches a local
                  strength minimum and is saturated at its base.

                  A sharp grain-size change occurs at this point from the saturated, gray-green medium to fine sand to a dry, greenish-
                  gray, clayey, silty, very-fine sand resulting in a perennial seep. The finer grained unit extends to an elevation of 1.8
                  in where it contacts a dry, dark gray, silty, very fine sand. The dark gray, silty, very fine sand is prone to spalling
                  along joint surfaces where exposed, especially between the northern end of the Scientists' Cliffs' property and Parker

                  Creek.


                                                                  Erosion Mechanispis


                  Site/Subsiw Scientists! Cliffs/Governor's Run

                  Lower SloW. The lower slopes at Governor's Run fall into two categories. Along most of the shore, small debris
                  fans of upper-slope material have built up to heights of two to five meters and are covered with herbaceous
                  vegetation. Also along these sections, a small sandy beach exists in front of the toe debris. The second lower slope
                  zone coincides with a narrow, low beach approximately 150 in long . Here the toe zone is free of debris and the
                  intact slope is exposed to wave activity during high tides. Along the same part of the shoreline, the cliffs are tall ( >
                  30 in) and seepage erosion has formed a substantial bench along the upper seepage zone (ephemeral seep). The
                  bench is approximately 5 in wide and heavily vegetated. The result is that very little upper slope material is
                  delivered from above the seepage zone to the toe zone. The lack of debris fans along this stretch of cliffs may be
                  apparently attributed to a lack of supply of debris from the upper slope to the slope toe, rather than to greater or
                  more focused wave energy at this location. Ibis is suggested by traces of isolated vegetation in triangular patches
                  that may have become established on debris fans that had accumulated along the toe during bench formation. Once
                  the bench was well-formed, the supply of upper slope debris diminished and the debris fans have been removed except
                  for traces of their uppermost portions. Similar vegetated debris fans are currently presentjust north and south of the
                  bench cut cliff, where upper slope material is still transported from cliffs of similar height to the toe zone.

                  Physical and chemical weathering result in disintegration of the clayey, very fine sand which comprises the intact
                  slope material along the stretch where it is exposed. Also, the slope toe is slightly undercut here. This is the only
                  section of the cliffs at this subsite that show evidence of spalling just above the toe.






                                                                            25











                 Most of the toe zone, both to the north and south of this section is covered with either a light mantle of debris
                 forming a laterally continuous wedge shaped deposit or a larger triangular debris fan. Light vegetation has become
                 established on the unconsolidated debris along most of the slope toe.

                 Midslolm A nearly uniform, fairly gentle incline occurs from the base of the debris fans at the toe to the base of the
                 root zone. A perennial seepage zone occurs at approximately 5 m above the beach where a gray-green medium to
                 fine sand overlies a gray-green clayey, silty, very fine sand. The seepage tends to keep the slope face below moist.
                 Below the seepage zone, the face is covered with a thin veneer of weathered debris which presents a generally uniform
                 planar surface with small rills on its surface. Above the seepage zone is a drier face composed of a gray, clayey,
                 sandy silt which coarsens upward to become a clayey, silty, very fine sand and is prone to fragmental disintegration
                 due to desiccation and other weathering mechanisms. Continuing upslope a seepage zone is encountered where the
                 clayey, silty, very fine sand meets a brown medium sand. Where the topographic surface behind the cliffs is low,
                 this interface is a perennial seep. Where the surface is high, it is an ephemeral seepage zone. Overlying the medium
                 sand is a thick shell bed with a brown medium sand matrix. At this subsite the shell bed is overlain by a one meter
                 thick zone of medium to coarse, orange-brown sand which also exhibits a saturated face where the topographic

                 surface is low.


                 UpMr SloM The upper slope at Governors Runs tends to be nearly vertical. As of October 1990, there were no
                 slope-top trees on the beach along the entire subsite. However, by summer 1991, an upper slope slump in the upper
                 sand bed had undercut a large tree, which subsequently toppled to the beach carrying a large root ball with it.

                 Erosion of the upper slope appears to be driven primarily by sapping erosion in a medium sand bed located at an
                 elevation of 18 m. The sand is very loosely consolidated and prone to sapping erosion at its interface with an
                 underlying shell bed. Sapping undercuts the materials lying above, causing them to fail. Material from these
                 Mures form fan-type debris piles along the toe zone.

                 The upper slope bench is located along the 150 m long section of Governors Run with little beach and toe debris.
                 The bench is formed within the upper medium sand that is prone to sapping erosion. The floor of the bench is
                 formed by the less pervious shell bed which underlies the sand sapping zone. The location of the bench at this
                 elevation suggests that the bench was formed by accelerated sapping erosion.

                 SWSubsite: Scientists' Cliffs/Scientists' Cliffs North and South

                 Lower SloM The entire length of the shoreline along the community of Scientists' Cliffs is partially protected by a
                 beach  built up behind evenly spaced groins. Along the southern portion of the shoreline, the slope toe is completely
                 protected by a wide beach and parking IOL To the north, the slope toe is closer to the shoreline, but everywhere
                 along the shore, the slope toe is above all but the highest of water levels. The result is that at most locations toe
                 debris has accumulated and become vegetated with shrubs and trees. In a very few places along the groin-protected
                 shoreline, the waves have removed all of the debris at the slope toe and eroded some intact material. At most places,
                 however, the intact toe material still maintains a relatively gentle slope.


                                                                            26










                  Midslo . Typically, the middle portion of cliffs along the Scientists' Cliffs Community is vegetated. Where
                  exposures are present, a perennial seepage zone is evident where a gray-green, medium to fine sand overlies a gray,
                  clayey, silty, very fine sand. Further upslope. is an ephemeral seepage zone where a brown medium sand overlies a
                  gray, clayey, sandy silt. Field inspection of this seepage zone indicates that it is subject to both piping and sapping
                  erosion when the seepage is active. (Piping erosion is similar to sapping erosion in that it is caused by groundwater
                  flow. However, the flow tends to be confined to narrow regions in the cliff face where the erosion creates holes that
                  often resemble pipes). Flow from this seepage zone produces seepage erosion of lower units. Field strength tests
                  indicate the shear strength of the materials comprising the cliffs to be at a minimum at the seepage interface.
                  Sapping and piping erosion undercuts the material above, causing it to slump or fall. In this way, bluff top
                  recession continues despite significant toe protection.

                  Mid-slope recession below the seepage zone occurs by physical and chemical weathering products being removed by
                  surface wash. Vegetative cover serves to reduce raindrop impact and dry the upper slope surface by interception and
                  evapotranspiration. However, roots of all plants contribute to the degradation of soil fiber by producing acidic
                  conditions around diem. Offsetting this effect is the binding action of the roots which forms mats. It is common at
                  Calvert Cliffs for failure to occur along the base of the root mat, causing the mat to slide downslope.

                  Jh=r Sl= The bluff top recedes by both seepage undercutting and surface wash of weathered material. Most
                  property owners have removed the tall trees from the cliff edge to prevent loss of root mass and associated soil when
                  trees fall during strong winds.

                  Site/Subsite: Scientists' Cliffs/ Parkers Creek

                  Lower SIM. The toe zone is composed of a silty, sandy, clay. The elevation of the toe zone is near mean low
                  water and the toe zone is subjected to nearly continuous wave undercutting which results in spalling of large blocks
                  from the nearly vertical lower slope. Removal of the slope debris is generally quite rapid; only debris from the
                  largest slope failures remains on the beach for periods longer than several weeks to a month.

                  A partial, ephemeral beach is present along portions of the Parkers Creek subsite. Active deposition and erosion of
                  beach sand has been observed. Near the northern end of this subsite, excavation of the beach uncovered spalled
                  blocks were noted to have been buried by beach depositional processes. Also, at this site, runoff from a heavy
                  thunderstorm (- 1.5 inches in one hour) was observed to erode the top IS to 20 cm of beach surface along the only
                  portion of this subsite observed to have even a small beach.

                  Midslg=. The active wave undercutting and retreat of the lower slope tends to steepen the midslope sections, which
                  initiates further spalling and shallow sliding in the midslope zone. Typically, spalls work their way up the steep
                  slope face to the perennial seepage zone where the lower sandy shell bed is located. Some spalls are sufficiently
                  large that they extend from beach level to the perennial seep approximately 12 m above the beach. Undercutting and
                  spalling tend to keep the slope face straight and nearly vertical. Above the seep, columnar slope sections separate
                  from the face along tensional fractures and topple or Call to the beach.


                                                                             27










                  WMr Sl= Weathered and leached materials near the bluff top tend to fail in undercut slumps that bury earlier
                  spalled material. Undercut root zones eventually collapse in cantilever type failures.

                  3.6 Calvert Cliffs State

                                                       General Site Description (Figures 3.7, 3.8)

                  The site encompasses the shoreline and cliffs from Rocky Point to 500 meters south of Grays Creek. The subsites
                  are Rocky Point (RP), Grovers Creek North (GVCN), Grovers Creek South (GVCS), and Grays Creek South
                  (GYCS).

                  The orientation of the cliffs is generally northeast to east-northeast except at Rocky Point where the cliffs face
                  northeast to east. There is no shore protection at this study site. A small beach is present during low tides, but
                  waves frequently reach the cliff base. Offshore sand bars were not evident during an aerial inspection of the CCSP
                  site in October, 1990.

                  The cliff height at the Rocky Point subsite varies between 15 and 35 meters and slope angles range between 65 and
                  85 degrees. The cliffs at the Grovers Creek North subsite are substantially lower, ranging between 12 and 18 meters.
                  Here, the slope angle is approximately 60 degrees. Both the Grover Creek South and Grays Creek South subsites
                  have slope angles of 60 degrees with the slope height varying between 15 to 30 meters at GVCS and 15 to 25

                  meters at GYCS.


                  The site lies predominantly within the Miocene St. Marys Formation. A small wedge of the highly fossiliferous
                  upper member of the Choptank Formation occurs just above beach level at Rocky Point, but disappears below beach
                  level in the Grays Creek South subsite. The materials composing the slopes of the entire site are interbedded clays,
                  silts, and sands. Some ironstone is present in discontinuous patches up to one meter thick. The stratigraphic units
                  above the water table tend to be highly leached and have a substantially greater fraction of coarse grain sediments

                  than those below the water table.


                  The surface drainage is quite similar across the CCSP site. Surface water at the site drains toward the cliffs from an
                  area extending approximately 250 meters back from the cliff face. The cliff face is interrupted in three places by
                  perennial streams. One or two groundwater seepage horizons are evident on the cliff face. A major seep occurs
                  between 10 and 15 meters from the cliff top at the contact between a coarse grain sandy unit overlying a gray clay.
                  A smaller volume of seepage is discharged from a thin sandy unit approximately 4 meters below the upper seep.

                                                           Geotechnical Properties (Figure 3.9)

                  The cliffs at Calvert Cliffs State Park range in height from 12 m to 35 m. Five groupings of materials constitute
                  the stratigraphy at this site. A silty sand comprises the portion of the cliff in which soils are developed and which
                  grades into a layer of sand with traces of gravels interbedded with large fractions of silt and clay. Below this,
                  approximately one quarter of the way downslope, the slope material is primarily composed of sand. About halfway



                                                                             28










                  down the slope, the materials become predominantly silts and clays which extend below sea-level where they contact
                  a satumted shell bed with a very fine sand matrix.

                  The elevation at the well-head is 20.0 m. The root zone and soils are developed in a moist, orange-brown, silty,
                  medium sand which is 1.6 m thick. A slightly moist, tan, medium sand containing traces of pea gravel and lenses
                  of stiff white clay occurs at 18.4 in and extends to 16.8 m. A 3.1 rn thick, slightly moist, light gray, silty clay
                  with lenses of coarse sand is encountered next followed by a light gray to tan, mottled, fine sand with small amounts
                  of silt and clay, the latter being saturated at about 12.3 m in elevation. Ile materials continue to be saturated as
                  they change to a dark gray color at 10.6 m. The grain size distribution remains remarkably similar across the color
                  change; however, the material strength declines steadily from the surface down reaching a niinimum at the color
                  change.

                  At 8.4 in in elevation the units change from a dark gray, fine sand to a gray, silty clay with lenses of fine sand. The
                  permeability contrast and saturation of the sand unit create a seepage zone at the base of the dark gray, fine sand. In
                  several places along the cliffs at the Calvert Cliffs State Park site, this seepage zone is responsible for undercutting
                  the weak sand above, resulting in small debris flows and slumps which create benches formed on the more cohesive
                  layer below.

                  The cohesive, slightly moist, gray, silty clay extends to an elevation of 3.0 m where the material changes to a
                  slightly moist, gray, clayey silt with traces of fine sand. This silt unit is 5.3 m thick and exhibits the highest
                  strength of all of the units in the Calvert Cliffs State Park profile; however, it is strongly jointed and tends to spall
                  in large blocks along joint planes.

                  During the field description, a dense shell bed was noted to exist below the silt unit at approximately -2.3 rn in
                  elevation, It is a cemented, saturated, fossiliferrous layer with a gray sand matrix. The shell bed tends to be more
                  resistant to wave erosion than the underlying strata, and less resistant than the overlying strata. Where these units
                  are exposed near beach level, an undercut nose can develop in the lower slope causing spalling of the silt above.

                                                                   Erosion Mechanism


                  Site/Subsite: Calvert Cliffs State Park/Grays Creek South

                  Lower Sl       Daily waves and tides are capable of removing all of the unconsolidated debris reaching the toe from
                  the upper portions of the slope. A shell bed in the toe zone is actively being undercut by normal daily wave
                  activity. The bed is densely fossiliferrous and the matrix surrounding the shells is a medium sand cemented with
                  calcium carbonate. The shell bed dips below mean high tide at the GRAYS Creek site and is exposed above water
                  level along approximately 200 ni of shoreline. Above the shell zone, the lower slope fails by surficial erosion of
                  weathered material by groundwater seepage and direct precipitation.

                  Midslg=. Above the shell bed and above the beach where the shell bed is below tide, the slope maintains a
                  relatively smooth, straight profile to the base of the root zone near the bluff top despite the existence of two sapping


                                                                             29.










                   zones and two major changes in material composition. An I I m thick sequence of clayey silts and silty clays
                   "tends from beach level to a contact with a unit of fine sand at which a permanent seep occurs. The mid-slope units
                   are eroded in nearly equal proportions by two processes, surficial removal of weathered material and sheet spalling.

                   Physical and chemical weathering reduce the outer few centimeters of the slope face to a loose veneer which is
                   removed by surface wash during rain storms. During rainfall, the weathered surficial material may become a viscous
                   slurry and flow slowly down the slope. Material which doesn't reach the toe dries on the slope face until the next

                   rain.


                   In addition to surface wash, the exposed surface material spalls in thin sheets along planes sub-parallel to the slope
                   face. Spalling surfaces are ubiquitous in materials with high proportions of silt. Large spalls are uncommon at this
                   subsite with the single exception of a large, blocky spalling event just south of the mouth of Grays CreeL Here,
                   the toe zone shell bed was sufficiently undercut to cause a 5 m tall X 5 m wide X 1-2 m thick block to fail along a
                   slope-parallel tension crack in Spring, 1991. Observers noted the widening of the tensional crack over a period of
                   several weeks prior to the collapse. Since the collapse, the less consolidated material above the spalling cavity has
                   slumped onto and buried the spalled blocks creating a fan like structure in the toe zone. Currently, such large block
                   spalling is an anomalous condition along this slope. It is worth noting, however, that the large spall occurred along
                   the section of slope undergoing the most severe undercutting.

                   Midway up the silt-clay sequence are two thin layers of fine sand separated by a massive silt layer. The sand layers
                   are each 15 to 30 cm thick and the separating massive silt ranges between 20 and 40 cm in thickness. The sands are
                   saturated and experience sapping erosion at the cliff face. The sapping zones are expressed on the cliff face as two
                   horizontal gaps and are laterally continuous along the entire extent of this subsite. While their undercutting effects
                   are minimal, they are capable of supplying a nearly continuous supply of water to the lower slope face. The
                   moisture tends to accelerate physical and chemical weathering and may promote the weakening of near surface
                   spalling faces.

                   Upper Slg=. Overlying the 11 m thick silt-clay strata is a 6 m thick sequence of predomin              y     es dov
                                                                                                                      and fm an            erlain

                   by a 4 m thick sequence of silts and clays which become progressively more fine-grained until the root zone is
                   encountered approximately 2 m below the bluff top. The fine-grained units near the surface are dissected in places by
                   drainage channels and do not form a continuous horizontal barrier to infiltrating water. However, they tend to retard
                   the rate at which the groundwater can move into the sandy units below. Hence, intense piping of groundwater at the
                   sand/silt-clay interface tends to be less common than sapping. A permanent seep exists at the base of the sand unit

                   at an elevation of 8-11 m.


                   A rare deep-seated rotational slump is apparent at the south end of Grays Creek South slopes. The rotational failure
                   surface originated in the saturated zone at the sand/silt-clay interface. Tle failure is intimately associated with a 0.5 -
                   I m thick lense of ironstone formed within the saturated lower portion of the fine sand unit. The majority of the
                   ironstone now rests as a debris pile resulting from a collapse of the layer. No witnesses have described the actual


                                                                                 30










                 failure, but the configuration of a small remaining block of ironstone on the current slope indicates that the silts
                 below were eroded by sapping and surficial erosion of weathered material, leaving the ironstone to form a cantilever
                 support for the relatively independent slope above. The ironstone overhang eventually collapsed, truncating the toe
                 of the upper slope and reducing its ability to maintain rotational equilibrium.

                 Site/Subsite: Calvert Cliffs State Park/Grover Creek South

                 The stratigraphy of this subsite is almost identical to that of Grays Creek South. Hydrologically, the seepage zones
                 are in the same positions relative to the stratigraphy but, somewhat less water may be present because of a smaller
                 surface collection area at the ground surface.

                 LDwer Sl=. Stratigraphically, the slope toe is entirely occupied by the shell bed described in the toe zone of the
                 north end of the Grays Creek South subsite. However, debris from slope activity above has completely covered the
                 slope toe. Above the beach level debris fans, the intact silt-clay formations are exposed and their faces stand at
                 steeper angles than the faces at Grays Creek South. The silt-clay exposures show evidence of numerous spalling
                 events. It is likely that the tide level shell bed was eroded from beneath the silt-clay formations causing the silt-clay
                 faces to be undercut and spall. Such a process is actively occurring at the north end of the Grays Creek South

                 subsite and is described above.

                 MidsloK Where the intact face is exposed, the slopes here tend to be steeper that those of the Grays Creek South
                 site. Spalling is more common and the individual events larger. This is principally due to the oversteepening of the
                 slope below translating up slope - the steeper the slope, the greater the tensile stress on spalling faces, and the more
                 frequent and larger the spalls.

                 In addition to spalling, physical and chemical weathering reduce the outer few centimeters of the slope face to a loose
                 veneer which is removed by surface wash during rain storms. During rainfall, the weathered surficial material may
                 become a viscous slurry and flow slowly down the slope. Material which doesn't reach the toe dries on the slope

                 face until the next rain.


                 Seepage and sapping erosion occurs at the same stratigraphic locations as at the Grays Creek South subsite, but all
                 seeps seem to be slightly less active than those at Grays Creek South.

                 U=Kr SIM. As the oversteepening proceeds upslope it undercuts the, leached and less coherent materials of the
                 unsaturated zone. These materials slump when undercut, building a fan-like pile at the toe on top of the blocky
                 debris previously spalled from the slope. The top two meters of the slope tend to stand in vertical faces or form
                 overhangs due to the binding effect of tree roots. It is evident that the undermining of the bluff top has occurred
                 rather rapidly. Trees and vegetative mats that have fallen from the bluff top are still alive indicating that their roots
                 have not been exposed long enough to kill the plants. It should be noted here that there are many more downed trees
                 on the beach along this section of slope than at the Grays Creek South subsite.




                                                                           31












                  Site/Subsite: Calvert Cliffs State Park/Grover Creek North to Rocky Point

                  Induration is the key difference between the slopes at Rocky Point and the other slopes of the Calvert Cliffs State
                  Park Site. Induration is apparent in all seepage zones. Laterally continuous, horizontally bedded ironstone
                  formations form sheets of high shear strength which increase in thickness and number moving north from Grover
                  Creek to Rocky Point. These sheets reinforce the slope and prevent major slumps or rotational events. However,
                  surface runoff and sapping erosion carry sizeable quantities of unconsolidated material to debris fans at the base of the
                  slopes.

                  Lower Slg=. Stratigraphically, the toe zone is entirely occupied by the shell bed described in the toe zone of the
                  north end of die Grays Creek South subsite. However, debris from slope activity above has largely covered the slope
                  toe. Between the narrow triangular tops of the debris fans the face of the shell bed is evident and it exhibits a nearly
                  vertical or, in some locations, a slightly concave profile.

                  Midslo= Immediately overlying the shell bed is an indurated sheet of ironstone nearly one meter thick and laterally
                  very extensive. The shell bed below is eroded to the degree that die ironstone is cantilevered in many places and
                  large rectangular fragments of ironstone litter the beach. From the bases of the debris fans on the beach to the base
                  of the root zone near the bluff top, the slopes exhibit a regular inclined profile which is less steep that the profile at
                  the Grover Creek South subsite and nearly equivalent to the incline of the profile at the Grays Creek South subsite.

                  Spalling is not as frequent along these slopes as at Grover Creek South and tends to occur in thin sheets. In addition
                  to spalling, physical and chemical weathering reduce the outer few centimeters of the slope face to a loose veneer
                  which is removed by surface wash during rain storms. During rainfall, the weathered surficial material may become
                  a viscous slurry and flow slowly down the slope. Material which doesn't reach the toe dries on the slope face until

                  the next rain.


                  Seepage occurs above the ironstone horizons and produces sapping erosion, particularly near the top of the silt-clay
                  unit. Within the overlying sand horizons, the thickness and induration of the ironstone decreases with increasing
                  elevation. These ironstone layers do lend some stability to the upper unsaturated zone, which is very tall in places.
                  Virtually no slumping of the unsaturated zone is evident, in contrast with the slumped unsaturated horizons at
                  Grover Creek South and at the Chesapeake Ranch Estate!s Laramie Lane subsite.

                  Physical and chemical weathering of the slope surface combine with seepage and storm runoff to erode material from
                  the slope, and deliver it to the debris fans below. Large gullies "tending the entire length of the slope are common
                  at this subsite. The gullies tend to terminate on ironstone sheets especially where the sheets are cantilevered over the
                  slope below.

                  11ppe
                        r Slopg. The bluff top is nearly vertical where bound together by tree roots. Virtually no trees are found on the
                  beach along this section. indicating a relatively stable bluff top.


                                                                               32













                 3.7 Chesmak Ranch Estates

                                                     General Site Description (Figure 3.10, 3. 11)

                 The site encompasses the shoreline and cliffs from Cove Point Hollow to Seahorse Beach. The subsites are Cove
                 Point Hollow (CPH), Little Cove Point (LCP), Laramie Lane (LL), Driftwood Beach South (DBS), and Seahorse
                 Beach North (SBN).

                 The cliff orientation ranges from east-northeast at the Cove Point Hollow subsite to southeast at Seahorse Beach
                 North. The shoreline along the cliffs is unprotected except for a few groins at Driftwood Beach and Seahorse Beach,
                 where no cliffs are present. A small beach is present during most tidal conditions along the entire site, except at the
                 locations where slide debris extends to the low tide line. One notable exception is at the Little Cove Point subsite,
                 where the cliff face extends into the water. One or two shore-parallel sand bars are found along most of the site.

                 North of Little Cove Point, cliff height ranges from 10 to 25 meters and the slope angles are shallow to moderate
                 ranging between 30 and 50 degrees. Cliff heights at the Little Cove Point subsite range between 16 and 22 meters
                 and the slopes are steep, varying between 70 and 85 degrees. The slopes at the Laramie Lane subsite are distinctly
                 different from those to the north or south. They range in height from 15 to 35 meters and are characterized by steep,
                 nearly vertical bases, more gentle mid-slopes (40-60 degrees), and a nearly vertical bluff top. Three large recent
                 slides have occurred in the upper materials at the Chesapeake Ranch Estates. The slide debris has accumulated at the
                 slope toe giving the. entire slope a moderate. nearly uniform profile at an inclination of approximately 65 degrees.
                 The debris is being gradually removed by wave action over a period of one to three years. The slopes at the
                 Driftwood Beach South subsite are 16 to 22 meters high and have slope angles of 60 to 80 degrees. At the Seahorse
                 Beach North subsite the slopes are 12 to 30 meters high and are inclined at angles of 65 to 85 degrees.

                 `17he site lies entirely within the Miocene St. Marys Formation. There is some question as to the age of the top 15
                 meters of coarse grained sediments. For our purpose, it is sufficient to note that the material properties of the upper
                 15 meters is distinctly different from the lower 15 meters of cliff. The lower portion of cliff is comprised of
                 interbedded fossiliferous sands, silts, and clays. Ile upper 15 meters is composed of coarse grained sands with some
                 pebbles and gravels and has very different geotechnical properties than the lower materials. Ironstone is present in
                 laterally discontinuous patches up to one meter thick.

                 From the Cove Point Hollow subsite to the Laramie Lane subsite, surface drainage originates from as far as 700
                 meters from the cliff face. Along the Driftwood Beach South subsite, drainage towards the cliffs extends 350 meters
                 from the cliff face. Surface drainage at the Seahorse Beach North subsite is essentially that of a hilltop.
                 Groundwater seepage is generally very active at the base of the coarse grained sands of the upper cliff sections. It is
                 particularly strong where topographic lows intersect the cliff face.




                                                                           33













                                                          Geotechnical Properties (Figure 3.12)

                  The cliffs at Chesapeake Ranch Estates range in height from 10 m to 35 m. The slope materials can be divided into
                  five major groups. The soil horizons and root zone are developed in a sandy material. Below the soil and root zone
                  is a thick, highly weathered, medium to coarse sand with traces of pea gravels and thin clay laminations. This unit
                  is moist throughout and is saturated at its base. A seepage zone occurs where the sand unit overlies a series of
                  interbedded sands and clays. About half way down the slope, the interbedded sands and clays give way to a distinct
                  massively bedded fine sand with a significant silt fraction. This bed is nearly 6 meters thick and grades into a gray,
                  clayey silt which extends below beach level.

                  The ground surface at the well site is at an elevation of 29.5 m. The stratigraphic unit containing the soil horizons
                  and root zone is approximately two meters thick and is composed of a moist, brown, silty, clayey sand.
                  Immediately below, at an elevation of 27.4 m, lies an extensive sand zone which is highly weathered and is subject
                  to iron staining; the color varying from tan to yellow to orange. A strength minimum occurs near the top of this
                  unit and a maximum near the base. Thin lenses of pea gravel and clay laminations are present but discontinuous in
                  this unit. The sands are nearly 12 meters thick and are highly porous and permeable resulting in a perennial seepage
                  zone where they meet a series of interbedded clays and sands at an elevation of 15.6 m. The clay units range in
                  thicknm from centimeters to nearly a meter. The interbedded sands are of similar thicknesses and tend to be thin
                  seepage zones. The saturated sands and clays of this unit are very weak and for the likely failure surface for the large
                  slides observed in this section of the cliffs.


                  The top of the gray, fine sand unit just beneath the interbedded sands and clays occurs at an elevation of 14.1 m.
                  About 30 percent of the material in this unit is finer than very fine sand resulting in a dense, massive texture. The
                  SPT indicates that it is moderately strong. A series of thin shell beds occur near the base of this unit and exhibit a
                  slight increase in the strength of the unit. Two permanent seeps occur in shell beds, each with a matrix of medium
                  sized sand. Below the shell beds, at an elevation of 6.2 m is a bed of moist, gray, clayey silt which also appears to
                  be massive and dense. However, the SPT indicates that the unit has a low to moderate strength.

                                                                   Erosion Mechanisins


                  SitelSubsite:Chesapeake Ranch Estates/Seahorse Beach North

                  Lower Sl= Physical and chemical weathering of exposed surface material reduces cohesion and causes fragmental
                  disintegration. Gravity and surface runoff transport the loosened material downslope creating a wedge-sliaped mantle

                  that thickens toward the toe.


                  Daily waves and tides and storm runoff are capable of removing most of the unconsolidated debris generated by
                  slopes 20 m or less in height. Taller slopes may have accumulations of upper slope debris at the toe. Intense wave




                                                                             34










                  action due to strong onshore winds and/or high tides removes large volumes of toe debris and may undercut intact
                  slope material; however, vertical slopes or overhangs indicative of intense undercutting are not observed at this site.

                  MidsloM. A strong perennial seep occurs at about 5 m above the toe from Seahorse beach to Driftwood beach. The
                  seepage zone marks the transition between a lower gray silty clayey very fine sand and an overlying thin interval of
                  interbedded medium sands and clays. The sands of the interbedded unit are continuously saturated, which maintains
                  the clays in a moist, plastic state. In addition, the sands are prone to piping and sapping which removes the sand
                  from the between the clays creating gaps which, eventually collapse. In the taller cliffs (> 25 m), the weight of the
                  overburden is sufficient to cause failure within the saturated clays and a sliding surface is produced along the
                  clay/sand beds. It is likely that the saturated sands contribute additional water to the already weakened surface and the
                  failure propagates along the clay/sand bed. Spherical scarps are evident with nearly vertical upper faces indicating

                  that the failure is rotational in nature.


                  Along sections without a recent rotational failure, a break in the slope profile typically occurs at the perennial seep.
                  The underlying saturated very fine sand offers more resistance to surficial erosion and stands at a steeper angle than
                  the looser interbedded sands above. Water from overlying seepage zones exits the slope face at sapping or piping
                  zones and undercuts the overlying material, transporting sediment and debris down the slope face to the slope toe via
                  gullies. Gullies on faces subject to piping originate in the middle of the slope and widen downward. Stormwater
                  runoff also washes over the entire slope face carrying weathered, loose debris to the slope toe.

                  Uppgr Slol&. The upper strata tend to be highly leached and weathered. The mid-slope rotational slides either
                  simultaneously carry into the upper slope materials or undercut them to such an extent that subsequent bluff top
                  failures are inevitable. The roots of trees and shrubs tend to bind the upper 1-2 m into a mass that fi-equently either
                  over hangs the upper slope or results in a vertical face at the bluff top. Retreat of the bluff top occurs when undercut
                  trees and portions of root mass eventually fall, along with spherical masses of soil.

                  Site/Subsite: Chesapeake Ranch Estates/Driftwood Beach North to Laramie Lane

                  Lower Slopg. Physical and chemical weathering of exposed surface material reduces cohesion and causes fragmental
                  disintegration. Gravity and surface runoff transports the loosened material downslope creating wedge shaped debris

                  fans that thickens toward the toe.


                  Daily waves and tides and non-catastrophic storm runoff are capable of removing most of the unconsolidated debris
                  generated by slopes 20 m or less in height. Taller slopes have accumulations of upper slope debris at the toe.
                  Intense wave action due to strong onshore winds and/or high tides removes large volumes of toe debris and may
                  undercut intact slope material. Here, in contrast to Seahorse Beach North, the toe debris seems to be more
                  vigorously removed by daily waves, tides, and storm run-off. Spalling of blocks of the clayey silt in the toe zone is
                  common and continuous. Ile spalling process is accelerated by groundwater leaching along nearly vertical tension
                  planes which are weakened and act as fracture surfaces for spalling events. Here, spalling at the base of the
                  perennially saturated clayey silt of the toe zone actively undercuts the remainder of the lower slope, forming nose-


                                                                           35










                   like profiles at the interface with the sandier unit above and vertical to concave faces in the clayey silt below. ne
                   permeability contrast at this interface creates a perennial seep along which sapping erosion occurs forming thin,
                   concave gaps where the sands have been removed.

                   A difference in the materials composing the toe zone is postulated to be the reason that spalling is more active north

                   of Driftwood Beach than north of Seahorse Beach. Field observations indicate that the toe zone strata are finer
                   grained north of Driftwood Beach than the equivalent material north of Seahorse Beach. It should be noted, however,
                   that a greater magnitude of wave undercutting could also be responsible for more active spalling at that site.
                   Therefore, it is imperative that the wave climate at the Chesapeake Ranch Estate site be evaluated under a variety of
                   wind, wave, and tidal conditions.

                   Midslopp. A strong perennial seep occurs at about 5 to 6 m elevation along the cliffs from Driftwood Beach to the
                   area of shoreline lying just east of Laramie Lane. The seepage zone marks the boundary between a gray clayey silt
                   and an overlying unit containing several fining upwards cycles of shell fragments in a matrix composed of fine sand
                   at the base of each cycle and fining to a silt at the top of each cycle. At the seepage interface, thin horizontal
                   trenches are formed by sapping erosion. The cyclic shell sequence is lightly cemented and is relatively strong, as
                   ndicated by field shear strength tests. The strength and cementation of this unit causes it to form nose like
                   pirojections in profile.

                   Above the cyclic shell beds is the same gray, silty, clayey, very fine sand found in the toe zone just north of
                   Seahorse Beach. Like the Seahorse Beach location, this unit does not spall, but is covered by a thin veneer of
                   weathered fragmental material. It is also prone to gullying by surface wash. At 15 m above the beach, the gray,
                   silty, clayey, very fine sand grades into the layer of interbedded, saturated medium sands and clays previously
                   discussed for Seahorse Beach location. As at Seahorse beach, a minimum shear strength is indicated in the SPT tests
                   for the seepage zone perched on the interbedded sands and clays. Where the overburden above the interbedded sands
                   and clays is sufficiently large (>25m), the saturated clays, weakened by sapping erosion, fail in rotational failures.
                   Spherical scarps are evident with nearly vertical upper faces indicating that the failure is rotational in nature.

                   Several sandy zones of varying permeability can occur above the interbedded sand/clay zone. The exact number of
                   zones on any slope face varies with the cliff height. Each of the permeability contrasts creates a perched water table.
                   At locations without a recent deep-seated slide, the seepage flow exits the slope face at sapping or piping zones,
                   undercuts portions of the slope above, and transports sediment and debris down the slope face to the slope toe via
                   gullies. Gullies on faces subject to piping originate at the permeability contrast and widen downward. Stormwater
                   runoff also washes over the entire slope face carrying weathered, loose debris to the slope toe.

                   UpMr Sl=. The upper strata are composed of medium to coarse sands with lenses of pebbles and cobbles and tend
                   to be highly leached and weathered. The mid-slope rotational slides either simultaneously carry into the upper slope
                   materials or undercut them to such an extent that subsequent bluff top failures are inevitable. The roots of trees and
                   shrubs tend to bind the upper 1-2 rn into a mass that frequently either over hangs the upper slope or results in a


                                                                              36










                 vertical face at the bluff top. Retreat of the bluff top occurs when undercut trees and portions of root mass
                 eventually fall, along with spherical masses of soil.

                 Site/Subsite: Chesapeake Ranch Estates/Little Cove Point

                 Lower Slo . Physical and chemical weathering of exposed surface material reduces cohesion and causes
                 disintegration. Gravity and storm runoff transports the loosened material downslope creating a thin, patchy mantle
                 of surficial debris on the slope toe. The geometry of the toe zone at Little Cove Point and north stands in striking
                 contrast to the toe zones of the slopes to the south of Little Cove Point. Here the toe is gently inclined away from
                 the beach crest at a shallow angle. It is apparent that waves are still able to remove the veneer of surface debris from
                 the toe just above beach level, but undercutting and spalling due to wave action in the toe zone are non-existent.
                 The material comprising the toe zone from south of Little Cove Point to north of Little Cove Point is a clayey silt
                 composition varies little along this length of cliff. Apparently, the wave energy striking the northeast facing slopes
                 of Little Cove Point is substantially less than that striking the southeast facing slopes.

                 A seepage zone exists approximately 5 m above the beach and at this interface sapping erosion truncates the gently
                 inclined profile of the more permeable unit above by removing intact slope material and undermining the gullied
                 slope above.

                 MidslM. Slumping and spalling are minimal north of Little Cove Point. The material comprising the upper
                 slopes north of Little Cove Point is stronger and partially cemented in places. Ironstone formations are common.
                 Slope erosion occurs principally through chemical and physical weathering and erosion by seepage and surface
                 runoff. Field inspection indicates that the seepage discharge north of Little Cove Point is significantly smaller than
                 that observed along the slopes from Driftwood Beach to Laramie Lane. Large gullies are present on most of the
                 slopes. An upper intermittent seepage zone also exhibits evidence of sapping erosion and is responsible for creating
                 significant overhangs above.

                 Up= Slo . 7le roots of trees and shrubs tend to bind the upper 1-2 m into a mass that ftNuently either over
                 hangs the upper slope or results in a vertical face at the bluff top. Retreat of the bluff top occurs when undercut trees
                 and portions of root mass eventually fall, along with spherical masses of soil.















                                                                          37













                 4. Mechanisms and controls of coastal slope failure

                 4.1 Wave undercutting and it., relation to other controllilg factors of coastal sloW erosion,

                 Undercutting by wave activity, whether currently active or not, is common to all our study sites. It is this
                 undercutting that initiates and, to some extent, maintains the slope erosion. The rate of undercutting depends on the
                 orientation of the shoreline, the offshore bathymetry, the elevation of the slope toe, the presence of slope toe
                 protection (e.g. bulkhead, beach), and the material properties.

                 In all cases we examine, wave undercutting is a basic environmental factor. In some cases, particularly where the
                 undercutting rate is very rapid, undercutting is the dominant environmental factor driving the erosion mechanisms
                 and rates for the entire slope. In other cases, however, including most of the slopes we examine, undercutting is
                 only one of several environmental factors controlling the rate of slope erosion. This is particularly true for the
                 middle and upper portions of the slopes, for which the recession rate is often more rapid than, and therefore relatively
                 independent of, the wave-driven recession of the lower slope. When recession of the middle and upper portions of the
                 slopes occurs more rapidly than recession of the lower slopes, a characteristic slope profile is formed in which the
                   'ddle portion of the slope is more gentle (has receded back from) the steeper lower slope. In these cases, the
                 mechanisms of slope erosion occurring on the middle slopes and, therefore, the factors controlling that erosion, are
                 not a direct function of the lower slope erosion. Wave action is needed to initiate slope erosion and to remove the
                 debris shed from the slope, but the mechanisms and rates of erosion of the middle and upper slopes are controlled by
                 local surface water and groundwater, slope geometry, and material strength, and not by toe undercutting. An extreme
                 case of this occurs at the NRL site, where complete protection of the slope toe has been in place for 45 years.
                 Erosion of the middle and upper slopes continues even after this long period of toe protection. The types of erosion
                 and the environmental factors controlling the future recession rates and ultimate stable form of the NRL slope are
                 independent of undercutting at the slope base.

                 4.2 Groups of sloM erosion mechanisms: ClassificatioKi of the Calvert Cliffs sloigs

                 The erosion mechanisms operating along the Calvert Cliffs are varied and complex. Most mechanisms operate to
                 some degree on all of the bare, eroding slopes, and more than one erosion mechanism generally contributes
                 significantly to the observed slope form and slope recession at any one site. A major part of CCSEP involves
                 identifying the dominant slope erosion mechanisms at each site and determining the critical values of environmental
                 factors controlling the dominant types of erosion and their rates. It is this information that is necessary for
                 determining the response of the slopes to change in external factors, such as sea level rise.

                 The complexity of the slope erosion is augmented by the fact that the types of erosion processes acting on any
                 individual slope may not be constant in time. Rather, a cyclic variation may exist wherein a period of direct toe
                 undercutting, slope oversteepening, and active, deeper slope erosion is followed by a period during which the slope


                                                                            38










                 debris protects the slope toe from erosion and surficial erosion processes cause the slope to become gentler. The
                 cycle begins again when the slope debris is removed from the slope base and erosion of the intact toe resumes. Such
                 cyclicity has been observed on other coastal cliffs (e.g. Fdil and Vallejo, 1977; Quigley et al., 1977) and may also
                 operate along portions of the Calvert Cliffs.

                 As an attempt to bring some order to this complex situation, we propose a system for classifying the Calvert Cliffs
                 according to their geometry and the relative rates of the dominant erosion processes. The goal of this classification
                 is identification of the dominant erosion processes from readily observable slope features. The classification system
                 also provides a conceptual basis for further investigation and application regarding:

                          (1) development of field experiments with which we will attempt to isolate critical values of environmental
                          factors that determine the erosion type and rate and the timisition between dominance of one erosion

                          mechanism and another;

                          (2) prediction of the range of possible erosion processes and their rates in response to sea level changes;

                          (3) a technical basis for developing and evaluating erosion mitigation projects.

                 Our classification system is based on three factors: (1) a distinct difference in material saturation and erosion
                 resistance typically exists between lower and middle sections of individual slopes, (2) the range of erosion
                 mechanisms that dominate the recession of lower and midslope sections are often different, and (3) the resulting slope
                 geometry of lower and midslopes is often considerably different.

                 'Me material difference is based on the common presence of a strong permeability contrast occurring typically within
                 5 to 15 m of the slope toe. Materials immediately overlying the permeability boundary are typically -porous,
                 granular in structure, and saturated, fon-ning a zone of groundwater seepage that is either permanent or continuous
                 during most of the year. The material below the permeability contrast is much less permeable, generally darker in
                 color, and massive in structure. The lower materials tend to be more resistant to surficial erosion p=esses related to
                 wetting and drying, freezeAhaw, and surface wash from diiect precipitation or groundwater seepage. Often, failure of
                 the lower slope materials occurs through spalling and falling of slope segments oversteepened by direct wave
                 activity. In some cases, the midslope materials overlying the permeability contrast also fail by spalling or shallow
                 sliding on a wave oversteepened slope, but more commonly, the midslopes fail by hydrologically driven processes
                 related to surficial erosion of weathered material by direct precipitation or groundwater seepage, or by deep-seated
                 failures along weak strata experiencing high groundwater pore pressures.

                 Different slope geometries result from the different properties and typical groups of erosion mechanisms in the lower
                 and midslopes. In most locations along the Calvert Cliffs, the rate of midslope recession appears to be more rapid
                 than lower slope recession and the midslopes are observed to retreat back from the lower slopes. In this case, one of
                 several common slope forms are produced, all of which have a more gently inclined midslope than lower slope.
                 When the rate of lower slope recession becomes even snialler relative to the midslope recession rate, die entim slope



                                                                            39










                   may erode to a gentler angle characteristic of midslope surficial erosion. In this case, the waves serve primarily to
                   remove the slope debris and perform only a small amount of direct undercutting of intact material. Where toe
                   protection is complete, waves cannot remove even the slope debris accumulated at the toe. Because a colluvial debris
                   fan builds at the slope toe, these slopes develop a profile of increasing slope angle with elevation. In the other
                   extreme case, where the lower slope recession proceeds more rapidly than the rate at which either surficial or deep-
                   seated slope failures erode the midslope, the entire slope becomes very steep and the midslope fails primarily by
                   shallow sliding or spalling.

                   The classification system contains four basic classes of slopes, organized according to the relative recession rates of
                   the slope base Rb and midslope Rm. Figure 4.1 presents schematic slope profiles and summarizes the classification

                   scheme.


                   Type I Rb = 0. Type I slopes no longer experience toe erosion. Debris eroded from the slope accumulates and
                   builds a gently inclined mantle up from the slope toe. A typical lower slope angle for Type I slopes is
                   approximately 35 degrees. The debris fan may terminate in the midslope section, in which case a three pan slope is
                   formed, with the slope angle increasing with elevation. After an extended period of time, the debris fan may entirely
                   cover the midslope and a two-part slope (fan/upper slope) exists.

                   Generally, undercutting by ephemeral seepage, surficial erosion by overland flow, and columnar toppling account for
                   the retreat of the upper slope. Upper slopes tend to be quite steep, ranging from 55 degrees to vertical. Three of our
                   study sites, NRLN, NRLS, SCS, have sufficient protection to prevent further toe erosion. These sites allow us to
                   observe the manner in which the toe and mid-slope regions build as the bluff top continues to recede.

                   Type H Rb << Rm. Type II slopes are slopes where waves can remove most slope debris from the base and may
                   occasionally erode some intact toe material, but at a rate slower than the hydrologically dominated erosion processes
                   operate on the lower slope. Sapping, piping, solifluction, and overland flow tend to dominate from near the base of
                   the root zone to the slope toe. The intact material near the slope toe will exhibit slope angles that are very similar
                   to those of the mid-slope. Slopes with relatively homogeneous materials throughout will exhibit a straight profile
                   from the toe to the bluff top. Slopes with materials of contrasting geotechnical properties at different elevations will
                   show slope breaks at material transitions, although the variation in slope angle will be smaller than the contrast
                   found between the lower slope and midslope typical of the more common Type III slopes. ne range of angles for
                   Type II slopes for a line drawn from slope toe to bluff top is 40 to 52 degrees. The angle of slope segments of Type
                   H slopes fall within a range of 35 to 65 degrees. The subsites at Little Cove Point and Scientists' Cliffs North fall
                   into Type 11. Classification of a slope as Type H is made on the profile of the intact slope material. For example,
                   Grays Creek South (Figure 3.8) has a relatively straight profile, which is a characteristic of some type R slopes.
                   However, the survey included a temporary debris pile at the slope toe creating a profile with a shallow toe zone
                   angle. Since the survey, the toe debris has been eroded and the toe zone of Grays Creek South is nearly vertical.




                                                                              40










                   Type (IM Rb < Rm. Type III slopes are the most common along the Calvert Cliffs. On these slopes, waves erode
                   the lower slope at rates sufficiently fast to cause spalling or falling of lower slope material. At the same time,
                   hydrologically driven processes in the midslope operate rapidly enough to cause the midslope to recede back from the
                   lower slope. The result is a slope that displays a distinct break in the slope angle at the permeability contrast
                   separating the lower and midslopes. Ile lower portions of Type III slopes have angles between 75 and 90 degrees,
                   whereas the midslope angles generally fall between 35 and 65 degrees. Different hydrologic conditions and midslope
                   erosion mechanisms produce different midslope profiles. Groundwater piping will create gullies which have their
                   heads at the pipe exit, whereas more laterally continuous groundwater sapping produces a more uniform erosion of
                   the slope below, resulting in a smooth, planar midslope. Type III slopes include Holiday Beach, Governors Run,
                   and Grays Creek South.

                   Type IV Rb - Rm. In these slopes, wave undercutting is sufficiently rapid that the recession rate of the lower slope
                   is greater than the rate at which hydrologically driven processes cause the midslope to erode. The midslope becomes
                   oversteepened and both lower and midslope erosion is driven by spalling and shallow sliding at a rate determined
                   directly by the rate of wave-driven undercutting. Relatively steep, straight slopes form at slope angles of 70 degrees
                   or more if the materials are relatively homogeneous. However, where vertical geotechnical contrasts exist, each
                   slope segment will fail at an angle characteristic of the material in each zone, resulting in a segmented, steep slope
                   profile. A potential for deep-seated slope failure exists in some Type IV slopes. This occurs where a soft clay layer
                   occurs within the saturated seepage zone at the lower/midslope boundary, and a sufficient thickness of porous and
                   permeable slope exists above the seepage zone, producing elevated pore pressures and high shear stresses within the
                   soft clay. The result is a rotational scarp extending upward through the unsaturated zone to near the bluff top. The
                   debris resulting from the slide accumulates at the toe in wedges that are removed by subsequent wave action. Type
                   IV slopes are characterized by an overall slope angle that is steeper than any other type of slope. Type IV cliffs are
                   found at the Randle Cliffs, Parker Creek, and Laramie Lane subsites.

                   It is worth emphasizing that the classification system is based on relafive erosion rates of the lower and midslope.
                   Although all Type IV slopes experience significant toe undercutting, all Type IV sites do not necessarily experience
                   greater wave energies, or have greater undercutting rates, than other slope types. For example, a Type M slope
                   might experience large lower slope recession rates, but would be classified as a Type Ell slope if the midslope
                   recession rate exceeds that of the lower slope. The slope measurements we have made to date indicate that the slope
                   angles characteristic of the four basic slope types fall into distinct, non-overlapping groups. These angles are
                   measured from the bluff top to the intact material at the slope toe. Table 3 presents the slope angles typical of each

                   type.











                                                                              41













                                                 Table 3. Summary of slope types

               Slow L)=                                         Bluff top to toe range (deg-=)

               Type 1                                           32 to 40

               Type H                                           40 to 52

               Type 111                                         52 to 65

               Type IV                                          65 to >90



               This is a potentially important and useful result. Our slope classification is based on observations of groups of
               erosion processes and rates that typically occur together, and on the slope geometry developed by these groups of
               processes If the type of slope and, therefore, the typical group of erosion processes, can be determined based on the
               overall slope angle, the classification of individual slopes can be done quite readily. Once classified into a particular
               type, the erosion mechanisms acting on that slope, and the environmental factors controlling that erosion, are
               known. Classifying slope type by angle can also provide the opportunity to make classifications from aerial
               photographs or detailed maps. In the next phase of CCSEP, we will be conducting surveys of additional slopes to
               test this potential simplification of our classification system.






               4.3 Environmental factors controlline the recession of each slQ=

               Environmental factors control the rate at which different erosional mechanisms act and, therefore, determine the
               dominant erosion mechanisms occurring at each location. For instance, low wave energies might be capable of very
               little erosion, allowing a colluvial fan to develop along the lower slope. In this case, slope erosion and recession
               rates are predominantly determined by hydrologic and material properties intrinsic to the slope itself. At a similar
               site, a much larger amount of wave energy would be capable of cutting into intact material, causing spalling and
               shallow sliding that would be far more rapid than any other erosion mechanism, thereby directly driving the recession
               of the entire slope. Identification of critical values of environmental factors controlling erosion (in this example, the
               level of wave energy) is central to a quantitative approach to predicting the slope response to changes in external
               variables, such as a sea level rise.

               Type I Rb = 0. Toe protection has been implemented for decades for the Type I slopes of this study. Wave erosion
               at the toe has been halted, resulting in the accumulation of debris eroded from the slopes above.




                                                                42










                  Above the debris fan, slopes attain angles characteristic of hydrologically dominated erosion. The rate at which this
                  erosion takes place depends on the amount of water available to the slope surface. Heavy rain from large convective
                  storms or hurricanes will create surface wash which removes weakened and weathered surface material. Erosion due
                  to the seepage of groundwater may result from long duration precipitation events or it may occur where there is a
                  very large groundwater recharge area, so that seepage occurs over extended time periods. A contrast in permeability
                  between adjacent slope materials is also necessary to produce seepage discharge at rates sufficient to cause erosion.

                  Bluff tops are typically bound by root strength and retreat is controlled by undercutting due to seepage or overland

                  flow surficial erosion.


                  Type 11 Rb << Rm. Wave action is capable of removing eroded debris, but hydrologic processes dominate the
                  recession of type II slopes. Two factors may control the response of the lower slopes. First, the wave climate over
                  time may be sufficient to remove the debris delivered to the slope toe from above, but not capable of great amounts
                  of additional erosion. Secondly, the material comprising the slope toe may be strong enough to resist significant
                  erosion by the waves - a rock slope would be an extreme case. An increase in toe erosion rate, which might cause a
                  Type 11 slope to become a Type III slope could be driven by and increase in water level, an increase in wave height,
                  or an increase in the frequency of wave events.

                  Below the perennial seepage zone, the rate of erosion is controlled by the amount of water which flows over the
                  lope surface. The source of the water may be from surface wash or groundwater seepage. Above the perennial seep,
                  in addition to overland flow, seepage erosion is capable of undercutting the overlying strata causing oversteepening
                  s


                  and collapse. Groundwater flow and material properties control undercutting rates, while overland flow, slope angle,
                  and material properties control surface erosion. A change in the rate of midslope erosion is most likely to be caused
                  by an increase in the groundwater seepage rate or duration. Bluff top recession is controlled by the rate of erosion
                  below the root zone and the extent of its capacity to resist cantilever type failures.

                  Type III Rb < Rm. In the toe zone, wave undercutting removes all debris delivered from upslope. and actively erodes
                  intact slope material. Midslope erosion type and rate depend on the configuration of the seepage discharge, quantity
                  of seepage discharge relative to surface wash; erodibility of slope surface. An increase in the toe erosion rate could
                  cause a Type III slope to change to a Type IV slope. That is, an increase in the wave energy could increase the rate
                  of lower slope erosion by spalling and shallow sliding. The spalling and shallow sliding in the lower slope would,
                  in tam, oversteepen the midslope causing shallow sliding there at a rate which exceeds the rate of erosion by
                  hydrologic processes. In this way, the slope would become steeper and dominated by spalling and shallow sliding as
                  it changed from Type III to Type IV.

                  Type IV Rb - Rm. The recession rate of lower slope is driven by wave erosion and is greater than hydrologically
                  dominated erosion rates typical of midslopes. Therefore, the midslope responds to oversteepening from below by
                  spalUg or shallow sliding. The rate of erosion due to sliding or spalling depends on the degree of saturation and the




                                                                             43











                 strength and composition of the near surface materials. Occurrence of deep-seated failure depends on the height of
                 upper slope-, pore pressures at failure zone, strength of material at failure zone



                 4.4 Field E=riments

                 Criterion Three of the site selection criteria was used to narrow the list of potential sites to those that provided the
                 best conditions for isolating and identifying critical values of the environmental factors that control the types and
                 rates of slope erosion. That criterion was: The properties of individual sites must permit between-site comparisons
                 in which a large variation in one factor observed along with only minor variation in all of the other controlling
                 factors. Each such comparison comprises a field experiment that will help us define the critical values of the
                 environmental factors controlling slope instability along the Calvert Cliffs.

                 The following discussion and Table 2 describes the field experiments we have identified.

                                                                    Material Strength

                 Large slope failures usually occur in materials that are relatively weak. Smaller failures and surficial erosion occur
                 in all materials but at different rates which are largely determined by material strength. The strength of a material is
                 determined by characteristics such as grain size, moisture content, cohesion, and internal friction. Slopes having
                 similar shoreline features, undercutting rates, and slope heights, but different material properties will be compared to
                 determine the role of material strength in slope erosion at Calvert Cliffs. Critical values of material strength and
                 pore pressures in weak horizons will be identified to provide a working model of slope failure at these sites.
                 Comparisons will be made between the following subsites:

                                    Randle Cliffs vs. Holiday Beach
                                    Parkers Creek South vs. Governors Run
                                    Rocky Point vs. Grays Creek South
                                    Little Cove Point vs. Driftwood Beach South
                                    Holiday Beach vs. Parkers Creek South
                                    Holiday Beach vs. Cove Point Hollow
                                    Parkers Creek South vs. Cove Point Hollow
                                    Little Cove Point vs. Seahorse Beach North

















                                                                             44












                                                           Slope Height

               The effect of slope height on slope erosion will be evaluated by making comparisons between slopes with similar
               shoreline characteristics, slope materials, and hydrologic conditions, but different slope height. These comparisons
               will principally be made entirely within one subsite or between subsites where sufficient control can be maintained.
               Subsites involved in slope height experiments include:

                               Randle Cliffs
                               Governors Run
                               Parkers Creek South
                               Scientists' Cliffs North vs. Scientists' Cliffs South
                               Grovers Creek North vs. Grovers Creek South
                               Laramie Lane
                               Driftwood Beach South vs. Seahorse Beach North


                                                         Wave Undercutting

               Coastal slope erosion is ultimately driven by wave undercutting. Slope erosion and undercutting often follow a
               cyclic pattern. Waves remove intact material from the slope toe, steepening and destabilizing the slope. Waves also
               remove the debris produced by slope failures, starting fresh erosion and beginning a new cycle. The magnitude,
               timing, and water level of the wave erosion is a dominant environmental factor which controls coastal slope erosion.
               We will investigate the effects of wave undercutting in two ways. In both cases, pairs of sites will be chosen with
               similar material properties and slope height, but different rates of wave undercutting. In the first case, we will
               contrast slopes with and without slope toe protection. These comparisons provide the strongest contrast in
               undercutting rates possible, and also provide a direct investigation of the effectiveness of toe protection works. This
               set of experiments may identify critical slope toe elevations below which wave undercutting drives the entire slope
               retreat and above which hydrologic mechanisms dominate. As sea level rises, critical slope toe elevations will rise
               commensurately. These comparisons will be made at:

                               Randle Cliffs vs Naval Research Lab North
                               Naval Research Lab South vs. Holiday Beach
                               Parkers Creek South vs. Scientists' Cliffs North
                               Scientists' Cliffs South vs. Governors Run

               The second field experiment on wave undercutting will be achieved using similar cliff sections that have a different
               orientation and, therefore, a different wave energy regime. Along the Calvert County shoreline, such an experiment
               is possible at two places, Rocky Point and Little Cove Point. At each location, there a significant change in
               shoreline orientation over a short distance, allowing the cliff height, material properties, and hydrologic domains to
               be held relatively constant.




                                                                45














                 5.0 Compar'son with Historical Erogion Rates

                 As discussed in section 1. 1, estimates of slope recession over a period of 100 years have been prepared from an
                 analysis of historical maps and modem aerial photographs (Slaughter, 1949). Historical, time-averaged erosion rates
                 provide valuable comparisons for future estimates of slope erosion. However, since coastal slope erosion processes
                 vary over relatively short periods of time, application of historical data to the prediction of erosion rates is restricted
                 to defming the long-term magnitude of the cumulative erosion of a series of short-term erosion episodes.

                 The purpose of this section is to identify the historical erosion rate at each study site so that an estimate of the long-
                 term rate of slope recession is available from the outset and to provide a measure of comparison for the erosion rates
                 determined in this project.

                 'Me historical erosion maps prepared by the Maryland Geological Survey provide erosion rates for shoreline
                 segments and are presented on 1:24,000 scale topographic base maps. An earlier study (Slaughter, 1949) produced
                 shoreline recession rates over a 100 year period. An update of these rates to 1988 is currently underway. Therefore,
                 the time span covered on each quadrangle varies firom map to map. The erosion rates are presented as:

                          S (or s) = slight erosion rate; < 2 feet/year

                          L (or 1) = low erosion rate; 2 - 4 feet/year

                          M (or m) = moderate erosion rate; 4 - 8 feeVyear

                          H (or h)  high erosion rate; >8 feet/year

                          A (or a)  indicates accretion

                 The historical erosion maps do not distinguish between beach erosion or slope erosion. They base their estimate of
                 shoreline erosion on the change in the position of the mean high tide line, or vegetation line where vegetation is
                 present, from the beginning of the period to the end of the period.

                                               Historical erosion ratesfor the Naval Research Lab site:

                 Two time periods are used to estimate erosion rates for the shoreline segments along the NRL site. The first is an
                 87 year period between 1847 and 1934, and the second is a 36 year period between 1934 and 1970.

                 The resolution of the map does not permit distinction between a beach and a submerged slope toe. However, the
                 bluff top is estimated to have receded approximately 125 feet over the two periods combined (123 years). Hence, the
                 average rate of bluff top recession for this site is I foot per year. The only exception to this erosion rate is in the
                 southernmost portion of the site at Holiday Beach where the maximum shoreline recession over the 123 year period
                 is approximately 275 feet or 2.2 feet per year. It should be noted that the slope toe along the Navy Research Lab




                                                                          46










                 proper has been protected since the 1930's and has experienced no erosion since then, but the bluff top continues to
                 recede.                          Historical erosion ratesfor the Scientists' Cliffs site:

                 A single 105 year period, from 1848 to 1953, was used to quantify the shoreline erosion at the Scientists' Cliffs site.
                 During that period the Parkers Creek South subsite shoreline eroded 300 feet for an average rate of approximately 2.8
                 feet per year. For a short segment of beach near the northern end of the Scientists' Cliffs community where an
                 erosion rate of approximately I foot per year is recorded over the period, the Scientists! Cliffs shoreline has accreted
                 or remained nearly stable, although bluff top retreat continues. The shoreline along the Governors Run subsite
                 shows no net loss or gain over the 105 year period, while the upper portions of the slope have receded.

                 The shoreline along the Scientists' Cliffs community has been partially protected by gabion groins which have
                 helped to establish a beach. Anecdotal information provided by Scientists' Cliffs residents indicates an average bluff
                 top recession of approximately 0.5 feet per year.

                                              Historical erosion ratesfor the Calvert Cliffs State Park site:

                 A single 94 year period, from 1849 to 1943, was used to quantify the shoreline erosion at the Calvert Cliffs State
                 Park site. Once again, the maps do not distinguish between beach or slope erosion, making the estimates near the
                 Cove Point or southern end of the site difficult to interpret. Cove Point is a marshy, low lying point of sand and
                 silt which has slowly been migrating south over the past 150 years. It is postulated that a significant beach was
                 present in the late 1800's and early 1900's on the northern portion of the current Columbia Liquid Natural Gas
                 property immediately south of the Calvert Cliffs State Park. This assumption is supported by the offshore remnants
                 of a salt marsh in this vicinity. The current salt marsh is well south of the state park and protected by a barrier

                 beach.


                 The historical erosion map indicates that approximately 400 feet (4.5 feet/year) of shoreline have been eroded from
                 the central portions of this site in the 94 year period. A lower rate of approximately I foot per year occurs just
                 south of Rocky Point (at the northern end of the site) and a higher rate of 6.4 feet per year is indicated for the
                 extreme southern portion of the site near the submerged salt marsh.

                 Two structures present on the state park property, one at the northern end just north of Grover Creek and one at the
                 southern end south of Grays Creek, help to establish a rate of bluff top recession between 1943 and 1987 of
                 approximately 4 feet per year (180 feet in 44 years).

                                             Historical erosion ratesfor the Chesapeake Ranch Estates site:

                 A single 96 year period, from 1848 to 1944, was used to quantify the shoreline erosion at the Chesapeake Ranch
                 Estates site. The rate of shoreline erosion during this period ranges from near zero at the mouth of Parker Moore
                 Creek near the central portion of this site to approximately 2 feet per year both to the north and to the south of

                 Parker Moore Creek.



                                                                             47










                  At Little Cove Point the shoreline has remained nearly stable, but the shoreline several hundred feet to the north and
                  south has receded an average of slightly over 2 feet per year. "Me maximum shoreline erosion over this 96 year
                  period was approximately 2.4 feet per year and occurred at the noithern end of the CRE site between Little Cove

                  Point and Cove Point Hollow.


                  It should be noted that the Chesapeake Ranch Estate property has been substantially developed since 1944. Field
                  observations indicate that the rate of slope erosion is accelerating north of Seahorse Beach and north of Driftwood

                  Beach.


                                      Surnrnary and discussion of the historical erosion rates along the Calvert Cliffs

                  Table 4 summarizes the historical erosion rates at each site. Generally, the historical rate of recession of the mean
                  high tide or vegetation line increases southward along the Calvert Cliffs. Notable exceptions occur where shoreline
                  protection has been constructed, where local induration has occurred, and at the southernmost study site, the
                  Chesapeake Ranch Estates, where the slopes are generally taller than those at the other study sites. The trend of
                  higher slope toe erosion rates toward the south correlates well with the decreasing age (and decreasing consolidation)
                  of the stratigraphic materials southward. Exceptions occur where factors other than the erodibility of the material in
                  die toe zone exert an influence. For instance, bulkheads and groins reduce or eliminate the wave impact on the slope
                  toe and reduce recession rates. Local induration provides increased material resistance to erosion and locally
                  diminishes recession rates. Tall slopes contain greater volumes of material than shorter slopes; material which must
                  be removed before shoreline recession can take place. For tall slopes, the rate of removal must be substantially
                  greater than that for shorter slopes for equal amounts of shoreline recession to be observed.

                  Local and short-term variations in shoreline recession (ie. variations within individual study sites) tend to be
                  obscured by long-term, time-averaged recession rates. However, such variations may be extremely significant
                  because of their implications for property owners, land-planners, officials responsible for public safety, and bay
                  sediment supply and transport evaluations. Both the Naval Research Laboratory and Scientists' Cliffs study sites
                  offer opportunities to evaluate the effect of protective structures on slope stability. Where shore protection is in-
                  place at both sites, the bluff tops continue to recede. However, recession is evident for the entirety of the
                  unprotected slopes at both locations. Scientists' Cliffs offers a particularly good site for evaluating the impact of
                  gradual increases in sea-level because the position of the slope toe relative to the water level gradually changes across
                  the length of the site. Here, the conditions range from no protection to complete protection. The two southernmost
                  sites (ie. Calvert Cliffs State Park and the Chesapeake Ranch Estates) have varying shoreline orientations and no toe
                  protection. These conditions allow the effect of wave climate on short-term slope stability to be evaluated. Also,
                  the differences in slope height between the two southern sites allows a comparison to be made regarding the effect of
                  slope height on short-tern failure modes and patterns of sequential erosion processes.






                                                                              48














                                                     Table 4. - Summaa of,Historical Erosion Rates
                                                          Historical erosion rate (ft/yr)
                 Site - subsite                           averaged over at least 96 years.          Comments

                 NRL - Randle Cliffs                                            I

                 NRL - Naval Research Lab North                                 1                   60 years of toe protection, bluff top
                                                                                                    continues to recede

                 NRL - Naval Research Lab South                                 1                   60 years of toe protection, bluff top
                                                                                                    continues to recede

                 NRL - Holiday Beach                                            2.2                 Highest recession where slope
                 SC - Parkers Creek                                             2.8                 heights are lowest.

                 SC - Scientists' Cliffs North                                  I

                 SC - Scientists' Cliffs South                        Stable shoreline              60 years of toe protection, bluff top
                                                                                                    continues to recede

                 SC - Governor Run                                         Stable                   Field observations indicate active
                                                                                                    slope erosion, historical map
                                                                                                    accuracy is questionable.
                 CCSP - Rocky Point                                             1.0                 Local induration present.

                 CCSP - Grover Creek North                                      4.5

                 CCSP - Grover Creek South                                      4.5
                 CCSP - Grays Creek South                                       4.5                 A higher historical rate of 6.4 ft/yr
                                                                                                    occurs in the vicinity of salt marsh
                 CRE - Little Cove Point                                   Stable                   Local induration present. Just north
                                                                                                    and south of LCP the average rate is
                                                                                                    approx. 2 ft/yr.
                 CRE - Laramie Lane                                             2                   Relatively tall slopes.
                 CRE - Driftwood Beach South                                    2                   Relatively tall slopes.
                 CRE - Seahorse Beach North                                     2                   Relatively tall slopes.















                                                                                49













                  6.0 Extrapolation of Observations to Other rortiong of the Chesapeake ]Jay Shoreling

                  There is very little variation in the climate and physiography over the Maryland portion of the Chesapeake Bay.
                  Therefore, the variation in slope materials and their orientation relative to bay wave conditions are the primary
                  factors that determine where shoreline erosion will occur. In addition to the eroding coastal slopes of the western
                  shore of the Chesapeake Bay, tall, eroding slopes are present in the northeastern portions of the bay and along many
                  of the bay tributaries. The mechanics-based methodology for evaluating coastal slope instability developed during
                  CCSEP may be extrapolated to the eroding coastal slopes baywide. Where similar materials occur, the particular
                  results we find for Calvert County may be directly applied. When extending this model to other locations, variations
                  in shoreline orientation (wave climate), slope height, and material properties must be accounted for. The wave
                  climate depends'on the geographic location of the slope under consideration and can be evaluated by assessing the
                  bathymetric configuration, principal wind direction, and slope toe elevation at the site.

                  A conservative extrapolation of the Calvert Cliffs results to other sites would require that the range of materials
                  comprising the slope in question be similar to those materials comprising the Calvert Cliffs. The geology of the
                  slopes bordering the bay must be considered in any such extrapolation.

                  The Calvert Cliffs are principally composed of the Chesapeake Group and are upper Tertiary, Miocene Epoch coastal
                  plain sediments ranging in age from the lower Calvert Formation at 21.5 million years through the Choptank
                  Formation to the upper Saint Marys Formation with an age of 10.4 million years years (Kidwell, 1984).

                  The Calvert Formation represents deposition in an inner to possibly middle shelf marine environment, the Choptank
                  is mainly marine inner shelf, and the Saint Marys Formation was deposited in a very shallow shelf to marginal
                  marine envirorunent (Olsson, et. al., 1988). The sediments are relatively undeformed and unlithified marine,
                  terrigenous silts, sands, and clays (Kidwell, 1982).

                  The Calvert Cliffs (Chesapeake Group) are composed of interbedded fossiliferous sands, gravelly sands, silts, and
                  clays. Ironstone forms in laterally discontinuous patches and is the most indurated material present in the slope
                  materials. There are typically large contrasts of material strength and hydraulic conductivity between stratigraphic
                  units in the Calvert Cliffs. Because these units dip gently along the shoreline, there are also contrasts in material
                  strength along the cliffs.

                  Figure 6.1 shows the surface distribution of major Cretaceous (146 million to 65 million years before present) and
                  Tertiary (65 million to 1.64 million years before present) coastal plain sediments along the Chesapeake Bay
                  (Wheeler, 1990). The materials baywide are all part of the same coastal plain depositional suite and are principally
                  interbedded sands, silts, and clays (Olsson, et. al., 1988). In surface exposure, they become older to the north. Thin
                  veneers of Pliocene and Pleistocene materials may be present at the surface around much of the bay.



                                                                             50










                 Referencing Figure 6.1 and moving from south to north (youngest to oldest) through the major formations exposed

                 at the surface:


                      Chesapeake Group - discussed above

                      *Aquia Formation - The Aquia is lower Tertiary in age (approximately 60 million years old) and is
                      comprised of a shelly glauconitic sand deposited in a very shallow shelf environment. It is overlain by the
                      Marlboro Clay a marginal marine deposit.

                      *Magothy Formation - The Magothy is composed of a series of cross-bedded sands with thin beds of clays,
                      silts, and scattered lignite. It was formed as a beach zone complex with related fluvial and estuarine facies.
                      It is upper Cretaceous in age (approximately 85 million years old).

                      *Potomac Group - The Potomac Group is the basal sequence of sedimentation on the coastal plain outcrop.
                      It is composed of white, gray, and red interbedded variegated silts, clays, and quartzose sands. It fluvial-
                      deltaic depositional environment of a major river system. The Potomac Group is lower Cretaceous in age
                      and spans at least 67 million years from 132 million years before present to 65 million years before

                      present.

                  An important application of the methodology developed by CCSEP is the prediction of slope erosion mechanisms
                  and rates at other locations along the Chesapeake Bay. Toward this end, Figure 6.2 presents a conceptual model
                  which outlines the data required and the logical sequence that could be used to estimate slope erosion at sites beyond
                  Calvert County. An important feature of this model is the relatively small amount of data needed to identify specific
                  mechanisms of slope erosion and the rates at which they operate.

                  Specific site assessments for any particular coastal slope would require the location of the slope, the elevations of the
                  slope toe and bluff top, and the average slope angle from the slope toe to the bluff top (or the horizontal distance
                  between the toe and the bluff top). The geometric data can be obtained from a detailed topographic map or from a
                  simple survey of the slope toe and bluff top. With this information, the type of slope (Type I, II, III, or M and,
                  therefore, the types and relative rates of erosion mechanisms, could be determined. With a map of the exposed
                  coastal plain sediments around the bay and a description of their general properties, the slope location may be used t
                  estimate the geotechnical and hydrologic properties of the slope materials. A map of wave climate for design storms
                  on the bay would provide an estimate of undercutting rates at the site. With this information, the general combined
                  CCSEP model could be applied to determine the dominant mechanisms of the slope erosion at the site, and the long
                  term recession rates. This information can then be used to evaluate slope protection methods, estimate non-point
                  source sediment supply to the bay, and determine policy on slope protection, setback distances, and public safety.
                  Prediction of the probability and timing of individual large slope failures in the short term will depend on the
                  particular geometry of the slope at any given time, and short-term predictions would require a detailed site
                  investigation of the hydrologic properties and slope geometry. This detailed information is not necessary, however,



                                                                             51










                for predicting the long-term recession rates, which are driven by the cumulative effect of many individual failures and
                are less dependent on the detailed geometry of the slope at any time.



















































                                                                           52













                7A References




                Edil,T.B.andL.E.Val1ejo(l977). Shoreline erosion and landslides in the Great Lakes. In ProcALhIntemational
                Conference of Soil Mechanics and Foundation Engineering in Tokyo, Japan, , 51-57.



                Kidwell, S. M. (1984). Outcrop Features and Origin of Basin Margin Uncomformities in the Lower Chesapeake
                Group (Miocene), Atlantic Coastal Plain. in The American Association of Petroleum Geologists Memoir,
                Interregional Unconformities and Hydrocarbon Accumulation, John S. Schlee (editior). The American Association
                of Petroleum Geologists. Tulsa, OK. pp. 37-58.



                Leatherman, Stephen P. (1984). Cliff stability along western Chesapeake Day, Maryland. MTS Journal, 20, pp. 28-

                36.




                Olsson, Richard K., Thomas G. Gibson, Harry J. Hansen, and James P. Owens (1988). Geology of the northern
                Atlantic coastal plain: Long Island to Virginia. in The Geology of North America, Volume 1-2, The Atlantic
                Continental Margin: U.S., Robert E. Sheridan and John A. Grow (editors). The Geological Society of America.
                pp. 87-105.



                Pomeroy, Jack (1990). Landsliding and Erosion Along the Calvert Cliffs: A Report on Recent Observations in the
                Southern Part of the Cliffs, Calvert Marine Museum Quarterly Newsletter, v. 14, no. 4.



                Quigley, R.M., P.J. Gelinas, W.T. Bou, and R.W. Packer (1977). Cyclic erosion-instability relationships: Lake
                Erie north shore bluffs. Canadian Geotechnical Journal, 14, pp. 310-323.



                Slaughter, T. H. (1949). Historical Erosion Maps, Maryland Geological Survey.










                                                                      53



                                                                                                   M MIMI M M M M







                                                                                 Tablo 1 - Physical Characterislics of CCSEP sftes and subsitos


                                                                        Site Name                  Site    Shorelinel SIM HeigbtMxpe              Toe            Long-            Slope Type
                                                                               Subsite Num         Nwne Drient"                                   At.Ct.         shore
                                                               (listed from north to south)        Abbrv.                                                        Ban


                                                                  Navel Resemh Lab                 NRL


                                                                                RArKUC Cliffs      RC           E                                 None           Yes                      IV


                                                                  Naval Research LAb North         NRLN       ENE          Ig.34130-90            Seawall        No                       I


                                                                  Naval Reseerch lAb South         NRLS       ENE          30-32 /30-90           seawall        No                       I

                                                                              Holiday Beach        HB         EING          20-34/70              None           Yes                      IIIA


                                                                     Sclenth" Cuffs                SC


                                                                          Parka Creek South        PCS        ENE          15-30/50-90            None           Yes              IV and IIIA


                                                                       Scientists Cliffs North     SCN        ENE          15-29 /45-60           Beach          yes                      IIIA


                                                                       Scientists Cliffs South     SCS        ENE          20-29135-60            Beach          Yes                      I


                                                                               Cxrmmor Run         GR         ENE          19-36 150-90           None           Yes                      IIIA


                                                                Calvert CUM State Park             CCSP

                                                                                 Roc!@j Point      RP                      15-35/65-85            None           No                       1118

                                                                         Gmver Creek North         GVCN       NE           12-19150-60            None           No                       IIIA

                                                                         Graver Creek South        GVCS       NE 1         15-30/50-60            None           No              HIA and IIIC

                                                                          Grays Creek South        GYCS       ENE          15.25 /5o- 6o          None           No                       TV


                                                              Chesapeake Ranch Estates             CRE

                                                                          Cove Point Hollow        CPH        ENE          10-25/30-90            None           Yes             UlAj" IIIC

                                                                            Uttle Cove Point       LCP    NE.E.ESE         16-22 /30-60           None     .     Vague                    11

                                                                               Lararnie Law        LL         ESE          M35 / 40-90            None           Yes                      111C
                                                                     Driftwood Beach South         DBS        SE           16-22 / "              .None          Yes                      111C

                                                                      Seahorse Bewl North          SBN        SE           12-30 16"!             None           vague                    RIC



           I                                                                       M M
 Eli M M M MM








                                                   Table 2 - CCSEP Experiments


                            NAVAL RESEARCH LAB      SC1E?f11STS CLIM'      C. C. STATE PARK      CHES. RANCH ESTATE:S
          Experiment          RC NRLNINRLS HB       PCS SCN SCS GR         RP GVCN GVCS GYCS CPH I LCP LL I DBS SBN
      MATERIAL PROPERTIES              I                                                             I          I

                                                     X                X
                                                                            X               X
                                                X    X
                                                X
                                                                                                  X
                                                     X                                            X
                                                                                                        X           X
          SLOPE HEIGHT                                                                                  X                X
                              )0(


                                                           X     X
                                                                      M          X     X
      SHOREUNE PROTECTION                                                                                           X    X
                               X    X
                                          X      X   X     X
     SHOREUNE ORIENTATION                                        X    X

                                                                                                     IM




I
I
I
I
I
I                    Appendix A
I
I
I
I
i
I
I
I
I
I
I
 -1
 -I








              Table Al:       Sedimentological parameters             split spoon samples
                              collected January 23-31, 1991           Navy Research Lab



                       Depth to top                                                      Weight
                Well      of sample     Water     Sand      Silt      Clay Shepard's       loss
               number     (ft)     (m)    M       M         M         M        class         M



                 NRLI       3.0    0.9  17.18     44.75     21.19     34.06    SaSiCl      9.53
                 NRLI       8.0    2.4  10.72     56.15     24.85     18.99    SiSa        8.41
                 NRL1     13.0     4.0  17.10     57.84     21.31     20.85    SaSiCl      9.12
                 N`RL1    18.0     5.5  22.92     70.20     14.45     15.35    ClSa        0.79
                 NRLI     23.0     7.0  34.09     57.26     22.77     19.97    SiSa        8.00
                 NRL6     25.0     7.6  31.00     56.12     24.80     19.08    SiSa.       6.75
                 NRLI     28.0     8.5  35.70     50.87     26.39     22.74    SaSiCl      9.12
                 NRL1     33.0   10.1   46.34     21.34     50.79     27.88    SaSiCl      9.30
                 NRL1     38.0   11.6   26.64     74.91     14.15     10.94    SiSa       11.93
                 NRLI     43.0   13.1   37.54     40.68     29.01     30.31    SaSiCl     15.56
                 NRL1     48.0   14.6   26.98     95.57       3.21     1.21    Sa         24.66
                 NRLl     53.0   16.2   26.02     87.86       8.63      3.51   Sa         10.31
                 NRL1     58.0   17.7   33.35     77.37     11.87     10.76    Sa.         4.74
                 NRL1     63.0   19.2   37.32     59.85     22.13     18.02    SiSa        9.63
                 NRL1     68.0   20.7   36.21     62.58     20.28     17.14    SiSa       13.23
                 NRL1     73.0   22.3   32.28     77.42     11.71     10.87    Sa          5.16
                 NRL1     78.0   23.8   31.27     69.64     17.84     12.52    SiSa       12.69
                 NRLI     83.0   25.3   32.73     40.32     35.63     24.06    SaSiCl     13.12
                 NRL1     88.0   26.8   37.57     19.65     48.07     32.28    ClSi       13.54








             Table A2:    Sedimentological parameters          split spoon samples
                          collected January 14-17, 1991        Scientists' Cliffs



                     Depth to top                                                Weight
              Well     of sample    Water    Sand     Silt     Clay Shepard's     loss
             number (ft)       (m)    (t)    (%)      M        (%)     class        M



              SC1      5.0   1.5    14.11    83.98    11.22    4.80    Sa         1.92
              scl    15.0    4.6    27.95    51.45    26.92    21.62   SaSiCl     ----
              SC1    20.0    6.1    13.90    $8.02     4.77    7.21    Sa        47.81
              SC1    25.0    7.6    13.90    91.oo     4.65    4.35    Sa        35.49
              SC1    30.0    9.1    23.43    83.56     7.64    8.80    Sa         3.73
              SC1    35.0   10.7    25.06    77.46    12.26    10.28   Sa        12.18
              SCI    40.0   12.2    29.22    64.04    17.82    18.14   ClSa       7.53
              SC1    45.0   13.7    29.68    43-99    32.36    23.65   SaSiCl     9.83
              SC1    50.0   15.2    28.44    25.66    40.08    34.26   SaSiCl    15.83
              SC1    55.0   16.8    14.76    82.70     8.47    8.83    Sa        32.49
              SC1    60.0   18.3    15.50    92.32     3.63    4.05    Sa         8.49
              SC1    65.0   19.8    19.31    93.74     4.89    1.37    Sa        13.61
              SCl    70.0   21.3    21.89    93.66     4.53    1.81    Sa         9.86
              SC1    75.0   22.9    26.74    66.30    14.96    18.74   ClSa      13.96
              SC1    80.0   24.4    24.13    75.71    10.92    13.37   Sa         7.94
              SC1    85.0   25.9    25.04    79.70    12.34    7.96    Sa         8.59








              Table A3:    Sedimentological parameters - split spoon samples
                           collected December 17-20, 1990        Calvert Cliffs State
                           Park




                      Depth to top                                                Weight
                Well    of sample    Water    Sand     Silt     Clay Shepard's      loss
              number (ft)      (m)     M      M        (t)      M        class        M



              CCSP1     5.0    1.5     3.01   86.19      7.20    6.61    Sa         2.83
              CCSPl   10.0     3.0   14.69    16.08    41.73    42.19    SiCl       6.95
              CCSP1   15.0     4.6   16.09    41.52    33.52    24.97    SaSiCl     2.24
              CCSP1   20.0     6.1   11.47    70.66    12.85    16.48    ClSa       2.06
              CCSP1   25.0     7.6   18.87    81.15      9.61    9.24    Sa         2.36
              CCSP1   30.0     9.1   18.48    78.76    11.16    10.08    Sa         3.02
              CCSP1   30.8     9.4   20.16    79.99    11.06     8.94    Sa         3.53
              CCSPl   35.0    10.7   22.18    79.58    12.18     8.24    Sa         2.41
              CCSP1   40.0    12.2   22.58    19.59    35.28    45.13    SiCl       6.20
              CCSPl   45.0    13.7   19.08    28.08    30.63    41.29    SaSiCl     9.49
              CCSPl   50.0    15.2   18.78    25-91    29.05    45.04    SaSiCl    11.40
              CCSP1   55.0    16.8   23.19    21-18    39.00    39.82    SaSiCl    13.39
              CCSP1   60.0    18.3   21.82    38.65    39.14    22.20    SaSiCl     7.80
              CCSP1   65.0    19.8   23.00      3.15   70.26    26.59    ClSi       7.77
              CCSPl   70.0    21.3   26.42    10.97    44.70    44.33    ClSi       9.26
              CCSP1   75.0    22.9   19.60    87.64      5.79    6.57    Sa        11.80








             Table A4:     Sedimentological parameters - split spoon samples
                           collected December 6-10, 1990 - Chesapeake Ranch
                           Estates




                      Depth to top                                               Weight
               Well     of sample    Water    Sand    Silt     Clay Shepard's      loss
             number (ft)        (m)   M       M       M        M        class        M



               CRE1     4.5   1.4    10.58    48.62   38.69    12.70    SiSa       5.69
               CRE1     9.5   2.9     5.46    90.62     3.95    5.43    Sa         1.68
               CRE1   14.5    4.4     4.97    93.91     3.21    2.87    Sa         1.64
               CRE1   19.5    5.9     5.95    94.36     2.49    3.16    Sa         1.64
               CRE1   24.5    7.5     5.58    94.13     2.47    3.40    Sa         1.69
               CRE1   29.5    9.0    10.89    92.80     1.70    5.50    Sa.        3.13
               CRE1   34.5   10.5    11.05    88.75     5.46    5.80    Sa         3.06
               CRE1   39.5   12.0    12.07    92.78     3.64    3.59    Sa         2.52
               CRE1   44.5   13.6    13.23    80.72     7.99   11.29    Sa         5.10
               CRE1   49.5   15.1    14.58    65.09   17.84    17.07    SiSa       3.48
               CRE1   50.0   15.2    26.57    10.27   30.10    59.62    SiCl       5.74
               CRE1   50.5   15.4    19.28    47.42   25.23    27.35    SaSiCl     7.93
               CRE1   54.5   16.6    13.31    69.99   14.89    15.12    ClSa       6.40
               CREI   59.5   18.1    17.83    75.63   10.94    13.43    Sa         7.09
               CRE1   64.5   19.7    20.60    69.95   17.82    12.23    SiSa       4.18
               CRE1   69.5   21.2    19.68    53.27   33.06    13.67    SiSa.     23.07
               CRE1   74.5   22.7    20.31    77.37   16.47     6.16    Sa        34.62
               CRE1   79.5   24.2    20.65    32.89   49.67    17.43    SaSi       9.94
               CRE1   84.5   25.8    22.73      5.00  38.02    56.98    SiCl      15.08












                                         FIGURE 2.1 STUDY SITE LOCATIONS:
                                     CALVERT CLIFFS SLOPE EROSION PROJECT
                                          \ANNE   .ARUNOEL lk.
                                     4         C UNT                   MARYLANO

                                                 260


                                                              CHESAPEAKE
                                                              '.BEACH

                                                      Naval Research
                                                       LabQrato


                                                             261
                                                           263    .:BREEZY POINT

                                                             402




                                                     wilsoo

                                         PRINCE
                                         FREDERICX
                                           231               -LQMI!    Cliffs e

                                                        00    2
                                                          d'   4






                                                                               Cal ert Cliffs
                                                                               State Park

                                                                                           COVE
                                                                                           POINT
                                  N
                                                        CIO&

                                                                               Ranch Estates

                                 0         3 ml
                                                                         LSOLOMONS
                                 0          51(m
                                                                       M ARYLAfNO
                                                                     AKE
                                                                   4P @E






                                  Figure 3.1 Study Site NRL:
                                  Naval Research lAboratory



                              0












                                              BeaCh
              tPo ars
                                                  Randle Cliffs (RC)

                           00
                                      Lot

                                                Randle Cliff
            \'A X,                              -Beach
                        @0_

                                                      Naval Research
                                      \111'  t
                                                     Lab North (NRLN)
                                       <
                                                  ayy


              _Ar
                                     'j


                                         V.             Naval Research
            "wo
                                                      Lab South (NRLS)

                                                     8 m
                                                     9
                                                      Locust Grove
                                                      Beach


                     G"
                                                        Holiday Beach (HB)
                                                   op
                   IV
                        Wwl
                       16 MILS



                                      \0
              UrM GRID AND 1987 MAGNETIC NORTH           Camp
                                                         Roosevelt
              DECUNATION AT CENTER OF SHEET



                                          V.

                                       SCALE 1:24 000


                                            MILES
               low   0    I=   "m    m    4= - 5=    ww                   10=

                   1                 0     KILOMETERS 1
                  1000               0      METERS   low               2000












                                                  Figure 3.2a Randle Cliffs North Slope Profile



                      35





                      30



                                                               Line showing angle of slope

                      25






                      20
                 Z            Seepage zone


                  ca
                      15






                      I v






                        5



                                                                                                      mean high tide
                        0  - -------------------------------------------





                        5

                            0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                                                 Distance from slope toe (m)












                              Figure 3.2b Randle Cliffs South Slope Profile



             35





             30





             25



                              Seepage zone

             20 --

          Z




             15






             10






               5




                                                               mean high tide
               0   --------- ---------------------------------





               5

                 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                       Distance from slope toe (m)











                              Figure 3.2c Naval Research Laboratory Slope Profile



               35





               30





               25

                                                            Seepage zones


               20

            Z




               15





               10                                               OP

                                                           01


                                                                  Possible limits of intact slope material

                 5

                              Slope debris                             rnean high tide
                 0   ---------------    0-----------------------------



                 5

                   0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                                           toe
                                            Distance from slope (m)









                                                                                                                           Figure 3.3: Naval Research Lab Geotechnical Profile




                  30.00                                                                                                                                                      30.00-
                                                                     WELL
                                                                  LOCATION                                                 SoH horizons and mot zone-,                                         GRAIN-SIZE                                  FIELD SPT                              PERCENTLOSS
                                                                                                                           moist, brown. sandy, silly clay                                   DISTRIBUTION                              BLOW COUNT                                 HC1 DIGESTION


                                                                                                                           Molst to dry, tan, silly. clayey
                  25.00                                                                                                                                                      25.00..
                                                                                                                           fine sand with layers of
                                                                                                                           ox,d                                  M
                                                                                                                              ized Iron                                 'X"



                                                                                                       Moist. tan, fine sand with traces of sift and


                                                                                                                           Moist, taM silly. clayey.
                  20.00                                          u                                                                                                           20.00--
                                                                                                                           fine sand with layers odf
                                                                                                                           oxidized Iron                                                   Sand

               (5                                                                                                                                                                                       Sift
               Z                                                              Intermittent                         Moist. gray-green. clayey, sandy sill
               Lu                                                                     Seep                                 Dry. gray-green, silly. sandy
               >                                                                                                           clay VAh usces 01 sheft
               0  15.00                                                                                                    Dry. gray, silly. s-an*cly clay                   15.00.
               M                                                                                                                                                                                                    Clay
               <                                                                                                           with sparse shall lenses
               E                                                                                                           Saluraded shell bed In gray
                                                                                                                           sand matrix - sorne sift present
               Z
               0                                                                        Permanent
                                                                                                Seep
               4  10.00                                                                                                                                                      10.00--
               >                                                                                                           Mist, gray-green, sIfty,
               LLI                                                                                                         clayey sand with sparsely
                                                                                                                           scatterd lenses of shags -
                                                                                                                           shells slightly more dense
                                                                                                                           nw base
                                                                       Water level in test wells,
                                                                       February 28, 1991
                     5.00                                                                                                                                                       5.00..
                                                                                                                                                             -le
                                                                                                                                   Dry. green. clayey,
                                                                                                                                   sandy sift with sparslay
                                                                                                                                                         as
                                                                                                                                   scattered shell leris :@@
                                                                                                              Dry, gre"ray, clayey slit with =.y
                                                                                                              scattered shell lenses In fine as          drix
                     0.00                                                                                                                                                      0.00
                          7o.oo        60.00       50.00        40.00        30.00       20.00        10.00          0.00      10.00         20.00                                           20 40 60 80                        5      10 15 2 0 2 5 3 0 0                        5      10 15 20 25
                                                                                                                                                                                          CUMULATIVE PERCENT
                                                    DISTANCE FROM CLIFF BASE (m)







                                                                                          re 3.4 Study Site SO
                                                                                 jFip                        CUM
                                                                                          Scientlsts'@@

                                                                    Y;



                                                                                                    WO I








                                                                                                                      /00



                                                                                                                                            Parker Creek
                                                                                                                                            South             (PCs)


                                                                                                00                                              Scientists
                                                                                                                                              Cliffs North
                                                                                                                                                   (SCN)



                                                                                                                                               Scientists
                                                                                                                                              -Cliffs




                                                                                                    kr-





                                                                                                                    IZ,3#

                                                                                                                                                                 Scientists
                                                                                                                                                               Cliffs South
                                                                                                                                                                     (S C S)

                                                lip
                                            178 MILS        O*W
                                                          le MILS
                                                                                                                                                                      Governor
                                                                                                                                                                      Run         (GRII
                                   UTM GRID AND igs MAGNETIC NORTH
                                     DECLINATION AT CENM
                                                                 I OF SHEET                                                                                   V
                                                                                                                                                                    :U


                                                                                                SCALE         1:24 000

                                                                                                             0
                                                                                                           MILES
                                       1000          0           1000        20M          3DOD       40DO        5000         6000         70M         ww          9DOO         IDWO
                                                                                                           FEET
                                                                                          0            KILOM       S_            I                                       J
                                              1000                                        0              M ERS                  1000












                                    Figure 3.5a Parkers Creek Slope Profile



               35





               30





               25





               20



                            Seepage zones

               15






               10





                 5




                                                                      mean high tide
                 0   -------------------------------------------





                 5

                   0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                       Horizontal distance along slope profile (m)












                                  Figure 3.5b Scientists' Cliffs North Slope Profile



               35



               30                                 Line showing angle of slope



               25





               20

            Z

                             Seepage zones
            Cd
            W
               15





               10





                 5




                                                                                  mean high tide
                 0        ---------------------------------------------





               -5

                    0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                         Horizontal distance along slope prorile (m)












                                     Figure 3.5c Scientists' Cliffs South Slope Profile



                35 --





                                                                 Line showing angle of slope
                30



                25                                                                    Z




                20
                                        Seepage zones
             Z




                15





             P.
                10

                                 Z                0, 0,         Possible Emits of intact slope material

                  5


                               Slope debris 0
                                         00                                            mean high fide
                   0 -------------       -------------------------------------





                   5

                     0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                                  Distance from slope toe (m)












                                                 Figure 3.5d Governor's Run Slope Prorile



                    35



                    30                                 Line showing slope angle



                    25




                                            Seepage zones
                    20

                Z




                    15






                    10






                       5




                                                                                                              mean high tide
                       0           @4 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -




                       5

                          0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                                      Horizontal distance along slope profile (m)








                                                                                                   Ficiure 3.6 Scientists' Cliffs Gegtechnical Profile



              30                                                                                                                             30.0
                                           WELL                                                                                                             GRAIN-SIZE                        FIELD SPT                      PERCENTLOSS
                                        LOCATION                                                                                                          DISTRIBUTION                     BLOW COUNT                        HCI DIGESTION

                                                                                            Soil horizons and root
                                                                                            zone; dry, orange,
              25                                                                            silty, very fine sand                            25.00-
                                                                                            Dry, tan, fine sandy clay
                                                                                            Moist, gray, silty, sandy da


              20                                                                            Moist to dry shell bed with                      20.00
                                                                                            brown, medium sand matrix


                                                                                          Dry, brown, medium sand
                                                   intermittent
          >                                                                                                                                              SAND
          a                                              Seep                               Dry, gray, silty sand
          Z   15                                                                            with some clay                                   15.00--
          LU
          0                                                                                 Dry, gray, clayey. sandy Silt                                       SILT
                                                                                                                                                                         CLAY
          E   10                                                                            Moist shell bed with brown,                      10.00--
                                                                                            medium to fine sand matrix
          Z                                      Water level in ten wells,
          0                                      March 25, 1991                                                                .......
                                                                                            Moist, gray-green to               .......
                                           N                             j
          4                                                                                 onve-green, medium to fine
          >                                                                                 sand - saturated at base
          W                                                                                                                    ........
          _j    5                                                                                                             1::::::::        5.00--
          LU                                                          Permanent
                                                                            Seep            Dry, greenish-gray, clayey,
                                                                                            silty, very fine sand



                0                                                                                                                             0.00
                                                                                            Dry, dark gray, silty,
                                                                                            very fine sand



                5 -F-                                                                                                                        -5.00          i
                                                                                                                               $00
                                                                                                                                  . On;
                                                                                                                               :0-



                   so              so               40              20                0              20              40                                    40     60      80          5 10 1 5 2 0 25 30 3 5 0               10 20 30 40 50
                                                                                                                                                      CUMULATIVE PERCENT
                                         DISTANCE FROM CLIFF BASE (m)







                                                                Figure 3.7 Study Site CCSP:
                                                                  Calvert Cliffs State Park






                                                A



                                                                       Rocky Point (RP)



                                                                              Grover        Creek North (GVCN)



                                                                                        iGrover Creek              South (GVCS)
                         TV


                                                                                                Grays Creek             South (GYCS)







                                                                                                         21








                                                                                20

                                                                                                                       178 MIL     (m.
                                                                                                                                 16 MILS




                                                                                                                 LITM GRID AND 1987 KAGNETIC: NORTH
                                                                                                                  DECLINATION AT CENTER OF SHEET




                                                                            SCALE       1:24 000

                                                                                       0
                                                                                     MILES
                                1000       0        1000     2000      3DW       4WD       50W       6DOO      7000               9000      10000
                                                                                      FEET
                                       I               S               0          KILOMETERS            1                               2
                                     low                                            METERS             low                             2WO
                                                                                                                                             dm












                                 Figure 3.8 Gray's Creek South Slope Profile



              35





              30






              25





              20

           Z



              15           Seepage zone





              10 --



                5    Slope debris

                                       Possible limits of intact slope material

                                                                      mean high fide
                0    --------   -----------------------------------





                5

                  0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                      Horizontal distance along slope profile (m)








                                                                                                                        Figure 3.9 Calvert Cliffs State Park Geotechnical Profile


                                                                             WELL
                 20.00 -                                                  LOCATION                                                                                      20.00-
                                                                                                           Soil horizons and root zone;                                                    GRAIN-SIZE                                   FIELD SPT                             PERCENTLOSS
                                                                                                           moist, orange-brown, med. sand                                  Grav?l DISTRIBUTION                                       BLOW COUNT                               HCI DIGESTION
                                                                                                           Slightly moist, tan, medium
                                                                                                           sand with traces of pea gravel
                                                                                                           & tralces of stiff white clav

                                                                                                           Slightly moist, light gray, silty
                 15.00                                                                                     clay with lenses of coarse sand                              15.00--


                                                                                                                     Moist, light gray/tan,
           >                                                                                                         mottled, silty, clayey fine
           a                                                                                                                        orninantly
           Z                                                                                                                         saturated at
           W                                                                                                                      nit
           0     10.00                                                                                                    aturated, dark gray, -                        10.00..
           00
                                                                                                                        fine sand with traces                                          Sand
                                                                                                                        of silt and clay
           E                                                                                       Permanent
           Z                                            I                                                  Seep
           0                                                                                                                      Slightly moist,                                           Silt           Clay
                                                                                                                                  gray silty day
           4                                                                                                                           1 -
           >                                                                                                                      with tenses of
           W       5.00 --                                                                                                        fine sand                                5.00--
           _j
           W                                     Li


                                                                             Water level in test wells
                                                                             March 25,1991



                    0.00                                                                                                                                                  0.00.
                                                                                                           Slightly moist, gray, clayey silt
                                                                                                           with traces of fine sand
                                                                                                                     sand (pred
                                                                                                                     fine sand
                                                                                                                     base of u

                                                                                                                        S


























                                                                                                                                                         .................
                                                                                                           Saturated, gray, very fine sand
                                                                                                           with traces of shells                        ..... ................
                                                                                                                                                         .................

                                                                                                                                                         ..................
                 -5.00                                                                                                                                                  -5.00-           i
                          70-00        60.00          50.00         40.00         30.00          20.00          10.00         0.00         10.00                                        20 40 60 80                         5 10 15 2 0 2 5 3 0 3 5 4 0                      4      6     8 10 12 14
                                                                                                                                                                                    CUMUIATIVE PERCENT
                                                  DISTANCE FROM CLIFF BASE (m)







                                                                              Figure 3.10 Study Site CRE:
                                                                               Chesapeake Ranch Estates




                            so


                                                                                                                                             cove Point
                                                                                             INT                                                     w (CPH)
                                                                                                                                          Hollo



                                              Fn

                                                                                                                                               Little       Cove

                                                                                                L
                                                                                                                                             Point          (LCP)



                                                                                                                                        ramle Lane (LL)





                                                                                                             Driftwood Beach South                                 (DBS)


                                                   IN




                                     U






                                                                                                                                                        G14




                                                                                                                                               178 MILS
                                                                        Seahorse Beach                       North (SBN)



                                                                                                                                       UTM GRID AND 1907 KAGNETIC NORTH
                                                                                                                                         DECLINATION AT CENTER OF SHEET




                                                                                            SCALE        1:24 000


                                                                                                      MILES
                                    1000                     low         2000         30M        40DO        Sm          60M         7000         BOW         9DOO       10000
                                                                                                       FEET
                                                                .6                    0            KILOMETERS               1                                       2
                                           1000                                       0              METERS                low












                                  Figure 3.11a Little Cove Point Slope Profile



               35





               30





               25





               20

           Z


            W  15



                        Seepage zone

               10






                5


                                                                     mean high fide.
                0






               -5

                   0   2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

                                           Distance from slope toe (m)












                                   Figure 3.11b Laramie Lane Slope Profile



              35





              30





              25
                                               Seepage zones



              20

           Z




              15






              10



                                                             Possible limits os intact slope material
                5

                                         Slope debris

                                                                            mean high tide

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









                5

                   0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
                             /-000000


                                      Horizontal distance along slope prorde (m)








                                                                                                           Figure 3.12 Chesapeake Ranch Estates Geotechnical Profile



                35.00 -
                                                                                                                                                                 35.00
                                                                                                                                                                                  GRAIN-SIZE                                 FIELD SPT                            PERCENTLOSS
                                                                     Wei                                                                                                        DISTRIBUTION                              BLOW COUNT                              HCI DIGESTION
                30.00                                             Location                                 Soil horizons arid root zone;                         30.00--
                                                                                                           moist, brown, silly. clayey sand



                                                                                                                                                                            Gravel


          93    25.00
          >                                                                                                Moist, brown to yellow                                25.00
          (5                                                                                               brown, medium to coarse sand
          z                                                                                                with traces of pea gravel and
          LU
                                                                                                           thin clay laminations;
          0                                                                                                saturated at baze
                20.00
                                                                                                                                                  .' @@ - 20. 00

                                                                                                           Saturated, medium to
          z                                                            U                                   coarse yetiowitan sand
          0                                                                                                with lenses of-                                                         Sand
          ll-                                                  W                                     Saturated, tantye5ow, silly sand
          *     15.00 -                                                              Permanent             Slightly moist, tan/gray clay                         15.00
          W                                                                                 Seep                Interbedded sands & clay
          .j
          Ul                                                                      Moist, dark gray, very clayey, silly, very fine sand

                10.00 -                                                                                                  Moist. gray, silly,
                                                                                                                        Clayey. fine sand                        10.00-.

                                                                  Waftr level in test wells,
                                                                  March 25, 1991                           several saturated cydes of shell                                                     Slit
                                                                                                           fragments In fine sands lining
                                                                                                           uPwards to she 1-tree sills
                   5.00                                                           Permanem
                                                                                        Seeps                                                                       5.00..
                                                                                                           Moist. gray. clayey SIR with a                                                           Clay
                                                                                                           0.2 m thick bed of shells In a
                                                                                                           saturated, very fine sand matrix



                   0.00                                                                                                                                            0.00
                        70.00          60.00           50.00          40.00           30.00           20.00           10.00            0.00                                     20 40 60 80                        0     10 20 30 40 50 60 0 5 10 15 20 25 30 35
                                                DISTANCE FROM CLIFF BASE (m)                                                                                                CUMULATIVE PERCENT
                                                                                                                                 s
                                                                                                                          "u a

                                                                                                                            ow
                                                                                                                              n   and


                                                                                                                                    y
                                                                                                                                        sent
                                                                                                                                                d

                                                                                                                            tan  gray   .1"Y
                                                                                                                          ad sands    &         -lay

                                                                                                                         hy,  very   fl..       -and
                                                                                                                         @Pojst.gr
                                                                                                                                    sy,         silly.
                                                                                                                          I.Y.Y. firt. and







                             Figure 4.1 - Classification of coastal slopes by undercutting rate and characteristic groups of erosion mechanisms



                                                                                 upper slope             upper slope          upper slope        upper slope




                                                                    midslope                   niidslope               midslope                 midslope






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

                                                 lower slope                     lower slope                 lower slope                   lower slope


                              32 - 40 degrees                               40 - 52 degrees                52 - 65 degrees                 65 - 90 degrees
                                    ------------------ ----           --- -----------               ---- ------------               --- ----------------



                               Type I                                  Tylle 11                          Type III                            T112e IV
                               R b=     0                             R b  << R   M                      R b  < R   M.                      R b   = R  M.
                     Slope debris accumulates at                  Hydrologic processes            Wave undercutting drives             Wave undercutting
                     base of slope. Midslope eroded               dominate erosion of both        shallow sliding and spalling         directly controls erosion
                     by groundwater seepage and                   lower and midslopes             in lower slope. Erosion of           of the entire slope via
                     direct runoff of precipitation                                               the midslope driven by               shallow and deep-seated
                                                                  Sites: SCN, LCP                 hydrologic processes.                landslides and spalling
                     Sites: NRLN, NRLS, SCS                                                       Midslope recession
                                                                                                  proceeds more rapidly than           Sites: RC, PC, LL
                                                                                                  lower slope recession.
                     R b: Rate of recession of the lower slope                                    Sites: HB, GR, GCS
                     RI.: Rate of recession of the midslope








                                                 Figure 6.1 Distribution of Coastal Plain Sediments
                                                         Around the Chesapeake Bay

















                                            Legend

                                     Potomac Group

                                     Magothy

                                     Aquia

                                     Chesapeake Group

                                     Quaternary sediments
                                bw










                                      Figure 6.2
                                         Conceptual rnodel for extending CCSEP results to predict coastal slope erosion along the Chesapeake Bay



                                                                                                                                         Predictive
                                                                Basic Input                   Data base                                  Capabilities


                                                              Slope geometry
                                                              (toe and bluff top              Classification
                                                              elevations and toe                 by t
                                                              to top angle).                                                                Erosion
                                                                                                                                         - mechanisms
                                                                                                                                         - long-term
                                                                                                                                          recession rates


                                                                                                                                     -----------
                                                                                                                                     I   Probability and
                                                                                                                                         timing of large,
                                                                                                                                         short-term events   i
                                                                                                                                         requires detailed   :
                                                              Geographic                                                                 topographic and     j
                                                              location                                                                   hydrologic site
                                                                                                                                        _!Rvestigat:12n


                                                                                              Wave/water level
                                                                                                  climate
                                                                                              (undercutting rate)


                                                                                              Slope materials
                                                                                              geotechnical and
                                                                                                hydrologic
                                                                                                 properties





























                                          . . . . . . . . . . .
                                                                              AM,




                            +













                Naval Research Laboratory        This photograph shows the boundary
                between the NRLN and RC subsites. Slope toe protection can be seen
                on the left side of the picture in the form of a bulkheiad. Where the
                toe is protected, the principal driving mechanism of coastal slope
                erosion, wave undercutting, is eliminated and the slopes are Type 1.
                Upper slope erosion will continue via hydrologic processes until a
                stable slope angle from slope toe to bluff top is achieved. Near the
                center the protection is terminated and the slopes stand nearly
                vertical. The right side of the photo shows Type IV slopes. The
                erosion of Type IV slopes is dominated by spalling and shallow   sliding
                and occurs at a rate determined by the wave undercuttind @aitd;







                                          Plate I










                                                        7 r'ZT)"WV77 'r













                                                                    7

                                                             --now
                                                                  --    ... .."'7-- 1 1 -




                          male.

















                                                                                               Ij

                                                                              f410"

                                                                               .wje-




                                                  --c-06.4     jlw-Az@-       7
                                                                                      MI, Ajok





                       Top  photograph - Scientists'  Cliffs North
                       Bottom photograph - Chesapeake Ranch Estates, Little Cove Point

                       Both slopes are Type H slopes in that the dominant erosion mechanisms from slope toe to
                       bluff top are hydrologically dominated. Note the lack of wave undercutting at each site.


                                                    Plate 2







































                                            Aj,

                                                 Ak

                                                                ""19W






                         Top photograph - Calvert Cliffs State Park, Grays Creek South
                         Bottom photograph - Calvert Cliffs State Park, Rocky Point

                         Both slopes are Type 1H slopes. HeTe, hydrologic processes control the rate of erosion in
                         the midslope and wave undercutting controls the rate of erosion in the toe zone. The contrast
                           I

































                         between the midslope and lower slope is clear in this photo; it occurs at the change from
                         dark to light material. Ironstone blocks can be seen in the foreground.
                                                       Plate 3

































                                                                                            41
                                                                                k4@

























                         Top photograph - Calvert Cliffs State Park, Grover Creek South
                         Bottom photograph - Naval Research Laboratory, Randle Cliffs

                         Both slopes are Type IV slopes. Here, wave erosion oversteepens the toe zone causing
                         sliding which retrogresses upslope until it reaches the bluff top. Hydrologic processes are
                         still active, but the dominant mechanism of erosion is shallow sliding. Note that at Randle
                         Cliffs, debris cannot accumulate at the slope base because of the water level.
                                                      Plate 4




































                                                 j.@











                                                   W
                            10                                                     4
                                                                                      7 -x
                                                                                                 Jp-






                                         jk   t


                        Top photograph   - Scientists' Cliffs, Parker Creek South
                        Bottom photograph - Chesapeake Ranch Estates, Laramie Lane

                        Both slopes are Type IV slopes. Spalling due to oversteepening by wave undercutting is
                        evident in the lower slope at Parker Creek. At Laranide Lane, large rotational slides which
                              Ing.
                                 @!3






















                        initiate on a saturated, weak clay in the n-Mslope deliver large debris piles to the slope toe.

                                                     Plate 5








































                             Calvert Cliffs State Park, Grays Creek South - This photograph is a
                             close-up of a large spalling event cause by wave undercutting. The slope is a
                             Type IV slope. The lower slope/midslope contact can be clearly seen where
                             the gray lower material meets the orange-brown material above it.









                                                       Plate 6



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