Shoreline erosion in coastal Louisiana inventory and assessment : final report to Louisiana Department of Transportation and Development

[From the U.S. Government Printing Office, www.gpo.gov]

COASTAL

RESOURCES PROGRAM

CZIC collection

Louisiana
Department of Transportation and Development

SHORELINE EROSION

COASTAL LOUISIANA.

INVENTORY

GB
459.4 --4ND ASSESSMENT
S53
1978

Shoreline Erosion in Coastal Louisiana:

Inventory and Assessment

Final Report to
Louisiana Department of Transportation and Development

George A. Fischer
Secretary

Paul R. Templet
@Coastal Zone Management Coordinator

Louisiana State University
Center for Wetland Resources

By: R.D. Adams, P.J. Banas, R.H. Baumann,
J.H. Blackmon, W.G. McIntire

August 1978

The preparation of this report was financed in part through a
grant from the U.S Department of Commerce under the provisions of
the Coastal Zone Management Act of 1972 and the Louisiana Sea Grant
Program maintained by NOAA,,U S Department of Commerce.

Notice

This document is disseminated under the sponsorship of the
Department of Transportation and Development in the interest
of information exchange. The State of Louisiana assumes
no liability for its contents or use thereof.

Table of Contents Page

List of Figures .............. ............: ...........................

List of Tables ........................................................ iii
Glossary ............................................................... iv

Chapter I Introduction .............................................. 1
Impacts of Erosion ..................................... 2
Geologic Factors Associated with Land Loss ............. 3
Shoreline Categories ................................... 6
Vegetation Units ....................................... 9
Climatic Influence on Land Loss ........................ 9
Cultural Influences on Land Loss ....................... 10
Role of the Atchafalaya River .......................... 11
Concept of Management Units ............................ 13

Chapter 2 Methods ................................................... 17
Assessment of Topographic Maps ......................... 18
Assessment of Aerial Imagery ............................ 19
Coastline Analysis ...................................... 20
Well-Defined Lakeshores and Inner Marsh Areas .......... 21

Chapter 3 Results and Discussion .................................... 24
Introduction ........................................... 24
State Summary .......................................... 24
Data Interpretation Key ................................ 30
Management Unit I-Pontchartrain-Breton Sound ........... 33
Management Unit II-Mississippi Delta ................... 41
Management Unit III-Barataria ........................... 45
Management Unit IV-Terrebonne .......................... 56
Management Unit V-Atchafalaya .......................... 64
Management Unit VI-Vermilion.@ ......................... 70
Management Unit VII-Mermentau... ....................... 79
Management Unit VIII-Calcasieu-Sabine .................. 93

Chapter 4 Current Erosion Mitigation Practices and Recommendations.. 106
Introduction ........................................... 106
Engineering Structures and their Applicability in
Louisiana .................... *'*'****'*"*..: ........ 106
Assessment of the Louisiana Coastline: Where is
Protection Justified? ................................. 112
General Management Concepts and Guidelines ............. 127

References ............................................................. 130

Appendix Shoreline Erosion/Mitigation Planning Synopses of
State Coastal Zone Management Programs .................... 134

List of Figures
Pa
ge

1. Land changes in the East Cove area of Calcasieu Lake 1952-1975 .... 8

2. Management Units of coastal Louisiana as used in this study ....... 15

3. Site locations in the Pontchartrain-Breton Sound and
Mississippi Delta Management Units ................................ 37

4. Place names in the Pontchartrain-Breton Sound and
Mississippi Delta Management Units ................................ 40

5. Land changes in the Middle Ground area 1958-1971 .................. 42

6. Site locations in the Barataria Management Unit ................... 51

7. Place names in the Barataria Management Unit ...................... 55

8. Site locations in the Terrebonne Management Unit .................. 59

9. Place names in the Terrebonne Managemen t Unit ..................... 63

10. Site locations in the Atchafalaya Management Unit ................. 67

11. Piace names in the Atchafalaya Management Unit .................... 69

12. Site locations in the Vermilion Management Unit .................... 74

13. Place names in the Vermilion Management Unit ...................... 78

14. Shoreline erosion along Grand Lake 1951-1974 ...................... 82

15. Site locations in the Mermentau Management Unit ................... 87

16. Place names in the Mermentau Management Unit ...................... 92

17. Land changes in the Black Lake Area 1952-1974 .................... 98

18. Site locations in the Calcasieu-Sabine Management Unit ............ 101

19. Place names in the Calcasieu-Sabine Management Unit ............... 105

List of Tables Page

1. Activities and-processes associated with the change of
wetlands to open water .........................................

2. Key to cross referencing index maps with basin summary
tables .......................................................... 31

3. Inner Marsh land loss categories ................................ 32

4. Relationship between barrier island erosion rates and
age of sediments ................................................ 33

5. Comparative rates of current (1950s-1970s) erosion with
Saucier (1963) for selected lakes in the Pontchartrain-
Breton Sound Management Unit .................................... 35

6. Erosion rates for sites analyzed in the Pontchartrain-
Breton Sound Management Unit .................................... 38

7. Erosion rates for sites analyzed in the Mississippi Delta
Management Unit .................................................. .43

8. Erosion rates for sites analyzed in the Barataria
Management Unit ... I............................................. 52

9. Erosion rates for sites analyzed in the Terrebonne
Management Unit ................................................. 60

10. Erosion rates for sites analyzed in the Atchafalaya
Management Unit ................................................. 68

11. Erosion rates for sites analyzed in the Vermilion
Management Unit .................................................. 75

12. Erosion rates for sites analyzed in the Mermentau
Management Unit ................................................. 88

13. Erosion rates for sites analyzed in the Calcasieu-
Sabine Management Unit .......................................... 102

14. Case history of shoreline erosion and mitigation efforts
on Grand Isle ................................................... 122

GLOSSARY

ACCRETION. Building of or increase in area of land by natural processes.

agent.
AEOLIAN. Associated with wind, which most commonly acts as a transport

BATHYMETRY. The measurement of depths of water-in oceans, seas, and
lakes; also, the information derived from such measurements.

BERM. The point on the beach that separates the foreshore from the
backshore.

BULKHEAD. Any structure or wall designed to stop bank collapse and
resist erosive forces.

CRUSTAL DOWNWARPING. A downward motion or movement of the earth's

crust.

DETRITUS.- A product of disintegration or wearing away.

DEWATER. To remove water from (such as by draining, pressing, or pumping).

EROSION. Wearing away; specifically, entrainment; detachment of particles
of whatever size or by whatever means, as illustrated by effects of
currents, water, wind, ice, etc.

such as a rise in sea level resulting from melting of continental ice
EUSTATIC. Simultaneous change of level occurring on a worldwide scale,

cover.

FETCH. Distance over which no, or negligible, obstruction interferes
with the shear effect of wind against the surface of a waterbody.

FLOTANT. Floating marsh; vegetation covered areas held together by
intertwined roots and plant debris above water or-soft ooze.

GROIN. Low, artificial wall of durable material extending from land
into water.

ISOSTASY. (Adj. ISOSTATIC). Equal weight or pressure, with reference
to part of the earth's crust.

JETTY. Structure ordinarily protruding into water, located with the
intent of influencing current direction; a wall built to confine currents,
such as at a river mouth. A more general term than GROIN or BREAKWATER.

LEACHING. The process of percolating water or other liquid in order to
remove a soluble part.

LITTORAL. Near shore. By some definitions limited to the tidal zone;
by others, to depths of 100 fathoms. A littoral current, caused by wave
action, sits more or less parallel to the shore (longshore current).
Littoral deposits accumulate in-nearshore, ordinarily shallow, water.

MACROPHYTE. A member. of the macroscopic plant life, especially of a
body of water.

MIDDEN. A refuse heap.

MORPHOLOGY. Pertaining to form or structure.

MUDFLAT. Deposit of ooze, clay, silt, etc., to water level along a
shore. If tidal range is appreciable, the flat is ordinarily submerged
at high tide.

MUDLUMPS. Elevations or structures caused by the rise of clayey material
through covering silt or sand. Known to exist only in the Mississippi
River Delta but suspected elsewhere.

OVERTOP. Pertaining to water, to move across a surface that ordinarily
confines its current or extent, e.g., over the crest of a natural levee.

PERTURBATION. Any effect that makes a small modification in a physical
or biological system.

PROGRADE. Advance (of shoreline) seaward, commonly as a result of
sedimentary accumulation.

REVETMENT. Retaining wall or facing created to prevent retreat of banks
of a stream, canal, etc.- It"may be composed of masonry, blocks of
concrete, fascine mats of trees, etc.

RIPARIAN. Relating to or living or located on the bank of a water
course (such as a river or stream) or sometimes a lake or a tidewater.

SCOUR. Mechanical wear on the bottom of a channel or bed of a body of
water, ordinarily resulting from erosion associated with turbulence and
frictional drag of currents.

SHORELINE. Boundary between land and water surface of a lake, sea, etc.

SUBAQUEOUS. Under the surface of water; submarine.

SUBSIDENCE. Lowering of the elevation of the land, a process that may
have various causes.

SWALE. A linear depression between somewhat higher surfaces.

TOPOG IRAPHY. Configuration of a surface; specifically, the surface
of the land or bottom of a water body. Characteristics depend on the
slopes present (if any) and differences in relief.

UPLIFT. The raising or elevation of an area of land relative to
sea level or to other surrounding areas. It need not be sudden
or violent.

Chapter 1

Introduction

The land area of Louisiana has increased during the past several

thousand years because land gain from Mississippi River sedimentation

processes has exc eeded processes of land loss. Recently (in terms of

geologic time) this process has been reversed, so that more land is

being lost to erosion than is being formed by sedimentation. Louisiana

is now losing more land than any other state (Gosselink and Baumann, in

press).

The concept that more land is eroding than is forming in Louisiana

is not new. It has been documented by Morgan and Larimore 1957, Gagliano

and van Beek 1970, Morgan 1973, Adams et al. 1976, and most recently by

Craig and Day 1977. Collectively these works suggest that erosion rates

have been accelerating. The accelerated erosion rate combined with the

highly dynamic nature of the Louisiana coastline area necessitate periodic

monitoring of erosion in order to identify the extent of the problem

both physically and culturally.

The objectives of this study are to develop a methodology that

would enable decision makers to:

1) Assess the extent to which shoreline erosion is presently

occurring in coastal Louisiana.

2) Determine the geographic variability of erosion rates across

coastal Louisiana and relate this to variability in the

physical and cultural environment.

3) Assess the implications of shoreline erosion on the physical

and cultural environment.

4) Designate areas for erosion control consideration.

5) Assess the.feasibility of structural and nonstructural

procedures for managing erosion along designated areas

of the Louisiana coast.

Impacts of Erosion

A basic understanding of the processes involved in erosion as found

in coastal ,Louisiana is necessary for rational management. For this

study, a broad definition of the term "erosion" will be applied.

"Erosion," as used here, includes all those natural processes that, when

active, result in the loss of vegetated areas to open water. The term

"landloss," which has.recently become popularized in the local literature

(e.g., Gagliano and van Beek 1970, Craig and Day 1977) is a more inclusive

term but can generally be used interchangeably with "erosion." "Land

loss" refers to any change of wetland vegetation to some other habitat

type. For example, the disposal of spoil on wetlands is often considered

a wetland loss but is not erosion. For the purposes of this report, the

two terms are used interchangeably, because this report is concerned

only with those wetland areas that have changed to open water.

The most obvious result of erosion is the physical loss of land.

The cumulative impact of all factors involved in wetland loss include:

(1) the loss of marsh habitat, which is an important part of nursery

grounds (this loss results in decreased productivity of sport and commercial

fisheries species); (2) decrease in fur production; (3) loss of pasture

land; (4) diminished possibilities of land use alternatives; (5) decrease

in waste assimilation potential; (6) lessened ability to act as a buffer

against high energy storms (e.g., tropical disturbances); and (7) hydrographic

changes that usually result in increased salinities, which in turn can

lead to further wetland losses. Although these changes are generally

considered culturally undesirable, they are nonetheless brought about

through both natural and cultural processes. The amount of marshland

man has intentionally changed to open water is small in relation to the

total area chan2ed. Based on Craig and Day's (1977) summary of previous

inventories and an inventory of Southwest Louisiana (Gosselink, in

press) intentional change, most of which is in the form of dredging,

accounts for approximately five to ten percent of the total loss; therefore,

direct intentional change is not the most serious factor. The indirect

loss caused by man's altering natural processes is felt to be far more

significant. Table 1 lists factors found to be associated with change

from marsh to open water. Often the change to open water is the net

result of the complex interaction of several of these factors; therefore,

the specific contribution of each component cannot be determined.

Geologic Factors Associated with Land Loss

Even,without man's activities, erosion would certainly occur along

some sections of the coast. Throughout the period when land building

forces were dominant, erosion played an important role in determining

the present morphology of the coastal area. All of coastal Louisiana

has experienced land gain but there has never been a time when the

entire area was building seaward concurrently. For example, many of the

chenier ridges in Southwest Louisiana were formed during intervals when

sediment supplies were reduced and coastline retreat temporarily replaced

shoreline progradation. Even in active delta lobes, part of the lobe is

undergoing deterioration as land is being formed in other parts.

Knowledge of the processes involved in the formation of the present

Louisiana coastal area aids in understanding much of the erosion occurring

today. Adams et al. (1976) provide an extensive summary of the geologic

Table 1

Activities and Proces,ses'Associated with the Change of
Wetlands to Open Water*

1. Wind-induced wave erosion.

2. Boat wake erosion.

3. Tidal scour (rip currents).

4. Subsidence.

a. Isostatic adjustments, e.g., crustal downwarping.

b. Differential consolidation of sediments because of textural
variability.

C. Consolidation of sediments due to weight of other features,
e.g., natural or artificial levees, spoil.

d. Eustasy (sea level rise).

e. Extraction of groundwater, oil, gas, sulphur, and other minerals.

f. Impounding and draining causing consolidation of dewatered
sediments.

5. Climatic Events.

a. Droughts.

b. Hurrican@s and other storms.

6. Biotic effects, e.g., muskrat and goose "eat-outs".

7. Marsh buggies and other wetland transportation vehicles.

8. Dredging.

9. Waste disposal.

10. Sediment diversion, e.g., dams, channelization, leveeing.

*Modified from: Adams et al. (1976) and Gosselink and Baumann, -in press.

setting of the Louisiana coast as well as a fairly extensive bibliography

leading to more detailed information. The reader is referred to the

above publication if more detail is required than is contained in this

report.

Throughout the Quaternary period, South Louisiana was the recipient

of tremendous quantities of sediments. The weight of these sediments

upon the crust of the earth has.caused isostatic adjustments. South of

a line approximated by Interstates 10 and 12 the coast is down@Warping

(sinking), but northward there has been uplift.

Occurring contemporaneously with coastal downwarping has been the

worldwide eustatic rise in sea level. This rise has been particularly

apparent during this century (Hicks and Crosby 1974). These two phenomena

have the same effect; that is, the land appears to sink in relation to

the level of the water. Both processes are assumed to occur at about

the same rates throughout coastal Louisiana.

The marsh surface must accrete vertically by accumulating organic

and inorganic sediment in order to keep pace with subsidence and sea

level rise. Areas with vigorous,stands of marsh vegetation have obviously

been able to maintain their elevation with respect to Mean Sea Level.

Other areas where vegetation has not remained viable have opened up into

ponds that gradually enlarge to form small lakes and irregular embayments.

These areas lose their potential to trap sediment, and subsidence and

sea level rise combine with the other factors outlined in Table 1 to

accelerate the erosion process.

Within the sedimentary sequences deposited by the Mississippi

River, textural (grain size) variability can be significant.

These sediments are geologically young and unstable. As

additional sediments are deposited, differences in grain size from

one area to the next can lead to differences in compaction rates.

The thickness of these sediments is another factor to be

taken into account when considering management alternatives.

Generally, the thicker the sedimentary sequence, the more potential

there is for subsidence. The impounding of marshes in Southeast

Louisiana is not practical because of the thick sequence of sediments

that often exceeds 100 meters in depth at the coastline. In contrast,

impounding in Southwest Louisiana, where the depth of Recent sediments

averages 7 to 8 meters at the coast, has been moderately successful.

Shoreline Categories

An understanding of the complexity of shoreline erosion can be

aided by a consideration of shoreline types.. Certainly the shoreline

bordering a fresh marsh lake, for example, would be expected to have a

different rate of erosion than a barrier island shoreline at the coast.

This report categorizes shoreline types into three categories: (1)

coastline, (2) well-defined lakeshores and bays, and (3) inner marsh

areas. The categories are presented and analyzed separately for each

management unit.

One would expect that well-defined lakeshores and bays would have

lower rates of er osion than the coastline that helps to protect these

inner areas. Thus the separation of these two categories was based on

the belief that there is a significant difference in the energy working

on the shorelines of these two broadly based categories. Results of this

study indicate that, in general, rates of shoreline erosion at the coast

are several times gre@ter than erosion rates of lakes and bays landward

of the coastline. Results of the analysis of these two categories are

reported in the form of linear retreat rates.

If one were to add the total losses attributable to erosion of the

coastline, lakes, and bays to thearea of dredged canals in wetlands,

and then to compare this, rate of loss to that reported by Gagliano and

van Beek (1970), one would find that these losses only amounted to ten

to twenty percent of the total wetland loss to open water. Thus, most

of the wetland loss is occurring within broad marsh areas that have

poorly defined shorelines. Consideration of these areas is necessary if

one is to fully evaluate the extent of land loss. Changes in these

inner marsh areas, however, cannot be evaluated in terms of linear

retreat. -For example, during the first time period examined, an example

site may have consisted of continuous marsh but in the second time

period, ponds may have developed. The absence of an initial shoreline

for comparison makes measurement of linear retreat extremely difficult.

A second example quite common in coastal Louisiana is that of an area

that consists of many small ponds during the first time period but

undergoes deterioration, which results in the coalesence of these ponds

into one lake. Figure 1 representin g changes in a marsh area along East

Cove on Calcasieu Lake illustrates the complexity of trying to measure

linear retreat for inner marsh areas.

In contrast to linear measurements of inner marsh,areas, measuring

the area of marsh versus water is a simpler task. The sample sites,

however, vary in size, so to make them comparable, the data are presented

as a percentage change. This is referred to as the change in the land/water

ratio, a concept that was originally devised by Gagliano and van Beek

(1970).

1952

P,S%e%3
C

C-

@.7

OPEN WATER

1975 MARSH

L Y'S
CALCXS%f-U

.4,

LA_

SCALE

0 2km

Figure 1. Land Changes in the East Cove area of Calcasieu Lake 1952-1975.

Vegetation Units*

Much of the environmental data, particularly biotic data, is presented

by vegetation type. Also, Gagliano and van Beek's (1970) analysis of

land loss is presented in several manners, one of them being by vegetation

type. For comparison, the sample sites used in this study have been

divided into vegetation types. All references to vegetation type used

throughout this report ar e mode led after Chabreck (1972) unless noted

otherwise.

Climatic Influence on Land Loss

The major role of climate with respect to land loss is the input of

energy. Tidal energies along coastal Louisiana are low, with tidal

ranges seldom exceeding one meter. These tides cause significant land

loss only in localized areas of tidal passes at the mouths of the estuaries.

The additional input of wind allows for wave development, and the changing

of wind direction (e.g., passage of a cold front) causes water movement.

Both of these components of wind energy can lead to erosion.

Normally occurring infrequent climatic events such as tropical

disturbances and droughts can lead to erosion. Tropical disturbances

are high,energy events that bring about direct physicalremoval of

wetlands and can indirectly destroy wetlands through the introduction of

saline waters in normally freshwater areas. The increased salinities

can cause "die-backs" and the subsequent destruction of root systems.

Without an extensive root system to bind the sediments, they are subject

to erosion from normal energy flow regimes.

Prolonged droughts are thought to contribute to land loss in two'

ways: the lowering of the water table may result in lethal concentrations

of salts, and compaction of sediments may occur in the relatively thin

dewatered layer.

Cultural Influences on Land Loss

With the exception of dredging, man's actions as an agent of the

conversion of wetlands to open water are largely unintentional. Boat

waves can cause physical removal of sediments, especially where unstable

spoil sediments border the waterway. This removal in turn can lead to

high maintenance dredging costs.

The extraction of oil, gas, and groundwater from the subsurface is

known to result in subsidence. Little, if any, widely distributed

documentation of this process/response relationship is available for

Louisiana. In the Houston-Gaiveston Bay area however, it has been the

subject of rather intense investigation (e.g., Kreitler 1977). The'

extraction of groundwater, oil, gas, or other minerals results in the

compaction of overlying interbedded muds, and this is translated to the

surface as subsidence.

Althoug-h the above practices have undoubtedly contributed to the

overall problem, it is felt that the most significant impact man has and

will have over the long term is his alteration of natural sediment

dispersion. From a macroscale perspective, whether there is a net gain

or loss of land is largely dependent on the balance between sediment

supply and those factors that tend to lower the elevation of the land.

The maintenance of the Mississippi Delta in deeper offshore waters ahd

the construction of artifical levees have served to eliminate much of

the primary source of sediment to the wetlands.

The in tricate network of canals is a two-way corridor that allows

saltwater intrusion, and whereas canals are expedient in'carrying away

stream flow and storm surges, they do so at the expense of overland flow

and deposition of sediments from overbank flooding. This not only deprives

the wetlands of sediment, but also leads to shoaling of the canals,

which subsequently requiremaintenance dred ging.

Other practices that divert sediments from reaching the wetlands

are:

1) The construction of dams such as the Toledo Bend

Reservoir. Dams are extremely effective barriers

to sediment transport.

2) Pumping of surface water for irrigation such as in the

rice growing area of Southwest Louisiana. Pumping decreases

downstream movement and may even cause stagnation. The

reduced water velocities lose their ability to transport

sediment.

3) Impounding of wetlands prevents sediments from moving

in and also prevents organics from exiting.

Role of the Atchafalaya.-River

The growth of the Atchafalaya Delta is one of the most significant

geologic'events in the modern development of coastal Louisiana. Its

effects are more widespread than those discussed in the basin level

(management unit) treatment provided in Chapter 3. The growth of the

delta is important because it has reversed the trend from land loss to

shoreline accretion in the Atchafalaya Bay area, and through time this

reversal should be apparent in other areas as well.

The Atchafalaya River has been a distributary of the Mississippi

River since the middle of the sixteenth century. It shortens the distance

to the Gulf of Mexico by 320 km over the present course of the Mississippi

River (Fisk 1952). This favored gradient would cause the river to

divert most of its flow through the Atchafalaya Basin to the saline

waters of Atchafalaya Bay and the adjacent Gulf of Mexico if the U.S.

Corps of Engineers (USCE) had not succeeded in establishing the control

structure at Old River. This structure limits the Atchafalaya to 30

percent of the combined Mississippi and Red River flow.

The lower Atchafalaya Basin is characterized by low lying swamps

and lakes, which,hav@e been trapping the Atchafalaya's sediment load

before it reached the coast. By the early 1950s, most of this low lying

area was filled and sedimentation began occurring in the lower river and

bay. The depth of Atchafalaya Bay had not changed appreciably since the

1858 survey until the influx of sediment in the early 1950s (Thompson

1951). From 1952 to 1962 a subaqueous delta began to evolve with deposition

of clays and silty clays at the mouths of the lower Atchafalaya River

and Wax Outlet.

Subaerial exposures appeared in 1971-72. These shoals were composed

largely of sediment derived from dredging of a navigational channel from

the Atchafalaya River Outlet through the Point au Fer Shell Reef. A few

small shoals not associated with dredge spoil also appeared during this

period on the eastern side of the navigational channel. The first

of three consecutive major floods occurred in the spring of 1973. By

the time the waters receded, well-developed natural subaerial lobes were

apparent on both sides of the channel. In subsequent years, the delta

has continued to increase its exposure above low water datum in direct

proportion to the magnitude of peak floods on the Atchafalaya River. A

6 m by 122 m navigation channel is maintained by frequent dredging from

the mouth of the Lower Atchafalaya River 19.3 km across Atchafalaya Bay

to Eugene Island. A bar channel is also maintained by dredging beyond

the Point au Fer Shell Reef about 22.5 km offshore in the Gulf of Mexico

(Roberts et al., unpublished ms.).

Along the Gulf of Mexico shoreline west of the Atchafalaya Bay,

extensive mudflats blanketed the shoreline in the late 1950s. These

mudIlats stranded numerous previously active beaches from near Atchafa-

laya Bay to Cameron Beach, some 200 km to the west. These deposits

separated the ephemeral shell beaches of the Chenier Plain from gulf

waters with a hundred meters or more of fluid mild (Morgan et al. 1953).

Subsequent colonization by marsh vegetation welded portions of these

mudflats to the shoreline. This process is the same one that formed the

Chenier Plain marshes, producing elongated wetlands parallel to the

coast and trapped between beach ridges marking former shorelines. This,

alternation of marsh and beach deposits resulted from shifts in the

locus of Mississippi River sedimentation. De ltas in the western portion

of the Deltaic Plain, such as the present Atchafalaya Delta, favor

progradation of mudflats with subsequent formation of marshes. As long

as a sufficient source of fine sediment is available in the offshore

zone, shoreline progradation will predominate. Deltas in the eastern

portion of the Deltaic Plain, such as the modern birdfoot delta of the

Mississippi River, favor shoreline retreat in the Chenier Plain marshes

and the formation of beach ridges at the retreating coastline (Howe et

al. 1935). The past seven thousand years of Mississippi River history

are characterized by shifts in delta location back and forth across

coastal Louisiana (Frazier 1967).

Mudflats are not actively forming on the Chenier Plain; in fact,

some erosion of previously deposited mudflat marshes has occurred. We

can anticipate that erosion will predominate over periodic mudflat

formation until sufficient offshore accumulations of Atchafalaya River

clays create a situation favorable to long-term coastal marsh progradation.

Concept of Management U its

Several factors relating to land loss are reasonably constant

throughout coastal Louisiana, others are more variable over space,

and still others exist in some locales but not in others. The result is

a wide spectrum of rates varying from excessive erosion to major accretion

across the coastal area. In order to systematically examine the variability

of erosion rates, it is necessary to divide the coast into units.. The

rate of sedimentation is an important factor governing land loss in

Louisiana. Whereas aeolian processes may transport some sediment and

are particularly important along beaches, the dominant agent of sediment

transport is water. There is little doubt that aspects of water such as

movement, quality, level, and quantity are responsible for much of the

diversity of elements of the landscape across the coastal area. These

aspects of water are variable over space and through time, but the

spatial aspect can be organized into basins and sub-basins. This traditional

procedure works well for upland areas where surface-water basins can be

geographically well defined. In the wetlands, physical barriers to

water movement are usually not as prevalent, which makes the lower parts

of these hydrologic basins somewhat less definable. Although some of the

hydrologic boundaries in wetlands are somewhat obscure, we have used

them as organizational (management) units for presentation of the land

loss data for:

1) Comparison of rates between different units within

coastal Louisiana, and

2) Comparison of land loss rates with other data sets that

are also organized by management units.

Figure 2 delineates Management Units as used in this report.

Criteria used for delineating these units were developed in comprehensive

studies previously completed by LSU Center for Wetland Resources personnel

=W WWI WK OR so Im As 100 '00,

I F

Lake
Am 1, -11 it rt ?'it i ft

CALCASIELI- SABINE
MERMENTAU

VERMILION 41.

I
ATCHAFALAYA
0 10 20 30 40 so
miles BARATARIA
93o 92' 91' TERREBONNE 90o

Figure 2. Management Units of Coastal Louisiana as uscd in this study.

under contract to the Louisiana State Planning Office, with funding

from the Office of Coastal Zone Management, U.S. Dept. of Commerce.

Chapter 2

Methods

There are two basic approaches to determining shoreline erosion, by

direct monitoring and by studying maps and/or aerial imagery. One can

directly monitor specific shorelines by establishing physical points of

reference and surveying these reference points at intervals through

time. Such a microscale appro.ach has the advantage of providing an

accurate account of erosion. However, it has the disadvantages of

requiring data collection over a period of time (usually years) and

requires many man-hours if there are numerous shorelines to be investigated.

Such a monitoring scheme is in practice in parts of California, Michigan,

New York, and Rhode Island. Areas where this intensive monitoring

effort is being conducted are not necessarily those where erosion rates

are high. Rather, it is more common for this effort to be initiated*

along sections of eroding coasts where cultural pressures are great.

The second basic approach deals with erosion from a macroscale

perspective. The use of aerial photography and U.S. Geologic Survey

(USGS) quadrangle maps provides a temporal data series over a wide

geographic area. The major disadvantage of using this approach is the

resolution of the data. Naturally, the larger the scale of the photography

or maps, the better the resolution of the data. Although a considerable

quantity of aerial imagery spanning over a forty year period for coastal

Louisiana exists, the quality and scale of much of the imagery is less

than adequate. Maximum resolution is five and ten meters, respectively,

for the two scales used. This resolution is generally adequate for

assessing areas of major erosion from which decision makers can decide

which areas, if any, require direct monitoring.

Because of the resolution of the data (photographs and maps) and

the degree to which erosion is generally occurring along Louisiana

shorelines, a minimum of ten years is required to make an assessment.

Longer time intervals beyond this minimum time requirement provide a

more accurate assessment of erosion rates; however, they also place more

dependence on average rates and provide less information on the periodicity

of erosion. For example, if one were to examine erosion during the past

one hundred years using only two time intervals, one might find a section

of shoreline to be stable when in reality the coast prograded for a

number of years and then retreated back to approximately its same position.

On the other hand, short-term assessment may also be misleading. For

example, approximately one-half of the erosion of several lakes in

Southwest Louisiana from 1952 to 1974 was the result of a single event,

Hurricane Audrey. If one were to examine the erosion during a ten-year

period, the results would indicate a considerably higher erosion rate

than a twenty year analysis, both of which included the same event.

Given the above limitations combined with problems of data availability,

the most recent twenty year period is considered the best representative

period for assessing present shoreline erosion.

Assessment of Topographic Maps

Topographic maps have an advantage over aerial photographs in that

the scaling has already been accomplished. The two best resolution

scales of USGS topographic maps for the Louisiana coastal area are

1:24000 (7-1/2 minute) and 1:62500 (15 minute). Although 1:24000 is

preferred, completion of these maps for all of.coastal Louisiana is

relatively recent, with final publication of some areas still forthcoming-

An assessment was made of the mapping accuracy of shorelines

depicted on standard USGS topographic maps. Those maps that were updated

with 1971 aerial photography were compared with high altitude color

infrared photography taken during 1972 (NASA mission 194). The 1,972

photography was enlarged to a scale of 1:62500 using a procedure outlined

later in this section. The photography is not tidally controlled;

however, the shoreline for lakes.hores and inner marsh areas is defined

as the shorewardmost point that supports emergent macrophytic vegetation.

Thus, unless water levels ar e excessively high (e.g., during tropical

disturbances in which vegetation is submerged) this shoreline is easily

and consistently depicted.

The results of the comparative analysis between aerial imagery and

USGS topographic maps indicate that the maps are within the standard of

accuracy used in this study for well-defined lakeshores but are of poor

resolution for determining marsh loss for less rigorously defined inner

marsh shorelines.

Assessment of Aerial Imagery

Numerous investigations have shown that color infrared photography

is the most cost efficient method for depicting the boundary of vegetation/open

water (Klemas et al. 1973, Daiber et al. 1976, Graff 1976). Black and

white infrared is often sufficient for delineating this boundary for

coastal wetlands; however, the numerous mudflats that are exposed predominantly

during low water levels accompanying cold front passages in coastal

Louisiana are not easily distinguished from vegetated areas during

period of low primary productivity. The addition of color enhances the

vegetation, hence, the boundary.

NASA 1974 .missions 289 and 293 are the most recent high quality

color infrared photography taken over a wide area of the Louisiana

coast. This, imagery covers approximately seventy percent of the area

south of Interstates 10 and 12. Areas not covered by this imagery

are covered by NASA 1972 mission 194.

Having established the 1972-1974 period as the baseline, data was

sought from approximately twenty years earlier. Black and white aerial

photography taken during 1952 by the United States Navy covers almost

the entire Louisiana coastal area. The scale varies with the mission
selected but is usualiy either approximately 1:20000 or 1:40000. In

addition, 1:20000 tidally controlled black and white infrared photographs

of the Louisiana coastline taken in 1953-1954 by the Jack Ammann Corp.

are available. Maps generated from this set of imagery (Morgan and

Larimore 1957) have been used as the basis.for determining the coastline

of Louisiana under the 1953 Submerged Land Act. Using this series as

a base and comparing it with 1969 USCE photomosaics, coastline erosion

has been analyzed.

Coastline Analysis

The same methods as used by Morgan and Larimore (1957) were

adopted for this study and are outlined below-

1) Measurements were made along lines perpendicular to the

1954 coastline.

2) Each perpendicular was located at each meridianal line,

except for the Chandeleur Islands, where each minute of

latitude was used. Thus the sampling points were approximately.

one nautical mile apart.

3) Linear changes in the 1954 to 1969 coastlines were rounded

to the nearest 30 meters and then divided by fifteen

to obtain an average annual change.

4) The values thus obtained were deemed representative of the

coastline to a distance midway to the next sampling station.

The entire coastline, except.for the active Mississippi Delta area,

was analyzed using this procedure. The delta proper cannot be considered

in the same manner as the remaining coastline because of the rapid

areal changes that result from processes such as deltaic sedimentation,

wave erosion, and subsidence of the thick sequence of unconsolidated

sediments, which are charact eristic of the active delta. One of the

resulting surface expressions of these processes is a highly irregular
C2

and poorly defined shoreline. For this reason, only sample areas within

the delta proper were examined and were analyzed by the procedure

outlined for inner marsh areas. For a more detailed analysis of

land change trends on the Mississippi Delta, the reader is referred to

Gagliano and van Beek (1970) and Morgan (1973).

Well-Defined Lakeshores and Inner Marsh Areas

An analysis of all shorelines in coastal Louisiana is a virtually

impossible task because there are literally hundreds of thousands of

kilometers of shorelines. Consequently, a representative sampling

procedure was developed. A completely random sampling was not practical

because of data limitations and the desire to analyze some specific

areas where erosion created immediate cultural problems.

Initial sites were selected by including a-minimum of one site of

each vegetation type within each management unit. Lakes and marsh areas

or portions of such sites where aerial coverage was not sufficient were

not evaluated. The final group of sites analyzed totaled more than

one hundred and represented several thousand ki lometers of

shoreline.

The outline of present (1972-1974) shorelines was made from

NASA high altitude color infrared photography. This imagery is

commonly available on 23 cm by 23 cm transparencies; however, the

scale in this form is not sufficient for an accuracy of 5 meters.

Thus,enlargement of the imagery was necessary. This was accomplished

by photographing the color transparencies with Ektachrome 64 color

slide film with a copy camera equipped with a Nikkon 55 mm flat-field

macro lens. The light table and camera were leveled to minimize

distortion. Care was taken to shoot th e sites in the center of the

slide as well as the center area of the NASA film frames;

The slides were projected on a vertical drawing board with a

Kodak Carousel projector equipped with a Kodak flat-field zoom

lens. The projector was leveled, and the projected image was centered

vertically and horizontally. The image was scaled with USGS quadrangle

sheets with a zoom lens. The shoreline was then traced by following

the land-water interface.

Establishment of the 1952 shoreline was accomplished by directly

tracing USGS 1:24000 qua-drangles, which were updated with aerial

photography taken between 1951-1953. Only a small portion of the total

coastal area is covered by this series. The first alternative method

used where this series was not available was the use.of US Navy (USN)

1952 low altitude black and white aerial photography = 1:20000.

Each frame was individually scaled. Lengths from permanent cultural

features to the shoreline were then measured. The same measurements

were taken with the 1974 shoreline, and the resulting differences in the

two measurements represent the change in the shoreline.

The final alternative method was to use USGS 1:62500 quadrangles

where no USGS 1:24000 were available and the USN 1952 imagery was of

insufficient quality. Dates of the photorevision of the quadrangles

vary between 1939 to 1964. Comparison was then made to the 1974 shoreline.

After establishing the shorelines for two different time periods

for each site, both the areal and linear chang e was determined by using

a Calmagraphic II digitizing system (0.25 mm sensitivity).

Inner marsh areas, because of their poorly defined shorelines, had

to be treated in a slightly different manner. Linear measurements could

not be made; therefore, these sites are represented by changes in the

land/water ratio through time (percent of land loss). The peripheral

boundary of each inner marsh is defined by either easily recognizable

cultural or natural non-marsh features-or by a grid area of not less

than 50 ha.

Based on reported land loss statistics for Louisiana (Gagliano and
van Beck 1970), an average expected rate of wetland loss is 42.8 km2

(0.2%/Yr). This value is used as a guideline for all basins and all

wetland types. Categories representing losses that deviated from the

average value were chosen on the basis of a normalized distribution of

the losses reported for each individual 7-1/2 minute quadrangle sheet by

Gagliano and van Beek (1970) and later modi fied wi th the addition of

results obtained from this study.

Chapter 3

Results and Discussion

Introduction

This chapter presents.the results of the shoreline erosion assessment.

The areas are organized by management units and then subdivided by

shoreline type. The rationale for this approach has been previously

discussed in Chapter 1.

Those persons who desire a more regional approach may refer to the

state summary section, which follows. The summary tables included at

the end of each management unit discussion are, comprehensive with respect,

to quantitative values for individual sites. Sites are listed according

to management unit, vegetation type, shoreline type, and parish.

State Summary

Louisiana has no rival with respect to the amount of coastal erosion

presently occurring. Land,.-Ioss in coastal Louisiana is attributed

largely to natural processes associated with deteriorating deltaic

sediments and is intensified by various ongoing cultural activities in

the area.

We have not attempted to assign a single land loss rate for the

entire area; however, Gagliano and van Beek's (1970) net value of 42.8
km2/yr (16.5 mi2/yr) appears a reasonable estimate. It is emphasized

here and shown elsewhere that a high degree of variability exists both

spatially and temporally with respect to the above mean annual total.

From a macroscale perspective, the variability in. natural erosion is due

primarily to differences in geologic conditions and the amount of energy

impacting an area.

Except for the Atchafalaya and Mississippi Deltas, most of

coastal Louisiana is presently sediment deficient. Erosional processes

are dominant over land building processes. Erosion appears more

critical on the coastline, where comparisons with previous studies

(e.g., Morgan and Larimore 1957) indicate that it is accelerating.

Most of Louisiana's coastline is composed of easily eroded peats,

uncemented sands, and shell hash. It is widely exposed to southerly

wave development, which is expended at the coast. Along areas such as
Marsh Island, where offshore oyster reefs dampen wave energy, and the

coastline leeward of the Mississippi Delta, erosion rates are lower than

neighboring areas of similar sediment composition.

All of the larger lake and bay shorelines along coastal Louisiana

are experiencing erosion except those in the Atchafalaya Management

Unit. The variability in erosion rates is due to the differences in wave

energy, sediment composition, and vegetation type (the latter two are

often related). Swamp forest is the wetland vegetation most effective

in retarding erosion; highly organic fresh marshes are the most easily

eroded. Southern shorelines (northerly facing), which have a tendency

to erode at a faster rate, reflect the greater strength of northerly

components of wind. Southern shorelines on larger water bodies generally

are comprised of a thicker sequence of Recent sediments than northern

shorelines, and this increase in subsidence potential may be a contributing

factor to the above trend. Generally, and particularly in Southeast

Louisiana, water bodies located in depressions near natural levees tend

to erode fairly rapidly. This rapid erosion is thought to be related to

the weight of these features, which cause instability in surrounding

sediments.

Gagliano and van Beek (1970) showed that the greatest loss of

wetlands overall in the state is associated with brackish marshes. Our

analysis supports the high rate for brackish marshes but it also indicates

..a high loss offresh marshes. We attribute this to a combination of

highly organic soils that are easily eroded, the effects of Hurricane

Audrey and subsequent droughts on the fresh marshes in Southwest Louisiana,

and the proximity of fresh marshes to intensive cultural development.

The Deltaic Plain of Southeast Louisiana is expected to experience

more erosion than the Chenier Plain of Southwest Louisiana. This expectation

is based an the difference in overall stability of sediments within the

two regions as discussed in Chapter 1. Although the detailed analyses

presented at the end of this section support this hypothesis, there is

much variation from site to site. A brief discussion-of each,of the

management units is presented below.

The Pontchartrain-Breton Sound Management Unit (Unit I) is the most

stable of the uni ts east of.the Atchafalaya River, but because of large

population centers around Lake Pontchartrain, the erosion that is occurring

poses an immediate problem. Comparison of results of this study with

Saucier (1963) indicates that erosion along Lake Pontchartrain may be

accelerating, which should be considered for future cultural development

along the lakeshore. The coastline of this unit is represented by the

Chandeleur Islands, which act as a buffer against erosion for the more

inland marshes. These barrier islands are eroding and b eing displaced

landward at an average rate of 5.4 m/yr (1954-1969). Most of this

displacement, however, has occurred as a result a singl e event: Hurricane

Camille (1969).

The Mississippi Delta Management Unit (Unit II) experiences rapid

areal changes associated with deltaic sedimentation and subsequent wave

erosion and subsidence. The works of Gagliano and van Beek (1970) and

-Morgan (1973) indicate that the delta is slowly prograding seaward but

has not increased in total area over the past twenty years. Thus the

gains in land area along some of the seaward margins of the delta are

negated by losses in other portions of the delta. The ephemeral nature

of many features and the general instability of the sediments are prohibitive

to cultural development.

The Barataria and Terrebonne Management Unit (Units III and IV) are

experiencing the highest overall loss of wetlands to open water. This

loss is partly attributable to the relatively young age of Lafourche-

Mississippi sediments that blanket a large portion of these two basins.

Brackish marshes are being lost to open water approximately three times

faster than the state average for all marsh-types. Fresh marshes are

being lost at an equivalent rate in the Barataria Unit but at a greatly

reduced rate in the Terrebonne Unit. The loss in the Barataria Unit is

associated with the easily eroded floating marshes bordering relatively

large freshwater' lakes, whereas the fresh marshes in the Terrebonne

Unit are receiving some benefit from the Atchafalaya River, especially

in the northwest part of the basin above Four League Bay.

Both of these units are undergoing severe erosion at the coastline.

The Lafourche Parish coastline area has the highest rate of retreat in

the state, amounting to some 207 meters between 1954 and 1969. The use

of structures at Grand Isle appears thus far to be moderately successful

in retarding erosion (see Chapter 4) but has been partly at the expense

of neighboring barrier islands.

Erosion is not presently considered a problem in the Atchafalaya

Management Unit (Unit V). Most areas of fresh marsh and bay shorelines

are advancing. Brackish marshes along the western end of Point Au Fer

Island are eroding at rates comparable to brackish marshes in the Terrebonne

Unit. Apparently Atchafalaya River sediments have not been deposited in

this area in sufficient quantities to reverse the trend. However,

continued growth of the Atchafalaya Delta is expected to influence this

area. Point Ch.evreuil marks the bay shoreline boundary between the

Atchafalaya and Vermilion Management Units' boundary. It also marks the

westernmost point of bay shoreline advance resulting from Atchafalaya

River-derived sediments.

Most of the bay and lake shorelines in the Vermilion Management

Unit (Unit VI) have remained stable or undergone small rates of retreat

during the time period examined. None of the marshes examined north of

East and West Cote Blanche Bays and north and west of Ve,rmilion Bay have

undergone more than average losses, and several examples have remained

stable. Considering the fetch across these bays, the rates of erosion

are lower than could be expected. The reduced rates are thought to be

caused in part by the dominant southerly and southeasterly winds as they

push sediment-laden waters from Atchafalaya Bay into East and West Cote

Blanche and Vermilion Bays.

A noticeable characteristic of erosion along the coastline of the

Vermilion Unit is the spatial variability. The coastline along Marsh

Island has remained essentially stable from 1954 to 1969 except for the

extreme eastern and western ends. The presence of offshore oyster reefs

in this area is apparently an effective agent in mitigating erosion.

West of Marsh Island to Freshwater Bayou Canal the coastline is generally

eroding, except for a small segment at Cheniere au Tigre that has prograded

slightly. A comparison of the 1954 to 1969 changes with the 1932 to

1954 changes (Morgan and Larimore 1957) for this section of coastline

shows@ that erosion rates-have generally increased. Whether this is a

trend or whether this simply reflects the effects of Hurricane Audrey

(1957) is unknown.

The Mermentau.Management Unit (Unit VII) is wholly within the

Marginal Deltaic Plain and is therefore expected to be generally more

stable. The relatively low loss rates of inner marsh areas supports

this assumption but the high rates of erosion for the coastline and

lakeshores is in contradiction.

Private landowners have constructed levees around certain areas of

White Lake in an attempt to retard the,high rates of erosion. The high

erosion along this lake as well as Grand Lake and Lake Misere is thought

to be related to-raised water levels resulting from management practices

associated with the Mermentau water management area. Lakes in more

brackish environments have generally faired better. Saline lakes

immediately landward of the coastline are filling in as a result of

storm deposits that wash over the beach.

Although the overall loss rate of inner marsh areas to open water

is low in the Mermentau area, specific locales have experienced high

rates of loss. The loss of some of these areas has been related to

natural phenomena such as hurricanes and droughts (Valentine, unpublished

ms.), but the loss of other areas is the unintentional result of poor

management practices of man.

The coastline from the mouth of the Mermentau River east to Dewitt

Canal has eroded an average of 165 meters from 1954 to 1969. Although

there is no cultural development along this rapidly eroding coastline,

much of the land is in public ownership.

The Calcasieu-Sabine Management Unit's (Unit VIII) coastline has

experienced a net progradation from 1954 to 1969. This progradation is

the result of the Calcasieu ship channel jetties, which trap sediment

coming from the east. West of these.jetties to Sabine Pass, the coastline

is either eroding at moderate rates or has remained stable. Comparison

of rates with those reported by Morgan and Larimore (1957) indicates

that much of this western sector had been accreting previously. Consequently,

communities of Peveto and Ocean View Beaches now have reason to be

concerned about erosion. Comparison of rates at Holly Beach indicate

that erosion has remained fairly constant, with most of it occurring as

a result of storms.

Considering the size of Calcasieu and Sabine Lakes, erosion rates

are generally low-Artificial oyster reefs in Calcasieu Lake have

helped to reduce erosion rates on the southern shorelines.

Brackish marshes east of Calcasieu Lake have experienced relatively

high rates of loss, and the area around Black Lake has the highest

density loss of.marsh for any example examined in the study. Losses on

the eastern margin of Sabine Lake are largely associated with cultural

activities.

Data Interpretation Key

An index map is located at the end of the discussion for each

management unit. On these maps are a series of code,numbers that

refer to an individual site in the accompanying summary tables. The

key is listed below in Table 2.

Table 2

Key for Cross Referencing Index Maps with Basin Summary Tables

The key is composed of a five digit code.:

lst digit - Management unit
2nd digit - Shoreline type
3rd digit - Vegetation type
4th and
5th digit - Site number

Management Units Code Number

Pontchartrain-Breton Sound 1
Mississippi Delta 2
Barataria 3
Terrebonne 4
Atchafalaya 5
Vermilion 6
Mermentau 7
Calcasieu-Sabine 8

Shoreline Type

Coastline 1
Well-defined Lakeshores and
Bays 2
Inner Marsh 3

Vegetation Type (after Chabreck 1972)

Salt Marsh 1
Brackish Marsh 2
Intermediate Marsh 3
Fresh Marsh 4
Swamp Forest 5
Non-wetland (Pleistocene) 6

For example, let us consider 23301. Reading from right to left,

this would translate as site number one, of intermediate marsh, in an

inner marsh area of the Mississippi Delta Management Unit. The number

will appear on the index map and again on the accompanying summary

table, which provides additional information about each site. This

includes the name of the site, linear rate of retreat (or percent of

land loss), parish the site is in, data sources, time period examined,

and the name of the latest U.S. Geologic Survey (USGS) quadrangle (7-1/2

or 15 minutes) that portrays the area. An additional map lists the

place names that appear in the text.

In the discussions of inner marsh land loss throughout this section,

qualitative terms are often substituted for the quantitative values that

appear'in the summary tables for each management unit. The terms that

appear and their equivalent range of land loss are listed below (Table 3).

The method used in determining these categories is outlined in Chapter

Table 3

Inner Marsh Land Loss Categories

Equivalent Percent of
Qualitative Term Land Loss (Gain)/Year.

Accretion All values of land gain> 0.025
Stable 0 0.025
Below Average > 0.025 to 0.10
Average > 0.10 to 0.30
Above average > 0.30 to 1.00
Excessive > 1.00

Management Unit I--- Pontchartrain-Breton Sound

Coastline Erosion. The coastline of the Pontchartrain-Breton Sound

Management Unit is represented-by an arc of discontinuous barrier islands

(Fig. 4 ). These islands (Chandeleur, Grand Gossier, and Breton) are

the product of the reworking of an older Mississippi Delta known as the

St. Bernard Delta complex. This complex was active from approximately

4800 years B.P. (Before Present) to 600 years B.P. (Frazier 1967). Thus

this area has been subsiding and eroding longer than most of the other

barrier island coastlines along Louisiana. Therefore, it should be

expected that erosion would occur along the Chandeleur/Breton Island

chain. at a rate less than younger Barrier Island coastlines to the west

along (Morgan and Larimore 1957). Table 4 shows the'comparison of

coastline retreat rates to relative age of sediments for those barrier

islands that have.not been structurally controlled.

Table 4

Relationship Between Barrier Island Erosion Rates-and Age of Sediments

Area Listed in Order Coastline Retreat 1954-1
of Increasing Age

Timbalfer islands 9.3
Isles Dernieres 8.0
Chandeleur Islands 6.9

The unconsolidated sands and other material that comprise the

Chandeleur Islands are subject to rapid changes during tropical disturbances,

when these islands are often breached or washed away. However, the

islands tend to gradually rebuild and reappear in other areas. Hurricane

Camille (1969) caused extensive damage to this area, and because the

latter set of photography used (1969) was post-Camille, the resulting

changes are included. Thus, the erosion rates may be somewhat greater

than other fifteen-year time periods. In addition, the reader is cautioned

in evaluating the results determined for the Chandeleur Islands because

many of them are barren; therefore, the land-water interface is less

rigorously defined. This, combined with the dramatic shoreline changes

associated with Hurricane Camille, makes it difficult to maintain the

same resolution of accuracy in measuring shoreline changes.

Well-Defined Lakeshores and Bays. Saucier (1963) documented erosion

along Lakes Borgne, Maurepas, and Pontchartrain. Using maps from the

1850s and large-scale air photos from the 1930s and 1950s, Saucier

concluded that erosion was dominant along these shorelines and that

erosion rates were accelerating. He summarized the causes of erosion as

follows:

If only the balance between subsidence and
sedimentation is considered to be a controlling factor
in shoreline movement, the lakeshores should be eroding
more rapidly at the.present time. To this factor,
however, must be added the facts that as the lake
(orlakes) increase in size, the length of fetch
increases and the depth of the lake proportionately
increases. Both of these would.have the effect of
accelerating shoreline retreat. The slight rise
in sea level which is apparently occurring at the
present time is another factor which must be considered
in this respect.

In regards to subsidence, there can be no doubt
that it is a prevalent process in the Pontchartrain
Basin today. Since the last opening of the Bonnet Carre
Spillway fn 1950, there have been no Mississippi River
sediments reaching the basin. The only other sources of
sediment are the-streams which drain the Prairie
terrace to the north and west andit is evident that
these contribute only insignificant quantities of alluvium.

Despite the opening of the Bonnet Carre Spillway since Saucier's

work, our analysis compared with Saucier's confirms that rates of erosion

are accelerating in Lakes Borgne, Maurepas, and Po ntchartrain (Table 5).

Table 5

Compatative Rates of Current (1950s-1970s) Erosion with Saucier (1963)
for Selected Lakes in the Pontchartrain-Breton Sound Management Unit

Lake Mean Rate or Erosion (m/yr/km

Saucier (1963) This study
1930s-1950s 1950s-1970s

Borgne* 1.5 2.0
Maurepas 0.6 0.8
Pontchartrain** 1.6 2.3

*From Chef Menteur Pass to Rigolets
**Includes only those shorelines that do not contain structures
designed to reduce erosion.

The variability found in erosion rates around the lakes parallels

those found by Saucier (1963) except for the shoreline near Frenier.

This discrepancy may be related to the influence of the Bonnet Carre

Spillway-

The pattern of relatively low rates of erosion along the north

shore near Mandeville was evident for both studies. Saucier (1963)

attributes this to the shallow depths (2 to 3 meters), to more resistant

Pleistocene sediments, and to a relatively more resistant marsh resulting

from firm washover deposits.

Comparison of rates of lakeshore erosion in the Pontchartrain-

Breton Sound Unit with other units in the Deltaic Plain reveals that

rates are considerably less for the Pontchartrain area. This is consistent

with the pattern found for coastline and inner marsh erosion.

Inner Marsh Land Loss. The marshes in this unit have been eroding

and subsiding for several thousand years so that the present marsh area

represents approximately 30 to 40 percent of the former maximum extent

of marsh. Although the area is still undergoing subsidence, most of the

more unstable marsh surfaces have been eroded away. The presence of the

Chandeleur Islands and the shallowness of Chandeleur and Breton Sounds

(former sites of marsh) help to reduce wave energies and should result

in a relatively more stable land/water ratio for those remaining areas

of marsh.

. Of the four sites of saline and brackish marsh.examined, two

remained stable and two experien ced average losses. This is consistent

with rates found for other types of erosion in the unit (lakeshore and

coastline) and is also consistent with the relationship between ages of

deltaic areas and rates of erosion originally discussed by Morgan and

Larimore (1957) and mentioned elsewhere in this report.

The example sites represent areas that, to the extent of our evaluation,

have not been greatly affected by man's activities; consequently areas

of higher land loss rates should be expected to exist in this unit.

However, none were found for natural areas.

41@

m 1 5 S I S S I p p I

124 01
2501

0
2503 2

'Z504

1220S

Rive(
,Vpi v 11101-11105
30'00
3101

12209

-7
1220

2
4 Ip 0
4
1@02
4

4
Z111125
1t126
29o3O'

r4-

23301

0 6 10 15 20 mi.

90.30. 90.w 5 10 15 20 25 30 Km. 89*30' 89,00'
=09

29oOO'

Figu-e 3. Site locations in Lhe Pontchartrain-Bretoa Eound and
Mississippi Delta Managcm6nt Units.

Table '6

Erosion Rates for Sites Analyzed in the
Pontchartrain-Breton Sound Management Unit

W
C

Retreat
M Z
Quadrangle & Rate
"01 Data Sources Dates or
C0W Site Area Parish Size(minutes) m/yr Land LOS3

11101 Chandeleur Islands St. Bernard Chandeleur Light 1954 air photos 1969 USCE 3.9
Lat. 30* 03' 7-1/2 Jack Ammann Corp. uncontrolled
photamosaics
11102 Lat. 30' 021 0

I1103 Lat. 30* 01' North Islands 0
7-1/2
11104 Lat. 30* 00' 0

11105 Lat. 29* 59' 2.1

11106 Lat. 29* 58' 2.1

I1107 Lat. 29* 571 3.9

11108 Lat. 29* 56' 3.9

I1109 Lat. 29* 55' 3.9

I1110 Lat. 29* 54' 6.0

I1111 Lat. 29' 53' 8.1
11112 Lat. 29* 52' New Harbor Islands
7-1/2 8.1
11113 Lat. 29* 51J 8.1

11114 Lat. 29* 50' 9.9

11115 Lac. 29* 49' 9.9
I1116 Lat. 29* 48' 9.9

11117 Lat. 29' 47' 9.9
11118 Lat. 29* 46' 14.1
I1119 La c. 29* 45' 14.1

I1120 Lat. 29' 44'
Stake Islands 3.9
7-1/2
11121 Lat. 29* 41' 24.0 ?

11122 Stake Islands 6.0 ?

11123 Curlew Islands Plaquemines Stake Island, 1954 air photos 1969 USCE 8.1 ?
Lat. 29* 39' 7-1/2 Jack Ammann Corp,. uncontrolled
photomosaics
11124 Lat. 29* 38' 8.1 ?
I1125 Grand Gossier Is. Grand Gossier Is. 14.1
Lat. 29* 321 7-1/2
11126 Lat. 29' 31' USGS Quadrangle 1974 NASA MX293 0
12101 East Lake Borgne St. Bernard Yscloskey 15 From 1952 photos 3.0
12102 East Lake Borgne Rigolets 15 USGS Quadrangle
From 1955 photos 1.6

12103 No. L. Jean-Louis St. Bernard Yscloskey 15 USGS Quadrangle 1974 NASA MX293 1.6
Robin From 1952 photos
12104 So. L. Jean-Louis Black Bay 15 USGS Quadrangle 1.0
Robin From 1946 photos
12201 No. L. Pontchartrain St. Tammany Co@ington 15 USGS Quadrangle 1974 NASA MX293 1.1
(1950) no photo
12202 No. L. Pontchartrain Slidell 15 date 2.4

Table 6 continued

V 0
Retreat
0
z Qu:drangle Rates or
Parish Si e(mInutts) Data Sources & Dates M/yr
c 0w Site Area Land Loss

L.,Pontchartrain near USGS Quadrangle NASA MX194
1 2203 Ch f Menteur Pas s Orleans Chef Menteur 15 from 1955 photos 1972 2.8
1 2204 NW L. Borgne St. Tammany Rigolets 15 1974 NASA MX293 2.0

1 2205 Orleans 2.6
1 2206 V L..B'O'rgne 1.8

1 2207 SW L. Borgne Chef Menteur 15 3.2
1 2208 St. Bernard St. Bernard 15 USGS Quadrangle 1.0
Prom 1952 photos
1 2209 1. 11 5.3

1 2210 SE L, Borgne Yscloskey 11 11,1
1 2211 SE L. Borgne St. Bernard Yscloskey 15 USGS Quadrangle 1974 NASA MX293 5.6
From 1952 photos

1 2212 N L. Levy Delacroix USGS Quadrangle 2.9
Belle Chase 15 (1951) no photo
date-

1 2213 S L. Levy Plaquemines 1.9
1 2401 NW L. Pontchartrain St. Tammany Covington 15 USGS Quadrangle 1.6
(1950) no photo
date
SGS Quadrangle 1972 NASA KX194 2.4
1 2501 NW L. Maurepas Li4ngton Pontchatoula 15 Y1951) no photo
date
USGS Quadrangle 0.7
1 2502 W L. Haurepas Springfield 15 (1939) no photo
date
USGS Quadrangle
1 2503 SW L. Maurepa a Mount Airy 15 (1939) no photo 1972 NASA MX.194 0.4
date

1 2504 SE L. Maurepas St. John the 015
Baptist
1 2505 E L. Maurepas Bonne Carte 15 USGS Quadrangle
from 1955 photos 0.5
1 2506 NE L. Maurepas Pontchatoula 15 USGS Quadrangle 2.4
(1951) no photo
date
1 2507 N L. Maurepas Tangipahoa 0.7

1 11011 NW L, Pontchartrain 2.5

1 2509 W L. Pontchartrain St. John the 3.8
Baptist
1 2510 W L. Pontchartrain Bonnet Carre 15 USGS Quadrangle 0
from 1955 photos
1 2511 Sw L. Pontchartrain 7.7
1 2512 S L. Pontchartrain St. Charles 2.9
1 3101 Bob's Lakes St. Bernard Lake Eugenie 15 USCS Quadrangle 1974 NASA MX293 0
from 1952 photos
1 3102 L. Jean-Louis Robin Black Bay 15 USGS Quadrangle
(1964) no photo 0.11
date
1 3 2 01 SE L. Borgne Pte. Aux Karchettes USGS Quadrangle
15 from 1952 photos 0.18

1 3 2 02 Spanish Lake Plaquemines Pointe a Is Hache USGS Quadrangle
15 from 1961 photos 0

m I s s I s s i p p

Milli eville

Lake Pontchartrain

V
Vvi Rive d,
vi
-30000' 0 011
e 40

41-
C)

29'30'

0 5 10 15 20 Mill

90'3U 90*OU 0 5_10 16 20 26 30 Km. 89'30'
-29100' -.4

Figure 4. Place nameG in the Pontchartrain-Breton Sound and
MisWjWipjjj<U&nagj@t Tjifts. j= M M M @m. m MI

Management Unit II--Mississippi Delta

The Mississippi Delta generally has a poorly defined, highly

irregular shoreline that is subject to the-very rapid changes that

result from periods of deltaic sedimentation, wave erosion, and subsidence

of unconsolidated sediment. Traditionally thought of as an accreting

area, evidence suggests that over the past fifteen to twenty years, the

Mississippi Delta has actually decreased in total area although it has

slowly prograded seaward (Morgan 1973). The growth of the delta has

certainly been slowed, and this trend should continue as long as the

main receiving basin of sediment is the deeper offshore waters.

The irregularity and ephemeral nature of much of the delta area

limits analysis to the inner marsh type method (percent area change).

Morgan (1973) presents a rather detailed account of land change trends

in the delta from the time of the earliest surveys to the present. In

addition, Gagliano and van Beek (1970) present data on some of the more

recent changes in the land area of the delta. The reader is referred to

these studies for a more detailed account.

A detailed analysis of the entire delta is not only a tedious task,

but results may be questionable because of the resolution of available

data. The low lying delta experiences rapid changes depending upon water

level. Thus, during spring floods, the actual exposed area of the delta

would be less than low water following the flood or low water occurring

during the winter months preceding the flood. To further complicate the

method of analysis, a given unit area will possibly experience both

accretion and erosion contemporaneously. Figure-5 portrays an area in

the delta that has experienced both net erosion and also localized

accretion during the time period examined.

CHANGES IN MIDDLE GROUND AREA. 1958-1971

77 MARSH
E] LAND LOSS

LAND GAIN

V:oh
MIDDLE GROUND

NORTH

96.
MUDLUMPS

,q
40t 7.

-N- . ....

SCALE
0 Ikm

Figure 5. Land changes in the Middle Ground area 1958-1971.

Table -7

Erosion Rates for Sites Analyzed in the
Mississippi Delta Management Unit

Retreat
Z adrangle Rate or
.0w
w Site Area Parish QU Data Sources & Dates m/yr Land Loss
Size(minutes)

USGS Quadrangle USGS Quadrangle
2 3,3 01 Middle Ground Plaquemines East Delta 15 from 1958 photos from 1971 photos 1.67

The only accurate method of evaluating rates of change in the delta

would be to prepare areal comparison (e.g., Fig. 5) of tide-control

photography for the entire delta; however, such an endeavor would be

excessively time consumin . The example deliniated in Fig. 5 had a net
9

loss of 1.67 percent per year from 1958 to 1971 but as can be seen from

this figure, the total change in the form of actual loss and gain was

considerably greater. This is an important management consideration,-and

net loss or gain should not be used when evaluating active deltaic

areas.

Management Unit III--Barataria

Coastline Erosion . The present coastline of the Barat aria Basin

Management Unit is the result of a complex series of e vents involving

delta bui-lding and subsequent deterioration. No fewer'than four'delta

complexes have contributed sediment to the area. They are (from oldest

to youngest): St. Bernard, Lafourche, Plaquemines, and Modern. This

long and complex history of sedimentation and deterioration is reflected

in both substrate characteristics and surface expressions. Consequently,

the coastline of this unit is represented by a number of features:

barrier islands, cheniers, bays, distributary mouths.

The artificial closing of the Bayou Lafourche distributary in 1904

and the creation of the man-made levee system along the Mississippi

River have effectively severed sediment supply to the area (Adams et al.

1976). Thus, except for small amounts of water coming in through the

locks on the Gulf Intracoastal Waterway and seepage through the Mississippi

levees, the Barataria Basin is a true hydrologic basin.

The nourishment of beaches along this coastline is dependent upon

littoral drift. Although most of coastal Louisiana experiences a dominantly

westerly drift, this area experiences seasonal shifts in the direction

of littoral drift. Suhayda (1976) and Murray (1976) discuss the processes

associated with waves and nearshore currents, respectively, offshore of

the Barataria unit, and Harper (1975) and Conatser (1971) have examined

those processes involved in producing an easterly drift from Belle Pass

to Barataria Pass.

The variability in littoral drift, waves, age of sediments, and

morphology has led to a corresponding variability in erosion rates along

the coastline of the Barataria unit.

In Lafourche Parish the coastline has retreated an average of 14

meters per year (1954-1969),

This area has experienced the highest rate of coastline retreat. This

retreat rate is attributed to several factors:

.1) The sediments are re-latively young, with Bayou Lafourche

representing the most recently abandoned course of the

Mississippi River.

2) There is wide exposure to wave attack from the south.

3) The presence of coarser-grained and unconsolidated sediments

of the east-west trending cheniers, which are easily eroded by

mechanical action.

4) Landward drifting gulf currents approach the coast in the

vicinity of Belle Pass and then divide into easterly and

westerly drifts. Therefore, longshore drift carries sediments

away but not toward the area.

The Grand Isle area has been eroding at its western end and accreting

at its eastern end in response to the easterly drift during the period

from 1954 to 1969. The construction of the west end jetty in 1972

appears to have stabilized erosion in this area. Because of the extensive

development of Grand Isle, various engineering solutions have been

employed, and these are presented in Chapter 4.

A detailed analysis of the erosion occurring along the Grand Terre

Islands is provided by Adams et al. (1976). That analysis indicates

that erosion on Grand Terre proper is occurring along most of the island,

which has been reduced in size from 385 hectares in 1956 to 318 hectares

in 1972. Erosion is occurring along both the eastern and western ends

(Pass Abel and Barataria Pass) as well as on the shorefront, particularly

along the western end.

Although for some time erosion has dominated along the Grand Terre

Islands, the construction of groins and the east-end rock jetty on Grand

Isle have served as barriers to- easterly moving sediments that nourished

Grand Terre beaches periodically during the fall and winter months

Thus the tradeoff for increased stability of Grand Isle is, in part, the

increased erosion of the Grand Terre Islands. The westerly drift of

sediments predominates during the rest of the year, but the leeward

position of this area in relation to the Mississippi Delta reduces the

strength of the westerly drift in comparison to other areas along the

Louisiana coast (Adams et al. 1976).

East of Cheniere-Ronquille, the coastline has.retreatedat an average

rate of 6.3 m/yr. The variability for the twenty-two examples examined

is significant, with retreat rates ranging from 0 to 14.1 m/yr. whereas

the erosion rates for this area are generally high, they are less than

the rates for the somewhat older Lafourche sediments to the west. This

is attributed to the mitigating effects of limited amounts of Mississippi

River sediments that are deposited via the weak westerly drift and to

the leeward location of the area in relation to the seaward protruding

delta, which reduces wave energies.

Well-Defined Lakeshores and Bays. A total of eleven lakes and bays

were examined which, combined with examples examined by Adams et al.

(1976), provide us with the most complete coverage of any management

unit.

Despite the more inclusive coverage for this unit, there remains a

high degree of variability, with expected patterns of erosion often

being masked by other factors. The impact of man's activities is particularly

evident in this unit, and this in turn adds more variables to a situation

already difficult to understand.

An examination of examples that are considered to have been the,

least affected by man reveals that erosion rates of lakeshores and bays

are generally higher than for -other units except for Terrebonne, which

has comparable rates. Shorelines around saline lakes and bays generally

have lower rates than their brackish or fresh couterparts. The relatively

high erosion rates for brackish areas is consistent with other units in

the Deltaic Plain and is in agreement with Gagliano and van Beek (1970).

Fresh marsh lakeshores and bays have experienced the highest rate

of erosion (4.67 m/yr) compared to saline (1.48 m/yr) and brackish (2.91

m/yr) for examples examined in the Barataria Management Unit. This is

not consistent with the work of Gagliano and van Beek (1970), but it

compares favorably with results obtained in this study for Southwest

Louisiana and the Terrebonne unit in the Deltaic Plain. Fresh marsh

shorelines along Lakes Cataouatche, des Allemands, and Salvador have

undergone severe erosion, particularly along their southern and southeastern

shores. This indicates that the stronger northerly components of wind-induced

may be the responsible agents, and the fact that the larger lakes have

higher rates of erosion further supports the hypothesis of wind-induced

erosion. These same winds, however, also affect brackish and saline

shorelines, but erosion rates there are considerably less. The high

rates of erosion along sections of fresh marsh lakeshores is attributed

to the unstable nature of the sediments comprising the marshes. These

areas are typically floating marshes (flotant) consisting almost entirely

of organics and are particularly,susceptible to breaking up in response

to high energy conditions such as in the case of cold front passages and

tropical disturbances.

Inner Marsh Land Loss. Land loss in the Barataria unit is high

relative to other units, with most examples being either in the above

average or excessive category -(0.3 to.1.0 percent/yr and greater than 1.0

percent/yr, respectively). The relatively high rates are to be expected

when one considers the relative age and depth of sediments, the lack of

continued inorganic sediment supply, and the degree of cultural activities

in the area.

Although the number of examples used are few, saline marshes appear

to be the most stable marsh type and are the least variable with respect

to loss rates from site to site. This is consistent with values determined

for lakeshores and bays and for saline marshes in general throughout the

Deltaic Plain. As pointed but by Saucier (1963), saline marshes represent

an advanced stage of deterioration that has already passed the stage of

maximum land loss rate.' In a sense, saline marshes are remnants, and

these remnants are either more resistant to erosion or have experienced

more favorable conditions for remaining in existence than their eroded

counterparts.

Brackish marshes in the Barataria unit have experienced above

average land loss rates (mean 0.8 percent/yr). Rates are highest

near the levees of Bayou Lafourche and associated distributaries and

the present Mississippi River. The weight of the levees increases the

instability of the marsh sediments, which is translated into localized

subsidence and depicted as land loss.

Fresh marsh areas have experienced land loss rates similar to

brackish marsh areas (mean- 0.8 percent/yr). The variability for fresh

marsh areas is high, and examples range from stable to excessive losses.

The variability in substrate is high and ranges from floating mats to

low lying levees with little or no surface expression. These areas are

close to population centers, which may cause indirect land loss through

the discharge of various waste materials via canals and natural waterways.

Swamp forest areas generally appear stable, showing little or no change.

90- 30- 90,00' 89
T

30'00
kq\, 'A,

"32410
32409;
J
C@11

0
_M201 3204,j Iz
203
4
Ln

29030'-
t MI R

332.0

311
3
2@ 1
31125 31130
3
\-13 1 1 1
1 5
16
120
,6A -0
0 10 15 20 Mi.
5 10 15 20 25 30 Km. 31101- Vill
31105-

Figure 6. Site locations in the Barataria Management Unit.

Table &

Erosion Rates for Sit es Analyzed in the
Barataria Management Unit

C 0
0 r_ .
E 0
Retreat
Site Area Parish Quadrangle & Rate or
Size(minutes) Data Sources Dates m/yr Land Loss
3 1 1 01 Long. 90* 13' Lafourche Belle Pass 15 1954 air photos 1969 USCE uncon-
Jack Ammann Corp. trolled photomosaics 8;1

3 1 1 02 Long. 90' 12' 14.1

3 1 1'03 Long. 90* 11' 24.0

3 1 1 04 Long. 90* 10' 21.9

3 1 1 05 Long. 90* 09' 20.1

3 1 1 06 Long. 90* 08' Leeville 7-1/2 14.1

3 1 1 07 Long. 90* 071 Caminada Pass 7-1/2 14.1

3 1 1 09 Long. 90* 06' 12.0

3 1 1 09 Long. 90* 05' Jefferson 9.9

3 1 1 10 Long. 90* 04' 9.9

3 1 1 11 Long. 90* 03' 3.9
3 1 1 12 Grand Isle 8.1
Long. 90* 02'
3 1 1 13 Grand Isle
Long. 90* 01' 3.9

3 1 1 14 Grand Isle. 3.9
Long. 90* 00'

3 1 1 15 Grand Isle 0
Long. 89* 59'

3 1 1 16 Grand Isle Grand Isle 7-1/2 0
Long. 89* 58'

3 1 1 17 Grand Isle Ft. Livingston 15 Adv.
Long. 89* 57'

3 1 1 18 Grand Terre 6.0
Long. 89* 56'

3 1 1 19 Grand Terre 0
Long. 89* 55' 1954 air photos 1969 USCE uncon-
3 1 1 20 Long. 39* 54' Jefferson Ft. Livingston 15 Jack Ammann Corp. trolled photomosaics 12.0
3 1 1 21 Long. 89* 53' 9.9
3 1 1 22 Long. 89* 52' 9.9

3 1 1 23 Long. 89* 50' Plaquemines 12.0
3 1 1 24 Long. 89* 49' 8.1

3 1 1 25 Long. 89* 48' 8.1
3 1 1 26 Long. 89* 47' 14.1
3 1 1 27 Long. 89' 46' 8.1
3 1 1 28 Long. 89' 45' Empire 15 3.9

3 1 1 29 Long. 89* 44' 3.9

Table.3 continued

Retreat
Quadrangle & Rate or 2
Site Area Parish Size(minutes) Data Sources Dates m/yr Land Loss
>

31 130 Long. 89* 43' 0

31131 Long. 89' 42' 0

31132 Long, 89* 41' 0

31133 Long. 89* 401 2.1

31134 Long. 89* 39' 6.0

31135 Long. 89* 38' 12.0

31136 Long. 89* 37' 9.9

31137 Long. 89' 36' 6.0

31138 Long. 89* 35' Bay Coquette 7-1/2 8.1

31139 Long. 89* 34' 2.1

31140 Long. 89* 33' 3.9

31141 Long. 89' 32' 3.9
1954 air photos 1969 USCE Uncon-
31142 Long. 89* 31' Plaquemines Bay, Coquette 7-1/2 Jack Ammann Corp. trolled photomosaics 9.9
31143 Long. 89* 30' 11 . . 11 11 .9.9
USGS Quadrangle 1974 NASA MX293 2.6
32101 L. Palourde Lafourche Leeville Caminada from 1952 photos
Pass 15

32102 L. Laurier 1.0
32103 Adams Bay Plaquemines Empire 15 USCS Quadrangle
from 1946 photos 1.8

1.
32104 Bastian Bay USGS Quadrangle 0.5
3@2201 Little Lake Lafourche Barataria 15 from 1945 photos. 2.1
32202 Little Lake Bay Dosgris 15 USCS Quadrangle
from 1952 photos 3.3

32203 Little Lake Jefferson 1.6
32204 Little Lake USCS Quadrangle
Barataria 15 from 1945 photos 5.6
32205 Unnamed Lake Lafourche Mink Bayou 15 USCS Quadrangle 2.0
from 1952 photos
32206 E L. Laurier Plaquemines, Pointe a la Hache USCS Quadrangle 2.0
is from 1946 photos

32207 Round L. 1. 1. . 1. 4.5

32@2 08 Round L. Jefferson 11 2.2
32 301 SE L. Salvador Lafourche Barataria 15 USGS Quadrangle
from 1945 photos 8.7

32 401 E L. Salvador Jefferson 13.2
USGS Quadrangle
32 402 NE L. Salvador Jefferson Ne. Orleans 15 from 1950 photos 6.8

Table,8 continued

c 00 Retre t
W .- - -
r. 11 Quadrangle Rat:
7-
W or
wwa) Site Area Parish Size (minutes) Data Sources Dates m/yr Land Loss
r
aw

USGS Quadrangle
32403 NW L. Salvador St. Charles N-O-& Hahnville 15 from 1950 photos 1974 NASA MX293 5.6

3Z404 SW L. Salvador Cutoff 15 USGS Quadrangle
(1939) no photo date 2.9

32405 SW L. Salvador Lafourche 1. 11 1.7

USGS Quadrangle
32406 L. Cataouatche Jefferson New Orleans 15 from 1950 photos 2.2

32407 L. Cataouatche St. Charles N.O.6 Hahnville 15 0.8

32408 Lac des Alle- St. John the Lac des Allemands USGS Quadrangle 0.9
mands Baptist is from 1945 photos

32409 Lafourche 5.0

32410 0.9

32411 St. John the 0.9
Baptist

32501 Lafourche 0.9

32502 St. John the 0
Baptist

32503 0 -
USGS Quadrangle
33101 St. Mary's Point Plaquemines Ft. Livingston 15 from 1960 photos 0.37

33102 L. Palourde Lafourche Leeville & Caminada USGS Quadrangle 0.09
Pass 15 from 1952 photos

33103 L. Grande E. Plaquemines Ft. Livingston 15 USCS Quadrangle 0.33
1 Ecail le from 1960 photos

33104 Bay Adams Plaquemines Empire 15 USGS Quadrangle 0.28
from 1960 photos
USCS Quadrangle
33201 Bavou Perot Lafourche Barataria 15 from 1961 photos. 1974 NASA mx273 .35
33202 Bay l'Ours Lafourche Barataria & Cutoff 0.26
15
33203 Turtle Bay Jefferson Barataria 15 0.76

33204 Dupre Cut Jefferson 1. 0.48

33205 Round Lake Plaquemines Pointe a Is Rache 15 0.31

33206 Unnamed Lake Lafourche Mink Bayou 15 USCS Quadrangle 1.25
from 1952 photos
33207 Venice Oil Field Plaquemines W. Delta & Venice USCS Quadrangles 0.90
from 1958 photos
33301 The Pen Jefferson Barataria 15 USCS Quadrangle 0.53
from 1961 photos
33401 SW L. Salvador Lafourche Catahoula Bay 15 USCS Quadrangle 1.20
from 1962 photos

90'30' 90,00 8

30'00'

'tb, I., e
.h,
whe

29o3O'

V:"

-Y
C-dratid I e
Wall
11y) 'Joy, Wall
DO
d Grand Isle

jv
0 5 10 15 20 ML

5 10 15 20 25 30 Km. Relle Pass

Figure 7. Place names in the Barataria Management Unit,

Management Unit IV--Terrebonne

Coastline Erosion. The Terrebonne Management Unit's coastline

extends east from 91*15' west-longitude on Point Au Fer Island to the

mouth of Bayou Lafourche at Belle Pass (Fig. 9). This section of

coastline is disjointed into.two natural units. The western portion is

.a more-or-less continuous shoreline extending from 91'15' west longitude

to the mouth of Bayou Grand Caillou at Caillou Bay. The eastern,portion

is more seaward and consists of a discontinuous series of barrier islands.

The erosion rates of these two portions are considerably different, with

the barrier island segment experiencing higher rates.

Along the western part of the unit, erosion is occurring at a rate

of 5.3 meters per year (1954-1969). This rate is similar to the rate of

coastline erosion for the Atchafalaya Management Unit's coastline along

Point Au Fer Island. As both areas are largely composed of Teche-Mississippi

sediments, this similarity is expected.

In contrast, the eastern part of the unit is eroding at a rate of

8.5 meters per year. The barrier islands that characterize this section

are comprised of somewhat younger Lafourche-Mississippi sediments and

are located in a more seaward position (receive more wave energy).

Therefore this higher rate is to be expected.

In contrast to the more continuous coastline west of Caillou Bay,

the barrier islands have highly variable erosion rates with erosion

dominating the eastern end and the gulfward-facing shore, and accretion is

commonplace on the downdrift end of these islands. Thus, these barrier

islands (Isles Derniers and West and East Timbalier) are not only experiencing

net retreat but are moving laterally along the coast because.of the

littoral transport of sediment.

Well-Defined Lakeshores and Bays. A total of ten lakes and bays

were examined for analysis (see Table 9) 4Ad all, with the exception

of Lake Verret, were undergoing erosion to some degree. As is typical of

the Deltaic Plain, erosion is dominant but,highly variable in the.Terrebonne

Management Unit. This unit and the Barataria Management Unit are experiencing

.,the highest basin-wide erosi6n rates in coastal Louisiana.

Patterns of erosion are more complex than in the Chenier Plain in

Southwest Louisiana. Lakes and bays that have not been modified to any

great extent by man and are not close to natural ridges (e.g., levees)

generally experience the same pattern of erosion as in the Chenier

Plain, with southern shorelines exhibiting greater rates of erosion than

northern shorelines. This, as outlined in the Calcasieu-Sabine and

Mermentau Management Unit discussions, 'is regarded as being related to

the stronger northerly winds and differences in sediment depth. The

rate of erosion, however, is far greater for the Terrebonne area than

Southwest Louisiana, and this difference may be related to the overall

greater instability of sediments in the Terrebonne Unit. In addition,

no clear-cut relationship was found- between the size of the waterbody

and the rate of erosion for Terrebonne as was the case in the Chenier

Plain.

No relationship could be determined between vegetation type and

rate of erosion except that the highest rates tended to be associated

with brackish marshes.

One pattern of erosion seems,to consistenly emerge both in this

unit and in the Barataria unit. All lakes examined that were located in

a depressed area between natural levees of small distributaries or

located parallel and close to large former distributaries (e.g., Bayou

Lafourche) exhibited high erosion rates, and in many cases these rates

were comparable to or even greater than rates found at the coastline.

This pattern has no relationship to vegetative type. The high rate of

erosion in these examples is probably related to subsidence induced by

the weight of the natural levees, which cause the unstable sediments to

consolidate. In many cases the long axis of these lakes parallel the

ridge, probably reflecting the axis of maximum depression.

Inner Marsh Land Loss. Six inner marsh areas representing all

marsh types were analyzed. All the examples exhibited above average

losses (0.3 to 1.0%/yr). Further examination of this category does not

reveal any relationship between vegetative type and landloss rate. One

notab.le exception is that the fresh marshes in the northwest par t of

Terrebonne Parish have lower land,loss rates than fresh or other marsh

types throughout the remaining parts of the management unit. This may

be related to the influence of Atchafalaya River sediments.

The high rate of land loss throughout the unit is consistent with

the high rates of erosion for the coastline and well-defined lakeshores

and bays. Overall, the rates determined for the Terrebonne Management-

Unit compared to other units support previous geologic evi dence associated

with land.loss; namely, areas of geologically younger deltaic sediments

and areas containing.thicker sequences of these sediments.will have

higher erosion. rates.

91*w 90 3a

30*00'
X

0q,

04f
+ 04,reh,

42402,r@@
Or3401

29'30' 42401
702
@@22 423
1-7
%4YO
32

411 COMI
1105
4110
0110
THS

15 20 Mi 41116-
0 5 10 41122
a 5 10 15 20 25 30 Km. TV'I @I 14 @-4 4
114@
LIMP 114
I 4113PI13 4114 ON

Figure 8. Site locations in the Terrebonne Management Unit.

Table 9

Erosion Rates for Sites Analyzed in the
Terrebonne Management Unit

C 0
Retreat
a
0z
Quadrangle & Rate
Site Area Parish Size(minutes Data Sources & Dates
C 0 .0 m/yr or Land Loss

1954 Air photos 1969 USCE
4 1 101 Long. 9l* 1V Terrebonne Oyster Bayou 15 Jack Ammann Corp. uncontro@lled
photomosaics 6.0

4 1 102 Long. 91' 13' 8.1

4 1 103 Long. 91* 12' 6.0

4 1 104 Long. 91* 11' 6.0

4 1 105 Long. 91* 10' 6.0

4 1 106 Long. 91* 09' 3.9

4 1 107 Long. 91* 08' 3.9

4 1 108 Long. 91* 07' 3.9

4 1 109 Long. 91* 06' 6.0

4 1 110 Long. 91* 05' 6.0

4 1 111 Long. 91* 04' 6.0

4 1 112 Long. 9l* 03' 6.0

4 1 113 Long. 91' 02' 3.9

4 1 114 Long. gl* oll 2.1

4 1 115 Long. gl* 00' 3.9

4 1 116 Long. 90* 59' Grand Bayou du 6.0
Large 7-1/2

4 1 117 Caillou Bay
Long. 90* 58' 6.0

4 1 1IS CaIllou Bay
Long. 90* 57' 6.0
4 1 119 Caillou Bay Terrebonne Grand Bayou du 1954 air photos 1969 USCE
Long. 90* 56' Large 7- 1/2 Jack Ammann Corp. uncontrolled 3.9
photomosaics
4 1 120 Caillou Bay Grand Bayou du 3.9
Long. 90* 55' Large 7-1/2

4 1 121 Caillou Bay
Long. go* 54' 3.9

4 1 122 Caillou Bay 3.9
Long. 90* 53'

3 Racoon Point Western Isles 21.9
Long. 90* 58' Dernieres 7-1/2

4 1 124 Isles Dernleres 6.0
Long. go* 57'

4 1 125 Long. 90* 56' 6.0

4 1 126 Long. 90* 55' Adv.

4 1 127 Long. 90* 54' 15.9

4 1 128 Long. 90* 50' Central Isles 6.0
Dernieres 7-1/2

4 1 129 Long. 90* 49' 8.1

4 1 130 Long. 90* 48' 14.1

4 1 131 Long. 90* 47' 8.1

Table 9 continued

Retreat
z
.0w Quadrangle & Rate
z000 Site Area Parish Size(minutes) Data Sources & Dates M/yr or Land Loss
>

41132 Long. 90* 46' 12.0
41133 Long. 90* 45' 6.0
41134 Long. 90* 44' Eastern Isles 3.9
Dernieres 7-1/2

41135 Isles Dernieres 8.1
Long. 90* 43'
4 1 1 36 Long. 90* 42' Terrebonne Eastern Isles 1954 air photos 1969 USCE
Dernieres 7-1/2 Jack Ammann Corp. uncontrolled 8.1
photomosaics
4 1 1 37 Long. 90* 41' 6.0
411 38 Long. 90,* 40' 6.0
411 39 Long. 90* 39' 6.0

411 40 Timbalier Is. Cat Island Pass
Long. 90* 31' 7-1/2. Adv.
411 41 Timbalier Is. Adv.
Long. 90* 30'
411 42 Timbalier Is. Timbalier Is. 7-L/2 3.9
Long. 90* 29' 12.0-
411 43 Timbalier Is.
Long..90' 28'
411 44 Timbalier Is. 9.9
Long. 90* 27'
411 45 Timbalier Is. 6.0
Long. 90* 26'
411 46 E. Timbalier Is. Lafourche Calumet is. 7-1/2 0
Long. 90* 22'
411 47 E. Timbalier Is. 27.9
Long. 90* 21'
411 48 E. Timbalier Is. 15.9
Long. 90' 20'
411 49 E. Timbalier Is. 14.1
Long. go* 19,
411 50 E. Timbalier Is. 120
,Long. 9W 18'
411 51 E Timbalier Is. Lafourche Calumet Is. 7-1/2 1954 air photos 1969 USCE 8.1
Long. 90' 17' Jack Ammann Corp. uncontrolled
photomosaics

411 52 Long. 90* 16' 20.1
411 53 Long. 90* IV 8.1

411 54 Belle Pass
Long. 90* 14' Belle Pass 7-1/2 8.1
421 01 Lake Felicity Terrebonne Lake Felicity 15 USGS Quadrangle 1974 NASA MX293 0.3
(1944) no photo
date

421 02 7.1
422 01 SE Four League Bay Lake Decade 15 USCS Quadrangle 2.3
from 1955 photos

422 02 SW Four League Bay 0.9
422 03 NW Four League Bay 2.2

Table 9 continued

Retreat
Quadrangle Rate or
d L
0 Site Area Parish Size(minutes) Data Sources Dates m/yr Lan
.C 0-ISI

4 2 2 04 Lost Lake
0.8

4 2 2 06 N L. Mechant
4 2 2 05 Lost Lake 2.6

Bayou du Large 15 USC 'S Quadrangle 2.3
from 1940 photos

4 2 2 08 L Boudreaux
4 2 2 07 S L. Mechant 1.3
Dulac 15 USGS Quadrangle e1944) 6.3
no photo date
4 2 2 09 N & E Catfish
Lake Lafourche Lake Felicity 15 2.5
4 2 2 10 S&W Catfish Lake 6.3
4 2 3 01 NE Four League Bay
Terrebonne Lake Decade 15 USCS Quadrangle 2.8
from 1955 photos
4 2 4 01 Lake Theriot Terrebonne Bayou du Large'15 USGS Quadrangle 1974 NASA MX293 3.4
from 1940 photo,,
4 2 4 02 Lake Fields Lafourche Houma 15 USGS Quadrangle 5.2
(1944) no photo
4 2 5 01 Lake Verret date
Assumption Napoleonville 15 USGS Quadrangle 0
from 1950 photos
4 3 1 01 S Caillou Lake Terrebonne Grand Bayou 15 USGS Quadrangle
4 3 1 02 : Lake Chien from 1952 photos 0.52
Lake Felicity 15 USGS Quadrangle 0.55
from 1963 photos
4 3 2 01 N Lake Mechant Lake Mechant 15
4 3 2 02 Lake Quitman Lak.e Quitman 15 0.68
4 3 4 01 Bayou Penchant 0.93
Morgan City SIw 15 USCS Quadrangle
from 1964 photos 0.33
4 3 4 02 L.ake Theriot Lake Theriot 15 USGS Quadrangle 0.97
from 1963 photos

91*oa 90*30'

30*00' x
a.
a.

'L@k

zo
04erCh,,

29'30

Caillou Bay 13
0 5 10 15 20 Mi Racoon Pt.
0 5 10 15 20 25 30 Km.
Isles i),t@teres Timbalier Islands

Figure 9. Place names in the Torrebonne Management UniL.
7_

Management Unit V-.-Atchafalaya

Coastline Erosion. The coastline of the Atchafalaya Management

Unit extends from South Point on Marsh Island to 91* 15' west longitude

on Point Au Fer Island (Fig. 11). The section of coastline from South

Point to North Point (Point Au Fer Island) consists of discontinuous

near sea level oyster reefs. The latter set of aerial photography used

(1969) was not tide controlled; therefore, changes in these reefs cannot

be analyzed. Field checks of these reefs, however, following cold

front passages during the winter of 1975-1976 indicated that fine-grain

sediments were deposited over portions of them. The source of sediments

are obviously associated with the Atchafalaya River. General field

observations indicated that much of these deposits were currently being

eroded.; therefore, no conclusions were made as to their permanence.

From North Point to 91*15' west longitude (11 km), the coastline is

bordered by brackish and saline marshes. Most of this section of coastline

is undergoing erosion at an annual rate of 5.8 m (1954-1969). A 3 km

section, however, has experienced a considerable advance of 7.7 m/yr.

The advance of this small section is attributed to the reworking and

redepositing of eroded sections further east along the shoreline rather

than an influx of new sediments.

USCE1975.uncontrolled photomosaics indicate that the trend may

have reversed with the accretion now occurring along the coastline at

the western end of Point Au Fer Island. The continued seaward advance

of the Atchafalaya Delta should result.in the further progradation of

this part of the coastline.

Well-Defined Lakeshores and Bays. Virtually the entire length of

shoreline around Atchafalaya Bay has prograded between 1955 and 1975.

Much of the new subaerial exposures appeared following the flood years

of 1973-1975 (see Chapter 1). Continued progradation of the shorelines

and growth of the delta is expected. The rate of growth cannot be

predicted because it is largely dependent on the duration and peak of

the spring floods.

Although net growth should continue around Atchafalaya Bay, erosion

and reworking of sediments will occur between flood period s. Thus the

new land formed following a flood period should not be thought of as

permanent or stable land at this stage of delta development.

Inner Marsh Land Loss. The fresh marshes bordering the northern

part of Atchafalaya Bay have experienced a net land gain from 1952 to

1975. These gains of inner marsh areas are in the form of pond filling

and subsequent colonization..@ The high density of essentially natural

waterways between Bayou Sale and east of the Lower.Atchafalaya River

facilitates the input of sediment over these marshes.

Dispersed throughout these fresh marshes and increasing in density

as one progresses north towards Bayou Teche are areas of swamp forest.

Although the total swamp forest area has remained stable, it has experienced

the same influx of sediment as the fresh marshes. The responses to

these changes are much slower for swamp forest species than for marsh

grasses. Because our analysis of land loss/gain is based on changes in

the amount of vegetated area over approximately twenty years, it is

possible for us to detect changes in marsh areas but not in swamp forest,

although both areas are influenced by the same processes.

In the Atchafalaya Management Unit, brackish marsh is limited to

the western part of Point Au Per Island. Losses in this area are comparable

to those determined for brackish marshes in the southwest part of the

neighboring Terrebone Management Unit. As both of these areas are

largely comprised of Teche-Mississippi age sediments, their rates.of

loss are expected to be similar. Apparently modern Atchafalaya sediments

have not influenced the brackish marshes on Point Au Per Island to the'

extent of reversing or even retarding land loss rates. The continued

growth of the Atchafalaya Delta towards Point Au Per Island, however,

should result in a future slowdown of the rate of land loss.

CZ@ U",

30'00'

Pont Chewouil 46i
Robbit'Island 534 g
29'30' 4 0

-53201

51104

0 5 10 is 20 Mi.

0 5 10 15 20 25 30 Krn. g

Figure-10. Site locations in the Atchafalaya Management Unit.

Table 10

Erosion Rates for Sites Analyzed in the
Atchafalaya Management Unit

0 0
a :44 0 Retreat
Quadrangle Rate or I
Site Area Parish Size (minutes) Data Sources Dates m/yr Land Loss
@20 :1-.0 ;1'- .1954 air photos 1969 USCE
5 1 1 01 Long. 91* 18' Terrebonne Point Au Far 15 Jack Ammann Corp. uncontrolled Adv.
photomosaics

5 1 102 Long. 91* 17' 3.9

5 1 103 Long. 91' 16' 9.9

5 1 104 Long. 91' 15' 6.0

5 1 201 North Point 2.1
Long. 91* 21'

5 1 202 Long. 91* 20' 8.1

5 1 203 Long. 91* 19' Adv.
5 2 201 So. Point to Point Au Fer 15 1952 USN air photos 1975 USCE uncon-' Adv.
Fishing Point Lost Lake 15 trolled photomo-
saics

5 2 4 01 Pt. Chevreuil to St. Mary Bayou Sale, Belle Adv.
Shell Is. Isle 15 Pt. Au Far

5 3 2 01 Pt. Au Fer Is. Terrebonne Point Au Far 15 0.50

5 3 4 01 Hog Bayou St. Mary Belle Isle 15 USCS Quadrangle
from 1964 photos Gain
5 3 4 02 Little Hog Bayou Point Au Fer & 1952 USN air photos Gain
Belle Isle 15
3 3 5 01 Bayou Blue Belle Isle 15 USGS Quadrangle 1972 NASA MX194 .0
from 1964 photos

5 3 5 02 Cross Bayou 0

30'W

Ou
t
Tqx Lak6
OutleIt

Point Chevreuil
Rabbit Island
1@1 I
29'30'

Atchafalaya Bay

North Point

0 5 10 20 mi.

0 5 10 is 20 25 30 Krn.

Fi-ure -I-!. Place names in the Atchafalaya Management Unit.

/69

Management Unit VI-'Vermilion

Coastline Erosion. The coastline of the Vermilion Management Unit

extends east from Freshwater Bayou Canal to South Point on the eastern

end of Marsh Island (Fig. 13). The area is naturally divided into two

sections, east and west of Southwest Pass. The coastline along Marsh

Island has been relatively stable from 1954 to 1969. Morgan and Larimore

(1.957) report similar findings for the period from 1932 to 1954. The

stability along this section is caused by the effectiveness of the

offshore oyster reefs in reducing wave energies. At the eastern and

western margins of Marsh Island, where no reefs are located in the

nearshore area, erosion is occurring at a rate of 5 m/yr.

From Freshwater Bayou Canal to Southwest Pass, the coastline is

eroding at variable rates, except for a 3 km section along Chenier Au

Tigre, which has prograded 3 m/yr from 1954 to 1969. West of Chenier Au

Tigre to Freshwater Bayou Canal, erosion is occurring at a rate of 5

m/yr. East of Chenier Au Tigre to Southwest Pass, the erosion rate is

.variable, from 3 m/yr to 9 m/yr, and averages 7.5 m/yr. As in the case

of the Mermentau Management Unit, these erosion rates are significantly

greater than those reported by Morgan and Larimore (1957) for the period

from 1932 to 1954.

Well-Defined Lakeshores and Bays. A total of three lakes plus the

shoreline around Vermilion and East and West Cote Blanche Bays were

examined. The three lakes chosen--Portage, Fearman and.Onion--are all

located on the western side of Vermilion Bay in brackish marshes.

Portage and Onion Lakes show essentially the same pattern, with

erosion occurring along the north shore at a rate of approximately 0.4

m/yr and the remaining shoreline being essentially stable. Both lakes

are similar in size and are directly connected to Vermilion Bay via a

tidal channel. A spoil bank resulting from the dredging of an oil

access canal through Onion Lake has divided the lake in half and may

have had an effect on shoreline changes.

Fearman Lake is considerably larger than the above lakes and is

connected to Vermilion Bay at either end via tidal channels. No det.ectable

erosion occurred between 1952 and 1974. Some minor accretion occurred

along its eastern shoreline where Fearman Bayou connects the lake with

Vermilion Bay.

Shorelines around Vermilion and West and East Cote Blanche Bays

have either remained stable or have experienced minor erosion. The only

section of shoreline that has eroded at a rate greater than 1 m/yr is

located between Southwest Point and Deadman Island along Southwest Pass.

Erosion here (3.5 m/yr) is related to tidal scour. Southwest Pass

reaches a maximum depth of 50 m, which indicates that tidal currents are

relatively strong and capable of considerable mechanical erosion.

Comparison of erosion rates of Vermilion and West and East Cote

Blanche Bays with other bays and large lakes across Louisiana shows that

the Vermilion Bay complex area has experienced considerably less erosion

than one would expect on the basis of fetch alone. The reduced erosion

rates must be due to the role of the lower Atchafalaya River.

Based on the recent subaerial growth rates of the deltas forming at

the Lower Atchafalaya River Outlet and Wax Lake Outlet and the changing

bathymetry in the surrounding bays, the shorelines around Vermilion and

West and East Cote Blanche Bays should stabilize and may experience

significant progradation.

Inner Marsh Land Loss. The marshes within the Vermilion Management

Unit generally have experienced lower loss rates than the state average

in areas that have experienced little modification by man. Areas of

intensive man-related activities have faired poorly regardless of wetland

type.

Salt marsh in this unit is limited to a small area on the east side

of Southwest Pass (Chabreck 1972). Analysis of sample sites on the west

side of Southwest Pass indicates that the percent of vegetation cover

has.remained stable in this area:.

Brackish marsh north of Chenier Au Tigre and immediately east of

Freshwater Bayou Canal has experienced above average land loss rates.

This marsh was originally part of the area west of Freshwater Bayou

Canal, which is discussed in more detail in the Mermentau Management

Unit section.

The remaining brackish marsh areas have all experienced average or

below average land loss rates. Losses are probably largely attributable

to natural processes of erosion and subsidence. Atchafalaya River

sediments apparently have no,t yet contributed enough sediments to these

inner marsh areas surrounding Vermilion and East and West Cote Blanche

Bays to reverse the trend. Loss rates determined for these areas between

1951 and 1974 are similar to those determined by Gagliano and van Beek

(1970) for the period from the early 1930s to 1951.

The area from Cote Blanche Island to Jaws [also known as Little

Bay] was the only intermediate marsh site analyzed. Land loss there did

not differ from those rates determined for neighboring brackish marshes.

The only fresh marsh area where there was adequate aerial coverage

for analysis is east of Forked Island. This area, however, is rapidly

becoming reclaimed for agriculture primarily for rice and pasture. The

deliberate modification of these wetlands precludes any meaningful

analysis of natural processes.

Two different types of swamp forest were chosen for analysis: a

swamp on the Vermilion River north of Intracoastal City and an interdistributary

swamp west of Charenton Canal. Both types of swamp have remained stable

with respect to percent cover.

-30,00

163501
635
63202 0
3203
@22@ 6
63301",/

4 230 I-V
2 6323
62207@---z 62215
622bel-'
22
62 '0
62 _7_j@-
6 3B3 21
2 2"M2111'
63201 6220-IS'
62217;

0.1.
651104@@' Point Chevreuil
2 6121
29130' ZZ
il@816 6121027 612 7
61218
2;1@,
612 Rabbit Island
'12 2@
61229

0 5 10 15 20 W

0 5 10 15 20 25 30 K@

Figure 12. Site locations in the Vermilion Management Unit.

Table 11

Erosion Rates for Sites Analyzed in the
Vermilion Management Unit

Retreat
Quadrangle Rate or %
Site Area Parish Size(minutes) Data Sources Dates m/yr Land Loss
c 0 W

1954 air photos 1969 USCE
6 1 1 01 L ng. 92* 06' Vermilion Cheniere au Tigre Jack Ammann Corp. uncontrolled 6.0
photomosaics

6 1 1 02 Long. 92* 05' 6.0

6 1 1 03 Long. 92* 04' Cheniere au Tigre 15' 6.0

6 1 1 04 Southwest Pass 6.0
Long. 92' 03'

6 1 2 01 Freshwater Bayou Canal Pecan island 15' 3.9
Long4 92* 18'

6 1 2 02 Long. 92* 17' 3.9

6 1 2 03 Long. 92* 16' 6.0

6 1 2 04 Long, 91* 11' 6.0

6 1 2 05 Long 92' 14' Cheniere au Tigre 15' 0
6 1 2 06 Cheniere au Tigre Adv.
Long. 92* 13'

6 1 2 07 Long. 92* 12' 3.9

6 1 2 08 Long. 92* 11' 8.1

9.9
6 1 2 09 Long. 92* 10'

6 1 2 10 Long. 92* 09' 9.9

6 1 2 11 Long. 92* 08' 1. 12.0

6 1 2 12 Long. 92* 07' 6.0

6 1 2 13 Southwest Pass- Iberia 1960 air photos 6.6
Marsh Is. Jack Aumann Corp.
Long. 92* 02'
6 1 2 14 Long. 92* 01' Iberia Cheniere au Tigre 19 60 air photos 1969 USCE 3.0
15 Jack Ammann Corp. uncontrolled
photomosaics
6 1 2 15 Long. 92* 00' Marsh Island 15 0
6 1 2 16 Long. 91* 59' 0
6 1 2 17 Long. 91* 58' 0
6 1 2 18 Long. 91* 57' 0
6 1 2 19 Long. 91* 56' 0
6 1 2 20 Long. 91* 55' Adv.
6 1 2 21 Long. 91* 54' Adv.
6 1 2 22 Long. 91' 53' 0

Tablellcontinued

r a.

a 0 Retreat
R
Quadrangle & ate or
Data Sources a Ll
r Site Area Parish Sixe(minutes) & Dates m/yr L ad
0W
>

6 1223 Long. 91* 52' 0
6 1224 Long. 91* 51' Mount Point 7-1/2 3.3
6 1225 Long. 91* Sol 0
6 1226 Mound Pt. 6.6
Long. 91' 49'
6 1227 Long. 91* 48' 6.6
6 1228 Long. 91* 47' 0
6 1229 South Pt. 9.9
Long. 91* 46'
6 2101 Southwest Pt. Vermilion Cheniere Au Tigre USGS Quadrangle 1972 NASA MX194 3.9
15 from 1948 photos
6 2102

6 2103 Indian Point Vermilion Cheniere Au Tigre 15 USCS Quadrangle 1969 USCE 0.9
from 1948 photos uncontrolled
photomosaics

6 2104 0

6 2106 0
6 2105 S Vermilion Bay 0.6

6 2107 Hell Hole 0.9

6 2201 Portage Lake 0

6 2202 0.2

6 2203 SW Vermilion Bay 0.9

6 2204 0

6 2205 0.8

6 2206 Fearman Lake Adv.

6 2207 0

6 2208 Redfish Pt. to Buck Cheniere Au Tigre 1972 NASA KX194 0
Pt. to Little White Abbeville 15
Lake

6 2209 Vermilion Bay near
Onion Bayou Abbeville 15 0.5

6 2210 Vermilion Cutoff
to Mud Pt. Cheniere Au Tigre 15 0

6 2211 Mud Pt. Adv.
J

Table 11continued

r
C!
Retreat
z Quadrangle Rate or %
w Site Area Parish Size(minutes) Data Sources Dates m/yr. Land Loss

6 2 2 12 Vermilion Bay Vermilion Cheniere Au Tigre USGS Quadrangle 1972 NASA M]U94 0.8
(Mud Pt. to Lake Abbeville 15 from 1948 photos
Cleodis)

6 2 2 13 Vermilion Bay Abbeville & Derouen 15 0
(Lake Cleodis to
Lake Cock)

6 2 214 W Cote Blanche Bay St. Mary Bayou Sale 15 USGS Quadrangle 0.4
from 1955 photos

6 2 215 W Cote Blanche Bay 0
(Jaws to Marone Pt.)

6 2 216 E Cote Blanche Bay 0.6
(Marone Pt. to Yellow
Bayou)

6 2 217 E Cote Blanche Bay 0
(Yellow Bayou to Bayou
Sale Bay)

6 2 301 Cote Blanche is. 0

6 2, 101 Cole Blanche Is. to 0.6
Jaws

6 3 101 Southwest Pass Vermilion Cheniere Au Tigre 15 USCS Quadrangle USGS Orthophoto 0
from.1948 photos Quadrangle 1974
photos

6 3 201 Freshwater Bayou Pecan Island 15 1952 USN photos 0.54
Canal

6 3 202 Green Is. Bayou Abbeville 15 USCS Quadrangle 1972 NASA HX194 0.24
from 1948 photos

6 3 203 Shark Island Iberia Derouen 15 1952 USN photos 1972 NASA MX194 0.08

6 3 204 Cypremort St. Mary 0.20

6 3 205 Freshwater Lake
Bayou Carlin Bayou Sale 15 USGS Quadrangle 0.07
from 1955 photos

6 3 3 01 Hackberry Lake Bayou Sale 1952 USN photos 0. 27
Jeanerette 15

6 3 5 01 Vermilion River Vermilion Abbeville 15 USCS OrthophotD 0
below Bancher Quadrangle from
1974 photos

6 3 5 02 Bayou Choupique, St. Mary Jeanerette 15 USGS Quadrangle 1972 NASA KX194 0
from 1962 photos

-30*00'

5 Y.
U Forked Wand

j
e
'Onion LZ@l
%Y% - cj-
@ I/

Cypremort Pt.
Fearm n h
est Cote Blanche

-f'@7 South",
P"rtage Lak?@F

lhenierv utt Tigre
rsh 1A @l C61,
Point Chevreuil
29*30'
South h,int Rabbit Island

10 15 20 Mi.

0 5 10 15 20 25 30 K.,

.Xigure 13. Place names in the Vermilion Management Unit.

ManaRement Unit VII--Mermentau

Coastline Erosion. The Mermentau Management Unit's coastline

extends east from the natural mouth of the Mermentau. River to the entrance

of the Freshwater Bayou-Belle Isle Canal System (Fig. 16). Beginning at

the natural mouth of the Mermentau River and moving east along Hackberry

Beach for seven kilometers to State Cut, the coastline is eroding at a

rate of 1.5 m/yr. This is a reversal of the trend occurring to the

immediate west of the Mermentau River, where accretion is 3.2 m/yr.

East of the State Cut for a distance of 60 kilometers.to Dewitt Canal,

the coast is eroding at a rate of 11.7 m/yr. This represents the highest

rate of coastline erosion west of the Isles Derniers in Terrebonne

Parish. The 11.7 m/yr retreat rate for 1954 to 1969 is slightly greater

than the 9.1 m/yr of retreat for 1932 to 1954 (Morgan and Larimore

1957). This difference is not felt to be indicative of a significant

trend because the increase probably reflects the effects of Hurricane

Audrey. This section of coastline is undeveloped and much of the land

is in public ownership.

East of Dewitt Canal the coastline is prograding at a rate of 9

m/yr for a distance of 3 km. Beyond this section to Freshwater Bayou

Canal, erosion is occurring at a rate of 4 m/yr. During the period from

1932 to 1954, both of these sections experienced accretion at a rate of

6.3 m/yr due to mudflat deposition. Thus it appears that the increase

in accretion east of Dewitt Canal (6.3 m/yr from 1932 to 1954 to 9 m/yr

from 1954 to 1969) is the result of the displacement of reworked sedimentfrom

the east.

Well-Defined Lakeshores. A total of ten lakes were examined in the

Mermentau Management Unit (Figs. 15 and 16). Lower Mud, Miller [also

shown as Tolan Lake on some ma ps], and Flat Lakes are saline to brackish.

The remaining lakes are all dominated by fresh marshes along their

shorelines except for the southwest shore of Grand Lake, which contains

intermediate marsh, and Lake Arthur, which borders on the Pleistocene

terrace.

Lake Arthur represents the only known stable lake north of Grand

Chenier in this management unit. Most of its shoreline consists of

subaerial Pleistocene sediments, which account for its stability. The

Mermentau River flows into,Lake Arthur from the northeast. At this

point, swamp vegetation borders the lake and this section has also

remained stable. At the southwest portion of the lake just above Lowry,

a small pocket of fresh marsh dominates the shoreline. This area has

been undergoing shoreline advance.

The remaining lakes north of Grand Chenier, which include Catfish,

Grand, Misere, Sweet, White, and Willow, all exhibit similar erosion

patterns. Southern and southeastern shorelines generally have higher

erosion rates than their northern counterparts and usually the larger
the lake, the greater the erosion rates. Insofar as all these lakes are

approximately the same depth, the above erosion pattern appears to be,

related to wind speed and direction as discussed elsewhere (see Calcasieu-

Sabine Management Unit discussion).

Based on size, Grand and White Lakes should have erosion rates

similar to Sabine and Calcasieu Lakes. Although the pattern of erosion

is similar, Grand and White Lakes have been eroding at a rate several

times greater than Calcasieu or Sabine Lakes, and they have eroded at a

greater rate than lakes in similar vegetation zones in the Deltaic Plain

where Recent sediments are considerably.thicker. This high rate of

erosion has led to the construction of levees along much of White Lake

and sections of Grand Lake. Many of these levees have been set back

from the present shoreline; therefore, it is not yet,possible to analyze

their effectiveness in retarding erosion. Case studies of the effect of

lake ridges and spoil deposits from neighboring lakes may provide some

insight into the future effectiveness of thes e levees.

Cheniere Du Fond is a lakeshore ridge located on the southeast

shore of Grand Lake.(Fig.14 From 1932 to 1951 it retreated back over

the marsh at a rate of less than 1 m/yr. From 1951-1,974 it has retreated

2.5 m/yr and has all but disappeared. Without the presence of this

ridge, shoreline erosion will probably accelerate. Based on the above

erosion rates, two questions arise:

1) , Why have they accelerated?

2) Why has Cheniere Du Fond all but disappeared as opposed-to

being thrown back over the marsh as it was in the past?

A brief examination of other areas along Grand and White Lakes

indicates that erosion rates there have-also accelerated by as much as

an order of magnitude. Erosion of lake shorelines south of Grand Chenier,
however, 'has not accelerated'. Examination of pre- and post-Hurricane@

Audrey air photos indicates that whereas Hurricane Audrey caused some

detectable erosion, it only accounts for a small portion of the total

accelerated rate.

To this point we have eliminated several possible causes (hurricanes,

depth of sediment, and fetch) but have not documented the cause. We

believe it is significant that the lakes that are experiencing high

erosion rates are all within the Mermentau water management area. The

@t,@ROIW-,
ISLAND

LATANIA
ISLAND

GRASSY
POINT
@ILAND
'W4

ACKBERRY
POINT 4Q

LLA
UMBRE
POINT

4Z- SHORT
POIN

ATFISH POINT
CONTROL STRUCTURE

TEBO DINT

CATFISH LIT L
CA s.
LAKE

BETTY
LAKE

LA.e
"IT kent E 013 S
-N- LO
tAt e

..O.ELI.t

Figure 14. Shoreline erosion along Grand Lake 1015i-197-4.

Mermentau water management area is a man-made holding area for water to

be used for rice irrigation. A series of control structures completed

in 1951 prevent saltwater intrusion into the area and hold fresh water

in. The structures have artificially raised water levels within the

system. This increase in water level may have been sufficient to raise

the height of wind induced waves from breaking onshore to breaking over

the shore and could explain why Cheniere du Fond has all but disappeared

instead of just being displaced further back over the marsh.

As exemplified by Grand Lake, the larger lakes in this area have a

tendency to round themselves. This is illustrated by the fact that

points (e.g., Umbrella Point, Short Point) along the lakeshore have the

highest erosion rates. Through erosion Grand Lake has incorporated

several other lakes (e.g., Catfish Lake). If the present trends continue,

it is expected that coalescing will continue until the area between Lake

Misere and White Lake becomes one lake.

Levees along the southwest shore of White Lake have successfully

retarded erosion. These lev ees combined with other levee systems

however, have impounded those marshes south and southwest of White Lake

and have consequently removed those areas as nursery grounds.

Saline to brackish lakes just inland from the coastline have either

remained fairly stable or have accreted. Miller's Lake has undergone

major accretion, and Flat Lake has remained stable except for a small

segment of shoreline that has accreted. The amount of accretion that

occurs in these saline lakes appears to be directly related to their

proximity to the coastline. Consequently, it is believed that the

accretion occurs infrequently and results from storm waves that wash

beach deposits back into these lakes. The dominant vegetation on these

accreting areas is oyster grass (Spartina alterniflora).

Lower Mud Lake, which is predominantly saline despite being part of

the Mermentau River system, has experienced a complex interaction of

erosion and accretion that is probably due to man's intervention. The

natural mouth of the Mermentau River is now silting in. Farther east

along the southern shoreline,.erosion is occurring and is greatest in

the vicinity of the State Cut (a man-made channel exiting to the gulf,

see Fig. 16). Oth er shorelines of this lake could not be assessed

because of cultural modification.

Inner Marsh Land Loss. Although coastline and lake shoreline

erosion rates are relatively high, inner marsh loss has been generally

below the state average. This is particularly true for the fresher

marshes within the Mermentau water management area. These findings of

ma
,low inner marsh loss rates are, however, somewhat misleading. Approxi tely

forty percent of the marshes in this area are impounded (Gosselink, in press).

This includes wildlife impoundments and@agricultural impoundments where

marsh vegetation has been replaced by other species. Our analysis of

inner marsh areas that change to open water does not include these

impounded areas. In addition, it could be argued that the entire Mermentau

water management area is a type of impoundment. Whereas we recognize

that this area is impounded periodically every year, water exchange does

occur during periods when the control structures remain open. Thus

although natural water exchange has been substantially modified, we have

included sample site s from within the Mermentau water management area

with the understanding that we are dealing with different circumstances.

There are no major areas of swamp forest in the Mermentau area.

Patches of swamp forest vegetation are present on the flood plains of

the Mermentau River, Bayou Lacassine, and Bayou Queue de Tortue,,but

these are primarily located north of the confines of the study area.

Based on the examination of a small area on the Mermentau River just

north of Lake Arthur, swamp forest appears to be stable with no detec-table

areas of loss or gain found.

Fresh marsh areas have generally experienced average to below

average losses. Much of the sawgrass (Cladium jamaicense) marsh that

was lost following Hurricane Audrey in 1957 has been revegetated but

largely by other species (see also Calcasieu-Sabine Management Unit).

The only fresh marsh area examined having above average loss rates was

the area between the road to Little Chenier and the Gulf Intracoastal

Waterway (GIWW). Known as part of the "Great Burn Area" by some of the

older local residents, it is bounded by the GIWW on the north, Highway

27 on the west, and Little Chenier Ridge and road on the south. Thus

the area is semienclosed by ridges, which may serve to reduce overland

flow and sedimentation and thereby contribute to land loss. This area,

however, has had a history of land loss predating the earliest aerial

photography and USGS quadrangle maps of the area. Lynch (1941) reports

that marsh fires occurring during the 1924-25 drought burned deeply into

the peat and destroyed the root system. Valentine (unpublished ms.)

reports that this area experienced prolonged flooding during 1940 with

die-offs subsequently occurring. The presence of ridges on three sides

may have lessened the ability of the waters to recede and thereby have

contributed to the excessive flooding. O'Neil (1949) states that this

area had recovered to a great extent although a species change was

evident. Valentine (unpublished ms.) reports that this area once again

opened up following Hurricane Audrey.

In summary, this area has had a complex history of die-offs and
revegetation with no @ingle cause being evident. The documentation of

this area is better than for most of coastal Louisiana. Thus, it serves

to indicate that marsh loss throughout coastal Louisiana may be the

result of the interaction of several factors rather than single cause-

effect relationships.

Brackish marsh areas have experienced higher loss rates than fresh

marsh in the Mermentau area, but these rates are generally less than for

brackish marshes in the Deltaic Plain. The only area of brackish marsh

with an above-average erosion rate,is located in the southeast portion

of the management area near Freshwater Bayou Canal. The paralleling

linear ponds that are forming here and on the east side of Freshwater

Bayou are believed to be caused by the loss of circulation due to the

spoil banks of Freshwater Bayou Canal, numerous oil access canals, and

the natural cheniers bordering these ponds. Prior to the dredging of

these canals, water drained through the swales into Freshwater Bayou.

The spoil banks of these canals have effectively blocked the natural

drainage flow thus causing water to accumulate in these swales.

Except for some areas where natural bayous drain into the gulf, the

salt marsh is limited to a narrow zone immediately landward of the

beach. No major losses are associated with this small area although the

snalt marsh appears to migrate inland as the coastline erodes.

73501

72"0

30000-
401 Al@
40 Ib
72 72405 9
72406 ' -,72430 q, 19

01 1
-1 724 423
2 4
7 73@O4@

L a.

3
72

72434--

72104
'71101-7 71111- 71@@
71105 71110- 71115 71120 C@ 72105
73202 Z
[FF F
_71,2
0 5 10 15 20 W. 71125 71 4 2913G

0 5 10 15 20 25 30 K-

Figure 15. Site locations in the Mermentau Management Unit.

Table 12

Erosion Rates for Sites Analyzed in the
Mermentau Management Unit

F-
r
r
Retreat
0 Z
2 Quadrangle 6 Rate or
00 Site Area Parish Size(minutes) Data Sources & Dates m/yr Land Loss

7 1 1 01 Mermentau River Cameron Sweet Lake 15 1954 photos 1969 USCE 0
Long. 93' 06' Jack Ammann Corp. uncontrolled
photomosaics
71102 Long. 93* 05' 0

71103 Long. 93* 04' 2.1

71104 Long. 93* 03' 9.9

71105 Long. 93* 02' 9.9

71106 Long. 93* 01' 8.1

71107 Long. 93* 00' Hog Bayou 15 6.0

71108 Long. 92* 59' 9.9

71109 Long. 92* 58', Cameron Hog Bayou 15 14.1

71110 Long. 92* 57' 9.9

71111 Club Canal 14.1
Long. 92* 56'

71112 Long. 92* 55' 9.9

71113 Long. 92* 54' 12.0

71114 Long. 92* 53' 9.9

71115 Long. 92* 52' 12.0

71116 Long. 92* 51' 12.0

71117 Long. 92* 50' 12.0

71118 Long. 92* 49' 12.0

71119 Long. 92* 48' 9.9
7 1 1 20 Long. 92* 47' Cameron Hog Bayou 15 1954 photos 1969 USCE 9.9
Jack Ammann Corp. uncontrolled
photomosaics
7 1 1 21 Long. 92* 46' 12.0
71122 Long. 92' 45' Constance Bayou 15 12.0
71123 Long. 92* 44' 12.0
71124 Long. 92' 43', 14.1
71*1 25 Constance Bayou 14.1
Long. 92* 42'
71126 Long. 92* 41' 14.1
71127 Long. 92* 40' 12.0
71128 Long. 92' 39' 12.0
71129 Long. 92* 38' 12.0
71130 Long. 92* 37' Vermilion 12.0
71131 Long. 92* 36' 12.0
71132 Long. 92* 35' 12.0
71133 Long. 92* 34' 14.1

Table 12 conLinued

Retreat
Quadrangle Rate or %
Site Area Parish Size (minutes) Data Sources Dates m/yr Land Loss
C0W
>

71134 Long 92* 33' 15.9

71135 Near Rollover Bayou 15.9
Long. 92* 32'

71136 Long. 92* 31' 15.9

71137 Long. 92* 30' Pecan Island 15 12.0
71138 Long. 92* 29' 1. 14.1

71139 Long. 92* 28' Vermilion Pecan Island 15 1954 photos 1969 USCE 14.1
Jack Ammann Corp. uncontrolled
photomosaics

71140 Long. 92* 27' 12.0
71141 Long. 92' 26' 8.1
1142 Long. 92* 25' 9.9
71143 Long. 92* 24' Ady.
71144 Long. 92* 23' Adv.
71145 Long. 92* 22' 9.9
71146 Long. 92' 21' 9.9
71147 Long. 92' 20' 2.1
71148 Near Freshwater 6.0
Bayou Canal
Long. 92* 19'
72101Lo@er Mud Lake Cameron Sweet Lake 15 1912 USN photos 1914 NASA MX294 Adv

72102 0

72103 0.4

72104 Miller Lane Hog Bayou 15 Adv.

72105 Fiat Lake Vermilion Constance Bayou 15 1974 NASA MX293 0
723Ol Catfish Lake Cameron Grand Lake West 15 USGS orthophoto 3.7
,Quadrangle from
1974 photos

72302 0.6

72401 Willow Lake Cameron Sweet Lake 15 1952 USN photos USGS orthophoto 0.4
quadrangle from
1975 photos

72402 1.9

72403 Sweet Lake 0.4

72404 1.1

72405 0.5

72406 2.0

72407 0

Table i2 continued

w r
Retreat
Quadrangle 6 Rate I
a0to fSite Area Parish Size(minutes) Data Sources Dates m/yr. or Land Loss

72408 Lake Misere Grand Lake West 15 USGS orthophoto
quadrangle from
1974 photos 0.6
72409 1.2
72410 Grand Lake East 0.8
Grand Lake West
72411 1.8
72412 NW Grand Lake Grand Lake West 15 0.8
72413 Grand Lake 1.1
Negro Island
72414 0 ?
72415NGrand Lake Grand Lake East 15 0.8
72416 Grand Lake 8.4
Rabbit Island

72417 Grand Lake Cameron Grand Lake East 15 1952 USN photos USGS orthophoto 0.8
Mallard Bay Is. quadrangle from
1974 photos

72418 Mallard Bay 3.6

72419 0.7

72420 3.9

72421 E Grand Lake 9.4

72422 Grand Lake 36.5
Umbrella Pt.

72423 Grand Lake 4.8
Umbrella Bay

72424 0.9

72425 Grand Lake 9.8
Short Pt.

72426 SE Grand Lake 0.9

72427 Grand Lake E&W 15 4.4

72428 SW Grand Lake Grand Lake West 15 3.3

724 29 Grand Lake 9.2
Hackberry Pt.

724 30 Grand Lake 0.8
Cypress Is.

724 31 NW White Lake Vermilion Grand Lake East 15 3.5

724 32NWhite Lake Forked Is. 15 0.8

Table 12 coatinued

r 0.

r Retreat
Quadrangle & Rate
e Data Sources & Dates m/yr. or Land Loss
C W Site Area Parish S e(minut a)
W
2 >
7 2433 E White Lake Vermilion Forked Is. & Pecan Is.15 1952 USN Photos USCS ortha- 4.5
photo quadrangle
from 1.974 photos

1 1414 1E White Lake Pecan Ir, 1, Con@tance 0*1
Bayo U 15

7 2435 Constance Bayou 1-5 119

7 2436 0.8

7 2437 White Lake- 3.8
Bear Lake

7 2438 SW White Lake 0.6

7 2439 Constance bayou 1.2
Grand Lake East 15

7 2440 SW Lake Arthur Jefferson Davis Welsh 15 Adv.

7 2601 Lake Arthur Vermilion Jennings 15 0

7 2602 Jefferson Davis 0

7 3201 Hog Bayou Cameron Hog Bayou 15 0.08

7 3202 Freshwater Bayou Ver milion Pecan Island 15 0.54
Canal
7 3401 Little Cheniere Cameron Sweet Lake 15 USGS ortho- 0.68
photo Quadrangle
from 1975 photos

7 3402 Lake Misere Grand Lake West 15 USGS ortho- 0
phot 0
from 1974 photos

7 3403 Grand Lac 1'Huit Grand Lake East 15 0.09

7 3404 N of White Lake Vermilion Grand Lake East 0.04
Forked Is. 15

7 3501 Lake Arthur Jefferson Davis Jennings 15 0

30'W

weef Lake

e wa

e,,
Grand Lake-,
cheni', 'atli.@h
Idg, Lah---@
+
JA I C@en@
d. . e
elklall F nrd

Pat)
Ki6k err' (I C6 White Lake
e Ch ta eNer

A-liller Lake
C

Flat Lake .4@ Conal

0 5 10 15 20 Mi

0 5 -.10 Is 20 25 30 Km
L- I I I
Figure 16. Place names in the Mermentau Management Unit.

Management Unit VIII--Calcasieu-Sabine

Coastline Erosion. Considered as a unit, the Calcasieu-Sabine

Management Area's coastline has experienced slight netadvance during

the period from 1954 to 1969. A more refined examination of this

segment of coastline reveals that the section from Sabine Pass to

Calcasieu Pass has eroded at a rate of 3.3 m/yr, whereas the section

east of Calcasieu Pass to the mouth of the Mermentau River has prograded

3.2 m/yr. Comparing these rates with those of Morgan and Larimore (1957)

for the period from 1932 to 1954 shows that some significant changes

have occurred. During the 1932 to 1954 period, the western section was

relatively stable with some portions experiencing moderate accretion.

Since 1954, the reverse has occurred, with moderate erosion dominating

most of this section. Although predominantly rural, this section

does contain'the recreational communities of Holly, Peveto, and Ocean

View Beaches, all of which are located at or close to the present

beach line. The post-Hurricane Audrey (1957) reconstruction and growth

of these communities took place largely within 100 meters of the shoreline.

The past history of the area indicated that only the erosion that

resulted from a direct hit by a tropical disturbance would be a significant

problem. The present history indicates that there is cause for alarm

even without the possibility of a tropical disturbance of the magnitude

of "Audrey."

The section east of Calcasieu Pass has prograded at approximately the

same rate as from 1932 to 1954. This section of coast is largely

unsettled except for the small community of Rutherford Beach at the

extreme eastern end of the section.

The dramatic change from accretion east of Calcasieu Pass to erosion

west of the Pass is believed to be due to the jetties constructed at

the mouth of the ship channel. The jetties trap sediment being carried

by the dominant westerly littoral drift and build out areas to the

east. At the same time, areas to the west are deprived of this

sediment and consequently erode. The Sabine Pass Jetties, however,

have not had the same effect. Areas immediately-to the east are now

undergoing erosion. Either these jetties are not effectively trapping

sediment or there is little sediment to'be trapped at this point along

the coast. Morgan and Larimore (1957) point out that from 1932 to 1954,

the Sabine Jetties were effective in trapping sediment; therefore, it

would seem that the latter would be the case.

Although the Mermentau River and other smaller bayous that drain

into the gulf undoubtedly contribute some sediment, the main source for

the eastern prograding section of the Calcasieu-Sabine Basin is

considered to be largely the result of the reworking and redepositing

of sediments originating further east along the coastline. The beach

along this section consists mainly of fine sands and shell hash, whereas

the suspended load of the Mermentau River at its mouth contains mainly

silts and clays (USCE 1961).

The history of sedimentation throughout the past several thousands

of years and the future possibility of increased sedimentation from the

Atchafalaya River along the Chenier Plain coast have been discussed in

Chapter 1.

Well-Defined Lakeshores. Four lakes were examined in the Calcasieu-

Sabine Management Unit, Black, Calcasieu, Mud, and Sabine Lakes (Fig. 18,19).

All, except for a small segment of Calcasieu and Sabine Lakes that contain,

saline marshes, are dominated by brackish marshes along their shorelines.

The only well-defined lakes in either fresh or intermediate marshes are

those along the Calcasieu River. These, however, have undergone extensive

cultural modification.

Both Calcasieu and Sabine Lakes are among the top twenty-five

largest lakes in the United States. They are relatively shallow, as is

typical in coastal Louisiana, averaging two meters (Barrett 1970). The

considerable fetch of these lakes (approximately 40 km along the north-

south axis has facilitated wave-induced erosion. The greatest amount of

erosion occurs along the southern and southeastern shorelines. Although

southerly components of wind occur with the greatest frequency in this

area, northerly components are generally stronger and have a frequency

percentage of sixteen from October through March (Murray 1976). These

periodic northerly winds are thought to be the main cause of the higher

erosion rates along the southern shorelines. Lakefront beaches composed

of large amounts of shell and other debris average 0.7 m above marsh

level along the southern shorelines and provide further evidence of wave

attack.

Calcasieu Lake has experienced a slightly higher rate of erosion

than Sabine Lake. Based on air photos taken six months prior to Hurricane

Audrey (U.S. Dept. of Agriculture (USDA]) and one month after (U.S. Navy

(USN]), the difference in the erosion rates of these two simV,,.7r lakes

can largely be attributed to this single event. The storm's center

passed through the vicinity of Calcasieu Lake and did the most amount of

damage in-this area (Morgan et al. 1958). Over half of the total erosion

of Calcasieu, Mud, and Sabine Lakes between 1952.and 1974 can be attributed

to Hurricane Audrey.

Oyster reefs along the southeast section of Calcasieu Lake are

effective in reducing wave action. Consequently, the shoreline leeward

of these reefs has retreated at a rate of 0.38-m/yr. That portion of

the southeast lakeshore thatis not protected by these reefs has

retreated at a rate of 1.1 m/yr. Oyster reefs have provided similar

protection from wave erosion along the coastline of Marsh Island

(see Vermilion Management Unit discussion).

Mud Lake is an oxbow lake of a remnant Calcasieu River course.

It's shoreline has remained fairly stable from 1952 to*1972, with

only the smallest detectable erosion rate (0.25 m/yr) occurring along

some portions of the shoreline. Of the erosion that has occurred, nearly

all can be attributed to Hurricane Audrey. The presence of ridges

(either levee remnants or transverse cheniers) located along much of the

shoreline has probably helped as a stabilizing agent. This, combined

with the lack of.a long fetch and shallowness of the lake (0.4 m),

has served to minimize erosion.

The Black Lake area northwest of the town of Hackberry is an

unusual case of shoreline erosion. No absolute quantitative value of

erosion can be assigned to much of the shoreline because of its

disappearance. A tentative value of greater than 10 m/yr has been

designated for the western, northern, and eastern shorelines. The

southern shoreline has remained stable because of the presence of

subaerial Pleistocene sediments that overlie the Hackberry salt dome.

The tentative erosion value would place this lake in the highest

designated category and, as such, would be the only example we st of

Terrebonne Parish. Black Lake has a fetch of approximately 3.5 km and

an average depth of 1.2 m. Based on. the size and erosion rates of other

lakes in this and neighboring management units, it seems highly unlikely

that such high erosion could be induced by wave action. The average

depth of,Recent material is.less than 2 meters; therefore, the subsidence

potential of the marsh sediments is relatively low. Consequently, the

disappearance of the lake shoreline is felt to be related to additional

factors. Some possibilities are outlined below.

Inner Marsh Land Lass. Marshes in the Black Lake area south of the

Gulf Intracoastal Waterway, west of Alkali ditch, and east of Cameron

Farms have experienced an 81 percent reduction from 1952 to 1974 (Fig. 17).

This area may well have the highest intensity of marsh loss for any area

of comparable size over a similar time period in coastal Louisiana and

therefore warrants some discussion. These marshes, which were characterized

as brackish by Chabreck (1972), were dominated by sawgrass (Cladium

jamaicense) prior to Hurricane Atidrey. Valentine (unpublished ms.) hypothesizes

that these marshes were destroyed as a result of the combined effects of

Hurricane Audrey in 1957 and subsequent drought periods extending through

the mid 1960s. Whereas there is little doubt that these marshes were

destro@yed contemporaneously with these climatic events, that does not

explain why other neighboring areas of sawgrass marsh in the Chenier

Plain have been recolonized (largely by more salt tolerant species) and

the Black Lake area has remained barren. Presently efforts are underway

to return some of this area to marshland through the use of impoundments.

Difficulties may arise because there has been extensive denudation since

the loss of vegetation as is evidenced by the increased siltation in

many neighboring canals where spoil banks are not continuous.

Although the exact cause(s) of this extensive loss cannot be
documented, a list of activities'and features on the landscape that have

been documented as or are suspected of being associated with land loss

in other areas may provide insight.

BLACK LAKE AND VICINITY-1952

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

@ISITRACOASTAL. WATERWAY.-

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

01
...... LA
27

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

... .........................
..... YA-:
....... 4'Lf .... bWt

.... ....... .
7 ...
...........
...........

... .......

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

BLACK LAKE AND VIC] NITY- 1`9744

N, .......... .

WA
'IN A OASTA L. TERWAY_

..........
..........
-----------
------------

-----------
27 -
-- -- ------------
1 :7 7

----------- -
----------------
H

-------- BA

------------ .........
t@@ --------------- ......... ......
ACKBERRT:@:.;;;@' ..... ..
............
DOME-@;@`@@::i'
.........................

........... ......
----------- 2

..........
...........
:j ----------

Fi-ure 17. Land cha
nges in the Black Lake Area 1952-1974.

The following occur in the vicinity of Black Lake:

1) Oil and gas extraction--numerous canals with associated spoil

banks have been dred ged throughout the extensive field

surrounding the Hackberry salt dome. The extraction itself

may have induced subsidence, as was the case in the Goose

Creek Oil field in Texas (Weaver and Sheets 1962). Bench

marks in the vicinity of Black Lake have subsided an average

of 0.6 m since the early 1950s (La-Dept. of Public Works,

unpublished data).

2) The dredging of the Calcasieu Ship Channel-has led to increased

salinities (Gosselink, in press).. The Black Lake area is

connected to-.the ship channel via Black Ba you.

3.) Spoil banks associated with the Gulf Intracoastal Waterway,

Alkali Ditch, Calcasieu Ship Channel, and Stark's North Canal

combined with natural topographic highs of the Hackberry

salt dome and the subaerial Pleistocene in the vicinity

of Cameron Farms have left Black Bayou as the only

drainage into and out of the Black Lake marshes. Consequently,

natural drainage may be severely modified, reducing its ability

to drain off saline waters associated with hurricane surges.

The Calcasieu-Sabine Basin as a whole has experienced the highest

land loss rates in comparison with other areas in the Chenier Plain and

has experienced rates comparable to management units in the Deltaic

Plain. However, the highest losses appear to be associated with fresh

and intermediate marshes. Brackish marshes, except for the Black Lake

area, have experienced rates of land loss lower than the Deltaic Plain

but similar to brackish marshes in other areas of the Chenier Plain.

Salt marsh does not comprise a significant amount of area in this unit;

therefore, no conclusions can be drawn. The southernmost point of swamp

forest on the Sabine River has experienced some minor losses. Marshes

in the vicinity of the Black Bayou, which drains into Sabine Lake, have

been highly variable in their loss rates. Those south of Black Bayou

that have had little cultural modification have experienced below average

losses; those located in the Black Bayou oil field extending north past

the Gulf Intracoastal Waterway between the Vinton Drainage Canal and Big
and Sassafras Islands as 'well as those west of these islands to the

Sabine River have undergone above average or excessive losses. These

areas have a high degree of ongoing cultural activities such as oil and

gas extraction and agricultural drainage canals.

100

33 -2

2 30'00
@P82601
22
terwa.v
AT

811211 1
811 1111- 113 R6114 T-
811 5 81110 81115 E-1120 81125 81130 81135 81140 81144

0 5 10 15 20 Mi

0 5 10 15 20 25 30 Km

Figure 18. Site locations in the Calcasieu-Sabine Management Unit.
8350,77
8350 '.. L:I-
8320@@-

101

Table 13

Erosion Rates for Sites Analyzed in the
Calcasieu-Sabine Management Unit

r
Retreat
0.3Z
Quadrangle Rate or
0W Site Area Parish Size(minutes) Data Sources & Dates m/yr Land Loss

8 1.1 01 Sabine Pass Cameron Sabine Pass 15 1954 photos 1969 USCE 14.1
Long. 93* 50' Jack Ammann Corp. uncontrolled
photomosaics

8 1 102 Long. 93* 49' 9.9

81103 Long. 93* 48' 9.9

81104 Long. 93* 47' 8.1

81105 Long. 93* 46' 0

81106 Long. 93* 45' 2.1

81107 Long. 93* 44' Johnson's Bayou 15 0

81108 Long. 93* 43' 0

81109 Long. 93* 42' 0

81110 Long. 93' 41' 0

81111 Long. 93o 40' 0

81112 Long. 93* 39' 0

81113 Long. 93*1 38' 3.9

81114 Ocean View Beach 0
Long. 93* 37'

81115 Ocean View Beach 0
Long. 93* 36'

81116 Ocean View Beach 0
Long. 93* 35'
81117 Ocean View Beach Cameron Johnson's Bayou 15 1954 photos 1969 USCE 2.1
Long. 93' 34' Jack Ammann Corp. uncontrolled
photomosaics

81118 Pe@eco Beach 0
Long. 93* 33'

811ig reveto Beach 3.9
Long. 93* 32'

81120 Long. 93* 31' 3.9

81121 Long. 93* 30' 2 1

81122 Long. 93' 29' Cameron 15 3.9

81123 Long. 93* 28' 6.0

81124 Holly Beach 3.9
Long. 93* 27'

81125 Holly Beach 2.1
Long. 93' 26'

81126 Long. 93* 25' 2.1

81127 Long. 93' 24' 2.1

81128 Long. 93* 23' 3.9

81129 Long. 93* 22' 3.9

81130 Calcasieu Pass 3.9
Long. 93* 21'

102

Table 13 continued

Retreat
Quadrangle& Rate or
Site Area Parish Size(minutes) Data Sources & Dates m/yr Land Loss

81131 Calcasieu Pass Adv.
Long. 93' 20'

81132 Long. 93* 19' Adv.

81133 Long. 93* IS' Adv.
81134 Long- 93* 17' Cameron Cameron 15 1954 air photos 1969 USCE Adv.
Jack Ammann Corp. uncontrolled
phocamosaics

81135 Long. 93' 16' Adv.

81136 Long. 93* 15' Adv.
81137 Long. 93* 14' Sweet Lake 15 2.1
81138 Long. 93* 13' 2.1

81139 Long. 93* 12' 0

81140 Long. 93* 11' 0

81141 Long. 93* 10' 0

81142 Long. 93* 09' Adv.

81143 Long. 93' 08' Adv.

81144 Long. 93* 07' 2.1
82101 SE Sabine Lake USCS Quadrangle 1972 NASA MX194 0.3
Port Arthur 15 from 1956 photos
82102 S Calcasieu Lake Cameron 13. 1952 USN photos 1974 NASA MX293 0.3
82201 E Sabine Lake USGS Quadrangle 1972 NASA MX194 0
Port Arthur 15 from 1956 photos
82202 SW Mud Like Cameron 15 1952 USN photos 1974 NASA MX293 0

82203 NW Mud Lake 0.3

82204 N Mud Lake 0

82205 E Mud Lake 0.3

82206 Calcasieu Lake 0
West Cove
82207 Calcasieu Lake Cameron Cameron & 1952 USN Photos 1974 NASA MX293 1.1
Fast Cove Sweet Lake 15

82208 Sweet Lake 15 0.3

82209 Cameron 15 0

82210 NE Calcasieu Lake Cameron & Cameron & 0.3
Calcasieu Sulphur 15

82211 Black Lake Cameron Sulphur 15 >10 ?

82601 Comissary Point Cameron 15 0.3
Calcasieu Lake

82602 Jubert Point 0
Calcasieu Lake

82603 Black Lake Cameron Sulphur'15 0

83201 Lost Lake Calcasieu Orange, Texas 15 1952 USN photos 1972 NA SA MX194 1.10,

83202 Phoenix Lake 0.85

83203 True Ridge Cameron Johnson's Bayou & 0.08
Port Arthur, TX 15

103

Table 13 continued

0
.r8 Retreat
rI"
W -. z
0 Quadrangle Rate or
r r
0 Site Area Parish Size(minutes) Data Sources & Dates M/Y Land Love

83204 Black Lake Cameron & 1974 NASA MX293 3.71
Sulphur 15
83205 West Cove Cameron 15 USCS orthophoto 0.22
quads from 1974
photos
83206 East Cove Cameron 1.19
Sweet Lake 15
83207 Alkali Ditch Sulphur 15 1974 NASA MX29j 0.44
83301 Webb Gully Calcasieu Orange, Texas 15 1952 USN photos 1974 NASA MX293 0.62

83302 Black Bayou Cameron & Prange, Texas 1.41
Oil Field Calcasieu Johnson's Bayou 15

83303 Deer Island Cameron Orange, Texas 15 0.44
83501 Turner Island Calcasieu USGS quadrangle 1972 NASA KX194 0.05
from 1959 photos

83502 Turner island 0.18

104

Lake Charles

A Big Is.,
Sassafras Is.
-1 W
zz

30'00'-
Hackberry
Stark's North Canal i 2-terwav

)cean-View Beach tSeach Bench

0 5 10 15 20 Mi.

0 5 10 15 20 25 30 Km.

Figure 19. Place names in the Calcasieu-Sabine Management Unit.

105

Chapter 4

Current Erosion Mitigation Practices and Recommendations

Introduction

The preceding chapters have concentrated on where and why erosion

is occurring in coastal Louisiana. The coastline is experiencing more

erosion than accretion, and this trend should continue throughout much

-of the coastal area for some time. The question, therefore, is what can

be done to mitigate erosion. This chapter addresses this question as it

pertains to the Louisiana situation and includes,:

1) A review of structural and non-structural measures currently

in practice in Louisiana and elsewhere and their effectiveness;

2) A discussion of a rationale for designating areas for

erosion control consideration and identification of such

areas;

3) General recommentations for co ntinuation of or change in

management policies and techniques that may directly or

indirectly affect the rate of erosion.

Engineering Structures and their Applicability in Louisiana

The principal forces causing shore erosion are the wind-induced

energy of waves and currents resulting from storms. Beach material

both above and below the still water level is loosened by the waves and

moved away by the currents. A crude estimate of wave force is that for

every one increment of wave height, storm forces have the potential to

scour the beach two increments in depth. Under equilibrium conditions,

the material transported away is replaced by material from updrift

areas. Natural beaches exist in dynamic equilibrium--responding to

external forces and gradually adjusting back to equilibrium. If, however,

106

material is not available to replace what is transported away, the

equilibrium is upset and erosion occurs.

A number of methods, from the dumping of automobiles and heavy

trash objects along a bluff face to costly offshore breakwaters, have

been devised to retard or stop erosion. Several of the more widely used

structural solutions to erosion will be discussed in terms of their

applicability along the Louisiana coast and lake shorelines.

Artificial Nourishment. Although it may be argued that artificial

nourishment is not strictly a structural technique, it does involve

heavy machinery in the form of trucks or dredges and can have immediate

significant impact both onshore and offshore. Artificial nourishment

has been used extensively where sand is available at a reasonable price.

Erosion protection is provided by raising the beach level suff iciently

to induce waves.to break and thereby dissipate their energy before they

reach the shore. This technique has the advantage of preserving the

beach in a near-natural state, but nourishment is not always the best

solution. Strong littoral currents.can remove the sand fill so quickly

as to make this technique uneconomical. Costs (1975) range from $1.15
to $1.50/m3 of dredged material to $3.80/m3 if the material must be

trucked in.

Artificial nourishment has been used in Louisiana, particularly at
Grand Isle, where more than 1.53 x 106M3 of material have been placed

since 1952. Much of this has been lost via littoral transport. Generally,

coastal Louisiana is a sand-deficient environment. Consequently, costs

of nourishment material are high. In the case of Grand Isle, nourishment

could be economically justified; however, few, if any, other areas in the

state could justify the cost.

107

Groins With or Without Nourishment. Groins are barriers built

perpendicular,to the shoreline, permeable or impermeable, normally at

some regular spacing. They have the ability to trap sand on their

updrift side if there is sufficient littoral drift, with a resultant

erosion of material on the downdrift side. Artificial nourishment may

.be necessary in areas of insufficient littoral sediment supply and also

to counteract the effect on the downdrift shoreline. Of the possible

structural devices, groin systems cause the fewest problems for recreational

use of the beach. However, without a comprehensive plan, single groins

or groin systems may not only prove ineffective, but they could aggravate

the erosion problem. Average costs of a groin field range from $330 to

$1150 per meter of shore protected (1973 dollars) depending on the type of

material used, spacing, and length of the groins.

Because of the finite amount of sediment being carried by littoral

drift, groins become increasingly less effective as new ones are added.

In the case of a natural section of shoreline that is owned by several

individuals, the decision of one landowner to construct a groin would

adversely affect the downdrift landowners and might or might not benefit

the updrift landowner.

Groins constructed on Grand Isle have been of only limited value in

stabilizing the beach and have required periodic nourishment. Moreover,

Grand Isle is an area where there is not a deficiency of littoral material.

In sand deficient areas, groins would not be effective. The Corps of

Engineers (USCE) determined that a groin field 9.7 km long, spaced at 76m

intervals, each extending 183.m gulfward, and costing $13 6illion

would be required to provide adequate stability to the Grand Isle shoreline.

This alternative was not cost effective.

108

Jetties. Jetties have essentially the same effect as groins in

trapping sediments on the updrift side. They are usually considerably

longer than groins and are often used to protect harbor or channel

entrances. If sufficient material is trapped, the littoral drift can

begin to move around the jetty and shoal areas develop. For navigational

purposes, it may become necessary to dredge this material away.

The Louisiana coast has numerous jetties--all of which exhibit some

accretion on the updrift side--that are used primarily to protect channel

entrances. Grand Isle now has a jetty on each end that aids in stabilizing

the island. A proposed extension of the east-end jetty was dismissed

because it would not significantly reduce erosion of the*central portion

of the island; it could have severe, detrimental effects on Grand Terre,

and it would only be effective at the east end where there is no appreciable

problem.

The jett ies at the mouth of the Calcasieu Ship Channel have effectively

trapped sediment, and there is measurable accretion occurring for a

distance of some twenty kilometers along the updrift coastline. W est of

the jetties on the downdrift side, however, erosion has been accelerating.

Revetments. Revetments are protective coverings of a beach,

bluff, or other feature that follow the natural (stable) slope of the

feature and usually extend below the stillwater level. Various materials

have been used, such as,rubble, concrete, stone, asphalt, or sand bags.

The prerequisite is that the material be strong enough to withstand the

wave energy in the area it is used. The revetment must also be constructed

high enoug h to prevent essentially all overtopping by waves, and the toe

must be protected from undercutting. Erosion has been observed to

increase at the toe during storms as a result of energy of the water as
it runs up and down. 109

Much of the Louisiana coastline consists of flat expanses of

marsh land where revetments would be ineffective. Revetments have

been used successfully along Lake Pontchartrain, at Holly Beach, and

in protecting the Coast Guard Station on Grand Isle, but their cost

of $250 @0- $500/m-reduces the corresponding cost effectiveness and restricts

usage.

The revetment at Holly Beach is highly cost effective when one

considers the alternative, which would be to require the relocation of the

coastal highway that links Louisiana and Texas and provides an

important hurricane evacuation route. Louisiana State Highway 82

is built on a narrow sand ridge that separates the Gulf of Mexico

from extensive coastal marshes and the impounded marshes of the

Sabine National Wildlife Refuge. The portion requiring protection

is a 5 km stretch just west of Holly Beach. The revetment was built

in 1970 and has survived several severe storms. It was constructed of

cellular cobbletop concrete blocks over plastic filter cloth.

The highway was breached or seriously damaged in 1957, 1961, 1963,

and 1969. Since the roadbed was only 15 meters from the gulf shoreline,

even winter storms with waves of 1 meter overtop the road. This

revetment was not designed to weather direct hurricane attack, but

was intended to reduce continuous maintenance problems that result

from normal winter storms. However, the revetment has weathered waves

generated by Hurricanes Edith and Fern in 1971 and suffered only

limited damage from Hurricane Delia in 1973.

Seawalls and Bulkheads. These are vertical structures paralleling

pth below
the shoreline that extend from above the high water line to a de

the scour line. A definite disadvantage is that waves striking these

110

walls tend to scour the bottom at the toe of the wall. This

deepening permits larger waves to enter, 'which increases the
probability of overtop ping and faifure.

Some seawalls and bulkheads have been constructed in Louisiana,

particularly along Lake Pontchartrain, but their high cost, $660/m and

up, makes them only rarely cost-effective, such as in heavily

industrialized areas.

Breakwaters. Both offshore and shore-connected breakwaters are

used primarily in conjunction with harbors or marinas to provide a

shelter from wave ac tion. Offshore breakwaters are more commonly used

and are placed far enough from shore so that littoral currents can

move along the shore behind them. The sand carried between them and

the shore tends to be deposited because of less turbulence in the

protected area unless they are very'far offshore or very short in

length. Breakwaters are also the most expensive of structures.

A proposed breakwater offshore of Grand Isle was d ismissed as

not being economically justifiable. To be effective in preventing

erosion or innundation of the island, the brea kwater would have to be

at least 4 meters above MSL. In addition, any breakwater would function

as a complete littoral barrier (by interrupting littoral sediment-

transport) with potential adverse effects on the Grand Terre Islands.

Riprap. Although this term is often used interchangeably-with

firevetment,""riprap" implies that there is no order to the placement of

the materials making up the structure. Riprap -are composed of irregularly

shaped stones or boulders and are usually the most economical of structures

but their effectiveness is only short term and as a rule they are not

ill

aesthetically pleasing. They are commonly found in South Louisiana

along the outside bend of river meanders and are used to protect campsites

and other lightly developed shorelines.

Levees. Artificial levees are sometimes used as protection against

erosion where the segment of shoreline to be protected is of considerable

length. Their effectiveness is variable, and subsequent unintentional

impacts such as theldeterioration of marshes behind the levees are

sometimes far worse than the erosion itself. In most instances, levees

are practical only where Recent sediments are relatively shallow (e.g.,

Southwest Louisiana). Except where the impounding of marshes is desired,

gates or culverts or similar structures should be constructed where

natural drainage intersects the leveelto allow for water exchange and

nursery access.

Assessment of the Louisiana Coastline: Where is Protection Justified?

The term "critical erosion" is commonly used to indicate an area

that warrants immediate consideration for erosion mitigation procedures.

It is a qualitative term that indicates that significant erosion is

occurring along sections of the coast where the present land use is

desirable but cannot be maintained with the present rate of erosion.

The USCE in its regional Shoreline Inventory of Louisiana (1971) uses

?1critical erosion" as a synonymous term with one of the directives of

section 106(a) of Public Law 90-483 approved 13-August 1968, which is as

follows:

... (2),identifying those areas where erosion presents

a serious problem because the rate of erosion, considered

in conjunction with economic, industrial, recreational,

agricultural, navigational, demographic, ecological, and

other relevant factors, indicates that action to halt such

erosion may be justified ....

112

The USCE's analysis of Louisiana shorelines (1971) resulted

in the identification of two general areas of critical erosion:

(1) Grand Isle and the western end of Grand Terre and (2) portions of

Lake Pontchartrain, mostly along the southern shore where,structures

were not already present. Benefit-cost analyses were made for other

areas but the resulting low ratios led to the recommendation that

federal projects should not be adopted for these other areas.

The USCE's 1971 assessment of Louisiana shorelines is used here

as a guideline, with the recognition that Louisiana's interests do not

necessarily always coincide with the USCE's recommendations. The state

may ultimately decide that additional (or fewer) areas warrant protection,

but a ny additional areas might have to be protected at the state's

cost.

For the purpose of this report, a reevaluation of the USCE's

(1971) assessment is now.necessary because:

1) Additional eroding shorelines have been included in this

study that were not analyzed by the USCE;

2) Several years have elapsed since the USCE assessment during

which time further economic development of shorelines has

occurred and rates of erosion have changed.

The determination of areas to be considered for erosion mitigation

procedures for this study was largely based on the types of land uses

affected. Areas studied include: those-where there has been significant

loss or destruction of public lands, including recreational areas,

historic sites, conservation areas, and areas where there has been

significant economic loss to private landowners. This method of

determination of areas to be considered is generally consistent with

the various methods developed by,other coastal states that have been

113

accepted by or proposed to the federal government. A review of several

such plans for other states is included in the Appendix. In order to

classify an area as having "critical" erosion, the key is to define what

constitutes the term "significant." A detailed benefit-cost analysis

must be performed. If the ratio of benefits to cost is greater than

one, then erosion is critical, and erosion protection measures can be

justified. Usually several analyses need to be performed for each area

because an analysis is necessary for each proposed alternative procedure.

Detailed bene.fit-cost analyses are not within the scope of this

effort. However, based on the results of the benefit-cost analyses

already performed by the USCE, we can suggest other areas that warrant

analysis. This study, therefore, does not define areas of critical

erosion; rather, it suggests areas that may qualify as critical and

consequently justify a benefit-cost analysis.

In additon to identifying possible areas of critical erosion, the

following geographical review includes suggested procedures for managing

erosion where appropriate. Because the USCE (1971) is a primary reference

for portions of the ensuing discussion, the geographic sequence of

discussion presented by the USCE (1971) has been followed to facilitate

comparison of information and viewpoints.

The first area, defined by the USCE (1971) as Zone I, extends from

the Sabine River to the Southwest Pass of Vermilion Bay and includes the

Calcasieu-Sabine, Mermentau, and part of the Vermilion Management Units.

Forty-eight-kilometers of the gulf shoreline are developed into

summer homes, commercial establishments for the tourist trade, and

public accessible beaches. An.additonal 72 km of undeveloped shoreline

are included in two wildlife management areas. The coastline fronting

114

Rockefeller Wildlife Refuge is undergoing extensive erosion. The lack

of natural coarse-grain sediment renders large-scale structural solutions

ineffective. Although mitigation is desirable, there is no apparent

cost effective solution.

The largest concentration of recreational development is at

Holly Beach, with 398 camps or surmer homes (Gary and Davis,

unpublished ms.). The other established tourists beaches at

Ocean View, Constance, and Peveto are much less developed structurally.

East of the Mermentau River, the shoreline is completely undeveloped

and for the most part has not been utilized for recreational purposes.

Erosion and accretion patterns are mixed over this area. From

Sabine Pass to Calcasieu Pass the shoreline is retreating at a

relatively slow rate. This retreat is in sharp contrast with the

USCE (1971) findings that reported this area as accreting. From

Calcasieu Pass to the natural mouth of the Mermentau River, accretion

is occurring, but no development exists except for a handful of

camps at Rutherford Beach. There is a high rate of erosion from the

Mermentau River to Chenier Au Tigre. Along so me sections, over

150 m of erosion has occurred between 1954 and 1969. A longer time-span

analysis indicates that in some places along this sector , over. 1200 m

of erosion has occurred in the last 150 years (USCE 1971). This sector

of coastline is undeveloped but a large portion of it is in public

ownership.

Erosion is occurring along the Southwest Louisiana coast because

of a sediment deficiency. The jetties at Calcasieu Pass have been

effective in trapping sediment. The source of this sediment is thought

to be largely the reworking of eroded sediments to the east. The

construction of additional jetties and/or groins is not recommended

115

because they would only compete for the small amount of sediment

available.

The small, largely recreational communities primarily located

west of Calcasieu Pass favor structural measures. Holly Beach is

the largest of these settlements; therefore, if structures are

justified at any of the areas, it would be there.

Holly Beach lost its two most gulfward streets paralleling the

beach, and 30 houses were in the foreshore zone by the early 1970s. In

1971, the USCE co nducted a study of the feasibility of possible measures

to protect the remaining shoreline. Based on the design criteria of a

1.5 m high stone covered dune and a 4.2 km long revetment to protect the

main highway, respective benefit-cost ratios of 0.3 and 0.5 were calculated,

and the projects were not undertaken. However, because of its proximity

to larger cities and the desire for recreation on the part of the people

who live in these cities, the Holly Beach area has a history of being

rebuilt after catastrophes such as hurricanes. Because there is insufficient
littoral material (estimated at 45,800 to 76,400 m3/yr in 1971) to

maintain a stable beach in this area, the most sound management approach

would consist of setback laws to protect new development and provisions

to prohibit the repair of severely damag ed existing structures on the

beach. As an interim partial solution, we recommend an examination of

the feasibility of placing spoil (resulting from maintenance dredging of

the mouth of the Calcasieu Ship Channel) into the nearshore gulf on the

west side of the jetties.

We further recommend that the revetment west of Holly Beach along

highway 82 be maintained because it is an important hurricane evacuation

route, the revetment has been moderately successful, and alternative

routes for highway 82 would result in higher construction costs because

116

of the more unstable nature of sediments located.inland of the highway's

present position.

The future for the gulf coastline of Southwest Louisiana may be

better than the present and recent past. The continued development of

the Atchafalaya Delta may ultimately result in increasing the sediment

supply to southwest Louisiana.

The effects of the continued input of Atchafalaya River sediments

should first be noticed along the eastern sections of coastal Southwest

Louisiana. A periodic monitoring scheme should be developed to note any

significant input of sediments along this section of coast.

The inland lakes and bays of Zone 1 (USCE 1971) are eroding at

variable rates. Calcasieu and Sabine Lakes, because of their low erosion

rates and lack of development, do not appear justified for erosion

control. Residents of small settlements on the northeast side of Calcasieu

Lake have taken it upon themselves to place riprap along the shoreline.

This appears to be a viable solution in this area of relatively stable

sediments.

Lake Charles, situated on the Calcasieu River floodplain and bordered

by the city that bears its name, has been the focus of a diversified

approach towards erosion mitigation. Beach nourishment along the north

shore has resulted in the formation of a new public beach. Filling and

placement of revetments along the east shore has resulted in additional

public access to the lakeshore. In addition to greater public access,

the area has increased its aesthetic appeal and has done so without the

closing off of any additional nursery areas. Although erosion is not

currently a problem, continued maintenance of the lakeshore in the form

of periodic beach nourishment and revetment repair will probably be

required.

117

The marshes east and south of Calcasieu Lake are eroding at a

rather high rate. Much of this area is in public ownership as part of

the Sabine National Wildlife Refuge. The proposal to construct.a levee

along the shoreline cannot be recommended at this point for the following

reasons:

1) The area is an important shrimp nursery and the levees, if

continuous, would prevent access to larval and juvenile

shrimp.

2) The presence of deep relict Pleistocene channels indicates

a, larger subsidence potential that may increase levee

maintenance costs.

3) At this point it is only speculation that levees would

halt the erosion of these marshes. The exact cause of

the erosion have never been accurately determined.

If the erosion of marshes is determined to be related to salt-

water intrusion, we recommend that alternative structures (e.g., weirs

and gates) be examined. If the levee were to function also as a hurricane

evacuation route and present roads are insufficient, we recommend the

examination of the feasibility of enlarging the present highway system

(La. 82 and 27) and/or the construction of a causeway.

Grand and White Lakes are eroding rather rapidly. Despite the

somewhat alarming rate of erosion, it is not critical because the shorelines

are essentially undeveloped. Erosion may be reduced by keeping the

flood gates of the control structures open from the fall through winter

seasons, thereby causing water levels to drop. This may be in conflict

with water requirement needs of the area, and the year-to-year fluctuations

118

in climate would necessitate a flexible schedule of the opening and

closing of the structures.

Zone II extends from Southwest Pass at Marsh Island to Point au Fer

and includes the Vermilion and Atchafalaya Managment Units. Of the 386

km of combined gulf and bay shorelines, only 3 km are developed--l km of

public beach (Cypremort Beach) and 2 km of summer and weekend camps.

Wildlife management areas account for approximately 35.4 km of the

undeveloped land, not including the newly designated Atchafalaya Delta

Wildlife Management Area.

Erosion rates for the Vermilion area appear to be decreasing when

results of this study are compared with those reported by the USCE

(1971). This undoubtedly is the result of sediments from the Atchafalaya

River.

Because of the extremely limited development in the area, the

natural protection afforded by Marsh Island, the extensive shell reefs,

and the relatively large sediment input from theAtchafalaya River and

consequent formation of a new delta, it is recommended that land use

management be the primary technique employed in the mitigation of

shoreline erosion.

Zone III (USCE 1971) is a small segment that e.s,sentially_is comprised

of Point au Fer Island. Although erosion is occurring along Four League

Bay, the gulf shoreline of Point au Fer Island, and in the.inner marsh

areas, the land is privately owned and is undeveloped. No-procedures are

recommended for this area.

Zone IV (USCE 1971) extends from Racoon Point on Isles Dernieres to

Sandy Point along the present Mississippi River Delta. It includes most

of the Terrebonne and all of the Barataria Management Units.

119

One of the characteristic features along much of the coastline in

Zone IV is the presence of ba-rrier islands. These features provide

natural protection from erosion for landward areas. These features are

ephemeral and are associated with the decay and reworking of deltaic

Their continued existence is dependent upon sediment supply.

The barrier islands of coastal Louisiana have a natural tendency to

erode and to be displaced landward, particularly after major storms.

Because of the dynamic and fragile nature of barrier islands and the

natural protection they provide, development should not occur on them,

and practices to enhance their maintenance should be encouraged, e.g.,

limited nourishment. These inlands should be left to migrate according

to the wave and current regimes and all structural measures should be

prohibited. Fortunately.much of the land encompassing barrier islands

is in public ownership. Thus, the dynamic behavior of these islands

does not adversely affect any present development with the exception of

one major area: G rand Isle and vicinity.

The USCE (1971) labeled Grand Isle and the western part of Grand

Terre Island proper (Fort Livingston) as areas of critical erosion. The

history of use of structures and beach nourishment, the long-standing

use of Grand Isle as a recreational community, and the intensive development

of this area provide an excellent case study of man's attempt to maintain

stability against a dynamic natural environment.

With 1353 camps, 308 hotel rooms, 5 marinas, and 7 charter boat

services, Grand Isle represents Louisiana's major seaside recreational

area (G ary and Davis, unpublished ms). An estimated 450,000 visitation$

per.year are made to the state park and the private beach, with two-thirds

120

of these visitations taking place between June and September. The beach

on Grand Isle varies from 7.6 to 122 m in width, is approximately 12.2 km

long, and has a.maximum elevation of 1.8 m. Almost 8.7 km of the

beach is private with public access, and the remainder is located within

a state park. There are 6.6 km of development associated with the oil

and fishing industries.

In addition to the extensive development, there are three major

potential changes that would affect Grand Isle within the next ten

years. Construction of the Louisiana Superport would undoubtedly benefit

the town in terms of new jobs and revenue generated from the@'predicted

$169 million annual income of the port. A long-delayed expansion of the
two-lane highway from Lafitte to La'r ose would shorten the driving time

between New Orleans and Grand Isle from 2.75 to 1.75 hours, thereby

making visits and short vacations to Grand Isle more attractive. The

third change, which is actually a result of the growth and potential of

Grand Isle, is a combination hurricane protection and beach erosion

project designed by the USCE and authorized by Congress in 1976. This

project consists of a 792 m long jetty at the. western end of the island

(that was constructed by Louisiana in 1972) and a 54.9 m wide vegetated

dune with a crown elevation of 3.5 m above mean sea level. The selected

design criteria was a 50-year storm, and the project.has a benefit to

cost ratio of 1.7. First costs will be $10.6 million, with a federal

share of $6.4 million. However, the money has not yet been appropriated.

The project also calls for periodic maintenance to be undertaken by

Louisiana.

Clearly, Grand Isle appears to have a favorable future for the

coming decades. The recreation-oriented economic activities are anticipated

121

to grow rapidly with no significant physical expansion of petroleum-

related facilities. It has been estimated.that the permanent population

of the town will increase from 2236 in 1970 to 3900 in 1980, and 6100

by 1990, and the summer visitor days will increase to over 11 million in

1985 (Gary and Davis, unpublished ms.). Because of present development

and the commitment to possible future development of the area and

that Grand Isle represents the only major access to the Gulf shore in

southeast Louisiana, it appears desirable to continue measures to stabilize

Grand Isle.

The real question is not one of desirability but of practicality.

The island has experienced severe damage to structures and loss of land

because of hurricane surges and shore erosion, which have threatened its

existence as a major recreational area. Table 14 lists past efforts to

stabilize the island and evaluates their effectiveness.

table 14
Case History of Shoreline Erosion and Mitigation Efforts on Grand Isle

Year ?robLem and 'litigation Effort Case Effectiveness

1853-1935 Western and receded 457 meters; accretion at
ease and.
1935-1955 1829 m of west end advanced 305 m gulfward; center Ineff:ctive ; isolacediscructures
of island receded 30 to 90 m; eastern end retreated accel rated erosion d rectly gulf-
152 m. No major action by any group other than ward and were undermined.
individual property owners prior to 1951. Verti-
cal bulkheads.

1951-1952 La. Hwy I threatened; Dapt..)f Hwys constructed Ineffective; constructed based on
4 to 152 m timber groins in one location and '_O to $480,000 easr-to-wesc Littoral t-anspocc .1hen
76 m timber groins In anocher, actually the reverse is the predomi-
nanc case; no maintenance since ini-
1954-1955 State Dept. of Public Works placed 8.8 X75-Sm-31 tial construction.
of sand as artificial nourisnmenc to graia 188,000 3.06 x 105 m3 of sand were lose from
systems. system in less than I ydar; beach
east or each groin system gained width
and volume and scabilized.
L956 Timber grain constructed L52 m gulfward by HumbLe More effective than Dept. of Hwys
Oil Co. and artificially nourished with dredge groins; trapped material on both sides
material from offshore. beneficcing shorelines; no maintenance;
effectiveness destroyed by conscruccion
of east-end Jetty.
1957 HLirricane Flossy in 1956 resulted 4n severe Sacisfaccary;initially 2.63 x 10@1 =J
eroslon and'scour; much of nour4snment 76,0(3() of sand ere estimated as necessary but
carried away; Dept.of Public works placed natural swell action aided in rebuilding
1.07 x .05 m3 sand along 7.2 km of beach. the beach.
1958-1959
Depc.of ?ublic Works built a 285 m jetty Within 4 years after conscruction,
305 m west of eastern end to stabilize, 150,000 7.65 . io@m3 of sediment trapped esc
Island. of Jetty; 1.21 x 105m" of island lost
ease of Iat cY.

122

Table 14 continued

Year Problem and Mitigation Effort Cost Effectiveness

1961- 1962 Damage from Hurricase Carla in 1961 and Satisfactory: Westward grain svste_m
previous storms; Dept.of Public Works unaffected.
placed 2.68 x 105m3 of sand within 10 groins $115,000
near center of island; est.ard-groin
field experienced loss while adjacent
shore on both sides was stable.
1964 To increase beach area and reduce shoaling Accretion due to the jetty extended
east of east-end jetty, Dept. of Public 200,000 2743 m westward totalling 9.56 x 10 5
Works extended this jetty by 427 m. m3@ Within 1 year, sufficient amount
of sand trapped by jetty that littoral
- drift be2an flanLinLjetty again.
1965- 1966 Extensive damage to dune line and jetty Reconstructed dune remained relatively
from Hurricane Betsy; large shoal east of 447,000 stable except near west end where
jetty scoured inland; DPWunder Corps of 1829 m of island receded up to 137 m from
Engineers specifications,borro,ed 4.21 x 1969-1971. Vegetation established
10-1m3 of sand from accretion west of jetty along remainder of dune aiding in
to rebuild natural dunes, stabilization.
1966 Repair of Jetty after Hurricane Betsy; 25,5oo
determined that jetty would not function 83.500 Satisfactory.
properly unless tied into shore and repaired
where failure occurred.
1967 Erosion of shoal east of jetty led to rapid By end of 1968, 274 m had failed as a
erosion east and north of lan6.ard end of 27,00(, result of overtopping, uplift pressure,
jetty;threatened Coast Cuard Loran Station; and leaching of the foundation.
constructed 305 m long revetment of nylon
material and concrete.
1970 Continued erosion near Coast Cuard Station; Satisfactory; dcsignLd for 1.5 m
30,760 m2 land lost since 1965: 176,000 waves accompanying 10 year storm; no
Corps of Engineers designed rubble mound maintenance required.
revetment, tying into east-end jetty 467 m
along pre-erosion shoreline.
1972 Rapid erosion of west end --loss of 60,000 m,@ Satisfactory; jetty does not interrupt
in 4 months of 1970; DPW,under Corps of Engi- west-to-east littoral drift.
neers specs,constructed 792.5 m jetty at west 1,065,000
:ndtto,divert tidal currents away from shoreline
as 0 Gaminada Pass and trap littoral material
moving east to west during periods of wave
approach from the east-southeast. Also
placed fill between jetty and west end of island.

1975- 1976 Hurricane Carmen(September, 1974) Completely Satisfactory.
destroyed existing low level dune along the
entire shoreline; emergency sand dune and beach
replenishment project (9 km of shoreline)
for Federal Disaster Administration in conjunc-
tion with U.S. Amy Corps of Engineers.

In spite of the various efforts to halt erosion of the gulf shore
on Grand Isle, a general recession of the beach continues along the
central and western portions of the island. The west end of the island
was finally stabilized in 1972 with the construction of a jetty. Grand
Isle is a very attractive recreation area, and much development ($42
million in 1970) already exists. Consequently, a plan was needed to
mitigate the effects of shoreline erosion. Several alternative plans
were designed by the USCE. The plan that was most favored (or rather,
least objectionable to all parties concerned,) and eventually authorized
by Congress in 1976 will be discussed below.'

123

The recommended improvements were designed to provide protection

from beach erosion and the hurricane-driven waves that occur once every

fifty years; this design hurricane is associated with 160 km./h winds.

Included in the plan are a stone jetty at the western end of the island,

a sandfill dune, and-.gulfside berm improvement. The dune, which would

extend along 12.1 km of shoreline, would have a 3.05 m wide crown, an

elevation of 3.5 m mean sea level, and would be protected from wind

erosion by vegetation. The beach would be widened to at least 55 m, and

slope from the toe of the dune at 2.6 m. to 0. 9 m. mean sea level (MSL)

where it would assume its natural slope to the bottom. The jetty has

already been constructed using emergency state appropriations. Sandfill

for the construction of the recommended dune and berm, estimated at 1.91
x 106m3, would be dredged from borrow pits 610 m offshore of each end of

the island.

The first costs associated with this project are $10.6 million, of

which $6.4 million is the federal share. In addition, periodic nourishment

of the dune and berm at five-year intervals will be necessary and that

responsibility will be borne primarily by Louisiana. Although the

$88,000 cost may appear high, since 1952, expenditures by local interests

to preserve the island have approximated two-thirds of the estimated

annual maintenance costs. Additional annual benefits include: prevention

of erosion damage to existing and future development over the life of

the project, estimated at $289,000; prevention of hurricane wave damages

to existing and future development, estimated at $378,000; $317,000 in

recreational development as a result of improvements; and $198,000 worth

of intensified land use (increased property value). The benefit to cost

ratio is 1.7.

124

The funds for this improvement plan have yet to be appropriated,

but this plan does appear to be cost effective, and implentation should

begin as soon as possible.

Erosion occurring..'along the inner lakes and bays in the Terrebonne

and Barataria Managmenet Units is occurring at rather high rates. There

is little man can do to halt these processes other than increasing the

supply of sediment over these marshes. Most of the shorelines are

privately owned and undeveloped No specific recommendations can be

made other than general land use management guidelines, which are included

later in this chapter.

Zone V (USCE 1971) is synonymous with the Mississippi Delta Management

Unit. The gulf shoreline exhibits essentially no development activity.

Oil and shipping industries account for 2.4 km of development along the

bay shoreline in South and Southwest Passes. South Pass is also the

site of 0.3 km of public docking facilities. Wildlife management areas

comprise much of the eastern, undeveloped delta. Because of the complex

changes associated with this highly dynamic area, land use management

should be the only technique employed in erosion mitigation.

Zones VI and VII (USCE 1971) is presented in this report as the

Pontchartrain-Breton Sound Management Unit. The coastline consists of

low relief, discontinous barrier islands. This entire coastline is

undeveloped and is Dart of the Breton Island National Wildlife Refuge.

The barrier islands have been designated as wilderness area, thereby

insuring no development. The area is inaccessible to most,of the public.

In addition to the landward movement of these islands, their overall
area@has been reduced by 259 km 2 from 1812 to 1954 (USCE 1971). Although

125

these islands are a valuable resource both as a biological habitat and

as a storm buffer against wave energy, their highly dynamic nature

precludes any economical cost-effective stabilization plan; thus, the

area should be left to natural processes.

Although Lake Borgne is presently eroding and the rate of erosion

appears to be accelerating, the shoreline is privately owned and undeveloped.

Therefore, no action is recommended.

Approximately forty percent of the Lake Pontchartrain shoreline is

presently developed. Erosion rates are variable, but there is an apparent

increasing trend. The present intensive development and the likelihood

of future development necessitates a more detailed examination than is

presented here.

The USCE (1971) has designated several areas of@Lake Pontchartrain

as areas of critical erosion. These are: Illinois Central Railroad

traversing the St. John the Baptist Parish shoreline, St. Charles Parish

levee, Orleans Parish levee, Fort Pike, Fountainbleau State Park beach,

and Mandeville. Recommended methods for mitigating effects of erosion

for these areas are structural with the exception at Fountainbleau. State

Park where beach nourishment was proposed.

The trend along Lake Pontchartrain is evident. Since nearly all of

the lake is eroding, the only item needed in order to warrant protection

measures under the formula for defining critical erosion is development.

Recent developments such as the north shore area south of Slidell included

the construction of a spoil levee, although this levee protects only the

newer devlopment and has left the previously built campsites unprotected.

Generally the type of structures used are levees or seawalls. These

have the effect of cutting off any inner marsh areas as nursery grounds

and interrupting the natural water exchange.

126

Further development of New Orleans East will require shoreline

protection along the lake shoreline as far east as South Point. Future

development should be encouraged only north of Lake Pontchartrain on-

nearby Pleistocene sediments. Stricter zoning and development policies

should be developed to insure that the state will not have to pay for

future protection against erosion of areas presently undeveloped. A

regional plan for the entire lake should be developed that precludes

using public funds for subsidizing private development in wetland areas.

General Management Concepts and Guidelines. Shoreline erosion

along Louisiana's coast and estuaries is a complex process that has

pervaded for at least several thousand years. However, within the past

century or so, erosion has dominated over land building processes.

The problem of erosion in Louisiana is by no means unique. Erosion

is occurring along sections of virtually every coastal state. However,
Louisiana is in a better position than most states to do something about"

it. First, much of coastal Louisiana is rural. Settlements requiring

coastal access have largely developed on more stable Pleistocene sediments

or along natural levees. Most of these preferred areas are being

utilized. Therefore continued growth of South Louisiana wil 1 place

increasing pressure to develop more hazard-prone areas. Secondly, the

processes that have extended Louisiana's coastline seaward for thousands

of years are still active.

To take advantage of these processes, a regional approach to

mitigating erosion is necessary. The deposition of Mississippi River

sediment into deep offshore waters can be diverted to more inland

areas, thus helping to curb erosion. Such a plan has been proposed by

127

Gagliano and van Beek (1970). Although the legal entanglements of such

a plan are numerous, the technology of implementing such a plan is

available. To the, west, the formation and growth of the Atchafalaya

Delta has reversed the trend from erosion to accretion in Atchafalaya

Bay and vicinity. The continued seaward and latitudinal growth of the

delta may solve the problem of coastline erosion of Southwest Louisiana.

A plan to provide for proper spoil placement needs to be adopted that

would insure maximum growth. Channelization for navigation is necessary;

however, a monitoring scheme needs to be developed to insure that

sediments will be carried to Southwest Louisiana via littoral transport

rather than being discharged through man-made channels into deep offshore

waters. It is impossible to predict when Southwest Louisiana will be

the recipient of sufficient amounts of sediment to retard erosion. In

the interim, developments such as Holly Beach will continue to be plagued

by erosion. Setback regulations and other building codes need to be

developed for that section of coast.

Other than Mississippi: and Atchafalaya River sediments, there is no

material available for extensive marsh and beach nourishment. Therefore,

most erosion control measures will be limited to small holding actions

where erosion is extreme and where economic or social values make these

measures cost effective.

The following general recommendations can help to lessenthe potential

for escalation of erosion:

1) Prohibit dredging immediately landward of barrier islands.

The removal of shell or creation of channels creates a

depression in which low lying barrier island sands can

become buried.

128

2) Avoid structural methods that would,deprive downdrift

shorelines of laterally moving sediment except in the

case of Grand Isle-and historic sites.

3) No large expenditures of'public funds are recommended

along the Chenier Plain coastline because these projects

will be left stranded inland as the result of extensive

mudflat deposits that are anticipated concurrent

with Atchafalaya River development.

4) Structural controls along lakeshores in the Chenier Plain

are effective where subsidence potential is minimal.

However, the design of such structures should not lead

to impoundment of adjacent marsh areas or interruption of

natural drainage patterns. Erosion along shorelines with

high subsidence potential (e.g., Deltaic Plain) can be

mitigated,only by means of limiting development.'

5) Inner marsh erosion can be mitigated by limiting dredging

practices that lead to extensive canal networks that disrupt

normal drainage patterns, increase saltwater intrusion, and

.increase freshwater runoff. Placement of continuous dredge

spoil across the marsh surface interrupts sheet flow and

sediment dispersal.

129

REFERENCES

Adams, R. D., B. B. Barrett, J.-H. Blackmon, B. W. Cane, and W. G. McIntire.
1976.' Barataria Basin: Geologic Processes and Framework. Louisiana
State University Center for Wetland Resources, Baton Rouge, La. Sea
Grant Publ. No. LSU-T-006. 117 pp.

Barrett, B. B. 1970. Water Measurements of Coastal Louisiana. La. Wild-
life and Fisheries Comm. and U.S. Fish and Wildlife:Service, Bureau
of Commercial Fisheries, Project 2-22-T of PL 88-309.

Chabreck, R. H. 1972. Vegetation, Water and Soil Characteristics of the
Louisiana Coastal Region. Louisiana State University, Agricultural
Experiment Station. Bulletin No. 664. AEA Information Series No. 251.

Clark, J. 1977. Coastal Ecosystem Management. A Technical Manual for the
Conservation of Coastal Zone Resources. J. Wiley and Sons. New York.

Conatser, W. 1971. Grand Isle: A barrier island in the Gulf of Mexico.
Bull. Geol. Soc. Amer. 82:3049-3068.

Craig, N. J., and J. W. Day Jr. 1977. Cumulative Impact Studies in the
Louisiana Coastal Zone - Eutrophication - Land Loss. Final Report to
the Louisiana State Planning Office, Baton Rouge, La.

Cratsley, D. W. 1975. Recent deltaic sedimentation, Atchafalaya Bay,
Louisiana. Master's thesis, Louisiana State University, Baton Rouge,
La. 142 pp.

Daiber, F. C., L. L. Thornton, K. A. Bolster, T. G. Campbell, 0. W.
Crichton, G. L. Esposito, D. R. Jones, and J. M. Tyrawski. 1976.
An Atlas of Delaware's Wetlands and Estuarine Resources. University
of Delaware, College of Marine Studies, Tech. Rept. No. 2.

Fisk, H. N. 1952. Geological investigations of the Atchafalaya Basin and
the problem of Mississippi River diversion. U.S. Army Corps of
Engineers. Miss. River Comm., Vicksburg. Vol. 1, 145 pp., Vol. 2,
36 plates.

Frazier, D. E. 1967. Recent deltaic deposits of the Mississippi River:
Their development and chronology. Gulf Coast Assoc. Geol. Soc.
Trans. 17:287-311.

Gag liano, S. M., and J. L. van Beek. 1970. Geologic and geomorphic
aspects of deltaic processes. Mississippi delta system. Hydrologic
and geologic studies of coastal Louisiana, Rept. No. 1, Louisiana
State University Coastal Studies Inst. and Dept. Marine Sciences,
140 pp.

Gary, D. L., and D. W. Davis. Unpublished manuscript. Camps and Recrea-
tion in Louisiana's Coastal Marsh. Nichols State University,
Thibodaux. 130

Gosselink, J. G., (ed). In Press. Final Report on A Characterization
of the Chenier Plain Coastal Ecosystem of Louisiana and Texas. U.S.
Fish and Wildlife Service, Dept. of the Interior. FWS/OBS-78/11.

Gosselink, J. G., and R. H. Baumann. In Press. Wetland inventories:
wetland loss along the United States coast. Paper presented at@the
Coastal Symposium of the AAG/IGU Joint Meetings. New Orleans,
April 1978.

Graff, J. M. 1976. Use of LANDSAT data to relate water depth to observed
area of inundation in coastal marshes. Master's thesis, Louisiana
State University, Baton Rouge, La. 66 pp.

Harper, J. R. 1975. Nearshore oceanography. Tech. App. IV. In J. G.
.Gosselink, R. R. Miller, M. Hood, and L. M. Bahr Jr. (eds). Louisiana
Offshore Oil Port: Environmental Baseline Study. LOOP, Inc., New
Orleans, La.

Hawaii Coastal Management Program and Draft EIS. 1978. NOAA, Office of
Coastal Zone Management. Washington, D.C.

Hicks, S. D., and J. E. Crosby. 1974. Trends and variability of yearly
mean sea level 1893-1972. NOAA Technical Memorandum NOS 13.
Rockville, Md. 14 pp.

Howe, H. V., R. J. Russell, J. H. McGuirt, B. C. Craft, and M. B. Stevenson.
1935. Reports on the geology of Cameron and Vermilion Parishes,
Louisiana Geol. Survey Bull. No. 6.

Klemas, V., F. C. Daiber, D. S. Bartlett, 0. W. Crichton, and A. 0.
Fornes. 1973. Coastal vegetation of Delaware. The Mapping of
Delaware's Coastal Marshes. University of Delaware, College of
Marine Studies. Publ. No..DEL.-SG-15-73. 29 pp.

Kolb, C. R., and J. R. Van Lopik. 1966. Depositional environments of,
the Mississippi River Deltaic Plain, southeastern Louisiana. Pages
17-61. In* Deltas and Their Geologic Framework. Houston Geol. Soc.

Kreitler, C. W. 1977. Faulting and land subsidence from ground water
and hydrocarbon-production, Houston-Galveston, Texas. Proc.
Second International Symposium on Land Subsidence, Internat. Assoc.
of Hydrological Sciences, No. 121, pp. 435-446.

Louisiana Dept. of Public Works. Unpublished field survey records. Baton
Rouge, La.

Lynch, J. J. 1941. The place of burning in management of the Gulf coast
wildlife refuges. J. Wildl. Mgmt. 5(4):454-457.

Marmer, H. A. 1954. Tides and sea level in the Gul f of Mexico, pp. 101-
118. In Gulf of Mexico, its origin, waters and marine life. U.S.
Fish a7n-d Wildlife Serv. Fishery Bull. 89.

131

Morgan, D. J.@ 1973. The Mississippi River delta: Legal-geomorphic
evaluation of historic shoreline changes. Master's thesis, Louisiana
State University, Baton Rouge, La. 369 pp.
Morgan, J. P. 1972. Impact of-subsidence and erosion on Louisiana coastal
marshes and estuaries. In R. Chabreck (ed.) Proc. of the Coastal
Marsh and Estuary Mgt. Louisiana State University Center for
Wetland Resources, Baton Rouge, La.

Morgan, J. P., and P. B. Larimore. 1957. Changes in the Louisiana shore-
line. Vol. 7, Trans. Gulf Coast Assn. of Geological Societies,.
pp. 303-310.

Morgan, J. P., L. G. Nichols, and M. Wright. 1958. Morphological effects
of Hurricane Audrey on the Louisiana coast. Tech. Rept. No. 10,
Louisiana State University Coastal Studies Inst., Baton Rouge, La.
53 pp.

Morgan, J. P., J. R. Van Lopik, and L. G. Nichols. 1953. Occurrence and
development of mudflats along the Western Louisiana coast, Louisiana
State University Coastal Studies Inst., Tech. Rept. No. 2, 34 pp.

Murray, S. P. 1976. Currents and circulation in the coastal waters of
Louisiana. Louisiana State University Center for Wetland Resources.
Sea Grant Publ. No. LSU-T-76-003. Coastal Studies Inst., Bull. No.
210. .33 pp.

O'Neil, T. 1949. The muskrat in the Louisiana coastal marshes. La.
Wildlife and Fish. Comm., New Orleans, La. 159 pp.

Oregon Coastal Management Program and Final EIS. 1977. NOAA.Office of
Coastal Zone Management. Washington, D.C.

Roberts, H. H., R. D. Adams, R. H. W. Cunningham, and L. J. Rouse Jr.
Unpublished manuscript. Evolution of the sand-dominant subaerial
phase, Atchafalaya Delta, south-central Louisiana.

Saucier, R. T. 1963. Recent geomorphic h istory of the Pon tchartrain
Basin. Louisiana State University Press, Coastal-Studies Series
No. 9. 114 pp.

Shlemon, R. J. 1972 * Development of the Atchafalaya Delta: Hydrologic
and geologic studies of coastal Louisiana. Rept. No. 8. Louisiana
State University Center for Wetland Resources, Baton Rouge, La. 51 pp.

Shlemon, R. J. 1975. Subaqueous delta formation-Atchafalaya Bay,
Louisiana. Pages 209-221. In M. L. Broussard (ed.), Deltas.
Houston Geological Soc., Houston, Texas.

Suhayda, J. N. 1976. Wave Action Offshore of Barataria Basin. In
Barataria Basin: Hydrologic and Climatologic Processes. LSU-T-76-010.

132

Thompson, W. C. 1951. Oceanographic analysis of marine pipeline problems.
Texas A & M Research Foundation, Dept. of Oceanography, Sec. II-
Geology, Project 25, 31 pp.

U.S. Army Corps of Engineers. 1973. Shore Protection Manual. U.S. Army.
Coastal Engineering Research Center. Fort Belvoir, Virginia. Vol. II
(Chpts. 5-8).

U.S. Army Corps of Engineers. 1961. Mermentau River and tributaries,
Louisiana, channels and control structures. Operation and-mainte-
nance manual. USA Eng. New Orleans District.

U.S. Army Corps of Engineers. 1971. National Shoreline Study: Inventory
Report - Lower Mississippi Region. New Orleans Dist., New Orleans,
La. 57 pp.

U.S. Army Corps of Engineers, Office of the Chief of Engineers. 1974.
Final Environmental Impact Statement for Grand Isle and Vicinity,
Louisiana. I

U.S. Army Corps of Engineers. 1976. Grand Isle and Vicinity, Louisiana.
Communication from the Assistant Secretary of the Army (Civil Works).
Includes DEIS, FEIS, and Reports from District Engineer.

Valentine, J. M. Jr. Unpublished manuscript. Plant succession after the,
Saw-Grass mortality in southwestern Louisiana. USFWS Bureau of
Sport Fisheries and Wildlife,*Lafayette,_La.

Weaver, P., and M. M. Sheets. 1962. Active faults, subsidence, and
foundation problems in the Houston, Texas area. In Geology of the
Gulf Coast and Central Texas. Houston Geological__@ociety, Houston,
Texas. pp. 254-265.

13@

Appendix

Shoreline Erosion/Mitigation Planning
Synopses of State.Coastal Zone Management Programs

The requirements regarding state shoreline erosion/mitigation

planning, article 923.26 of interim-final 305/306 regulations subsection

305(b)(9), March 1, 1978, are as follows.

In order to meet the requirements of subsection
305(b)(9) of the Act and to coordinate these require-
ments with those of subsections 305(b)(3) and 306(c)(9),
States must include a planning process that can assess
the effects of shoreline erosion. Evaluation must
include assessment of ways to mitigate, control or
restore areas adversely affected by erosion. This pro-
cess must include:

(1) A-method for assessing the effects
of shoreline erosion;
(2) Procedures for managing erosion
effects, including non-structural
procedures;
(3) Articulation of State policies per-
taining to erosion, including
policies regarding preferences for
non-structural, structural and/or
no controls;
(4) A method for designating areas for
erosion control, mitigation and/or
restoration as areas of particular
concern or areas for preservation
and restoration, if appropriate;
(5) A mechanism for continuing refine-
ment and implementation of necessary
management policies and techniques,
if appropriate; and
(6) An identification of funding programs
and other techniques that can be
used to meet management needs.

These requirements insure that the impacts of prosion will be

considered in the overall management plan of the state. The

purpose of assessing the causes and effects of shoreline erosion is to

explicitly determine state policy for handling erosion control,

mitigation, and/or restoration be it structural, non-structural, or

non-control. All state plans submitted after 1 Octobe r 1978 or plans

approved after that date must include provisions for fulfilling the

134

above regulations. Several of the state plans that have already received

approval as well as several other submitted plans will be reviewed in

the following section with respect to article 923.26--Shoreline Erosion/Mitigation

Planning.

The Massachusetts Coastal Zone Management Plan is by far the most

comprehensive shoreline erosion/mitigation planning to date.

This plan emphasizes non-structural solutions to erosion problems,

citing both long-term effectiveness and federal program emphasis (e.g.,

National Flood Insurance Program) as determining factors. The report

points out that non-structural solutions more closely simulate natural

processes, are aesthetically more compatible with natural landforms, and

are less likely to cause adverse effects on.adjacent areas. They are

also considerably less expensive. Structural measures are to be reviewed

on a case-by-case basis and only selectively permitted, such as in areas

where natural buffers have been irrevocably lost, if adjacent or downdrift

effects are minimized.

The method employed by Massachusetts in assessing the effects of

shoreline erosion consisted of classifying these effects as "critical"

or "moderate," based on how the land was used. The areas chosen for

classification consisted of: recreational beach, other public lands or

facilities, private property, and conservation lands. Based on the

above criteria, affected coastal areas were then classified as areas of

particular concern or areas for preservation and restoration.

Non-structural protective and restorative measures such as beach

nourishment, dune stabilization, zoning, and acquisition of hazard-

prone areas by state or local government are to be given preference over

135

structural solutions. However, regardless of the type of solution used,

the plan explicitly defines the conditions under which federal and/or

state monies may be used to finance the solution measures. The conditions

include: a greater than local significance and substantial public

benefit from the area in question; adequate regulations to prevent the

deterioration of the area-once stabilized or restored; established

design criteria for the solution to be employed; and identification and

acceptance of the responsibilities associated with future maintenance.

Structural measures should be restricted to cases where, in addition to

the above criteria, non-structural solutions have been evaluated as

ineffective, too costly, or otherwise infeasible and where the implementation

of said structural measure will not seriously impair natural processes

or adversely affect adjacent or down coast areas. A number of.state,

local, and federal departments have been assigned to regulate, permit,

and carry out the reviewed solution measures.

The California management plan tends toward the opposite approach

of that taken by Massachusetts in that structural solutions are not

viewed with such disdain. Its major policy is that structural (e.g.,

breakwaters, groins, revetments) solutions that alter natural shoreline

processes shall be permitted when required to serve coastal-dependent

uses or to protect existing structures or public beaches in danger of

erosion and when designed to eliminate or mitigate adverse impacts on

local sand supply. In addition, stability and structural integrity must

be assured from any activity in the coastal zone, and these activities

are not to create.or to contribute significantly to the erosion or

destruction of the site or surrounding area or in any way require the

136

construction of protective structures that would adversely affect natural

landforms.

The state's basic approach to shoreline erosion/mitigation planning

is to prevent development in areas prone to erosion rather than to

construct protective works. However, where protective structures are

permitted, based on the above policies, their Department of Navigation

and Ocean Development is authorized to plan, design, and administer

funds for the construction of the projects. This department, along with

several federal agencies, is responsible for the assessment, based

primarily on aerial photography and subsequent beach profiles, gf eroding

and erosion-prone areas along the California coast.

The Wisconsin plan only briefly discusses the problem of shore

erosion because at the time of its preparation, article 923.26 was not

mandatory. Wisconsin's general policy is to regulate, via the appropriate

state agencies, any development in the coastal zone so that the rate of

bluff recession and other types of eroding shorelines would not be

accelerated. A setback of 23 meters (75 feet) from the high water mark

is required in unincorporated areas unless an existing development

pattern exists. -Structural protection from erosion is permitted so long

as it does not interfere with navigation or damage fish and game habitat.

The plan is mandated to support local and state efforts in identifying

and designating hazard areas as areas of special management concernland

to assist in the development of specific management policies as well as

to provide financial and technical support to implement these policies.

Information 'regarding recession rates, littoral drift, slope failure,

and alternate erosion control measures is presently lacking, and the

137

plan hopes to remedy this deficiency by supporting research and public

education on these prob lems.

The Rhode Island shore erosion mitigation plan is to be completed

during the first year of program implementation. The plan recognizes

the natural protection offered by barrier beaches and dunes and assigns

a high priority to the preservation and protection of the "shoreline

system" (e.g.,. beaches, cliffs and bluffs, wetlands, dunes). Permits are

required for any activity on the shoreline system. The use of non-

structural methods to solve erosion problems is encouraged, particularly

in areas of non-critical erosion. Areas of critical erosion (as defined

by the Corps of Engineers) may justify the use of structural measures.

The plan requires that all permit applications for erosion control

projects demonstrate that non-structural methods have been fully

evaluated as possible solutions to the problem. Where non-structural

methods are deemed unsuitable, it mus@t be demonstrated that the

proposed structural solution will have a reasonable probability of

controlling erosion-at the site and will not,cause adverse impacts in

or around adjacent areas.

The North Carolina program has not yet established a firm policy

on shoreline erosion mitigation planning. It is state policy to

control the location and design of structure and to prevent damage to

natural protective features such as beaches, dunes, and inlet lands.

The need for an inventory and analysis of erosion-prone areas as well

as for an analysis of current shore erosion management practices is

recognized and is assigned a high priority in the state's policy

development process. The policies so developed will also recommend a

138

state participation formula that considers social, physical, and,economic

thresholds that could give priority to requested erosion control projects.

The State of Oregon prefers land-use management practices and non-

structural solutions for erosion mitigation. However, where shown to be

necessary, structures are to be designed so as to minimize adverse

impacts on currents, erosion, and accretion patterns. Regarding the

land@use management program, permitted uses are to be based on the

capabilities and limitations of, for example, beach and dune areas to

sustain different levels of use or development. Additional considerations

include the need to protect areas of critical enviromental concern,

scenic, scientific, or biological importance, and significant wildlife

habitat. Oregon requires: (1) a site investigation report financed by

the developer (2) the posting of performance bonds to assure adverse

effects can be corrected and (3) reestablishing vegetation withiIn a

specific time. In addition, if littoral drift is interrupted, methods of

sand bypass are to be investigated and provided where possible. Protective

structures are permitted when: (1) visual impacts are minimized (2)
necessary beach access is maintained (3) negative impacts on adjacent'

property are minimized and (4) long-term costs (e.g., maintenance) to

the public are avoided.

In Hawaii, land-use management is used extensively to preclude

development in erosion-prone areas. Where this is not appropriate, non-

structural techniques rather than structural techniques are used whenever

possible to mitigate shoreline erosion. Non-structural techniques, such

as the replenishment of beaches, have been used successfully. Structural

techniques are most often employed where development of the shoreline

has occurred or where valuable public beaches are threatened by erosion.

139

I
. I
I
I
I
I
i
I
I
I
I
I
I
I
I
I

@@t .-I- ",
... .0- RIIIIIIIIIIII
3 6668 14109 5275