_LOUISIANA'S ERODING COASTLINE: ..

r-----""!!!!!��.,�COMMENDATIONS

' PROTECTION \ ' 0 Louisiana's Eroding Coastline: Recommendations for Protection 0 a by:

J .L. van Beek K.J. Meyer-Arendt

Coastal Environments, Inc. S.M. Gagliano , President Baton Rouge, Louisiana il This study was funded by: G Office of Coastal Zone Management D National Oceanic and Atmospheric Administration Department of Commerce Q June 1982 0 0 prepared for: Section 0 Louisiana Department of Natural Resources Baton Rouge, Louisiana

This document was published at a cost of $4.22 per copy by the Louisiana Department 0 of Natural Resources, P.O. Box 44396, Baton Rouge, Louisiana, for the purpose of carrying out the requirements of the Louisiana Coastal Zone Management Program under the authority of Act 361 of 1979. This material was printed in accordance with the standards for printing by state agencies established pursuant to R.S. 43:31 and was purchased in accordance with the provisions of Title 43 of the Louisiana Revised Statutes. This project was financed through a grant provided under the Coastal Management Act of 1972, as amended, which. is administered by the U.S. Office of Coastal Zone Management, National Oceanic and Atmospheric Administration. 0 0 0 0 0 {J D il 0 tl D 0 a 0 0 0 0 0 0 0

Table of Contents List of Figures

List of PigtJ.res •••••••••••• ••••• •••••••••••••••••••••••••••••••• • •••••••••• iU Figure 1. L

Figure 2a. Louisiana Shoreline Sehematie ...... 6

List of Tables, • • • • • • • • . . • • • • • • • . • . • • . • • • •• • • •• •• • •• • • •••• •••••••••••••••••• ill Figure 2b. Louisiana Shoreline Sehematie ...... 1

Figure 3. Impact of Level Rise upon Shorelines ••••••• •••••• o o ••••• o • o o • o 5

Ackrlowledgements ••••••• ••• • ••••••••••••••••••••••••••••••••••••••••••••• lv Figure 4. Hurricane Effeets Upon Chenier PJain Shoreline •••••••••••••• o • o o •• 9

Figure 5. Physieal Processes Along the Louisiana Shoreline •••••••••• o • o •••••• 10

CHAPTER I. INTRODUCTION ••••••••••• • •••••••••••••••••••••••••••••••••• 1 Figure 6. Currents Within Tidal Passes •••. .•••. .•••••••••••••••••• , ••••• ••• 11

Figure 7. Role of Tidal In the Sediment Transport System ••••• o •••• o ••• o 12

CHAPTER D. PROCESSES OF SHORELINE Figure 8. Geologie Cross Section, Wine Pass and Cat Island Pass ••••••• •• 12

AND WETLAND DETERIORATION ...... 3 Figure 9. Impaet of Canals Upon Wetland Deterioration ..•••• • ••••• • •••••••• o 13

BaekgttotiDd •••••••••••••••••••••••••• ••• ••••••••• ••••••••••••••••••••• 3 Figure 10. Impact of Canal Dredging Upon Tidal. Development,

...... Subsidence ...... 5 Bast Timbalier lslara<:l • •• •• • • • • • • • • • • • • • • • • • • • • • •• • • •• •• • • • •• • • • 14 0 Energy Input •••••••••••••••• • ••••••••••••••••••••••••••••••••••••••••• 8 Figure 11. Effects of -Parallel Canals Upon Barrier ••••••• •••• o ••• 14 Sediment Supply and 1'r8.11Sp0rt •••••••••••• •••••••••••••••••••••••••••••• 9 Figure 12. in the Louisiana Coastal Zone ••••• •••••••• o •• • ••••• ••••• 16

The Role of Tidal Inlets ••• .••••••••••• • ••••••• •••• •••••• ••••••••••••••• 11 Figure 13. Shoreline Change, Hydrologic Unit 1 ...... 18 0 Man-Induced Effeets •• •••••••••••••••••••••••••••• • ••••• ••••••••••••••• 12 Figure 14. Shoreline Change, Hydrologie Unit 3 •• o •••• ••••• • •••••••• o •••••••• 19 Sum mary of Causes • • • • •• • •• • • •• • •• • • •• • •• • •• • •• • • • • ••••••••••••••••••• 14 Figure 15a. Shoreline Change, Hydrologic Unit 4 (Barrier Islands) •••••• o o •••••••• 22

Figure 15b. Shoreline Change, Hydrologic Unit 4 (Mainland) .•••••• o ••••• •••• o •• o 22

CHAPTER m. CHARACTERIZATION OF THE BARRIER SHORELINE 17 Figure 16. Bathymetrie Changes, Cat Island Pass Area, 1891-1980 o. o •••• o o. o •• o 24

Hydrologic Unit 1: Chandeleur-Breton ••••••••• o •• o o •• 0 •• o o • o • o o ••• o o •• o • o 17 Figure 17. Shoreline Change, Hydrologic Unit 6 ..•• •••• ...••••••• o • o o •• o o ••• o 25

Hydrologic Unit 3: Barataria •••••••••••••••••••••••••••••••••••••••••••• 18 Figure 18. Shoreline Change, Hydrologic Unit 7 •••••••• ••••••••••• o • o •• ••o ••• 26

Hydrologic Unit 4: Terrebonne-Timbalier ••• o o •• o ••••••• 0 •• o ••••••••••••• o 21 Figure 19. Shoreline Change, Hydrologic Unit 8 •••• o • o ••• •••••• o •• o ••• o o o ••• o 2'1 0 Hydrologic Unit 6: Vermilion •••••••••••••••••••••••• • ••••••••••••••••••• 25 Figure 20. Land Use Patterns in Coastal Louisiana ...... ••..•••• o •••• o • 30 Hydrologie Unit 7: Mermentau •• .•• ••••••••••.•.••••• .••••••• • •••••••••• 26 Figure 21. Habitat Change, Delacroix and Vicinity, 1955-1978 ••••••• , • o • o •••• •• 31

Hydrologic Unit 8: Calcasieu-Sabine •••••••••••• 0 •••••• 0 • 0 ••••••••• 0 • 0 0 • 0 2'1 Figure 22. Habitat and Shoreline Change, Port Fourehon and Vicinity,

1955-1978 •• •••• •••..•••••••••••• •.••.••••••• •••• • •••••••••••• 32

•••••••••• • ••••• o CHAPTER IV. IMPACTS UPON LAND USE PATI'ERNS ...... 29 Figure 23. Habitat Change, Boudreaux and Vicinity, 1948-1978 33

Hydrologic Unit 1: Chandeleur-Breton •••••••• 0 •• 0 •••• 0 •• 0 ••••••••••••••• 0 29 Figure 24. Shoreline Change, Holly and Vieinity, 1833-1978 • o o ••••• • o o o •• 34

Hydrologic Unit 3: Barataria .•••••••••••••• ••••• •••••••••••••••••••••••• 31 Figure 25. Recommended Restorative Measures Alongthe Louisiana Shoreline •• o 40

Hydrologic Unit 4: Terrebonne-Timballer ••••••• o.o •••• 0 •• o •••••••• o o •• o •• 33 Figure 26. Recommended Demonstration Project, Grand Terre Islands Hydrologic Unit 6: Vermilion •••••••••••••••••••• •••••••• • ••••••••••••••• 33 and Vieinity ••.••••••••••••••• •••••••••• •••••••• •••••••••••••• 41

Hydrologic Unit 7: Mermentau •• •••.•••• ••••••••••• ••••••••••••••••••••• 34 Figure 27. Recommended Demonstration Project, Eastern Isles Dernieres o o o ••• o. 42

•••• , • 43 D Hydrologic Unit 8: Calcasieu-Sabine •• o o ••••••••••••• 0 •• o •• o •••• o • o •••••• 34 Figure 28. Recommended Demonstration Project, Holly Beaeh and Vieinlty

CHAPTER V. REMEDIAL MEASURES ...... 35

Rigid Versus Flexible Solutions •• 0 •• o •••••••••••••••••••••• o •• o •• o ••••••• 35

Sources of Nourishment Material ••••••• • ••••••• o •••••• 0 • 0 ••••• ••••••••• • 37 Technolog-y- and Engineering • • • • • •• • • • • • • • • • • • •• • •• • • • • • ••••••••••••••••• 37 List of Tables Applications Along Louisiana's Barrier Shoreline •••••••••• 0 ••• 0 ••••• 0 ••• 0. 0 38

CHAPTER VI. CONCLUSIONS ••• •• o •• o •••• o •• o •• o ••••••• o •• o...... 45 Table 1. Active Processes and Relative Severity of Louisiana's

...... REFERENCES ...... 46 Hydrologic Units ••• ••••• ••••••. ..•. ••• ••••••••••••••••• ••• •••• 15 Table 2. Severity Ranking Matrix of Louisiana's Barrier

APPENDIX Shoreline Subunits • • • •• • • • • • • • ••••••••••• ••• ••••••••••••••••••• 39

iii 0 0 0 0 Acknowledgements 0 tl This study was funded by the Office of Coastal Zone Management, National Oceanic and Atmospheric Administration, Department of Commerce, through the Coastal Management Section of the Louisiana Department of Natural Resources. We 0 wish to thank Mr. Joel Lindsey, CMS Administrator, and Mr. David Chambers, CMS Project Officer, for their support in realizing this study.

Simultaneous with the present study, a report was prepared for the Terrebonne Parish Police Jury concerning that parish's D barrier system. Accordingly some results as set forth in the present report are based in part on jointly developed approaches. We wish to acknowledge this commitment of the Policy Jury and its Committee to a joined effort of state and local government in dealing with Louisiana's coastal problem. 0

We wish to acknowledge the contribution by members of Louisiana State University's research community through an open exchange of ideas and information, and thank in particular Dr. I. Mendelssohn, Messrs. S. Penland and R. H. Baumann of the 0 Center for Wetland Resources, Dr. R. Boyd and Mr. P. Howard of the Department of Geology, and Dr. J. Suhayda of the Department of Civil Engineering. Access to historic maps and photographs was facilitated by Ms. Joyce Nelson of the School of Geoscience Map Library. 0 Special thanks are extended to Mr. Larry Dement of the Section, U.S. Army Corps of Engineers, New Orleans District, and Mr. Bill Jack of the Highway Engineering Section, Louisiana Department of Transportation and Development, for their input regarding coastal engineering requirements. D

Among the staff of Coastal Environments, Inc., we are indebted to Dr. Sherwood M. Gagliano, Dr. Paul Templet, and Dr. Karen Wicker for their contributions through discussions and critical evaluations. Douglas O'Connor, Michele Meyer-Arendt, \] and Elizabeth Roberts provided assistance in data compilation. Cartographic drafting was by Michele Meyer-Arendt and Curtis Latiolais and layout by Nancy Sarwinski. Typing was by Bettye Perry. Susan Pendergraft was responsible for report editing and production. 0 0 0 0 0 iv 0 0

Chapter I 0 Introduction This report is the result of a study directed at assisting the State of Louisiana in development of a plan for the protection and management of its first line of coastal defense. That is the natural system of barrier islanm, barrier , and associated wetlands facing the o· of Mexico. The need for such action is becoming increasingly urgent as wetland losses and saltwater intrusion accelerate, water levels rise, n and an ever greater number of people is affected by these changes. The present study represents one of a number of responses by the State 0 Legislature and Governor David C. Treen to the urgent nature of Louisiana's coastal problems.

Authorization for the present study resulted 0 from enactment in 1979 of subsection G, Section 213.10, of Title 49 which directed development of a critical coastline and barrier islands 0 indexing system under the State and Local Coastal Resources Management Act. More recently, in November 1981 this was followed by 0 passage of Act 41 by the State Legislature creating the Coastal Environmental Protection Trust Fund, and by the appointment of the Governor's Task Force on . Example of deteriorating barrier island characterized by extensive wa.shover development. 0 Through these joint efforts implementation of coastal erosion control measures is presently being realized in a number of demonstration projects. To arrive at recommendations for protection and the shoreline. Local and economic impacts of management of Louisiana's Gulf shore, the coastal erosion and associated wetland deterio­ To assist the State in these considerations of report first considers active processes, natural ration on present land uses are therefore coastal erosion problems and in program and man-induced, to which documented changes evaluated and weighed as elements in recom­ 0 development, major aspects of the present of the shoreline and coastal wetlands can be mending specific protection measures. report were advanced through the Coastal related. In this manner the is divided into Management Section of DNR. These advance a number of process-based units as a On the basis of the combined information con­ 0 recommendations included presentations to the requirement for functional design. cerning perceived causes, trends and rates of Secretaries of the Department of Natural change, and anticipated impacts, recommenda­ Resources and Department of Wildlife and tions are made for each of the coastal units in Fisheries, to representatives of the Governor's A second element in the development of a pro­ the form of measures considered most feasible Office, and to the Joint Legislative Committee tection plan is the benefits to be derived from for protection and management. These recom­ on Natural Resources. Accordingly, this report protective measures. While many intangibles are mendations are further detailed in the form of 0 restates earlier recommendations while placing involved in this regard, a direct approach is to three projects that demonstrate the proposed them in a broader perspective. consider land uses in the immediate vicinity of approaches.

1 0 0 0 D D 0 D 0 0 0 0 0 0 0 0 0 0 u 0 0 In the Deltaic Plain, each delta lobe experiences thus account for a net seaward progradation of phases of aggradation and degradation. The the land mass. When the delta-switching mech­ former represents the growth phase, when nuvial anism redirects the locus of active sedimenta­ input and sedimentation rates are at their maxi­ tion to a more distant location (the eastern mum. In time, favorable gradient advantages sections of the Deltaic Plain, for example), wave 0 trigger diversion at some upstream point on the action reworks the shoreline sediments into a river. This delta-switching mechanism initiates barrier within a cycle of marine the gradual abandonment of a particular river transgression. (When sufficient elevations are and the onset of the phase of degrada­ attained, the beach ridges become colonized by 0 tion within the associated delta lobe. As the live oak trees [Quercus virginiana] , or chenes in introduction of sediments slowly decreases (due French, thereby leading to the use of the term to increasing nuvial discharges being directed to chenier in describing these ridges.) The se­ [J the new locus), active sedimentation cannot keep quence of delta systems has thus led to the pace with the compaction and settlement of the present physiography of the Chenier Plain, char­ recently deposited land mass. Even the large acterized by a series of inland-stranded, D expanses of marshgrass, which first colonized east-west-trending cheniers within a vast marsh the deposited sediments and assisted the aggrad­ plain. As the active delta has occupied a posi­ ation phase by the production of organic matter tion 200 mi (320 km) east of the Chenier Plain and entrapment of fine sediments carried in since historic times,_ the shoreline is generally G suspension by tidal forces, cannot maintain a eroding and can be characterized as an active surface above when subsidence barrier. becomes a dominant factor in the delta cycle. Marine processes become more important within With the exceptions of the Atchafalaya the abandoned delta lobe, as an intricate tidal /Cote Blanche Bay area and the present channel network develops and wave action birdsfoot delta of the Mississippi River, the affects the outer edge, or deltaic . The entire Gulf-fronting shoreline of Louisiana con­ 0 waves rework the outer deltaic sediments, win­ sists of barrier islands or barrier beaches. These nowing out the fine material and concentrating areas comprise the focus of study of this report. the coarser material in a landward and long­ 0 shore-migrating ridge, or . ElevatioQs with­ Louisiana's modern-day barrier shoreline can be in this outer deltaic rim are higher than in more roughly divided into three components: the inland marsh zones because of the wave and Chandeleur system, the Terrebonne-Barataria 0 processes. The combined processes of subsi­ system, and the Chenier Plain system (Figure 1). dence and marine forces reworking the outer rim The Chandeleur system, including Breton Island, lead to a gradual disappearance of the sea ward is a barrier island chain, separated by 25 mi (40 Chapter II marshes and a formation of a barrier rim. This km) from the mainland by Chandeleur and 0 landward-migrating barrier rim may occur as a Breton Sounds, which represents the outer rim of continuous chain, a series of barrier islands, the St. Bernard delta complex. The Terrebonne­ Processes of Shoreline Erosion or a mainland-fringing barrier beach, depending Barataria system extends from Point au Fer to (1 upon an interplay of factors which include sand Sandy Point and is comprised of a series of small and Wetland Deterioration supply, wave climate, tidal-exchange forces, and barrier island chains which developed following stage of the delta cycle. A conceptual model of erosion of the Caillou and Caminada-Moreau 0 barrier evolution has been formulated by deltaic , and transgression of nanking researchers at Louisiana State University barrier . This system is associated mainly Background (Penland and Boyd 1981; Penland et al. 1981). with various deltaic lobes of the Lafourche delta 0 system. The Chenier Plain system consists of a The barrier islands and barrier shorelines of The Chenier Plain of southwest Louisiana, down­ long, continuous barrier beach backed by marsh Louisiana originated in the deltaic system of the drift of the Deltaic Plain, was created by alter­ or beach ridges. (Marsh Island, while deltaic in Mississippi River. During the last 8000 years, nating processes of progradation and transgres­ origin, exhibits shore characteristics similar to 0 five major delta complexes containing sixteen sion related to proximity of the active those further west and is thus generalized as an separate delta lobes have built the vast Deltaic Mississippi . During periods of a appendage of the Chenier Plain system.) The Plain of south-central and southeast Louisiana relatively close active delta, deltaic clays and shoreline is primarily sandy, with stretches of (Frazier 1967), as well as the Chenier Plain of fine carried in suspension by westerly coast­ finer silts and clays near river mouths and ac­ southwest Louisiana (Byrne et al. 1959). al currents become welded to the shoreline and creting associated with pro-delta clays

3 0 0 0 TEXAS lOUISIANA LOUISIANA MISSISSIPPI 0

lATON • ·--• ---..., 0 •ouo•� ·::---.... 1 '

• LAFAYETTE D � • . � D [J 0 VIII 0

v 0 SYStEM 0 II LEGeND 0

Berrier Islands and ShoreUnes Reference Shor•Un• Sch•'"attc Point• for ... .. D / \ LOU.StAHA COASTAL ZONE. liMlTS . . J �. HYDROLOGIC UNITS .(H.U.) ·•. v .. u � � 0 0 so

0 "' tp ... •• u u Figure 1. Louisiana's Barrier Shoreline. D

4 0

of the Atchafalaya River delta. (Additional Subsidence Galveston, Texas seawall, relative subsidence 0 characteristics of Louisiana's shoreline are pre­ rates of 2.6 ft/century [0.79 cm/yr] were sented on Figure 2a and 2b in schematic form.) A dominant process contributing to shoreline .derived [Price and Parker 1979] .) erosion and land loss in coastal Louisiana is the n downward movement of the land surface in rela­ Since the Mississippi River has been harnessed Created by marine forces, the overall role of the tion to sea level. This is caused by a variety of effectively by protection levees, and overbank barriers is to cushion the impact of the sea upon factors, which include , tectonic flow and crevassing have been virtually elimi­ more fragile marsh deposits. And since the processes such as crustal downwarping, folding, nated, the lack of newly introduced sediments 0 initial settlement of the coastal zone, the and faulting, and compaction of sediments due to has resulted in an "accretion deficit." Sedimen­ barriers have played no small role in buffering overlying weight, extraction of water and hydro­ tation is now limited to the reworking of bottom damaging storms and hurricanes and "absorbing" carbons from the subsurface strata, and wetland sediments by tidal forces, and the rate of marsh much of the wave energy expended upon reclamation (Adams et al. 1976). build-up is no longer keeping pace with the Louisiana's shores. Barrier islands and tidal subsidence rate. Recent sedimentation studies inlets until now have been important regulators For the sedimentary environment present in the in lower Barataria Basin indicate vertical accre­ both of water exchange between the Gulf and Deltaic Plain, the factor of crustal downwarping tion rates of 1.35 cm/yr (4.4 ft/century) in 0 the bays and of transfer of wave energy from the is considered very important. Estimates of long­ streamside marshes and 0. 75 cm/yr (2.5 Gulf into the bays. As barrier islands erode and term subsidence rates, based upon radiocarbon ft/century) tot marshes 45 m (147 ft) from tidal inlets widen, the impact of the sea upon the dating of buried peat deposits, have ranged from streamside (Delaune et al. 1978). In other words, u bay areas and lower marshes increases. averages of 0.35 ft/century (0.1 cm/yr) assuming only the natural levees of the tidal channel are steady sea level (Frazier 1967; Gagliano and van barely keeping pace with the subsidence rate, Beek 1970) to 0.78 ft/century (0.2 cm/yr) for the whereas slightly more distant marshes show an The entire barrier shoreline of Louisiana is char­ Lake Pontchartrain area (Kolb and van Lopik accretion deficit. It is in these latter regions 0 acterized by erosion and shoreline retreat as 1958), the latter incorporating an assumed sea that marsh breakup and land loss will tend to well as naturally high subsidence rates. Prior to level rise rate of 0.32 ft/century (0.1 cm/yr). dominate. This pattern is quite common in the [} the twentieth century, erosion and retreat rates (Considerable variability in subsidence rates is , as well as in more inland marshes were partially offset by renewed sediment input. found across the Deltaic Plain, and these two (see Appendix, Plate 26 for example). Annual overtopping of the Mississippi River nat­ estimates represent averages.) A refined esti­ ural levees during spring flooding provided sedi­ mate of 0.1 ft/century (0.035 cm/yr) for the sea The combined factors of subsidence and sea level 0 ments necessary to maintain interdistributary level rise component of relative subsidence was rise have a direct effect upon shoreline erosion wetlands. Tidal forces aided in distributing derived by sedimentary analysis of the geologi­ (Figure 3). Formulas have been developed to these sediments within the gulfward marshes. cally stable Sable region of south Florida theoretically arrive at shoreline retreat rates 0 Numerous distributaries received freshwater in­ (Scholl et al. 1969). (Bruun 1962; Weggel 1979). A rough estimate of put during the spring , and valuable coarse Louisiana conditions can be made by using a sediments were funnelled to and distributed Short-term trends, as observed by analysis of formula modified from Bruun (1962), along the shoreline. Bayou Lafourche, for exam­ gauge records, indicate much higher relative (x = ab) ple, was an important conduit for river sedi­ subsidence rates. Swanson and Thurlow (1973), h+O ments until early in this century. Today, the after subtracting out 0.035 cm/yr (0.1 Mississippi River is totally contained by artifi­ ft/century) for estimated eustatic sea level rise, cial levees throughout the Deltaic Plain. Fluvial examined subsidence patterns along the Gulf sediments are not only no longer being intro­ Coast for the 1948-1971 period and noted a duced into the interdistributary swamps and significant change in rates occurring about 1959. marshes, but are lost to the steep slopes of the At Bayou Rigaud, for example, subsidence rates 0 ...... Outer by way of the passes of were calculated at 0.27 cm/yr (0.9 ft/century) I the active delta. (The sole exception to this is for 1948-1959 and 1.29 cm/yr (4.2 ft/century) for �======�=== ·=�·:�:.... the regulated Atchafalaya River, which is pre­ 1959-1971 (Swanson and Thurlow 1973). Up­ .,...... 0 sently building a delta in Atchafalaya Bay and dating of the 1973 study and inclusion of the contributing to accretion on the Chenier eustatic component led to a calculation of a Plain shoreline. Nonetheless, land accretion is subsidence/sea level rise rate of 1.30 cm/yr (4.3 still minor in comparison to the overall erosion.) ft/century) for 1954-1979 at Bayou Rigaud The result of this modern cutoff of sediments (Baumann 1980). Comparable rates (over 4 has been increased shoreline erosion and severe ft/century [ 1.2 cm/yrJ) were derived for Bayou land loss presently amounting to over 40 sq mi/yr Chevreuil in upper Barataria Basin and Calcasieu 3. Impact of Sea Level Rf3e Upon 0 2 Figure (100 km /yr) per year within the coastal marshes Pass near Cameron (Baumann 1981, personal Shorelines (after .8nam 1962). of the Deltaic Plain alone (Gagliano et al. 1981). communication). (For the east end of the

6 -150 �------�--� ·45 0 Annual Shoreline Change. 1955-1978 -100 -30 ... . 0 ,.. .� •50 -15 � - E fJ +50 �------�� +15 Structural 0 Modi flea tlon 1 Q Phyelcal Characterlltlcs 0

Shorefront [J

Land Use

TERREBONNE­ (J Hydrologic CALCASIEU-SABINE MERMENTAU VERMILION TCHAFALAY TIMBALIER Unlta a. 7. 6. 5. 4. 0 Subuntts D A c B B A G F 0

Place Name• 0 0

Longitude D Reference Points A a � cc' D

PHYSICAL CHARACTERISTICS SHOREFRONT LAND USE STRUCTURAL MODIFICATIONS a Oil end G•• -Urban J JeUie• 0 R Revetmeat 0

Q G,olne 0 FltJureJa .. 0

6 � 0 •1150 ·•a Annual Shoreline Change, 19&5-1e7a I •100 , , •30 0 t ;::;, •SO • � 115 /� \j\_ .f ' i • I 0 MO.Ioll I I 0 D \, •ccretlon. '• +150 +115 0 Structural Modification• R R J GJ J J J D Ptlre•cal 0 Chuacterlatlce

Shorefront

Land Use

HydroJoglc TERREBONNE-TIMBALIER BARATARIA CHANDELEUR-BRETON MISSISSIPPI DELTA Unite 4. 3. 1. 0 2. Subunit• 0 E A 0 0

Reference Point• D E H 0 PHYSICAL CHARACTERISTICS SHOAEFRONT LAND USE STRUCTURAL MODIFICATIONS E watar m Marth/Scrub 011 and - Urban J .lattlat

Legend Beach Q Martb/Parched lmmmml... cr••tto••• 0 (hwy. aooeee)

Q Grolne 0 0

0 7 0 whereby x is the amount of recession, a is the Longshore movement of sediment becomes Using linear wave theory, shelf batilymetry, and 0 vertical displacement of sea level relative to apparent in the migration of the barrier islands, bottom sediment conditions (BLM 1979), a land, b is the distance from shore to the first in the lateral movement of inlets, and in shore­ general estimate can be made as to wave condi­ depth -contour, Q, the distance beyond which line erosion and accretion where the beach zone tons along Louisiana's shoreline. This was done D little sediment transport takes place, and h is is interrupted by structures such as groins and by Becker (1972) on the basis of hindcasted data the dune height on the shore. For the jetties. Longshore transport by waves results and in this study on the basis of of.fshore obser­ Terrebonne-Timbalier shoreline, the equation be­ where sediment is placed in suspension by the vations (Suhayda 1982, personal cornmunication). comes shoaling and breaking waves and moved as a Our estimates indicate that most of the total 0 result of the longshore component of water mo­ annual wave energy is provided by offshore = 4 ft/centur x 8000 ft x tion associated with the wave or the longshore waves having a significant height (H ) of 10-15 ft (4 l s + 18) eet generated by the waves. This transport (3.1-4.6 m) and approaching fro:n the southeast. 0 or 1455 ft/century (446 m/century). That is, the may be augmented or opposed by tidal- and Resulting from shelf conditions, wave energy combined processes of subsidence and sea level wind-generated current, in particular near the associated with these waves is highest along the rise (estimated at over 1.2 cm/yr or 4 tidal passes. The extent and direction of long­ modern delta and the Fourchon area. Lowest 0 ft/century) are calculated to account for 15 ft shore transport are controlled largely by the energy conditions are found in the area of the (4.5 m) of the annual shoreline erosion. Wave breaker height and direction of wave approach. Atchafalaya delta. Energy levels along the action contributes to the actual higher retreat Chandeleurs are higher than those along the rates, but subsidence/sea level rise is a very Most of the sediment transport takes place in Chenier Plain. 0 significant factor in shoreline erosion. the surfzone involving the interactive processes between shoaling and breaking waves, tidal cur­ rents, and surfzone topography. Longshore bars play a major role in this regard as a storage A second consideration is the direction of wave 0 mechanism and as avenues for longshore trans­ propagation. For the above wave spectrum, Energy Input port. These interactions have not been very well longshore energy flux (as a measure of longshore defined along the Louisiana coast, and a general transport) was smallest in the Atchafalaya Bay n lack of information exists concerning average area (because of the low wave energy) and Waves nearshore wave conditions or wave climate. highest along the Chenier coast. Of further interest were the comparatively low values 0 Under the prevalent condition of subsidence and found in the area of Fourchon, Grand Isle, and Because the major economic interests in a limited sand supply, the reworking of sedi­ Grand Terre, indicating that offshore movement Louisiana affected by waves are offshore oil and mentary deposits is the main process by which of sediment is the more important element in gas development and navigation, most data col­ 0 Louisiana's barrier system is maintained. Waves the shoreline erosion in at least that area. are a controlling factor in this process by pro­ lection efforts have focused on offshore condi­ viding much of the energy necessary to entrain tions and are proprietary. Some efforts have and move the sediments and by determining been made to define the offshore wave climate 0 sediment retention. Movement of sediments as a on the basis of wave conditions hindcasted from result of wave action generally is considered in weather observations and by using ship and plat­ two directions: onshore-offshore and longshore. form data. These summaries show a dominance Hurricane Effects of southeasterly waves from 2 to 6 ft (0.5 to 0 Onshore-offshore movement is often reflected 1.5 m) high (Becker 1972; Glenn and Associates Hurricane and major storm surges play a signifi­ by rapid changes, such as erosion and washover, 1972; Suhayda 1976). As expected, most of the cant role in the erosion of barrier islands and during a storm and the subsequent return of highest waves occur during the fall and winter shorelines. Striking the Louisiana coast approxi­ 0 sediment to the beach after a storm. These and are associated with hurricanes and fronts. mately once every three years (Neumann et al. changes are controlled primarily by wave steep­ Only general conclusions can be drawn directly 1978), hurricanes account for as much as 90% of ness and the extent to which water levels are from offshore wave data relative to beach shoreline retreat. The impacts of hurricanes 0 elevated by storm-surge. Offshore-onshore change. As waves travel shoreward, significant upon the Louisiana coast have been documented move11ent is important for at least two reasons. changes occur as a result of bottom topography for the Chenier Plain coast (Morgan et al. 1958), One is that major storms such as hurricanes may and sediments. Changes in height and direction the Caminada-Moreau headland and adjacent is­ cause offshore movement of sediments to depths of travel take place as waves are increasingly lands (Adams 1970; Penland and Ritchie 1979}, 0 from which they will not be returned by subse­ affected by the shelf bottom. Consequently, and the Chandeleur Islands (Boyd and Penland quent fair weather conditions. The second considerable variation in surfzone conditions 1981; Kahn 1980; Nummedal et al. 1980; Wright reason is that onshore-offshore components of exists along Louisiana's coast because of differ­ et al. 1970). lJ wave action are the dominant control over sort­ ences in shelf topography, sediment character­ ing and retention of sediments placed on the istics, and angle between the shoreline and A considerable proportion of shoreline retreat is beach as nourishment. approaching waves. attributed directly to hurricanes. Based upon 0

8 0 D

analysis of historic maps and storm records, such as the Isles Dernieres where available sand Sediment Supply and Transport 0 hurricanes were found to account for 50-90% of supply is insufficient to reseal breaches, perma­ total shoreline retreat in the Chandeleurs (Kahn nent tidal inlets develop. In addition to dis­ 1980). Hurricanes Camille (1969) and Frederic rupting the sand transport system, inlet develop­ Louisiana's barrier islands were formed by depo­ D (1979) each caused 130-260 feet (40-80 m) of ment induces increased tidal scouring and island sitional and erosional processes characteristic of shoreline erosion (Kahn 1980). Hurricane Audrey erosion. On the central Chandeleur Islands, the degradational phase of the delta cycle. (1957) accounted for dune crest setbacks of however, washovers that become ephemeral tidal Following abandonment of a delta lobe by the 50-300 ft (15-90 m) along the Chenier Plain inlets following hurricanes tend to gradually re­ main flow of the 1\1ississippi River, marine forces 0 coastline (Morgan et al. 1958). Inspection of seal themselves (Boyd and Penland 1981). This begin to dominate, particularly at the outer rim pre-and post-Audrey aerial photographs of Holly is attributed to a more abundant sand supply in of the delta lobe. Via transgressive erosion of Beach indicates both dune crest setback and this area. The islands which comprise the the deltaic headlands, finer sediments are win­ 0 shoreline retreat of 100-120 ft (30-36 m). southern Chandeleurs are much lower in eleva­ nowed out and carried offshore, while coarser tion and subject to higher erosion during storms remain to be redistributed as and (Kahn 1980). Many of these islands (such as the beach ridges by wave action. Longshore currents 0 Curlews) disappeared completely following in the nearshore zone redistribute some of these Hurricane Camille (Wright et al. 1970). sands laterally, in the form of flanking barrier spits. So, in addition to a gradual inland migra­ In southwest Louisiana, beach profiles surveyed tion of the active beach ridge (as a combined 0 before and after Hurricane Audrey in 1957 pro­ result of subsidence/sea level rise and wave EQUILIBRIUM BEACH vided insights into storm-related morphologic attack), of sediment accounts for changes (1\1organ et al. 1958), as illustrated in lateral growth of the barrier beach. As tidal 0 schematic form on Figure 4. At Holly Beach, for exchange forces lead to breaching and develop­ example, a gulf-fronting, sandy barrier beach ment of tidal inlets, the barrier spits are severed _ _ --- :c- _ � _ _ = - � :� ;; .:__���- �: ------:---- and become flanking barrier islands. (The ridge abuts a thin (3-6 ft or 1-2 m) layer of ------�------:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-::-:-:-:-:-:-:-:-:-�� ��:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:; ";._: -:--:� ------Timbalier Islands and Grand Isle represent nank­ organic marsh deposits overlying gulf bottom 8!!!-/--F;/!J!jj' - - - J;------0 ------silts and clays (Fisk 1955). During hurricanes, ------ing barrier islands of the Caminada-Moreau water levels completely inundate all surface headland, for example.) features, and the beach dune crest becomes 0 eroded (in a dominantly inland direction) and flattened. Following the return of water levels Sandy barrier beaches, characteristic of the to mean sea level, the dune crest, lower in Caminada-Moreau deltaic headland and most of D elevation, has shifted landward and the beach is the Chenier Plain coast, are maintained by ero­ very wide. As a new equilibrium profile sion of cheniers and beach ridges and reworking develops, the shoreline retreats to a position IMMEDIATE of in situ sands. Dominant nearshore currents POST-HURRICANE STAGE roughly approximating the pre-hurricane profile. account for longshore transport of reworked While some of the beach sand becomes lost to sands, the direction of which is dictated by a the offshore, much is carried onto the "new" combination of prevailing and waves and

------angle of shoreline orientation. As a generaliza­ dune by wave action until a dune height compar­ ------=------_---_ _-_--_--_ ------_-:._-:_------=- - - - -_-:.______- _ - - - - - � tion, shorelines oriented counter-clockwise of ------_ _ _ _ _ -:_--- - -.=------_- - able to the pre-hurricane height is attained -.<§}��:�·;·��-���!�:�;��:�:���=-�-==-:�_-�:::�;_�-�:_�------_ ------: ---: - - - :_ _-:.,.- -::::-;::----:---:-:-:-:-::::j::=:=-:::-::::-:-:-:-:-:-:-:-:: :::� =-=�-:-:-::::-:-:-:-::::-: :::::::::�-=- -- 0 (Morgan et al. 1958). : : -§:; ENE-WSW (azimuth of less than about 67'? will RETURN TO EQUILIBRIUM exhibit dominantly eastward drift patterns, while more east-west or southeast-northwest-trending 0 ellorelln• r•traat � shorelines display westward drift patterns. In the Chenier Plain, overall drift patterns are Hurricane effects upon the barrier islands are �;i�iJ.�· ·::::;;�;:.:;•·�:::.:,�;:;:;;- ��:::.:;,��4��;:;::���:;;;;;�,..�1!""-�""'��:�r:i-:i�.-.:;r�:-:��·����-:�O::-::�:-:I dominantly westward, and the distribution of usually more detrimental than upon barrier · sand beaches generally reflects the erosion of - - D ------shorelines such as in southwest Louisiana. While :---:-:--: -:-:- - ---:-:-:-:-:------:-:-:------=�-:-:-:-:-:----:-----:-:-:-- updrift beach ridges and cheniers. Sediments similar mechanisms of dune and shoreline retreat eroded from the Caminada--:'vloreau headland are �L.....:;.,;l a are at play, the barrier islands lack the extensive Send a Sheila Merah Gulf Bottom transported to both flanks and historically nour­ marsh backing. As a result the potential for (oraanlc clar•t (ol•r•. anta) ished both the Timbaliers and Grand Isle. (The breaching and accelerated erosion because of highest shoreline retreat rates and the point of tidal scouring becomes more significant. In Figure 4. Hurricane Effects Upon Chenier bifurcation of sediment transport occur near the 0 areas where island widths are precariously nar­ Plain Shorelfne (a(te,. FUk 19SS; present site of Port Fourchon.) The physical row, high shoreline setback following a major Morgan et al. 1958). processes base map (Figure 5) displays directions o storm may induce breaching. On island chains of net sediment drift across the state . . 9 0 lJ TEXAS LOUISIANA LOUISIANA MISSISSIPPI D 0

LAFAYETTE li 0 0

,._.�. • J '• 0 0 I 0 VI LEGEND 0 I A I Hydrologic subunits v I I Dominant sediment transport

Fluvial sediments F 0 \) II Shore Characteristics 1 Sand 0 2 Marsh

3 Mud �·- 0 \ LOUISIANA COASTAL ZONE LIMITS Structures ! Jetties • t. .\ HYDROLOGIC UNITS (H.U.) * Revetments .. v .. 0 * Groins I 0 0 25 50 Ship channels

I 0 50 .. .. .,. 10' - • • 0

Figure5. 0 Q.

10 (J 0

Barrier islands and beaches are maintained by recent development of the Atchafalaya delta, The D marine processes which rework the sediments has been shifting westwe�.rd, in part because of Role hayward and alongshore. Where barrier islands longshore processes [Wells and Kemp 1981] .) of are still flanking deltaic headlands (an early Tidal Inlets stage of delta lobe deterioration best displayed Fluvially-introduced sediments are presently 0 at the Caminada-Moreau headland), sediments contributing very little toward nourishment of eroded from the headland and transported the barrier islands and beaches. The major Tidal inlets, while serving as important conduits alongshore contribute to the nourishment of passes of the Mississippi River delta extend onto for water exchange between estuarine bay areas those islands. In older delta lobes where the the slopes of the Outer Continental Shelf, and and the open Gulf, disrupt sediment transport 0 mainland has been detached from the barrier rim coarse sediments (that are not dredged) are lost patterns and contribute to the deterioration of due to subsidence, the barrier islands are main­ to deep, offshore waters. The Atchafalaya River barrier islands. Longshore migrating sediments tained only by the reworking of in situ coarse and Wax Lake Outlet have contributed coarse entering a tidal inlet are picked up by the swift D sediments. The Chenier Plain barrier beaches sediments to Atchafalaya Bay, and small deltas ebb or currents in the inlet throat and are also due to erosion and reworking of sedi­ have developed since the early 1970s. While deposited in the form of fans, or ebb- and flood­ ments in combination with longshore transport finer sediments are being transported to the tidal deltas, at the points where current velo­ 0 processes. (The zone of recent mudflat accre­ Chenier Plain coast by longshore currents, the cities diminish. During flood tide, sediments are tion near Freshwater Bayou, reflecting the coarser material is remaining within the bay. carried in suspension by landward flow and depo­ sited on the inner bar, and during ebb tide, flow 0 and sediment movement is toward the Gulf (Figure 6). For the Barataria Basin tidal inlets, 0 0 FLOOD TIDE EBB TIDE 0 0

0 GULF OF IUJIICO GULF OF 11/EJIICO

--·· MAJOR FLOW - - - .. MINOA FlOW 0 Figure 8. Currents Within Tidal Pa:JSes.. 0

ebb-tidal currents were found to be slightly D higher in velocity than flood-tidal currents (Marmer 1948). Where the sediment supply is abundant or an inlet is in early stages of devel­ 0 opment, a considerable portion of the trans­ ported sediment is able to bypass the inlet (during ebb tide) in the form of offshore migrating along the ebb-tidal delta and reattach­ 0 Tidal inlet during ebbing tide (Belle Passin background). ing to the downdrift barrier island (Figure 7). One effect of ebb-tidal deltas is the refraction 0 11 0 0

decreasing amounts of sediment are able to Man-Induced Effects bypass the inlet, and ever-increasing amounts n �lood•Ttdel Delle become tied up in the tidal deltas. Thus, the Shoreline erosion and wetland deterioration rates erosion rate of the barrier islands is accelerated have accelerated greatly during the twentieth as less sediment remains available for century (Gagliano et al. 1981), ana a large pro­ replenishment. portion of this acceleration can be attributed to lJ the influence of man. The largest impact upon the Deltaic Plain has been the harnessing of the In addition, if a tidal inlet migrates bayward Mississippi River for flood-control and naviga­ 0 because of shoreline retreat and/or laterally tion purposes, while additional impacts have because of longshore processes, valuable sedi­ resulted from the reclamation of wetlands, ex­ ments become tied up in relict tidal deltas and traction of subsurface hydrocarbons, canal­ thus, removed from active sedimentary pr dredging, and modification of the shoreline. [1 cesses. The tidal deltas may continue to absorb� incoming wave energy and thus afford some Figure 1. Role of Tidal Inlets fn the Sediment measure of protection to proximate shoreline 0 Tramport System. areas. of waves, which tends to foster a reversal of Two basic types of tidal inlets are recognized, Q dominant longshore transport at the adjacent migrating and stable (FitzGerald and Hayes spits of the downdrift barrier island (FitzGerald 1980). Inlets generally migrate when longshore and Hayes 1980). This _process accounts for transport is dominant in one direction and sub­ accretionary trends at downdrift spits and the surface sediments are largely unconsolidated 0 often bulbous outline of the updrift end of sands. Deeper inlets, entrenched in organic and barrier islands (Hayes 1979). As the tidal inlets gulf bottom clays, are less likely to migrate. deepen and widen through time (due to factors of Examples of both inlets can be seen at Wine 0 subsidence, sea level rise, shoreline erosion, and Island Pass and Cat Island Pass in Terrebonne Parish (Figure 8). a resulting increase in the tidal prism), ever- 0 0

Pipeline canal bisecting island. 0

The harnessing of the Mississippi River and the 0 clearing of log jams on its tributaries have effectively limited overland flow and associated sedimentation within the interdistributary basins 0 of the Deltaic Plain. The construction of dikes along the river began with the first settlers, but it was not until after the 1927 flood that the 0 present levee system was completed. With the exception of occasional levee breaks during flood stages, Mississippi River waters (and valuable ..... �------�------_.------�--_.------�----�----�delta-building sediments that are carried in a them) are confined to the channel until the extreme lower reaches. The process of cre­ vassing has been virtually eliminated, and for­ Figure 8. Geoklgfc CroasSection, WfneUland Pass and Cut JIZOJKI PotJB(after USACB 19tJ1). merly active distributaries such as Bayou D Lafourche have been sealed off for flood control. a

12 0 0

The only active distributary today is the In addition to direct wetland loss due to dis­ deeper conduits (natural bayous, dredged canals, D Atchafalaya River, regulated to 3096 of placement by water and spoil deposits, a major or dredged bayous), even small, lineal scars Mississippi River flow at its point of divergence, effect of canalization in wetlands is hydrologic through the marsh (trapping canals, or train­ which is presently delivering sediments to modification. Canals trending perpendicular to asses) contribute to saltwater intrusion and 0 Atchafalaya Bay. A subaerial delta has been the shoreline tend to accelerate water exchange, marsh breakup (Figure 9). Canals trending paral­ building during the last decade (Meyer-Arendt i.e., saline bay waters are able to penetrate lel to the shoreline orientation disrupt normal and van Beek 1980), and pro-delta clays are further inland, and during low water periods flow patterns in that the associate.d spoil banks 0 actively accreting on the Chenier Plain coast fresher, upper basin waters are flushed bayward create hydrologic impoundments. The conse­ (Kemp and Wells 1981). more rapidly. The saltwater intrusion process is quent lack of renewed sediment introduction by the more serious impact as fresh marsh species, tidal processes increases the land loss potential Were it not for the regulation of Atchafalaya rooted and floating (flotant), cannot maintain within the impounded area. In the barrier shore­ 0 River flow at the Old River Control Structure themselves. The marsh tends to break up and line environment, normal-to-shore canals can near Simmesport, the Mississippi River may have turn to open water, although limited colonization develop into major tidal inlets, as has occurred been captured by the Atchafalaya. But, for of the remaining land by more salt-tolerant between Belle Pass and East Timbalier Island 0 economic reasons, the Mississippi channel is marsh species takes place. The process of marsh (Figure 10). Canals dredged parallel to shore on maintained, and consequently sediments impor­ breakup via saltwater intrusion is accelerated by the barrier island or beach (or directly behind it) tant for delta-building are being funneled lineal waterbodies which act as conduits. Al­ tend to act as sand traps as the shoreline re­ through the lower passes onto the slopes of the though most destruction is related to bigger and treats bayward (Figure 11). 0 continental shelf. By keeping the Mississippi River in its present position, the high land-loss rates of former delta lobes cannot be offset by ., ... t1•00' ···�------+ ww�------+ 0 land gained in active deltas. Hydrologic Unit 5 LEGEND (Atchafalaya Bay) is exhibiting some land gain, but because of the regulation of flow and main­ WATER tenance dredging of the lower channel through D the Atchafalaya delta, wetland growth is being LINEAL WATER BODIES 0 hindered (van Beek and Meyer-Arendt 1981). y The reclamation of wetlands by man has serious­ TREES ly affected hydrologic and sedimentary pro­ II cesses. Reclamation projects undertaken to allow urban and agricultural expansion remove SPOIL D large tracts of wetlands from the natural II system, thereby disrupting overland flow pat­ wa•...... _.lL------+ MARSH (Fr••" In 1•s2 a 1•aa, terns and reducing available nutrient supply to 1932 1955 D lnt•rm•dl•t• In 1114 a 1171) 0 valuable estuarine-dependent species (e.g., 11'00' ...... shrimp). Reclamation projects are often accom­ ··�------��------+ panied by construction of pumping stations and D drainage canals. Canals tend to channelize out­ t � :aqoo 3CflO � �· flow and remove water from upper portions of basins much faster than overland flow or mean­ � dering bayous would permit. The net effect of 0 this forced drainage is increased flooding poten­ tial in middle and lower portions of interdistribu­ tary basins and increased summer drought l potential in upper basin wetlands. Much in the western portion of the state has been leveed for wildlife management purposes. While water levels and salinities can be regu­ lated to maintain an optimum habitat (such as 1964 1978 for waterfowl), the lack of tidal exchange pre­ cludes the introduction of renewed sediments, as 0 well as the export of important nutrients Figure 9. Impact of Canals UponWetland Deterioration. (Gosselink et al. 1980). 0

13 0 0

Extensive canal-dredging activity is usually natural patterns of headland erosion and long­ directly related to extraction of subsurface shore sediment transport to downdrift-flanking D hydrocarbons, a process which may account for barrier islands and spits, the sediment supply to increases in subsidence rates. While subsidence the distal ends of the flanking barriers becomes linked directly to oil and gas extraction is nor­ cut off. A case in point is Timbalier Island in n mally associated with shallow fields comprised Terrebonne Parish. Originally a flanking barrier largely of unconsolidated sands (Kreitler 1976), of the Caminada-Moreau headland, the island oil and gas extracted from depths as great as accreted westward over 4 mi (6.5 km) during the 8000 to 9500 ft (2400 to 2900 m) can influence last century, as a result of renewed sediment 0 surface subsidence rates (Erickson 1976; nourishment and longshore littoral processes. Schoonbeck 1976). Many of the wells drilled in Very little outside sediment now reaches the -·- coastal Louisiana tap fields at 18,000 to 25,000 island because of: a) widening of tidal inlets Q below surface, and whether this deep-drilling (natural and man-induced), b) construction of affects subsidence rates has yet to be deter­ sediment-trapping jetties at Belle Pass, and c) Canal Figure 10. Impact of Dredging Upon mined. A significant increase in the rate of extensive dike construction on East Timbalier 0 Tidal balet Development, Ecut landward migration of the salt-marsh zone has Island. Sand no longer is transported alongshore Timbalfer Island. been attributed to the petroleum industry (Monte to Timbalier Island, and the island is not only 1978). eroding rapidly at its eastern end, but is re­ orienting itself in a more east-west alignment in 0 response to prevailing waves (Penland and Boyd 1981). Shoreline modification at Grande Isle Direct effects by man upon Louisiana's shoreline (groins and jetties), on the eastern flank of the 0 include canal construction, maintenance Caminada-Moreau headland, occurs near the dredging, and shoreline protection construction. downdrift end of the sediment transport system, Twelve major navigation channels bisect the and disruptions in sediment transport have been Gulf shoreline, and channel training jetties are in less severe. (Shoreline erosion and modifications 0 place at eight of them. Much sediment, valuable will be discussed in more detail in Chapter ill.) for the maintenance of barrier islands, beaches, and wetlands, is dredged annually from these 0 channels to maintain sufficient water depths. At sites of coastal settlement or development (e.g., Grand Isle, Peveto Beach, East Timbalier), ero­ Summary of Causes sion control measures such as groin fields and 0 rip-rap dikes have been constructed in attempts to stabilize the shoreline. Approximately 14 mi Each of the eight hydrologic units that comprise (22.5 km) of the state's 300 mi (480 km) of the Louisiana coastal zone is affected by some 0 barrier shoreline have been modified via shore or all of the above described physical processes, protection measures. natural or man-induced, in varying degrees of magnitude. While some processes, such as subsidence/sea level rise, may be relatively uni­ D form across the coastal zone (with the exception of the active Mississippi River delta), others 0 A significant impact of shoreline structures is occur at varying intensities which are difficult the disruption of sediment transport processes. to quantify. As a general rule, the greatest In cases where jetties have been constructed at number of detrimental forces acting upon the the outlets of navigation channels to minimize shoreline occur in the degradation phase of 0 shoaling, sediments accrete updrift of the jetty Mississippi River delta lobes. These hydrologic (or at least erode less rapidly), while the down­ units (1, 3, and 4) are characterized by a defi­ drift shoreline, starved of sediments, erodes ciency of sediment, tidal inlet widening, and 0 more rapidly. This process is cartographically barrier island deterioration. Table 1 presents best illustrated at the mouth of the Gulf-Empire shoreline erosion and land-loss statistics for each of the hydrologic units and outlines the Ff(lur$ ll. BflectiJ of Shore-Parallel Canaia Waterway (Plate 26), and also at Belle Pass, physical parameters important within the res­ D Upon &rrfer IaknfL where a prominent downdrift offset has devel­ pective shoreline areas. As an accurate quanti- oped (see Figure 10). Also, by disrupting the 0

14 0 J

J

PROCESSES IMPACTING THE SHORELINE SEVERITY RANKJRQ6

(1 = most severe)

Probability of Hurricane Amountof OCeuiTence Development'I Sh«eline6 Shore1Jne1 Land Tidal Bari-ier Elrtensive Shore- Shore- Within OU c!c Gu Canall- Within Lit Hy*ologic Gulf Share Le� Retr..t Lola Lest winds winds Sediment Inlet Island llne Land llne Hurricane toni � 4 4 Unit Name Deacrlption (mDea) (ft/yr) Rate2 Hurrtcane3 >74 mpb >125 mph Slaldenee Deficiency Drift Wi� Deterioration Actlvity zation Modification LolliS Erasion Pldlabillty n.u.s z- MBAN

I Chandeleur- Barrier Breton Islands 41 32.8 -3.5 1979 996 496 X X XX XX XX ------3 2 2 3 6 3.2

II Mississippi Active Delta Delta -- -- -13.3 1969 996 496 XX X ------XX X XX ------

Ill Barataria Barrier Islands & Beaches 52 27.2 -3.9 1974 1396 296 X XX XX XX XX XX XX XX 2 3 1 1 1 1.6

IV Terrebonne- Barrier Timbalier Islands &: Beaches 72 35.7 ·4.0 1974 996 096 X XX XX XX XX XX XX XX 1 1 3 2 5 2.4

�' Atchafalaya Active - - -- Delta -- -- +0.5 1974 9% 096 X ------X -- X ------

VI Vermilion Barrier Beach &: Shell reefs 43 11.6 -1.6 1957 6% 0% X X X -- -- X X -- 6 5 6 5 4 5.2

VII Mermentau Barrier Beach &: Mudflats 54 30.3 n.a. 1957 6% 1% X X XX -- -- XX XX X 4 4 5 6 3 4.4

VIII CalcSJlleu· Barrier Sabine Beach &: Mudflats 46 8.9 n.a. 1961 8% 4% X X XX -- -- X X XX 5 6 4 4 2 4.2

1 annual average rates 1955-1978 2 in ac/mi2/yr, averaged over the hydrologic unit south of coastal defense line 3 minimum wind speed of 111 mph (179 kph) on Saffir-Simpson scale (Simpson and Rieh1 1981) 4 within 2 miles of gulf shoreline 5 below coastal defense line 6 Barrier HUs only 7 in area 0

Table 1. Active Processes and Relative Severity of Louisiana's Hydrologic Units. 0

15 0 fication of the relative impacts of these pro­ island and shorelines (and adjacent littoral zones) On the basis of the parameters outlined on Table cesses would prove quite difficult, only relative discussed in this report. Each of the plates 1 and additional processes and morphologic char­ importance (none, light, or heavy) is outlined on contains littoral habitats for 1955 and 1978, acteristics (shoreline orientation and dominant the matrix. The severity of overall land loss interpreted from 1955 black-and-white aerial sediment drift patterns), the hydrologic units are within the Louisiana coastal zone is best photography and 1978 color-infrared aerial divided into subunits (see Figure 5): The next 0 depicted cartographically (Figure 12). imagery (NASA 1978; PIC 1955-1956; Tobin chapter will present brief descriptions of the 1955-1956). Areal measurements of the eleven individual shoreline segments, examining domi­ Plates 1 through 31, contained in the Appendix, delineated habitats are provided (for both nant processes, rates of shoreline erosion, land 0 provide 1:50,000 scale coverage of the barrier periods) in bar graph form on each of the plates. use, and impacts of future barrier deterioration. 0 legend LOUISIANA COASTAL ZONE ac/ml 2 /yr LOSS LAND CHANGE RATES 1955-1978 0

ALL VALUES AVERAGED OYER THE GROSS LAND ARI!A WITHIN EACH 7.5 MIN. TOPOGRAPHIC QUADRANGLE  GAIN 0 moderate ( 1-2) 0 IO low (0-1) 0 0 0 0 0 0 (j 0 r.texJco COASTAL ENVIRONMENTS, INC. IllIIATOII IIOUCIE.LA. 7\leOZ 0 Figure 12. Land Loss in the LouisianaOCI8t C al Zone. D D

16 J

L1 former St. Bernard delta lobe, the islands are 30000' N latitude (Figure 13). Shoreline erosion comprised primarily of sand and shell. It has rates increase to the north and south from this been assumed that because of the age of the point. The shoreline erosion graphs presented J Chandeleurs (180Q-3000 years - Frazier 1967) for each of the hydrologic units display average and a levelling of initial subsidence and compac­ annual erosion rates for both the 1955-1978 and tion, a reduction of shoreline retreat rates on 1954-1969 periods. The former were developed 0 this island chain resulted (Morgan and Larimore specifically for this report, while the latter were 1957). Previously noted mechanisms of island adapted from work by Louisiana State University maintenance include the landward migration of (LSU) researchers (Adams et al. 1978). Both sets the islands across their own back-barrier man­ of data are presented for comparative purposes. groves (Russell 1936) and the washing up of nearshore relict deltaic deposits onto the islands The northernmost 3 mi (5 km) of Subunit A by wave action (Kwon 1969). The 1955 and 1978 consist of a low, narrow, recurved subject to D aerial imagery, however, indicates high erosion sheet overwash processes, while higher central rates averaging 32.8 ft/yr (10 m/yr) (Plates 27- and southern sections are subject to channel 31). Except for isolated cases of washover fan washover processes. Although erosion rates of development, there has been virtually no about 40 ft/yr (12 m/yr) characterized the south­ 0 landward migration between 1955 and 1978. ern 9 mi (14 km) of the subunit, little back­ Coupled with the high shoreline retreat rates, it barrier marsh has been created by overwash is apparent that erosion of the Chandeleurs is processes since 1955. The only land use in the presently quite high. It has been estimated that area is a lighthouse and wharf near the northern 50-90% of shoreline erosion on the Chandeleurs tip of Chandeleur Island. is a direct result of hurricane activity (Kahn 1980), and the high erosion rates of recent South decades may well be related to storms, espe­ Chandeleurs (Subunit B) cially Hurricane Camille which severely The southern portion of the Chandeleur Islands, breached the islands in 1969. which includes the south tip of Chandeleur Island, the Curlew Islands, and Grand Gosier Island, exhibits extremely high erosion and land Three distinct subunits can be identified along loss rates (Plates 28 and 29). Much of this 0 the Chandeleur-Breton shoreline: the northern erosion is the result of Hurricane Camille in and central Chandeleurs, the southern 1969, which created a large, shallow tidal inlet Chandeleurs (including Grand Gosier and the between Chandeleur Island and Grand Gosier Curlew Islands), and Breton Island. Island. The former Boot Island and most of the Stake Islands have submerged into subaqueous shoals. Palos Island has become absorbed by the Chapter III southern recurved spit of Chandeleur Island. This spit has shifted inland almost 1 mi (1.6 km) North-CentralChandeleurs (Subunit A) since 1955. A slight southwestward elongation 0 Characterization of the of the spit indicates southward sediment trans­ Because of prevailing southeasterly winds and port, although this may relate to flood-tidal Barrier Shoreline waves, sediment transport is to the north over currents. The Curlew Islands (Plate 29) are most of Chandeleur Island. Receiving a greater composed primarily of beach and subaqueous Q Hydrolo1ic Unit 1: relative input of sediments, Subunit A exhibits sand . the highest dune crest elevations--up to 4 m (13 Chandeleur-Breton ft)--and the lowest shoreline retreat rates with­ A recurved spit abuts the tidal inlet to the north, in the total hydrologic unit (Kahn 1980). While but even the central portion of the islands exhi­ The Chandeleur-Breton barrier is a transgressive average retreat rates between 1955 and 1978 bits shoreline retreat rates of over 35 ft/yr (10 barrier island arc approximately 41 mi (66 km) in were 33 ft/yr (10 m/yr) over the whole subunit, m/yr). A net sediment transport to the south is length. Representing the outer rim of the rates of less than 16 ft/yr (5 m/yr) occurred at evidenced by the increase in land area at the

17 0

-100 -30 1·168•• Hydrologic Unit 3: I I Barataria

The barrier shoreline of the Barataria Basin � -80 -24 originated during various cycles of Mississippi ' River sedimentation, primarily associated with ' the Lafourche and Plaquemines-Modern delta \ complexes. At the western end, the barrier [ \ ...: beach and downdrift-flanking islands (Grand Isle, -eo ' -18 "" Grand Terre) have formed by deposition and i ...... \ subsequent erosion of the Caminada-Moreau -E [ £ \ headland and numerous distributary mouth ac­ Ill ' Ill c:J " cretion ridges. Beaches at the eastern end ' . z I z originated by erosion of former Mississippi River c \ c z -40 I -12 z distributaries and historic subdeltas. 0 u ' I u Ill � - -.1 CURLEW I Ill li I ISLANDS � ... _ ... Ill �-"' Ill The concave shape of the shoreline, in addition I a: to a sheltering effect of the active Mississippi -20 I -� -e 0 8z I z River delta, accounts for great variation in lit­ • - ' � (I) toral transport patterns. Based largely upon ' r \ I sediment drift patterns, at least six major shore­ ,- GRAND GOSIER line subunits are identified. Fourchon Beach \ I 0 \_J 0 (Subunit F) exhibits westward drift, while along u BRETON the Caminada-Moreau beach and Grand Isle (Sub­ �AND units E and D), sediment drift is well defined in ---- 1954-1989 an easterly direction. Along the rest of the 1955-1978 hydrologic unit shoreline, bidirectional transport [ 20 e patterns are noted. A net westward drift char­ acterizes Subunit A, while in B and C no direc­ 29°55' ' 40' 35' ' 25' 3o•os" 3o•oo· so· 45 30 tional dominance is apparent (see Figure 5). u LATITUDE Figure 13. Shoreline Change, Hydrologic Unit 1. u Shoreline erosion rates averaged 27.2 ft/yr (8.3 southern spit. Grand Gosier Island (Plate 28), a distributary mouth accretion ridges), has been m/yr) over the whole Barataria shoreline during narrow, low, but vegetated island in 1955, has severed into two islands which are experiencing the 1955-1978 period. The highest rates of been dissected by storm activity and now con­ high erosion rates (Plate 27). The northern erosion (over 100 ft/ yr or 30 m/yr) occur in the sists of two small island remnants. A small island has remained relatively fixed in position Grand Terre Islands and are attributed to tidal­ clump of mangrove remains on the stable north­ (except for shoreline erosion along the north­ exchange processes (Figure 14). The highest ern island. The southern island is but a 1-mile facing beach), while the southern island is exper­ nontidal erosion rates exceed 70 ft/yr (21 m/yr) [ (1.6 km) long subaerial shoal which has migrated iencing truncation of its east-west-trending in the vicinity of Port Fourchon, while almost bayward and accreted slightly at the southern tip beach ridges by the dominant southeasterly stable conditions occur immediately west of (indicating net sediment transport from the waves. The back-barrier of the island is also Grand Bayou Pass. [ north). Shoreline retreat rates, not counting the eroding. Dominant sediment drift is to the high rates associated with spit recurvature, south, as seen by the accreting south spit. A average about 31.8 ft/yr (9. 7 m/yr) in this sediment deficiency is apparent, however, and u subunit. the Mississippi River-Gulf Outlet (MRGO), which The Barataria shoreline is the site of one of two is dredged through the barrier chain immediately major road-accessible beaches in Louisiana. Breton Island (Subunit C) north of Breton Island, may be acting as a Over a thousand recreational camps are found at sediment trap and intercepting longshore sands Grand Isle (Gary and Davis 1979), and dozens of D Breton Island, containing a backbone of older migrating southward. A wharf and radio antenna new camps have been constructed in recent beach ridges (indicating a possible origin due to are located on the northern island. years around Port Fourchon. 0 18 [ 0 however, and strong evidence for this is con­ 11.,,. firmed by the erosional tr�nds to the west of the " jetties and the westward accretion of the Lanaux 0 -30 -100 Island spit.

Grand Bayou Pass to Qua tre Bayoux Pass (S ubunit B -80 -24 ) This shoreline reach, the inside of the concave 0 Barataria barrier arc, represents a converge nce ...: zone of longshore currents and sediment drift . >- ' -eo -18 Theeastern 3.5-mi (5.6 km) stretch, from Grand = 0 - ' Bayou Pass to Chaland Pass, is oriented WNW­ ILl I 0 ILl ENE and exhibits very stable conditions (Plate I 0 z z 25). Shoreline retreat has averaged only 7 ft/yr oC I % c -40 I • -12 % (2.1 m/yr) during 1955-1978, a rate attributable 0 u (,) ILl I ,, to a combination of the shoreline's orientation � - ILl 5 I I !i and its position within the barrier arc. The _, _, ILl 11.1 reach from Chaland Pass to Cheniere Ronquille CIC CIC Point exhibits shoreline erosion rates of 35 to 40 0 0 -20 -8 0 % % ft/yr (10.7 to 12.2m/yr). The highest erosion (I) (I) rates (58 ft/ yr or 17.7 m/yr) occur where open 0 water (Bay la Mer) or a high pipeline canal density characterizes the back-barrier zone. 0 0 0 1954-1989 Ht55•1978 20 4------�------�------�---��------�------r------�------,------�------+8 0 90• 1s 10' 05' 00' 50' 45' 40' 35' 30' 25'

LONGITUDE 0 Figure 14. Shoreline Chtlnge,Hydl'ologfc Unit 3. 0 Sandy Point to Grand Bayou (Subunit A) aged 35 ft/yr (10.5 m/yr); and 2) the jetties at the mouth of the Empire-to-Gulf Waterway have 0 The easternmost zone of the Barataria barrier disrupted the normal sand transport system, re­ system, this stretch of shoreline is oriented sulting in retreat rates averaging 35 ft/yr (10.5 Empire-Gulf Waterway jetties. WNW-ESE. Available sand supply diminishes to m/yr) immediately downdrift (west) of the 0 the southeast, and past Sandy Point only occa­ jetties, and decreasing westward. In addition, sional "perched pocket beaches" are found along the Lanaux Island spit has accreted westward A sediment deficit is apparent in this subunit. the active delta's marsh shoreline (Plate 26). and now shelters Bastian Island, previously ex­ The only distinct evidence of sediment transport 0 posed to the Gulf. is seen by the slight eastward spit accretion at Shoreline retreat, under natural conditions, aver­ Chaland Pass. While this may indicate sediment ages approximately 15 to 20 ft/yr (4.5 to 6 m/yr) Judging by the pattern evident near the jetties, transport to the east, the spit recurvature may in this subunit, but two major exceptions to this sediment transport is dominantly from the east, represent tidal exchange processes. The marsh 0 pattern are found: 1) the strip of marsh gulfward reflecting prevailing southerly winds. A slight area immediately behind the barrier shoreline of Bay Coquette, abutting the tidal inlet leading erosional trend can be detected immediately has been affected heavily by canalization, and to Sandy Point Bay, has been adversely affected east of the Empire-to-Gulf-Waterway jetties, shore-parallel canals near Cheniere Ronquille by a shore-parallel, double-pipeline canal (acting indicating a small amount of sediment transport Point are causing accelerated shoreline retreat as a sand trap), and shoreline retreat has aver- from the west. Net transport is from the east, by acting as sand traps (see Figure 11).

19 0 0

Grand Terre Islands (Subunit C) Grand Isle (Subunit D) Theis 1956). Erosion accelerated downdrift from the groin fields, however, and during 1954-1955, This shoreline segment, extending from Cheniere Grand Isle, the downdrift-flanking barrier island t, 150,000 yd3 (880,000 m3) of sand fill were Ronquille Point to Barataria Pass, is subject to of the Caminada-\1oreau heSiC'Hand, has devel­ pumped between several of the groins. One­ high erosion rates because of a large sediment oped into a rnajor fishing and recreational

Located between two major tidal passes, backed by large waterbodies (Bay Melville, Bay Dispute), 0 and criss-crossed by pipeline canals, the eastern Grand Terre Islands are characterized by consi­ derable shoreline erosion and retreat. The 0 westernmost portions of these islands consisted of sand spits and vegetated washover fans that have eroded greatly in recent decades. The tip of the western spit is retreating inland at a rate 0 exceeding 115 ft/yr (35 m/yr), while average retreat rates are 40 to 50 ft/yr (12 to 15 m/yr) in this zone. A dominant sediment transport 0 pattern is not readily apparent, and the small recurved spits appear to be more related to water exchange through the tidal passes. 0 0

The western end of Grand Terre, containing a Louisiana Wildlife and Fisheries field station and 0 the historic Fort Livingston, is eroding due to tidal-exchange processes. Sediment drift is bi­ directional, and it has been postulated that groin 0 and jetty construction on Grand Isle has inter­ rupted the longshore movement of sediments that is dominantly eastward during the fall and winter (Adams et al. 1978). The width of the 0 beach in the vicinity of Fort Livingston, however, indicates accretion. Tidal exchange appears to be a more dominant factor than Critically eroding shoreline, Grand Isle. longshore sediment drift. 0 20 0 J Periodic destruction of the dune at Grand Isle by Plate 22 and Figure 13). Sediment drift is Port Fourchon is presently booming as an indus­ hurricanes has instigated several recent dune toward the east, and shoreline erosion rates trial and recreational center. Considering the J construction and and protec­ decrease steadily eastward along the subunit. high shoreline erosion rates and potentially des­ tion projects. The last severe storm was Hurri­ tructive hurricane impacts, this zone of develop­ cane Carmen in 1974, although lesser storms The rapid erosion along the Caminada-Moreau ment is in a precarious position. As the shore­ (e.g., Hurricane Bob in 1979) periodically remove coast is attributed to the headland's position at line continues to retreat, Port Fouchon will valuable island-protecting sands to the offshore the apex of the offshore Mississippi Canyon, gradually evolve into a (if not an (USACE 1980). Several beach protection meas­ which tends to focus incoming waves and encour­ island), and the adjacent shoreline areas will be ures (e.g., sand-filled cloth tubes) were experi­ age sediment transport divergence. Processes of deprived of their traditional source of sediment mented with during the mid-1970s (Dement erosion include sheet washover and littoral drift. nourishment. 1977), but success was limited. Present plans Dune crests are generally only 3 to 3.5 ft (1 m) call for a comprehensive $14 million beach high, and numerous washover locations occur. replenishment and dune construction project to Gulf water level set-ups of only 2 ft (0.6 m) be implemented in the early 1980s (USACE induce small-scale washovers (Penland and 1980). Ritchie 1979), although most of the shoreline erosion (over 70%) is attributed to tropical cy­ clones (Penland and Boyd 1981). Sheet washover and shoreline retreat are quite pronounced where Longshore sediment transport is from the west, large waterbodies (e.g., Bay Champagne) are and sand trapping by the east jetty has ac­ directly behind the barrier beach. Based upon counted for net accretion, averaged over the beach profiles surveyed over a three-year period, Grand Isle shoreline (Plate 23). Average shore­ quantitative estimates of longshore sediment line change rates of +5.9 ft/yr (+1.8 m/yr) were drift were made (Harper 1977). An estimated calculated for the 1955-1978 period. Histor­ 660,000 yd3/yr (530,000 m3/yr) is eroded and ically Grand Isle experienced erosion at the transported out of the Caminada-Moreau system western end (adjacent to Caminada Pass) and (Harper 1977). The USACE (1972) estimates that accretion at the eastern end. The western spit 300,000 yd3/yr (230,000 m3/yr) are trapped by was structurally stabilized in the early 1970-;, the jetty at the east end of Grand Isle. The and as a consequence, the immediate downdrift remaining 360,000 yd3/yr (275,000 m3/yr) are area was deprived of natural beach nourishment presumably intercepted by Caminada Pass and material. Average erosion rates of 31.6 ft/yr tied up in nearshore shoals or lost to the offshore (9.6 m/yr) for 1955 to 1978 occurred in this zone. (Harper 1977). Industrial development at Port Fourchon. Another area of erosion is found near the central portion of the island, where erosion rates of 11.8 ft/yr (3.6 m/yr) were calculated. The large number of recreational camps directly on the Fourehon Beach (Subunit F) Gulf shoreline makes Grand Isle quite vulnerable, in terms of potential property damage and loss At a point approximately at the mouth of Pass Hydrologic Unit 4: of life, during hurricane events. Fourchon, longshore sediment drift diverges, east to nourish Grand Isle and west to nourish Terrebonne-Timbalier the Timbalier Islands. Shoreline erosion rates are highest at this point of diversion (70 ft/yr or The Terrebonne-Timbalier hydrologic unit can be 21 rn/yr) and gradually decrease in both direc­ divided into three generalized shoreline seg­ Caminada-Moreau Beach (Subunit E) tions. The Fourchon Beach shoreline has exper­ ments (which can be further subdivided into a ienced average retreat rates of over 42 ft/yr (13 series of subunits): the Timbalier Islands, the This 10.5-mi (17 km) stretch of shoreline, ori­ m/yr) during 1955-78, although the extension of Isles Dernieres, and the mainland coast from ented northeast southwest, co'llprises the rapidly the Belle Pass jetties in the 1960s has reduced Caillou Bay to Point au Fer. The Timbalier eroding shoreline of the Caminada-'\1oreau del­ the rates somewhat. Sand that normally would Islands formed as a result of erosion of the taic headland which supplies sediment for the have been carried westward to the Timbalier Caminada-\foreau headland and westerly long­ downdrift barrier island of Grand Isle. While Islands is now intercepted by the jetties, and shore drift-induced spit accretion. The Isles erosion rates averaged 41.1 ft/yr (12.5 m/yr), the high erosion rates consequently have been re­ Dernieres represent the outer barrier rim of a western edge of the subunit, near Port Fourchon, duced east of the jetties but substantially in­ complex delta lobe formed by a number of is subjected to the highest nontidal shoreline creased west of the jetties. Not all sediments distributaries associated with the Lafourche retreat rates in the state (on the order of 70 are trapped by the jetties, as some natural sand delta complex (Frazier 1967). The Gulf coast of ft/yr or 21 m/yr between 1955 and 1978) (see bypassing occurs (Dantin et al. 1978). the Caillou headland and Point au Fer Island, J 21 ] [ characterized by broken barrier beaches and (Penland and Boyd 1981). Today, a noticeable continuous barrier beach respectively, represents downdrift offset (indicating accelerated shore­ the outer rim of the delta lobe of Bayou Black line retreat) characterizes the coastline imme­ [ and associated distributaries (Frazier 1967). dia tely west of Belle Pass. High erosion in this -u Shoreline erosion rates are high on the barrier area has been accelerated additionally by exten­ - island segments and moderate on the mainland � sive canalization. A shore-parallel pipeline ! [ barrier shoreline (Figure 15a and b). • canal has increased shoreline retreat rates just ; -ao -· • • • c c west of Belle Pass, and a normal-to-shore rig cut z z Island A) u u East Timbalier (Subunit dredged into the back barrier has evolved into a .. 0 [ I o ! :l ---· tiU•tlll .. major tidal inlet (see Figure 10). Average shore­ .. .. • - tiU•tiU • The entire Timbalier Island chain has been im­ line retreat rates of about 55 ft/yr (17 m/yr) for 0 I • pacted severely by works of man in recent the 1955-1978 period are found in this subunit. • ao +------,------r-----�----�------�-----.------+. • • ., ... 11' 01' eo• ••• [ decades, and nowhere is this better displayed LOIIQITUDI than on the East Timbalier shoreline segment Another major interruption in the longshore sedi­ (Plate 21). Historically a flanking barrier ment transport system has been the construction spit/island of the Caminada-Moreau headland, of rip-rap breakwaters along most of East Figure 1Sb. Shoreline Change, Hydrologic Unit 4 [ East Timbalier has been partially deprived of its Timbalier Island. To protect oil company inter­ (Mainland). sediment source following construction and sub­ ests, almost $11 million was spent between 1966 sequent extension of the Belle Pass jetties. and 1980 on construction and maintenance of [ Prior to jetty construction, even frequent hurri­ two parallel breakwaters--one on the beach and canes caused little reduction in island area one in the back-barrier zone (Anonymous 1980). While the project is considered successful with regard to protection of oil company structures [ -100 -30 and perhaps even a minor reduction in shoreline erosion rates, the breakwaters are frequently breached during storm events. Little sand beach remains seaward of the outer dike, and along \ c some reaches a and beach are found -8o I -24 r 1 within the two dikes. Very little sand is present­ r ly migrating along the shoreface, the slope of I which is believed to have steepened in recent [ I - ..: years. The westernmost 2 mi (3 km) of the I ... r.. -60 -18 ...... \ island have detached themselves from the re­ = .... ! veted portion and now remain as migrating sand u w ' w � I � shoals in Little Pass Timbalier. z z I c %c -40 I -12 % TimbalierIsland (Subunit B) u • u u I \ w w I ' z i! ::::i Timbalier Island, the westernmost downdrift ... ' ,- , nanking barrier island associated with erosion of w BELLE PASS -20 "l \ I \ � the Caminada-Moreau headland, is eroding rapid­ c 0� I ""-- -6 0 % \ ly at its eastern end and accreting at its western \

22 [ Timbalier), less sand is reaching Timbalier Westward growth of Timbalier Island has not most of the Isles Dernieres, although eastward Island. Its sediment supply diminished, the island occurred since 1955, and this is attributed to the drift patterns are evident along Whiskey Island is undergoing a phase of reorientation to prevail­ diminished sediment supply and the proxi mity of and along the easternmost section of Eastern ing waves. Although shoreline retreat rates Cat Island Pass, through which the Houma Isles Dernieres. This reversal of dominant drift averaged 24.5 ft/yr (7 .5 m/yr) between 1955 and Navigation Channel is maintained. It has been direction may relate to tidal exchange forces. 0 1978, erosion rates as high as 52 ft/yr (16 m/yr) estimated that about 650,000 yd3 (500,000 m3) are found at the eastern spit, while accretion of sediment are eroded from Timbalier Island Eastern Isles Dernieres is the largest of the rates at the western spit approach 10 ft/yr (3 each year (Meyer-Arendt and Wicker 1982). An Dernieres barrier islands, and widths of almost 1 m/yr). average of 350,000 yd3fyr (270,000 m3fyr) was mi (1.6 km) characterize the western half (Plate dredged for maintenance of the navigation chan­ 18). Shoreline erosion rates (see Figure 15a) A small fishing village existed briefly on nel between 1966 and 1980 (Broussard 1981), and decrease from 65 ft/yr (20 m/yr) at the western 0 Timbalier Island at the turn of the century. calculations based on historic bathymetric charts end to less than 20 ft/yr (6 m/yr) near the Present land use consists of two clusters of (1891-1974) indicate a sediment load of at least eastern end. The eastern spit, abutting Wine recreational camps and several oil company stor­ 300,000 yd3 (23 0,000 m 3) is being deposited Island Pass, accreted seaward 200 ft (61 m) age tanks and well-heads. Numerous canals have annually on the outer bar (ebb-tidal delta) of Cat between 1955 and 1978; this is attributed to tidal been dredged in the central portion of the island, Island Pass. Even though Timbalier Island has dynamics (see Figure 7). The high shoreline and several potential was hover sites have devel­ not accreted westward in recent decades, the retreat rates, coupled with the narrow island oped. To minimize impacts of washover events dominance of westerly drift can be seen in the widths in the eastern half, have increased the 0 on existing land use, two experimental shoreline westward shift of the 2-fathom depth contour potential for breaching and washover develop­ protection measures have been installed. A and the 1982 realignment of the navigation chan­ ment. A permanent breach opened following the 2000-ft (600 m) rip-rap breakwater was con­ nel (Figure 16}. passage of Hurricane Carmen in 1974, and an structed by the Louisiana Office of Public Works active washover is located immediately west of in 1975, and in 1981 a sand fencing/vegetative Wine Island(Subunit C) the eastern spit. stabilization project was begun by oil company interests in conjunction with LSU researchers Wine Island, the easternmost extension of the The east-flanking barrier spit of the Central 0 and USDA Soil Conservation Service personnel. historic Isles Dernieres, is situated between the Isles Dernieres has retreated landward at rates Both projects appear to have stabilized their major tidal inlets of Wine Island Pass and Cat of over 66 ft/yr (20 m/yr) and now has absorbed respective shoreline segments, but the impacts Island Pass and has been subjected to such high the formerly sheltered Whiskey Island. A 1981 0 of a hurricane or long-term erosion have yet to erosion that just a small sand shoal remains overflight revealed that this island has now been be measured. The rip-rap is presently slightly today. In response to the westward-shifting Cat severed from the Central Isles Dernieres and seaward of the adjacent natural shoreline, and Island Pass, Wine Island has migrated 0.6 mi comprises a separate barrier island. (Because of its disruption of sediment transport processes (1 km) to the west since 1955 (Plate 19). The its sm all size and isolated position, it is assumed can be seen readily by the accelerated erosion island disappears periodically following storm that Whiskey Island, like Wine Island, will evolve downdrift of the dike. events. into a sand shoal in the near future.)

0 Eastern Isles Dernieres (Subunit D) Land use in this subunit is limited to isolated oil company activities and a recreational camp clus­ The Isles Dernieres barrier island chain, the ter (about 20 camps) along Trinity Bayou. As the outer rim of delta lobes associated with early shoreline continues to retreat, this settlement phases of the Lafourche delta complex, is erod­ will be endangered and will require relocation. ing and fragmenting at rapid rates. As recently Near the eastern end of the island, a leveed oil as the late 1800s, Isles Dernieres was one contin­ company treatment pond is gradually filling in 0 uous island with the exception of one small with sand as the shore retreats. breach. The barrier has been maintained by a reworking of sediments and longshore drift pro­ WesternIsles Dernieres (Subunit E) 0 cesses, although the available sand supply is relatively small. Considerable breaching and The Central and Western Isles Dernieres have tidal inlet development have occurred on the experienced high erosion rates and the total 0 Isles Dernieres. Based largely upon sediment disappearance of one island between 1955 and drift, the Isles Dernieres are subdivided into two 197 8 (Plate 17). The Central Isles Dernieres are subunits, the dividing line being the apex of the deltaic marsh deposits being eroded by wave ac­ Caillou headland on the Central Isles Dernieres tion. Longshore sediment drift has led to the Barrier Island washover. (approximately 90° 49' 00" W longitude). Sedi­ building of low barrier spits, one of which has ment transport is dominantly westward over accreted westward a distance of 1.5 mi (2.4 km).

23 0 The westernmost island in the Dernieres chain, Although no westward accretion has occurred in pleasure resort nourished during the 1850s. Last Island, represents a downdrift-nanking recent decades, a 1981 overnight indicated Since an 1856 hurricane inundated the island and barrier island of the Caillou headland. Similar to substantial widening of the beach near Raccoon over 300 lives were lost, no further attempts to Timbalier Island in morphologic characteristics, Point (west end). Last Island contained a fishing settle the islands were made (Peyronnin 1962; Last Island has eroded most at its eastern end. village in the early nineteenth century, and a Sothern 1981).

GI'Bild Bayo u des Ilettes to Oyster Bayou eo••o· at' se• s7' ae· eo•aa· s•• aa· s2' s1' eo•ao• (Subunit P) o7· rr------�------�------,------r------�------,------r------�------�T------� The mainland shoreline adjacent to Caillou Bay, 0 relatively protected in the shadow of the Isles 1978 Dernieres, primarily consists of marsh, although the occurrence of incidental sand beaches in­ Q creases westward toward Oyster Bayou. Pro­ Ot' ceeding west from Grand Bayou des Ilettes, the first small, perched pocket beaches are encount­ 0 1878...... _ ered a few miles southeast of Bayou Grand ,, Caillou. From there west to Bayou de West, the shoreline is quite discontinuous because of the numerous bayous - functioning as tidal channels ­ 0 which into Caillou Bay. Discontinuous sand-shell barrier beaches are found on much of the shoreline, and in increasing amounts toward 0 the west. Between Bayou de West and Oyster Bayou, the barrier beach is fairly continuous, although still "perched" upon protruding marsh 0 deposits in the eastern sector.

Shoreline erosion rates, averaging 12.6 ft/yr (3.8 0

.... ····· �·-··· ...... OS' ...-· · . . m/yr) between 1955 and 1978, increase from ..· almost 0 in the eastern portion of the subunit to about 20 ft/yr (6 m/yr) near Oyster Bayou. The 0 . . . �· � HOUMA NAVIGATION CANAL higher erosion rates in the west, also evidenced \ ( 1882 •ll9nment) by the more seaward extent of the original property lines (surveyed during the 1830s and 02' 1840s), are due to a more gulf-exposed location 0 which, in turn, explains the more developed �----�--�----�----�--�----�----�----�--��--�LAND AREA FATHOM DEPTH CONTOURS 2 barrier beach and higher shoreline berm eleva­ tions. 1881 0 1891 Pointau Per Island Subtmit G) 1934 I ( 1934 0 The westernmost subunit within Hydrologic Unit 1955 1974 0 1 2 ... 4--the shoreline between Oyster Bayou and Point au Fer--comprises a continuous sand-shell 1878 1880 1 0 2 km barrier beach fronted along its northwestern 0 reaches by extensive mud deposits. Shoreline erosion rates, which averaged 16.7 ft/yr (5.1 m/yr) during 1955-1978, are quite variable along 0 the subunit (ranging from 0 to 31.3 ft/yr [ 9.5 Figure 16. Bathymetric Changes, Cat btland Pass Area, 1891-1980 (1980 and 1982 data courtay of .Brou8sard 1981). m/yr 1 ). This is due to localized resistant head­ lands, accreting mudnats, and westward sedi­ ment transport factors. Oyster reefs occur at D D 24 0 0

Point au Fer, and recent observations indicate MarshIsland, South Coast (Subunit B) Nearshore currents are westerly, but evidence of that fine-grained sediments from the developing littoral transport is seen only in the westernmost Atchafalaya River delta were being deposited on The south shore of Marsh Island, from Southwest reaches of the subunit, where the beach has them (Adams et al. 1978). What role is played by Pass to South Point, is fronted for the most part slightly increased in width (Plate 11). A large active deltaic sedimentation further southeast by extensive shell reefs and is quite irregular in amount of suspended fine sediments is being 0 along Point au Fer island is not yet well docu­ outline (Plates 11-13). The reefs serve to break transported by the "Atchafalaya Mud Stream" mented. incoming waves, and shore erosion is minimal in south of Marsh Island (Wells and Kemp 1981), but this subunit. Between 1955 and 1978, erosion shoreline mud accretion is presently most active rates averaged 11.8 ft/yr (3.6 m/yr). The along the Chenier Plain coast, further to the western and eastern reaches of the south shore west. (the latter confined to between Mound Point and Hydrologic Unit 6: South Point) are less well-sheltered by shell Vermilion reefs. Erosion rates aproach 20 ft/yr (6 m/yr), and continuous sand-shell beaches characterize Rainey Wildlife Sanctuary(Subunit C) these shoreline reaches. The shoreline of the Vermilion hydrologic unit is Between 2 mi (3.2 km) west of Cheniere au Tigre comprised of two sections: the easternmost sec­ The central portion of the subunit is charac­ and Southwest Pass, the shoreline is primarily tion of the Chenier Plain (centered on Cheniere terized by numerous, often tree-covered, head­ sand-shell beach, and sediment transport is bi­ au Tigre), and Marsh Island, the westernmost lands. These occur in areas where shell reefs directional. Shoreline erosion rates average 11.0 section of the Deltaic Plain (the early Teche occur within a few feet of the shore. Some short delta complex). The two components are separ­ ft/ yr (3.4 m/yr) in this subunit and increase beaches are in evidence (Plate 12) and have from 4.4 ft/yr (1.3 m/yr) in the west to a high of ated by Southwest Pass, a deep, entrenched tidal probably resulted from erosion of in situ shell ft/yr (5.3 m/yr) near Southwest Pass. inlet linking Vermilion Bay with the Gulf. Shore­ 17.4 deposits. Continuous barrier beach development Closer to Cheniere au Tigre, eroded chenier line erosion rates are low in this area (average: is restricted to areas where reefs are absent 11.6 ft/yr or 3.5 m/yr between 1955 and 1978), a deposits provide sediment nourishment for the (Orton 1959). shoreline to the east. Near Southwest Pass are fact attributed to 1) the antiquity of the asso­ ciated delta cycle (Morgan and Larimore 1957); SOUTHWEST PA SS 2) shore protection provided by extensive near­ I shore oyster reefs (Orton 1959); 3) recent Atchafalaya River mud accretion along the shore (Adams et al. 1978); 4) a more resistant shoreline MARSH ISLAND and source of beach nourishment at Cheniere au Tigre; 5) lower nearshore wave energies (Becker 1972); and 6) localized reversal of the overall - -40 -12 - .. dominant westward sediment transport (Figure "'.. " "' 17). The two major shoreline segments are ...... ,- ' ' E subdivided into five distinct subunits, based upon - - morphologic characteristics and sediment drift \ w w II patterns. " -20 , ____,, -e c:J z I z c I c Marsh Island, East Coast (Subunit A) % z () I (,) I J More directly oriented toward prevailing wester­ w I \ w � 14 .• z ly currents and less well-protected by offshore z 0 . . ..J ,, 0 - oyster reefs, the east coast of Marsh Island ..1 .. ..1 w w (Lake Point to South Point) exhibits higher a: a: J ·-- 1954-1tt89 shoreline erosion rates (17 .4 ft/yr or 5.3 m/yr) 0 0 than the south shore of the island (Plate 13). % 1.955-1978 z Cl) - Cl) The shoreline is primarily marsh, although short 20 8 stretches of sand-shell beach are found at points 92° 20' 1 0' 00' 91° 50' 40' and minor headlands. Nearshore currents are dominantly north-northeast along this coastline LONGITUDE (CEI 1977), but because of available coarse beach material and low wave energies, longshore Figure 17. Shoreline Change, Hydrologic Unit 6. sediment transport is not apparent.

25 D some nearshore shell reefs, though not enough to while in the eastern third newly accreting mud­ km/yr] .) Average erosion rates are roughly 30 significantly protect the shoreline from erosion. flats are slowing the rates of erosion. The zone ft/yr (9 m/yr), although considerable variability 0 Tidal-exchange forces also contribute to erosion of mudflat accretion has steadily been shifting exits within the hydrologic unit. Three distinct in this area. westward since the 1950s (Wells and Kemp 1981), shoreline subunits are identified. in response to an increased sediment load carried D Cheniere au Tigre (Subunit D) in the Atchafalaya Mud Stream and longshore Freshwater Bayou Canal to Flat Lake (Subunit A) transport processes. As the mudflats begin to The stretch of coastline from Tigre Point to accrete along the highly erosive Chenier Plain From the mouth of the Freshwater Bayou Canal west of Cheniere au Tigre is oriented NE-BW, barrier coast, the rates of shoreline erosion to approximately Flat Lake, the shoreline con­ 0 and net longshore sediment transport is to the diminish. This trend can be seen on Figure 18, sists of irregularly alternating stretches of northeast (Plate 10). The eastern and western which shows that erosion rates have diminished marsh, sand-shell beach, and mudflats (Plates 8 thirds of the subunit consist of sand-shell beach, substantially east of Flat Lake. To the west, and 9). The greatest proportion of sand beach Q eroded from the headland at Tigre Point and beyond the present influence of the mudflats, (and highest shoreline erosion rates) is found in from Cheniere au Tigre. Between the two erosion rates remain high, partly because the the western portion of the subunit, where the reaches of sand beach, the shoreline consists of accretion of mudflats reduces the ability of accretion of mudflats has become important in marsh, although until the early 1970s extensive longshore transport processes to remove sand recent years. 0 mudflats accreted here (Wells and Kemp 1981). from that area for downdrift nourishment. The (The zone of active mud accretion has since locus of mudflat accretion is expected to con­ Shoreline erosion rates, which averaged 16.8 shifted westward, into Hydrologic Unit 7 .) tinue to migrate westward and presently critical ft/yr (5.1 m/yr) between 1955 and 1978, increase 0 Average erosion rates approached 10 ft!yr (3 shoreline erosion rates will be reduced. (The from net accretion or low erosion near Fresh­ m/yr) between 1955 and 1978, although the Tigre leading edge of the mudflat accretion zone is water Bayou to over 40 ft/yr (12 m/yr) of erosion Point headland (at the approximate point of estimated to be migrating westward at average near Flat Lake. Localized erosion near Fresh­ 0 sediment transport divergence) eroded at rates rates of approximately 0.8 mi/year [ 1.3 water Bayou reflects the removal of mudflats of 22.6 ft/yr (6.9 m/yr).

IIERIIENTAU•GULF NAVIGATION CHANNEL 0 / Bill Ridge (Subunit E)

The shoreline from Tigre Point to the Fresh­ u water Bayou Channel is comprised of a narrow sand-shell beach which developed as a result of erosion of the Tigre Point headland and subse­ 0 quent westerly longshore drift. Shoreline retreat rates averaged slightly over 10 ft/yr (3 m/yr) -eo -18 during 1955-1978, and were uniform over the FRESHWATER BAYOU CANAL whole subunit. At the mouth of Freshwater \ 0 - Ba ou Canal, maintenance dredging of 1,000,000 - .. g .. � yd (764,000 m3) every 18 months is required =-- ...... -12 ...... � -40 � \ E (USACE 1976). This reflects the high volumes of .... 0 fine sediments introduced by way of the - Ill v' Ul Atchafalaya Mud Stream. To minimize shoaling, " l Cl z z plans call for construction of jetties out to the

26 J deposited in the 1950s. Evidence of the influ­ combination of the easily erodible marsh de­ Although shoreline erosion rates are not as high ence of mudflat accretion upon erosion rates is posits plus a reduction in sediment supply in this unit as along most of the barrier islands, seen by the reduction in shoreline erosion rates because of updrift sand trapping by the naviga­ or even most of the Chenier Plain coast in between longitudes 92° 25' and 92° 33' (see Figure tion channel jetties. The more resistant Hack­ Hydrologic Unit 7, the consequences of con­ 18). The average rates for the 1954-1969 period berry Beach chenier has withstood erosional tinued erosion are much more serious in view of J (Adams et al. 1978) have decreased significantly stresses, although a truncation of the updrift enq the extensive use in this zone. Outside of the for the 1955-1978 period. of the chenier is evident (Plate 5). The Hack­ Port Fourchon-Grand Isle shoreline in Hydrologic berry Beach spit has accreted westward since Unit 3, the only road-accessible sand beaches in J 1955, and the Mermentau has been Louisiana are found in this unit, and several deflected westward in response. recreational settlements have developed since Flat Lake to Mermentau-Gulf Navigation the 1930s. In spite of Hurricane Audrey striking Channel (S ubunit B) the area and totally destroying the beachfront communities in 1957, recreational reconstruction The 30-mi (48 km) stretch of coastline from Flat Hydrologic Unit 8: has proceeded at a rapid pace. Lake to the Mermentau-Gulf Navigation Channel Calcasieu-Sabine J jetties consists of fairly continuous, narrow sand Sediment transport is dominantly westward along beach that is eroding at rates of approximately this hydrologic unit shoreline, although two 40 ft/yr (12 m/yr) (Plates 5 through 8). Inter­ The westernmost of the eight major hydrologic reaches of little or no transport exist immedi­ ruptions of the sand beach continuity are limited units, the Calcasieu-Sabine shoreline, is com­ ately east of the jetties where the shoreline to mouths of bayous and canals and where the posed of sandy beaches and also extensive mud­ orientation approaches northeast-southwest. beach is washing over into large waterbodies, flats, the latter occurring on the �ast sides of Based on shore characteristics and transport such as at Big Constance Lake (Plate 7). The the Sabine and Calcasieu Pass jetties. Shoreline pattern, four subunits are delineated. present trend of a westward shifting locus of erosion rates averaged 8.9 ft/yr (2.7 m/yr) over mudflat accretion is expected to offset the high the entire unit between 1955 and 1978, but Rutherford Beach to Calcasieu Pass(Subunit A) shoreline erosion rates beginning at the eastern considerable variability was encountered (Figure J end of the subunit. 19). The highest erosion rates occurred near the From the mouth of the Mermentau River to mouth of the Mermentau River and adjacent to Calcasieu Pass, the beach grades from one of The sand-shell shoreline along this subunit is the navigation channel jetties. coarse sediment to one of fine. Coarse sands 0 maintained by high erosion rates and the west­ ward littoral transport of eroded sediments. Prior to construction of a navigation channel CALCASIEU PASS from Lower Mud Lake to the Gulf, longshore -eo -18 J sediment transport processes accounted for con­ tb siderable westward accretion of the Hackberry Beach spit and a continual westward deflection � of the natural outlet of the Mermentau River. ,.. -12 ...... While the jetties presently exhibit patterns of E - reduced updrift erosion and accelerated down­ w w 0 drift erosion, the overall impacts of the naviga­ (:J z tion channel have not yet been evaluated z c c -8 :z: adequately. :z: j (,) (,) w r- I/\ ' , w \1 - ! z '--J I \ :i " w... w 1\ I \ HackberryBeach (Subunit C) \ 0 0II: 0II: ,, :z: The Hackberry Beach subunit, extending from :z: (I) (I) 1964-1989 the Mermentau-Gulf Navigation Channel jetties to the natural mouth of the Mermentau River, 1955-1978 exhibits high erosion rates immediately down­ 20 +------r-----,------�----��----�------r-----.------r-----,------t e drift of the jetties and stable conditions where 9a•so· 40' ao· 20' 10' aa•oo · the Hackberry Beach chenier is directly situated LONGITUDE against the coastline. The high erosion rates (up B. to 42.6 ft/yr or 13 m/yr) along a 3-mi (4.8 km) Figure 19. Shoreline Chartge, Hydrologic Unit reach downdrift of the jetties are attributed to a

27 J eroded from the Hackberry Beach chenier beach, and littoral sediment transport is domi­ flanks of Calcasieu Pass. In the vicinity of migrate alongshore (westward), naturally bypass nant in a westerly direction. A narrow beach Peveto Beach/Constance Beach, erosion rates the mouth of the Mermentau, and reattach to ridge fronting the coast characterizes most of are almost double the subunit average, up to 16.5 the shore near Rutherford Beach. Proceeding the subunit, although accretion ridges associated ft/yr (5 m/yr). It is in this area that undermining westward, the proportion of coarse sediments with Calcasieu Pass and Sabine Pass sedimenta­ of the coastal highway by wave action is a decreases until, near Cameron Beach, the shore­ tion occur at both ends of the subunit (Plates 2 serious problem. Following a survey by the line consists of a wide band of intertidal mud­ and 3). The Gulf Coastal Highway (La. 82) USACE (1971), the Louisiana Department of flats fronting marshland. follows the shoreline along most of the subunit, Public Works constructed gobi-block revetments and much recreational development has occur­ along a 3-mi (5 km) stretch of highway along [ Shoreline erosion rates averaged 13.7 ft/yr (4.2 red. While overall shoreline erosion rates are Peveto Beach (Dement 1977). The revetment m/yr) over this subunit between 1955 and 1978, comparatively low, the proximity of the highway mats have not successfully withstood storm although localized sections experienced much and recreational settlement to the shore makes impacts, and plans call for reinforcement of the [ higher retreat rates. The recreational commu­ coastal erosion a serious problem. revetments during the early 1980s. nity of Rutherford Beach, dating to the 1940s and presently containing about 35 recreational Longshore sediment drift is dominantly westerly dwellings, was laid out on a precarious site at When highway construction in the 1930s first along this subunit. Sands eroded from beach the mouth of the Mermentau River, directly allowed easy beach access to the public, recrea­ ridges in the Holly Beach vicinity, and from across from the westward-accreting Hackberry tional beach settlements developed (Meyer­ truncation of the Sabine accretion ridges near Beach spit. As the spit builds across the river Arendt 1981). Holly Beach, Peveto Beach, Peveto Beach/Constance Beach, are being trans­ [ mouth, the channel becomes deflected against Constance Beach, and View Beach all had ported westward by littoral processes and depos­ the opposite shoreline, thus causing increased their origins during this period. Recreational ited along the shoreline west of Long Beach. erosion (Plate 4). Net shoreline erosion rates at growth has been strong since the 1930s, in spite Rutherford Beach, as a combined result of of occasional damaging hurricanes. Hurricane Westof Long Beach (Subunit C) [ fluvial and marine processes, averaged over 34 Audrey in 1957 totally destroyed all beachfront ft/yr (10 m/yr) between 1955 and 1978 (see development and breached the coastal highway. The shoreline in this subunit consists of sand Figure 19). The other zone of observed high The community of Peveto Beach, previously situ­ which has been transported from further east. [ shoreline retreat rates is east of the Calcasieu ated at the eastern end of the Sabine accretion The shoreline has accreted here at an average Pass jetties, the site of extensive mudflats. ridges (that were severely truncated by the rate of 3.7 ft/yr (1.1 m/yr) between 1955 and Although shoreline erosion has been high, the storm), was never rebuilt. Holly Beach and other 1978. Accretion rates of over 13 ft/yr (4 m/yr) [ measured rates of up to 34.8 ft/yr (10.6 m/yr) smaller settlements between Peveto Beach and occur along localized reaches. Sediment trans­ are slightly misleading because of the variance Long Beach were quickly rebuilt, however. A port is westerly, although rates of transport in water levels between the 1955 and 1978 sets 1981 overflight and ground survey identified ten decrease as the shoreline takes on an increasing of aerial photography. The wide band of inter­ beach subdivisions in the area and inventoried northeast-southwest orientation. The western [ tidal flats was prominently exposed on the 1955 existing structures. In order of importance, end of the subunit contains the westernmost sand imagery and submerged on the 1978 imagery. these included Holly Beach (583 structures), beach in Louisiana. (Partly owing to the in­ Constance Beach (117), Chaisson Subdivision creasing distance from the highway to the beach, u Because of the fine-grained nature of the beach (38), Ocean View Beach/Little Florida (14), and no recreational development has occurred in this sediments along most of this subunit--and con­ Long Beach (6). Commercial development is subunit.) sequent low recreational appeal--coastal land restricted to Holly Beach, which contains a use is not very developed. Recreational develop­ number of small businesses and numerous motels [ ment is restricted to Rutherford Beach, although and rooms for rent. Sabine Mudflats (Subunit D) prior to Hurricane Audrey in 1957 some recrea­ tional development existed at Broussard's Beach [ and Cameron Beach, south of Cameron. The final subunit in the Calcasieu-Sabine hydro­ Shoreline erosion rates averaged over 10 ft/yr (3 Although no direct settlement on the shoreline logic unit consists of marshy shoreline, fronted m/yr) over the subunit (1955-1978), although presently exists south of Cameron, several town for the most part by mudflat deposits. While a higher average rates occurred adjacent to the pattern [ subdivisions are located within 0.5 mi (0.8 km) of of accretion formerly characterized this Calcasieu Pass jetties and at the zone of accre­ subunit, the coast. recent trends indicate significant shore­ tion ridge truncation at Peveto Beach. Although line erosion (Plate 1). Average retreat rates of mudflats occur on the west side of the jetties, a 9.6 ft/yr (2.9 m/yr) were calculated, although [ thin strip of sand beach comprises the shoreline. adjacent to the Sabine Pass jetties rates of 32.2 Calcasieu Pass to LongBeach (Subunit B) Retreat rates exceeded 40 ft/yr (12 m/yr) here, ft/yr (9.8 m/yr) were found. Sediment transport and it is surmised that the jetties (and mainte­ patterns are not apparent, and on the basis of From the Calcasieu Pass jetties to slightly west nance dredging) have removed a source of sedi­ the shoreline orientation, bidirectional drift is of Long Beach the shoreline consists of sand ment that was formerly redistributed along the inferred.

28 [ J 0 Chapter IV Impacts upon Land Use Patterns When reviewing land uses in Louisiana's coastal area various trends can be observed. Some reflect changes in the natural system; others are the result of external economic forces. Exam­ ples include respectively the abandonment of agricultural operations in response to saltwater intrusion and the industrial expansion along the coast associated with offshore oil and gas ex­ J traction. Comparison of these trends illustrates a growing conflict that must be given full recog­ nition. That is the conflict resulting from con­ vergence of the seaward expansion of industrial and urban development and the landward expan­ sion of the Gulf of Mexico.

Gulfward expansion of urban and industrial development occurs for numerous reasons. These include dependence on natural levee ridges, the distance to marine operations and related fuel costs, the location of existing development, and existing and newly created waterways. Agricultural development shows a similar trend as market prices allow larger risks associated with more floodprone areas. However, irrespective of the validity of these reasons, the natural processes of subsidence and erosion continue as part of the deltaic system, and resultant environmental changes are increasingly felt. Urban expansion along natural levee ridge.

In response to these changes, in particular in­ terioration. Major land use patterns are southern edge of the Almonaster-Michoud creased flood frequencies and levels, structural displayed for the areas gulfward of, and Industrial Development Corridor) to near Chef measures are often proposed and implemented. immediately landward of, the first major inland Menteur Pass. From that point, U.S. Hwy 90 is These include flood protection measures, ranging development shown on Figure 20. followed to the Pearl River. Land use patterns from hurricane protection levees to lower back­ consist of a mixture of urban area, agriculture, J levees, as well as measures directed to stem and industrial development along the protected saltwater intrusion, such as structural barriers. natural levees of the Mississippi River and Bayou In recent years extensive back-levee construc­ La Loutre. Between Paris Road and Chef Hydrologic Unit 1: J tion has taken place to protect the communities Menteur Pass an industrial corridor is situated at the lower ends of the smaller distributary Chandeleur-Breton north of the Gulf Intracoastal Waterway and ridges, especially in the parishes of Terrebone, west of Chef Menteur a strip development of Lafourche, Plaquemine, and St. Bernard. For the most part, land use in this hydrologic stilt recreational camps flanks Hwy 90 (which unit is protected by back-levees of the follows the distributary ridge). Mississippi River and Bayou La Loutre. In The following paragraphs examine present devel­ Orleans Parish, the first inland line of Land use gulfward of these leveed areas, other opment within each of the hydrologic units, development follows Paris Road from the than isolated r.ecreational camps and oil industry associated development of protection measures, Mississippi River back-levee to the Intracoastal installations, is restricted to the lower Bayou La and ramifications of continued erosion and de- Waterway, then along the northbank levee (the Loutre and Bayou Terre aux Boeufs distributary J 29 J 0

TEXAS LOUISIANA LOUISIANA MISSISSIPPI 0 0 0 LAFAYETTE i 0 0 0 I I / VIII I 0 / VII 0 VI v c Ill LAND USE LEGEND .. II

f'- -AWARD EXTENT OF EXISTING MAJOR DEVELOPMENT IV II AGRICULTURE MIXED URBAN/TRUCK FARMING/INDUSTRIAL E1) ,. . .. LOUISIANA COASTAL ZONE LIMITS MAJOR OIL AND GAS FIELDS l \ 0 ...... FN!:�I URBAN/INDUSTRIAL • • ! HYDROLOGIC UNITS (H.U.) • \• c COASTAL INDUSTRIAL SITES . v . [ • COASTAL SETTLEMENTS

RECREATIONAL CAMP STRIPS OR CLUSTERS C>40 unlt•lma2) 0 21I 10 0 RECREATIONAL CAMP CLUSTERS (8-at unlt•lml2) [ ..... 0 10 -- ...... t1' .. •• lklontetw. [ Figure 20. Land Use Patterns (after Davis and Gary1979; LouisiaM Department of Canservation 1973; Louisiana Offiee of State Planning 19'12;and Wieker et aL 1980). u 0 ao [ J Hydrologic Unit 3: ridges. Land use is primarily urban and settlements of Barataria and Lafitte), numerous J agricultural with scattered sites of industrial Barataria recreational camp clusters, small fishing development. Settlements along these ridges - Existing major development in the Barataria settlements (e.g., Grand Bayou, Bayou Gauche), such as Ycloskey, Hopedale, Reggio, and hydrologic unit follows primarily the back-levees isolated industrial complexes (e.g., Leeville, Delacroix - are facing problems of subsidence of the Mississippi River and Bayou Lafourche, Grande Ecaille), and the shorefront and saltwater intrusion. Comparison of 1955 and which are flanked largely by agricultural land urban/industrial/recreational centers of Port 1978 conditions around Delacroix (Figure 21) (dominantly sugarcane) and urbanized land and Fourchon and Grand Isle. indicates a large increase in waterbodies. In industry at the southern edge of greater New addition to new canalization, old canals and Orleans (see Figure 20). Much wetland has been Land loss rates within the wetlands exceed 4 reclaimed for agricultural and urban expansion acres er square mile of gross land area per year bayous have widened and many new lakes have � "2 appeared. Sections of the ridge have been back­ along Bayou Lafourche, near Des Allemands, and (ac/mi /yr), or 0.6 ha/km /yr, adjacent to Bayou leveed since 1955, as seen by the back-levee south of New Orleans by means of back-levee Lafourche, and the recent construction of back­ canal outlined on Figure 21. construction. Gulfward of these levees, land use levees in that area was undertaken as a protec­ is limited to the Bayou des Families/Bayou tive measure against flooding due to hurricanes. Barataria distributary ridge (containing the Similarly, the natural levee of the Mississippi River (west bank) is protected by back-levees as HABITATS LAND LOSS far south as Venice, the site of much oil industry development.

The greatest potential for property damage by shoreline erosion processes (both normal and storm-surge related) lies in the development W41' sites of Grand Isle and Port Fourchon. Grand Isle, described in greater detail previously, is the targeted recipient of $14 million in shore protec­ tion measures (USACE 1980). An even greater potential threat exists at Port Fourchon, an industrial and recreational center near the mouth of Bayou Lafourche (where shoreline ero­ sion rates exceed 70 ft/yr 21 m/yr] ). A tank 1155 1955-1978 [ farm has occupied the site since the 1950s LI!QI!ND (Figure 22), but rapid industrial development did not take place until the early 1970s. Judging by HUITATI LAND LOll the 1932, 1955, and 1978 overlays of the Port • DEVI!LOPIII!NT LJ CHANGE FROM LANDTO WATER Fourchon vicinity, shoreline retreat has been 0 rapid. The selection of this site for industrial []' AGRICULTUitE development has not been wise, and it is antici­ pated that a considerable amount of shoreline protection will be required in the near future. l]j NATURAL LEVEE RIDGE (Although the extension of the Belle Pass jetties has slightly retarded erosion rates at Fourchon 11 FOREST Beach, overwashed beach sands are already starting to fill in some of the treatment ponds at • SPOIL VEGETATION , the site.) M 1178 NON-FIII!IHIIARSH Grand Terre Island, east of Grand Isle, is the site of a Louisiana Department of Wildlife and Si WATIR Fisheries field station and the historic Fort . .. '- Livingston. The island is eroding mostly at its ... - . ... N� ends, and tidal-exchange processes account for most of this erosion. While shoreline retreat J rates are not as severe as at Port Pourchon, Figure 21. Habitat Change, Delacroi% and Vicinity, 1955-1918. some shoreline protection will be required in the near future.

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] .tl. ,,, .. SlVliBVH ] 0 resent evelopment (excepting the salt domes), Hydrologic Unit 4: tion measures because the conversion of drilling p � sites from onshore to offshore (as the shoreline 1s co�fmed to recreational development Terre bonne-Tim balier . retreats) requires the expenditure of even great­ {pr1mar1ly at Cypremort. Point and near Intracoastal City), commercial fishing centers With the exception of several north-south er amounts of money. Recreational camp clus­ (Cypremont Point, Intracoastal City), some oil trending distributary ridges, the first inland high ters (of a dozen or so camps each) are found on industry installations, and USACE lock ground in the Terrebonne-Timbalier hydrologic Timbalier Island and Eastern Isles Dernieres, but structures near the mouth of Freshwater Bayou unit is encountered at the east-west trending presumably recreationists are aware of hurri­ Canal and near Intracoastal City. None of these distributary ridges of Bayou Black and Bayou canes and island erosion threats. (Recreational areas are particularly threatened, except in Blue. These ridges, in conjunction with the camps are numerous throughout the lower bayous cases of a severe hurricane. Land loss rates back-levees constructed along Bayous du Large, and marshes of Terrebonne Parish.) within the marshes are moderate to low and Grand Caillou, Petit Caillou, Terrebonne, Pointe shoreline erosion rates along the Gulf ar also au Chien, and a segment of Bayou Lafourche low. Cheniere au Tigre, a permanent settlement� above Golden Meadow, comprise the limits of Hydrologic Unit 6: until the 1940s and now seasonally occupied by existing major development in this unit. Along Vermilion descendants of the original settlers, is situated many of these distributary ridges, back-levees directly on the coast. Several camps along the 0 were not constructed until the 1970s, in response Land use south of the Pleistocene terrace and eastern reaches of the "island" are located at the to increases in subsidence, marsh-to-water the natural levee of Bayou Teche, the limit of conversion, and flood potential. To illustrate these points, the example of the village of HABITATS LAND CHANGE Boudreaux along Bayou Grand Caillou is provided (Figure 23). Subsidence factors have led to a gradual narrowing of the ridge lands, and agriculture along the natural levees has decreased because of 1) urbanization, and 2) abandonment due to increasing wetness. Wetland forests have been killed off by in­ creasing salinities and hydrologic impoundments, and marshes have become more saline. Consi­ derable forest and marsh have converted to open water, especially to the east of Boudreaux. The 1955-1978 potential for higher water level set-up by winds, LEGEND and subsequent flooding, contributed to the re­ HABITATS LAND CHANGE cognition of a need for back-leveeing.

or to The southern distal ends of the Terrebonne dis­ D WATER Em MARSH FOREST WATER

tributaries, south of the back-leveed sections, to contain many small co:nmunities, recreational E1 FRESH MARSH � AGRICULTURE FOREST camps, motels and marinas, and some industry . 101 or (mainly fishing-related). These zones are quite � NON•FREIH MARSH � I'RE8HMARSH FOREST to vulnerable to increased saltwater intrusion and NON-I'RESHMARSH land loss, which are very severe here. As the surrounding marshes turn into open water, the 11 FOREST danger of storm-surges increases the threat to these areas. Back-levee construction is not very EJ AORICUL TURE feasible here because of the narrow widths of the natural levees. The value of the marshland • DEVELOPMENT as a protective buffer is recognized readily in these lower distributary ridges. • SPOIL VEOET TIONA

Land use along the Gulf shoreline is presently restricted to several recreational camp clusters 0 and oil and mineral industry installations on and behind the barrier islands. Several of the oil companies have experimented with shore protec- Figure 23. Habitat Change, .Boudreauz andVicinity, 1940-1978.

33 J 0 water's edge, but the high relative elevation of Hwy 82. The greatest potential for damage lies The recreational centers of Rutherford Beach, the chenier (10 ft MSL [ 3 m MSLJ ) and low in the erosion of the surrounding protection Holly Beach, Constance Beach, and several smal­ 0 retreat rates and periodic accretion of mudflats levees, which would lead to the inflow of saline ler subdivisions south of Johnsons Bayou contain reduce the overall dangers. The developing water. Some of the levees are near the Gulf over 800 structures (Meyer-Arendt 1981). Prac­ industrial center near the Freshwater Bayou shoreline, which is retreating rapidly. Isolated tically all of these settlements are threatened by 0 Canal locks is also in an area of relative oil drilling structures may be impacted by the shoreline erosion (see earlier section for more shoreline stability, although hurricanes would high shoreline erosion rates, but little other land detailed discussion). An area of particular con­ lead to severe impacts. (The numerous use would be affected. cern to the state is the stretch between Holly unpopulated cheniers in the area support a large Beach and Constance Beach. Hwy 82 near [ cattle-grazing industry.) Peveto Beach is frequently overtopped, and ex­ isting revetments have not adequately withstood Hydrologic Unit 7: Hydrologic Unit 8: the force of the sea. Historically, the highest [ shoreline retreat has been between Peveto Beach Mermentau Calcasieu-Sa bine and Holly Beach, but in recent decades the zone As in the Vermilion hydrologic unit, little danger of highest erosion has shifted westward and is to land use as a result of wetland deterioration Continued shoreline erosion could prove quite now between Constance Beach and Peveto Beach 0 and shoreline erosion is foreseen south of a line serious to the extensive recreational develop­ (Figure 24; Plate 2). No severe hurricane has following the edge of the Pleistocene terrace ment along the beaches of the Calcasieu-8abine struck this coast since Carla in 1961. Construc­ and the first inland cheniers (along which La. hydrologic unit. La. Hwy 82, which dictates the tion of camps has greatly increased since that Hwy 82 runs). Development has historically been position of the first inland line of development, time (Meyer-Arendt 1981), and a severe hurri­ restricted to the cheniers, although recently an follows cheniers and beach ridges which are cane would cause extensive property damage in industrial center developed along the Mermentau situated close to the Gulf. The only developed the area. 0 River just south of Hwy 82. The Rockefeller areas south of the highway consist of beachfront Wildlife Refuge, containing a number of housing recreational settlements and several urban units and other structures, is located south of subdivisions south of Cameron. 0 0 LEGEND and Overlapping Shoreline• 1833 Shoreline - 1934 1955 0 ml km 0 I IIIII 1934 Shoreline ===- State Hlghwaye ! � J 1955 Shoreline Beachtront Settlement• 0 -- 1978 Shoreline I Recreation Camp• Deetroyed by Hurricane Audrey, 1957 1 I 7 8 ehorellne 0 [ [ M E X I c 0 [

Figure 24. Shoreline Change, Holly Beach andVicinity, 1833-1918. [ 34 ( J

Chapter V Remedial Measures

Rigid Versus Flexible Solutions A variety of measures are available for protec­ tion and stabilization of Louisiana's shoreline. Ranging from seawalls to beach nourishment, all could be implemented given sufficient time and money and could be expected to reduce erosion at least for some time. Benefits must, however, be weighed against cost, both for construction J and maintenance. Possibly the process of selecting remedial mea­ sures should begin with an economic analysis of direct costs and of lost benefits that would result from various rates of shoreline retreat and erosion of the barrier islands. This would then determine the amount of money one could rea­ sonably commit to erosion protection measures given the cost and effectiveness of such measures.

Alternatively one may begin the selection pro­ cess with consideration of available measures and of constraints posed by the natural environ­ ment relative to long-term effectiveness of Shore protection, East Timbalfer Island. those measures and to compatibility with coastal processes. This route has the likely advantages modifying the littoral transport system in such a The limited sediment supply along the Louisiana of reducing the number of measures that need be way that more sediment is retained along a coast proves a major constraint to employment considered in future analyses and is followed particular shore segment. The effect may range of the above measures on a selected basis. In here in part also because of the scope and from reduced erosion to deposition and may particular, along most of the barrier islands, objectives of the present study. involve reorientation of the shoreline relative to employment of these measures along limited wave approach, reduction of wave heights, or shoreline segments could in many cases cause When considering available measures, a division collecting of sediment to be used for breaching of the beach system in adjacent shore into three general categories may be made. One redistribution. segments. Application of the measures along the category includes seawalls, revetments, bulk­ barrier islands, therefore, is likely to require a heads, dikes, and other similar structures whose Both the first and the second categories have functional design that wo"Uld extend along at primary function is to maintain a fixed boundary one important element in common. That is that least an entire island and possibly include down­ between land and sea by replacing the mobile employment of each of these measures repre­ drift islands within the same chain. shore sediments with rigid materials. These sents a perturbation of the littoral transport structures are usually the most costly because of system so that the sediment supply to adjacent construction methods, materials cost, the 1:1 areas is adversely affected. Commonly, these The utilization of permanent structural measures ratio between structure length and protected measures have been employed to reduce erosion over extensive lengths of shoreline is extremely length of shoreline, and the level of storm along a limited shoreline segment, resulting in at costly. Such cost is further augmented by fre­ intensity they must be able to withstand. least a temporary acceleration of erosion in quent exposure to hurricane conditions. Since adjacent areas. Although undesirable, this type most of the shoreline retreat occurs as a result The second category includes various types and of situation may be warranted if existing devel­ of hurricane landfall, the structures, to be effec­ combinations of groins and breakwaters. In this opment is of sufficient economic value, reloca­ tive, must be able to withstand hurricane-level case, the beach remains the basic shore protec­ tion of development is not feasible, and adjacent forces requiring high structural integrity or large tion method, while direct function of the areas have an adequate sediment supply to with­ volumes of materials. Both contribute to cost J measure is to protect the beach deposits by stand the adjustment. increases.

35 [

A third constraint relative to permanent struc­ protection measures should be directed at re­ Sand tures is subsidence. Retreat of the shoreline and storing and maintaining integrity of the Nourishment [ landward migration of the barrier islands are beach/dune system as a means to reduce the rate of shoreline retreat and erosion rather than on largely a response to regional subsidence and The erosion of Louisiana's barrier islands and maintaining the shoreline in a fixed position. To associated adjustment of the shore profiles. beaches can best be retarded by the introduction [ insure continued protection by the barrier beach Since subsidence will continue independent of of material for periodic nourishment. Modes of shore protection measures, the tendency for in­ system, management must be for an orderly retreat with minimal loss of sediment. This application include beach nourishment, dune re­ land migration of the shoreline will remain. construction, and filling of wa terbodies and cre­ Permanent protection structures therefore must approach is the most cost effective while pro­ [ viding the necessary time to adequately plan and ation of marsh habitat in the back-barrier zone. arrest all sediment loss from the beach system These measures can help minimize high shoreline or will be gradually separated from the shore. implement a long-term coastal protection system. erosion rates, offset loss of land area due to Yet, even if the first were feasible, subsidence subsidence, retard washover development, and [ would still result in a gradual submergence of provide a foundation for landward-carried sedi­ the shore and an increased frequency of over­ ments to build upon in the back-barrier zone. topping of the protection structures. [

Beach nourishment can be conducted utilizing A similar separation of permanent structures several basic methods: nearshore dumping, [ from the beach may occur if design is inade­ stockpiling, direct placement, and continuous quate. For example, overtopping of shore­ supply (or bypassing). Nearshore dumping entails connected, parallel breakwaters during storms disposing the fill material in the nearshore zone may result in seaward transport of sediment of active sediment movement (less than 2 fath­ ( from behind the breakwater. Subsequent return oms) and allowing the material to be distributed of sediments during low-energy conditions is onto the beach by coastal processes. Stockpiling prevented as a result of the breakwater, result­ entails disposing the fill material directly upon [ ing in accelerated erosion, undermining of the the beach in one location and allowing longshore breakwater, and breaching of the remaining, transport processes to move the material to reduced beach system. downdrift areas. Direct placement is the nour­ 0 ishment (or creation) of beach over its contin­ uous length. The continuous supply method re­ When considering constraints, costs, economic fers to a system of bypassing, whereby sands are justification, and long-term benefits, it becomes Beach restoration at wa.shover associated with rig-cut. mechanically (or hydraulically) moved past inter­ D evident that none of the above measures are ruptions in the sediment transport system such likely to be cost effective or successful as an as jetties or navigation channels. overall approach to Louisiana's coastal erosion c problem. Any successful approach must deal As indicated, the suggested approach involves with 1) the difference between the Chenier Plain two major elements. The first task is one of Dune construction consists of building up the and Deltaic Plain systems, 2) the irrevocable restoring integrity of coastal segments in a man­ elevations of the barrier island or active beach 0 subsidence and associated system responses, ner compatible with natural system trends. This ridges, and is best suited for areas that have 3) the limited availability of sediment and, cor­ restoration must involve restoring a minimal been subjected to breaching or extensive wash­ respondingly, major changes resulting from in­ sediment supply and beach barrier apron to re­ over development or where the potential for terruptions of littoral transport, and 4) the reali­ duce breaching and minimize loss of sediments such erosive processes exists. The actual dune [ zation that Louisiana's barrier beach/island sys­ from the active land/water interface. The se­ need only be approximately 60 ft (18 m) wide and tem should be viewed as a front line of defense. cond task is one of maintenance that must focus 4-6 ft (1-2 m) high at its crest. Where breaches It must, however, also be recognized that on retaining available sediments within each unit need to be sealed to effectively restore a barrier [ present high rates of shoreline retreat and as landward migration takes place. To the island or beach, it may be necessary to fill the coastal erosion are not necessarily nature's largest extent possible, such retention should breaches with rock so that a dune can be con­ normal course of events. focus on promoting storage of sand through dune structed. Two important supplementary mea­ 0 development along the existing shoreline and in sures in dune construction are the installation of particular on newly developing spits. Permanent sand fences--to trap and build up wind-blown When taking the above factors into account, an structures should be utilized only where necessi­ sands--and the planting of dune-stabilizing vege­ overall approach suggests itself which focuses on tated by essential development or where func­ tation. These two measures serve to stabilize 0 retention of materials within a fiexible rather tional design assures no adverse affect on down­ the introduced nourishment material by reducing than a rigid system. That is, where possible, drift littoral systems. the potential for erosion by winds and waves. 0 36 [ 0

Back-barrier bay fill and marsh creation are comprised of subsided delta-mouth bars, outer adjacent to the tidal inlet required overfill of 0 island nourishment methods that can be applied rims (former barriers) of delta lobes, and only 1.02 (USACE 1980). Detailed sediment effectively on the bay side of the dune crest. To filled-in relict channels. Offshore of the analyses need to be conducted at the other major prevent loss of valuable sediment due to over­ Chenier Plain coastline are numerous exposed navigation channel mouths (e.g., Calcasieu Pass, wash processes, it is important that a certain Pleistocene outcrops and coarse-sediment-filled Freshwater Bayou Canal, Empire-Gulf 0 barrier island width--and fairly solid land channels. Considerable field research still needs Waterway, Mississippi River-Gulf Outlet, etc.) to area--is maintained. (In Louisiana, an absolute to be conducted, specifically seismic analyses to determine the optimum potential of dredge spoil. minimum acceptable width is 650 ft [ 200 m] , accurately map the deposits and vibracore inter­ Even the USACE is increasingly regarding dredge 0 although optimum widths range from 1500-2000 pretations to determine thicknesses of the sand­ material as a natural resource rather than a ft [ 450-600 m] .) Bayous, ponds, and especially bodies. This research is particularly valuable in waste product (Walsh 1977). dredged canals located within 650 ft (200 m) of the nearshore zone, as the costs of pumping 0 the Gulf shore should be filled with introduced nourishment material onto eroding beaches The Mississippi and Atchafalaya Rivers transport sediment. If the width of a barrier island is less would be reduced substantially. much coarse material to the Gulf, and this could than this minimum critical width, a potential for be used to help reduce barrier island and beach erosion. While the mining and overland transport breaching exists and additional back-barrier hab­ The ebb-tidal deltas of tidal inlets contain large 0 of river sand may presently be economically itat needs to be created by pumping in nourish­ volumes of coarse material, and recent evidence unfeasible, the diversion of a portion of ment material. To create back-barrier marsh indicates that these volumes are steadily in­ Mississippi River flow south of Empire would habitat, finer nourishment material (that may be creasing (see earlier section; also Howard 1982). help alleviate problems of saltwater intrusion, 0 incompatible with beach sediments) can be util­ The ebb-tidal deltas have been described as good land loss, and barrier shoreline erosion in that ized. A back bay retaining dike would prevent potential sources of nourishment material, the area (Unit 3A) by filling in the deteriorating excessive slumping, and the seeding of marsh removal of which would have only limited ad­ marshes behind the Gulf shoreline. Unlike the grasses (S artina alterniflora) or mangroves verse environmental impacts (Walton and Dean 0 Mississippi River that is tunnelling most of its (Avicennia germinans will accelerate stabliza­ 1976). In 1981, the outer bar of Redfish Pass ( sediments to the offshore slopes of the continen­ tion Meyer-Arendt and Wicker 1982). Consider­ was dredged to provide sand nourishment for a tal shelf, the Atchafalaya River sediments are able research and experimentation with marsh private resort beach on Captiva Island (Olsen 0 actively contributing to a building phase (van habitat creation has been conducted by the 1982). A small jetty was constructed at the Beek and Meyer-Arendt 1981). In addition to the Dredged Material Research Program Section of downdrift end of the beach to trap the sands that delta development in Atchafalaya Bay, accreting the U.S. Army Engineer Waterways Experiment might be transported back into the inlet by the mudflats in Hydrologic Units 6 and 7 are reduc­ 0 Station in Vicksburg, Mississippi (Saucier et al. reversal of transport processes caused by waves ing shoreline erosion rates in that area. As the 1978). refracting around the outer bar (Olsen 1982). Atchafalaya delta continues to grow, increasing­ 0 Sourcesof Nourishment Material ly coarse sediments will reach the Chenier Plain In those inlets where navigation channels are coast and further minimize erosion problems Potential sources of nourishment material, to maintained, much maintenance dredging is re­ there. apply to Louisiana's eroding barrier islands and quired to prevent shoaling. The repeated dredg­ 0 beaches, are found in offshore and nearshore ing of the natural outer bar (and subsequent sand deposits, outer bars (ebb-tidal deltas) of offshore dumping of the spoil) removes large Technology andEngine ering tidal inlets, and the sediment-laden Mississippi quantities of valuable material that would be and Atchafalaya Rivers. Additional sand depo­ well-suited for nourishment purposes. The sedi­ Once the optimum borrow sites for beach nour­ sits occur in land-stranded cheniers and beach ments of the Cat Island Pass section of the ishment material are located, engineering speci­ ridges, inner bars (flood-tidal deltas) of tidal Houma Navigation Channel (from which an esti­ fications need to be worked out and technologic inlets, and in sediment sinks such as the numer­ mated 400,000 yd3 or 306,000 m3 of sediment constraints evaluated. Regarding the engineer­ 0 ous estuarine bays. However, these Iatter loca­ are dredged annually) have been categorized as ing, detailed calculations regarding volumes of tions are considered less feasible because of 70% sand, 5% shell, and 25% (USACE 1975). fill and beach design need to be made. Based environmental constraints (negative impacts If the nourishment material to be applied to upon sediment analyses, overfill and renourish­ 0 upon wetlands), as well as economic/technologic eroding beaches is finer than the native beach ment factors must be established. Cost projec­ limitations (for example, thin sand layers and a material, an overfill factor (which accounts for tions must be based upon available technology, reduced cost-effectiveness), although more re­ the finer sediments that will be winnowed out by distances involved in the transport of fill mater­ search needs to be conducted in these areas. wave action) is calculated (Dean 1974). At ial, and number of booster stations required if Grand Isle, the USACE examined borrow areas the material is to be hydraulically pumped. A large volume of coarse material is contained due south of the island and adjacent to Barataria in offshore deposits (BLM 1979). In the central Pass. It was found that the offshore area (that Primary movers of fill are usually hydraulic or 0 and eastern portions of the Louisiana coast, was finally selected) yielded material that would hopper dredges, the latter preferred because of these sand bodies are former deltaic deposits, require an overfill factor of 1.4, while the area their high mobility and ability to dredge under

37 0

1976). trapping of wind-blown sands and a building up of oceanic conditions (Richardson A combin­ Hydrologic Unit 1: Chandeleur-Breton ation self-contained vessel and dredge, the hop­ the dune. (Experimental sand-fencing and dune 0 per can either directly transport fill material construction on Timbalier Island have so far The Chandeleur-Breton Island chain has exper­ proved quite successful.) Although a complete into the nearshore zone and deposit it by opening ienced extensive erosion in recent decades, much the split hull or by pumping it hydraulically. If closure of existing tidal inlets in the barrier of it the direct result of hurricane activity. the distance to the nourishment site is over 3 mi island chains is unfeasible and unrealistic 0 Subunit A contains an abundant sand supply (as (because of the advanced stages of development (5 km), a floating or moored booster pump may seen by the well-developed dune system), al­ 1978). characteristic of many of the inlets), the restor­ need to be installed (Souder et al. Hopper though numerous washovers occur there. Sub­ ation measures will reduce the rate of further dredges have been employed successfully in units B and C are quite sand-deficient and the 0 deterioration, thus lengthening the projected life beach nourishment projects in New Jersey, islands are breaching and rapidly eroding. Po­ 1981), spans of the islands. Florida, and Virginia (Hobson and should tential restoration measures in Subunit A entail be evaluated for use in Louisiana. primarily sealing off the washovers, constructing By nourishing the beaches with compatible, 0 dunes across them, and applying fill material to coarse-grained sediments, a presently deficient narrow back-barrier areas. Subunits B and C, sediment supply can be revitalized and net ero­ much lower in elevation and more subject to sion rates offset. Although shoreline retreat will ' sheet washover, would require a more compre­ 0 Applications along Louisiana s not be stopped totally, erosion rates are ex­ hensive plan involving dune construction, back­ pected to decrease, thus prolonging the life of Barrier Shoreline barrier fill, and beach nourishment. To properly the islands. On barrier beaches, such as west of restore breached islands such as Breton and 0 Calcasieu Pass, shoreline retreat rates are anti­ In view of the overriding natural factors of Grand Gosier, a framework will need to be cipated to be stabilized (except for setbacks as a subsidence and associated shoreline retreat, res­ constructed in order to contain nourishment ma­ result of future hurricanes). toration measures should be restricted to those terial. This in turn will provide a base upon 0 deemed compatible with the dynamic nature of which to reconstruct the islands. the Louisiana coastline. The installation of Additional structural measures that may be con­ structed to reduce the loss of nourishment ma­ coastal defense structures such as seawalls, re­ Although restoration measures can be applied to terial (to tidal inlets or less critical downdrift 0 vetments, and rip-rap dikes is not only extremely the Chandeleur-Breton island chain, the question subunits) include sand-trapping jetties, groin costly but functionally unsound. While short­ of the economic feasibility of such restoration fields, or offshore breakwaters. However, de­ term benefits may be realized, the long-term must be considered. The islands lie 25 mi (40 tailed field study--examining wave conditions, 0 outlook includes subsidence and scouring of the km) offshore from the mainland, and it is un­ littoral transport, and tidal hydraulics--is imper­ structures, removal of valuable sand to the off­ likely that a restored Grand Gosier Island, for ative prior to recommendation of such measures. shore, and a potential development of a new example, will afford much more protection than Also, impacts of such measures upon downdrift shoreline inland of the protective structures. if left untouched. Several 5-mi (8 km) wide tidal 0 reaches plus costs of maintenance must be ser­ inlets would have to be artificially reduced in iously considered. The greatest hope of maintaining a healthy bar­ size to significantly constrict water exchange. rier shoreline lies in the application of sediment Even so, between the islands and the 0 nourishment. To reduce potential for island mainland could still generate erosive waves. In Based upon the characteristics and observed breaching (and consequent development of per­ view of the anticipated negative benefit-cost trends within the various subunits, a matrix manent tidal inlets) and minimize washover de­ ratios, no action is presently recommended, al­ ranking the severity of erosion and outlining velopment, sediment fill is needed to 1) seal though the possibility of pumping dredge spoil 0 potential methods of restoration was developed existing breaches and washovers, 2) construct from the Mississippi River-Gulf Outlet upon ad­ using several key variables (Table 2). These dunes to mesh with existing adjacent dunes, jacent islands instead of an offshore disposal 3) included loss of shoreline areas, total land loss fill back-barrier sand traps such as canals, area should be examined. D bayous, and ponds, 4) widen the back-barrier within the littoral zones, and extent of zone to a minimum island width of at least 650 development proximate to the shoreline. Fac­ ft (200 m), and 5) nourish the beach. Various tors accounting for relative wave energies (per Hydrologic Unit 2: Barataria ancillary measures should augment these techni­ hydrologic unit) were included, although hurri­ 0 ques, the most important being the planting of cane probabilities (based only on past occur­ Restorative measures are highly recommended vegetation as a stabilizing measure. Dune gras­ rences) were omitted. The chances of hurricanes along the Barataria shoreline because of direct ses should be planted to minimize erosion of the making landfall are considered to be uniform potential impacts upon developed areas as well constructed dune by wind and waves, and the across the state. In addition to the ranking of as upon the natural resource base. 0 back-barrier zone should be planted with marsh the subunits based on those criteria, subjective grasses and/or black mangroves to minimize judgments regarding potential restoration have In Subunits A and B, the beach is narrow and slumping and back bay erosion, as well as to trap been made. Specific recommendations are out­ sand-deficient and the marshes in the littoral D sands eroded from the dune. The installation of lined on Figure 25, and are discussed by hydro­ zone are exhibiting extremely high land loss sand fences along the dune will assist in the logic subunit in the following pages. rates. A feasible method of restoration here u

38 J

SBVKRli'Y RAJIKIIfQ MATRIX RBIIBDIAL IIBABDRP.S J ..._t_ TJI*ol Dewelopment5

Sediment SllaNUM SheiN Shcntroat Tot.l Bldat!JW Storm &.ell P,._cl Hydrolacie H,.._,lcJiie Bro.ian Deftlopnlent �ent Urbu- ooa:a. Belief! Land SheiN Wave Surp sediment N-uh- R•t.. Pilot � tc.5 1.-1 Unit Bublrit Name = {ft/Jr)l (mU.)S (mU.)6 t.-)5 � Drllllnc lleereatJmW Prot.dlan o::r B-.,T Helctltl Mean Rank!JW Dlvenion manti lllud10 Projeet

A North & Central Chandeleurs NW -33.0 23.0 0 1-9 0 0 0 0 7 2 u 7.6 8 0 0 0 0 1 B South Chandeleurs sw ·31.8 11.0 0 0 0 0 0 0 3 8 27 2 4 8.4 8 0 0 0 0

c Breton Island SW ..-70 .0 2.7 0 1-9 0 0 0 0 1 17 21 9.0 11 0 X X 0

A Sandy Point to Grand Bayou Pass w -21.8 12.5 0 10-49 0 l( 0 0 2 8 12 5.8 3 X X X 0 B Grand Bayou Pass to Chenlere RonqulUe E-W -29.1 9.1 0 0 0 X 0 0 11 9 27 10.8 Ul X X X 0 1!-W .11 10-49 X , c Grand Terre Islands -29.2 8.4 0 0 0 9 18 15 1 8 7.8 7 0 X X X D Orand Isle 1! +5,9 7.1 8.72 1,350 II 0 X II 24 27 1 Jl.8 21 0 0 0 0 1! Camlnade-Moreau Beach 1! -41.1 10.5 .OS ISO l( X X 0 12 5 5 5.8 4 0 X 0 0 p Pourchon Beach w -42 .3 3.0 .23 ISO X II X X 13 21 " 9.4 13 0 X 0 0

A East Tlmballer Wand w -54.8 8.8 4.4 50 l( X 0 X 8 3 9 5.! 1 0 X X 0 B Tlmballer Island w -24,5 8.7 .51 1-9 0 l( X X I 14 22 10.4 15 0 X X 0 c Wine Island w -- 0.1 0 0 0 0 0 0 4 ------·- 0 0 0 0

4 D Eastern Isles Dernleres B·W -41.9 10.7 0 10-49 II X X 0 10 • 13 5 3 7.0 5 0 X X X B Western Isles Dernlern w -35.2 8,9 0 0 0 0 0 0 s 12 27 10.4 Ul 0 X X II F Grand Bayou des llettn to Oyster Bayou w -12.8 17.8 0 1-9 0 X 0 0 14 13 18 10.8 18 0 0 0 0 G Point Au Per Island w •18.7' 17.3 0 1-9 0 X 0 0 18 1 20 10.2 IS 0 0 0 0

A Marsh Island (eut eout) Nl! -17.4 8.1 0 0 0 0 0 0 17 20 27 15.0 25 0 0 0 0 B Marsh Island (south eout) w -12.0 20.7 0 so 0 X 0 0 19 11 • 9.8 14 0 0 0 0 I c Rainey WUdllfe Sanctuary 1!-W -10.2 9.3 0 1-9 0 X 0 0 23 22 18 8 5 14.4 23 0 0 0 0 D Chenlere Au Tlsre Nl! -12.8 4.5 0 1-9 0 0 X 0 28 23 19 15.8 27 0 0 0 f) E BUI Rid(e w -10.7 3.8 0 10-49 X 0 0 0 25 25 14 15.0 24 0 0 0 0

A Freshwater Bayou Canal to Plat Lake w -18.8 15.7 0 10-49 l( X 0 0 18 10 10 8,4 • 0 0 0 0 l 8 Plat Lake to Mermentau-Gulf Nev. Channel " ·40.0 29.9 .04 100 0 X 0 0 15 1 7 3 1 5.4 2 f) 0 0 0 c Haekberry Beaeh w -21.2 7.3 0 10-49 0 X 0 0 20 19 1l 10.8 20 0 X 0 0

A Rutherford Beaeh to Caleaaleu Pass w -13.7 13.9 .59 850 X X X 0 22 15 3 9.2 12 0 0 0 0 B Caleaaieu Pasa to Long Beach w ·10.1 18.8 8.80 700 X X X X 21 18 2 9.0 10 0 X 0 X 2 � c West of Lone Beaeh w +3.7 8.1 0 300 X X 0 0 28 28 4 .. 12.8 22 0 0 0 0

D Sabine Mudfiats 1!-W -9.8 4.4 0 1-9 0 X 0 0 27 24 17 15.0 28 0 0 0 0

I dominant longshore sediment transport 8 shoreline erosion rate x shore length 2 average rate, 1955-1978 1 at shoreline, haaed uponsoutheast winds and refraction ot 12.5 It 3 cult shore only � baaed upon 100-year Roodalevat1o 111 1.55 (USACE 1970) 4 includes shore protection structures 9 Includes potential use of drec1p 'POll 10 x � within littMal zone as displayed on Plates 1-31 seal breaches, build dunes, back-barrier fW, and reveptate

Table 2. J

39 0 0 TEXAS LOUISIANA LOUISIANA MISSISSIPPI 0 0

LAFAYETTE 0 lE 0 0 ,

I / 0 / / VII 0

LEGEND 0

Seaward extent of exletlna maJor development Ill 0 Presently affected by Atchafalaya River sedimentation II 0 Recommended Restoration 0 �· .. l � LOUISIANA COASTAL ZONE LIMITS Diversion of fluvial sediments � ' . . HYDROLOGIC UNITS (H.U.) Beach nourishment / ·� [ .. v ..

Seal breaches, build up dune, fill back-barrier (widen If neceesary), and revegetate t N [ 0 25 50 - Sites of pilot proJects mllee 0 50 E3 I 0 .. 111 ... kllometere u Figure 2S. Recommended Restorative Measures Alorv the LoufsfanG Shoreline. 0 40 [ ]

would be the diversion of Mississippi River flow 26). Major breaches should be sealed and dunes Beach nourishment is also needed on Grand Isle and sediments into the marsh areas. This would, constructed. Where depths are already great, (Subunit D). The USACE has already developed in several years, create sufficient land area to introduced sand fill would be subject to removal a comprehensive plan for the island (USACE restore lost wetlands and cushion the impacts of by tidal currents, and rockfill may be necessary 1980). A thorough study of Caminada Pass needs J future severe storms. Perhaps two diversion to seal the breach before introduction of to be made, however, to determine its role in the sites could be installed downriver of Empire, the nourishment material. Numerous shore-parallel removal of alongshore-migrating sediments exact locations and outlined management areas pipeline canals dissect the islands and serve as eroded from the updrift Caminada-Moreau of which would be determined in detailed future sand traps. These canals, and other waterbodies shoreline. Q studies. Although a portion of the diverted immediately behind the shoreline, should be fluvial sediments may contribute to offset the filled and revegetated. In addition, the beaches Erosion of the Caminada-Moreau beach (Subunit beach sediment deficiency, it is recommended need to be nourished. (The two small islands on E) supplies sediments to downdrift Grand Isle, J that sediment fill be applied to breaches and the east side of Pass Abel may be past the point and it is recommended that this process be washovers, dunes be built up, and the beaches be of economically feasible salvage, although this allowed to continue. Although erosion rates are nourished. needs to be determined by field survey.) high, no significant development has taken place J in this subunit, and as the shore continues to In Subunit C, the eastern Grand Terre Islands and erode into the beach ridges in the littoral zone, a the islands near Cheniere Ronquille Point have Grand Terre itself is relatively healthy in com­ continued supply of sand to Grand Isle can be eroded at extremely high rates since 1955, and parison to the rest of the subunit, although expected. One feasible recommendation in this the adjacent tidal inlets have been widening shoreline erosion has been high near the flanking subunit is the sealing of one washover on correspondingly. It is highly recommended that tidal inlets. The beach should be nourished along Caminada spit, near the beach terminus of this area be designated a demonstration (pilot) the island, and a feasible sediment source may mmer's Road. This would reduce the amount of project and remedial measures be applied before lie in the spoil that is dredged from Barataria sediment lost to the back-barrier bay behind the the shoreline deteriorates much further (Figure Pass. spit.

Subunit F, the shoreline fronting Port Fourchon, has historically eroded rapidly and provided sedi­ .... ment supply to the Timbalier Islands. Since the extension of the Belle Pass jetties in the 1960s, erosion rates have been reduced significantly. However, development has occurred quite close to the Gulf shoreline, and beach sands are pre­ sently being washed into the treatment ponds adjacent to an oil-storage tank farm. Based upon historic trends, it would have been best if no development occurred in this area, and the headland were allowed to continue to erode. However, in view of the recent development of the industrial/recreational Port Fourchon, it may (or may not) be economically beneficial to erect a more permanent shore protection structure . · . (such as a dike along the south and east side of LEGEND - the zone of development). Careful consideration ·-· ------� must be given to this prospect, as not only would �-----..---...... ::or FILL l IIIVIGITATI (o.nel•) construction costs be high, but maintenance FILL RIVIOI!TATI a Uteck llerrler) costs would become prohibitive as the adjacent I lAND FILL shoreline erodes and Port Fourchon develops into ,. ROCK CLOIURI a peninsula. At present, it is recommended that

o t ••• to eo aooo ••oott ... FIAIIBILITY DITIRMINATION sediment fill be applied at the beach terminus of H ••• the Fourchon Road in the amount necessary to maintain the beach in its present position at that location. It may be feasible to utilize spoil Figure 26. Recommended Demonstration Project, Grand Terre Islands andVicinity. dredged from Belle Pass as beach nourishment material. J 41 J [

Hydr ologic Unit 4: Terrebonne-Timbalier between Cat Island Pass and Wine Island Pass are mum width of 650 ft (200 m), and build up the shallow, and if some kind of framework could be dune in potential washover areas (Figure 27). [ As in the Barataria hydrologic unit, continued constructed, fill (or dredge spoil) could be pump­ One abandoned oil company treatment pond lo­ erosion of the barrier islands and beaches in the ed in and a foundation for a new Wine Island cated on the island should be filled with sedi­ Terrebonne-Timbalier unit will have serious con­ established. ment, and the entire beach nourished. Consider­ able sand deposits in the ebb-tidal delta of Cat [ sequences not only upon shoreline areas but upon The Isles Dernieres (Subunits D and E) are in Island Pass and dredge spoil from the lower inland marshes as well. The extensive settle­ need of major restoration efforts. Eastern Isles Houma Navigation Channel are potential sources ment along the lower distributary ridges of Dernieres, precariously narrow along its eastern of fill material. In the western half of the Terrebonne Parish makes the impact of high land half, was breached in the mid-1970s and has not [ island, washovers should be closed off and water­ loss rates and shoreline erosion particularly rehealed. It is recommended that a demonstra­ bodies directly behind the beach filled with in­ serious. tion project be undertaken here to close the troduced material. breach, widen the back-barrier zone to a mini- [ Subunit A, extending from Belle Pass to the u· western end of East Timbalier Island, has eroded greatly following installation of the Bene Pass 0 jetty extension. Extensive canalization has oc­ curred here, and one canal developed into a tidal inlet, separating East Timbalier Island from the [ mainland. It is recommended that this inlet be sealed and a back barrier built up with intro­ �s r e s duced sediment. Beach nourishment should be provided, possibly by utilization of Belle Pass [ dredge spoil. On East Timbalier Island, it would be feasible to introduce fill material between the two parallel existing dikes that follow most [ of the length of the island. Sand nourishment introduced west of Belle Pass should migrate Menorove alongshore (provided the existing inlet is sealed) 0 and revitalize the beach fronting East Timbalier. Weter Exletlng Levee Timbalier Island (Subunit B) is eroding primarily c along its eastern half, where many washovers between relict beach ridges are found. Dune development should be encouraged in these loca­ height u ut.m•n 4 tions and beach nourishment provided. The cen­ 2o; 10A 4L�o ::::;,:=:;=00 ::::;,==00 :;:=::;reoo:::, tral and western portions of the island contain 2 •ddth (ft)4 several large canals in close proximity to the beach, and these should be filled to reduce SCHEMATIC CROSS-SECTION [ further erosion. Some effort at sealing off washovers has already been made in this subunit, and additional dune restoration measures should [ be taken in remaining washover locations. The feasibility of constructing a sand-trapping jetty at the western end of the island should be �PROPOSED ACTIONl A Build Dune Rnegetete [ examined. This measure would not only make l available a source of nourishment material, but D Becktlll RevegeUte would reduce the amount of shoaling in the lower [tBJ Houma Navigation Channel. Rock Fill [

Wine Island (Subunit C) has been reduced to a [ mere shoal, and restoration of the island would Figure21. Recommended Demonstration Project, Ea.stem Isles Demieres. prove quite costly. Nonetheless, water depths [ 42 [ 0 The sealing of washovers and back-barrier fill The shoreline from Flat Lake to Hackberry Works is presently planning renewed revetment also is feasible in Central Isles Dernieres, which Beach (Subunit B) is sub ject to great erosion, and T-groin construction. As a third demonstra­ 0 is eroding rapidly. Western Isles Dernieres, now although in view of the westward-migrating lo­ tion project in beach restoration, it is recom­ composed only of one srnall island, is presently cus of mudflat accretion, no remedial action is mended that a beach nourishment project be so isola ted that considerable costs are antici­ recommended at this time. As the shoreline implemented, not only to supplement the con­ D pated in the restoration of this island. These advances toward the leveed management areas struction of revetm ents and groins, but to min­ islands have historically afforded some measure of the Rockefeller Wildlife Refuge, the levees imize anticipated increased erosion to those of protection to the mainland coast north of may require reinforcement or relocation inland. beach communities (especially Constance Beach) Caillou Bay, and total removal of Western Isles Downdrift of the Mermentau-Gulf Navigation downdrift of the reveted shoreline (Figure 28). Dernieres will increase erosion along that coast. Channel jetties (Subunit C), erosion has accel­ Part of the required nourishment should be pro­ Restoration measures of washover sealing and erated because of the jetty construction. It is vided by redirecting the dredge spoil from back-barrier fill are feasible short-term mea­ recommended that material dredged from the Calcasieu Pass which is presently deposited in an sures, and the feasibility of a sand-trapping jetty channel be placed onto the beach or nearshore offshore dumping area. By depositing the dredge at the west end should be examined. zone west of the channel to reduce this recent spoil parallel to the shore in the shallow near­ increase in retreat rates. shore zone immediately west of the Calcasieu 0 The mainland shore of Caillou Bay as far west as Pass jetties, the coarser material will be retain­ Oyster Bayou (Subunit F) is presently not criti­ ed on the beach and enter the westward long­ cal, and no recommendations can be made pre­ shore transport system. Additional beach fill sently. Subunit G, extending from Oyster Bayou Hydrologic Unit 8: Calcasieu-Sabine I should be dredged from offshore where abundant 0 to Point au Fer, currently is receiving some sand deposits are known to occur {BLM 1979). A sediment input from the Atchafalaya River (via Shoreline erosion in the Calcasieu-Sabine hydro­ long-term beach restoration project might in­ Fourleague Bay), and high, localized, shoreline logic unit, while not as high as rates within the clude the installation of a series of sand-trapping 0 retreat rates are expected to be at least partly Deltaic Plain, may have more serious conse­ groins (to be constructed from west to east, offset by increased sedimentation. quences in view of the extensive beachfront beginning downdrift of Long Beach), although a development, particularly west of Calcasieu more detailed feasibility study should be con­ 0 Pass. ducted prior to recommendation. Hydrologic Unit 6: Vermilion

0 The Vermilion hydrologic unit exhibits compar­ Subunit A, between the natural mouth of the atively low shoreline erosion rates, and no Mermentau River and Calcasieu Pass, is fronted restoration measures are presently largely by mudflats and exhibits relatively low 0 recommended. A large proportion of the shore­ shoreline retreat rates. The only serious erosion line in this unit (most of Marsh Island) is has occurred at the resort community of Ruther­ protected by shell reefs, and it is important that ford Beach. Erosion has occurred primarily in this natural protection not be removed by shell­ response to a deflection of the Mermentau River 0 dredging operations. Active sedimentation from mouth by the westward-accreting Hackberry the A tchafalaya River also is expected to in­ spit. Since construction of the Mermentau-Gulf crease and help alleviate erosion by further Navigation Channel in the early 1970s, much of o·· reducing wave energies in this hydrologic unit. the outflow of the river has been diverted, and the natural mouth has shoaled accordingly. Ero­ ' ,.. . sion rates should decrease at Rutherford Beach .,.,. N because of the diversion, and no remedial mea­ Hydr ologic Unit 7: Mermentau .t 0 sures are recommended at this time. The eastern half of the Mermentau hdyrologic Figure 28. Recommended Demonstration Pro­ unit shoreline (Subunit A) is receiving active ject, Holly Beach and Vicinity. 0 Atchafalaya River sedimentation in the form of Between Calcasieu Pass and Long Beach (Subunit accreting mudflats, and shoreline erosion rates B) lies a zone of extensive recreational develop­ are comparatively low. The zone of mudflat ment. From Holly Beach to Peveto Beach, La. accretion has shifted westward during the last 20 Hwy 82 hugs the shoreline. This important east­ years, from the Cheniere au Tigre vicinity to west artery and hurricane evacuation route is near Flat Lake (Wells and Kemp 1981), and it is being undermined by wave attack and is fre­ Subunits C and D, from West of Long Beach to expected that this westward migration will con­ quently overtopped during storms. Existing re­ the Sabine Pass jetties, do not exhibit serious tinue as the Atchafalaya River and Wax Lake vetments have not adequately withstood the for­ erosion problems, and no remedial measures are Outlet deltas develop further. ces of nature, and the Louisiana Office of Public recom mended at present.

43 0 0 0 0 0 0 0 0 0 0 0 0 n 0 0 0 0 0 0 J

,..

J Chapter VI

Conclusions 0 Shoreline erosion and wetland deterioration in coastal Louisiana are driven by three major, related processes: subsidence, redistribution of Westem end of Timbalier Island. 0 sediments by waves and currents, and saltwater intrusion. Now, as in the past, these processes are the dominant force in changing the coastal zone when and where severed from the 0 changes that reflect primarily responses to sub­ natural process will be the most cost-effective Mississippi River's supply of fresh water and sidence and wave erosion. In addition, these approach to management of the barrier systems. sediment. However, while this condition has At the same time, physical integrity of the always prevailed in part of the deltaic plain changes are accelerated through various activi­ of man which affect the movement of water retreating system must be maintained by mini­ 0 (since even under natural conditions the ties mizing loss of sediments from natural or man­ Mississippi River supported full development of and sediment. These changes entail increasing salinities, loss of wetlands commensurate made causes. It is within this framework that only a single delta lobe), the observable and and management measures are recommended in 0 perceivable changes presently occurring greatly areal gain of major water bodies, rising water levels, and rapid erosion of the Gulf shore. order to achieve a continuing protective function exceed those of the past in rate and extent. and a deceleration of shoreline erosion and retreat. 0 The physical integrity of Louisiana's wetlands is The continuing decline in the physical integrity dependent on Mississippi River water and sedi­ of the coastal zone gives ever greater impor­ ment. In his economic endeavor man has chosen tance to the barrier beaches and islands that Development and implementation of a shoreline to apply more than two thirds of the Mississippi form the seaward boundary of the coastal zone. protection plan should be an integral part of a 0 River resource to causes other than coastal zone This importance derives from their protective long-term coastal management effort. Such an maintenance. Remaining water and sediments function with regard to both human life and effort must recognize that, while further loss of distributed through the Atchafalaya River have property and the renewable resources repre­ coastal wetlands is unavoidable and future 0 therefore become even more valuable to the sented by the remaining estuarine wetlands. It is changes will necessitate either retreat of natural system. But without a commitment for for that reason that the present report makes development from the coastal zone or their use toward wetland restoration and delta recommendations for the implementation of a increasingly greater levels of protection, the 0 growth, that option is being similarly reduced as shoreline management and protection plan. maintenance and protection of the coastal zone a result of present and future development and can in part be achieved through natural related needs for flood control and navigation. The basis of such a plan must be the recognition processes. This would involve maximum feasible Further leveeing of the Lower A tchafalaya River that subsidence cannot be halted and that the diversion of Mississippi River freshwater and should be avoided so that maximum land building sediments composing the barrier islands and sediment, and full utilization of Atchafalaya and wetland nourishment can occur in this area. beaches are a finite resource. Under those River fiow and sediment without further levee conditions, to maintain a barrier system on a construction. It is by integrating shoreline 0 As a consequence of these present limitations on seaward sloping surface requires shoreward management and protection with these measures the total Mississippi River resource application, migration as illustrated by the present barrier that the greatest long-term benefits can be nearly the entire coastal zone is now subject to islands. Recognition of and abidance by this achieved. 0 45 0 0

References Bureau of Land Management (BLM) 0 1979 Map of Bottom Sediments, Vegetation, and Endange red Wildlife. U.S. Department of Interior, BLM Outer Continental Shelf Office, New Orleans. Adams, R. Byrne, J. V., D. 0. LeRoy, and '?· M. Riley 0 . . .. 1970 Effects of Hurricane Camille and Laurie on the Barataria Bay . 1959 The Chenier Plam and 1ts Stratigraphy, Southwestern Lomstana. Louisiana State University,Coastal Studies Institute, Coastal Studies Bulletin Transactions, Gulf Coast Association of Geologi cal Societies 9:237-260. 4:47-52. 0 Coastal Environments, Inc. (CEI) Adams, R. D., B. B. Barrett, J. H. Blackman, B. W. Gane, and W. G. Mcintyre 1977 A Jetty from Point Chevreuil: An Evaluation of a Proposal to Reduce 1976 Barataria Basin Geological Processes and Framework. Louisiana State Sedimentation in the Cote Blanche Bays and Vermilion Bay. Prepared for 0 University,Center for Wetland Resources, Technical Repo rt 8. Louisiana Department of Culture, Recreation and Tourism, Baton Rouge.

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Baumann, R. H. Dean, R. G. 1980 Mechanisms of Maintaining Marsh Elevation in a Subsiding Environment. M.S. 1974 Compatibility of Borrow Material for Beach Fills. Pages 1319-1333 in Thesis, Department of Geography and Anthropology, Louisiana State Proceedings, 14th Coastal Engineering Conference. University, Baton Rouge. 0 Delaune, R. D., W. H. Patrick, Jr., and R. J. Buresh 1978 Sedimentation Rates Determined by 137Cs Dating in a Rapidly Accreting Salt 1981 Personal Communication, November 30, 1981, Center for Wetland Resources, Marsh. Nature 275:532-533. u Louisiana State University, Baton Rouge. Dement, Lawrence Beall, A. 0., Jr. 1977 Two New Methods of Erosion Protection for Louisiana. Shore and Beach 0 1968 Sedimentary Processes Operative Along the Western Louisiana Shoreline. 45(1): 31-38. Journal of Sedimentary Petrology 38(3):869-877. Erickson, R. C. 0 Becker, R. E. 1976 Subsidence Control and Urban Oil Production--A Case History, Beverly Hills 1972 Wave Energy Studies Along the Louisiana Coast. J.. ouisiana State University, (East) Oil Field, California. Proceedings of the Anaheim Symposium, Center for Wetland Resources, Hyd rologi c and Geologi c Studies of Coastal International Association of Hydrological Sciences 121. Louisiana 12. 0 Everts, c. H. Boyd, R. and s. Penland 1980 Human Influence on the Sediment Budget of a Barrier Island. Proceedings of 1981 Washover of Deltaic Barriers on the Louisiana Coast. Transactions, Gulf the Second Symposium on Coastal and Ocean Management. Coastal Zone 80 0 Coast Association of Geological Societies 31. 11:863-880. Broussard, R. Fisk, H. N. 0 1981 Personal communication, December 2, 1981, U.S. Army Corps of Engineers, 1955 Sand Facies of Recent Mississippi Delta Deposits. Pages 377-398 in 4th Waterways Experiment Section, New Orleans. World Petroleum Congress, Rome Proceedings, Section 1-C.

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Kahn, J. H. Myers, H. B. and A. R. Theis 1980 The Role of Hurricanes in the Long-Term Degradation of a Barrier Island 1956 Beach Erosion Control, Grand Isle, Louisiana. Shore and Beach 24:19-23. Chain: Chandeleur Islands, Louisiana. M.S. Thesis, Department of Marine Science, Louisiana State University, Baton Rouge. National Aeronautics and Space Administration 1978 Flight request 0754, uncontrolled prints at 1:24,000, October 8, 9, 10, 15, Kolb, C. R. and J. R. van Lopik 1978. Flights 78-143, 78-144, 78-145, 78-148. U.S. Environmental Protection 1958 Geology of the Mississippi Deltaic Plain, Southeastern Louisiana. U.S. Army Agency, Remote Sensing Operations Branch, Remote Sensing Division, Engineer Waterways Experiment Station, Vicksburg. 120 pp. Environmental Monitoring and Support Laboratory, Las Vegas. 0 47 0 0

Saucier, R. T., C. C. Calhoun, Jr., R. M. Engler, T. R. Patin, and H. K. Smith 1978 Executive Overview and Detailed Summary. U.S. Army Engineer Waterways Neumann, c. J., G. W. Cry, E. L. Caso, and B. R. Jarvi men Experiment Station, Dredged Material Research Program, Vicksburg. 0 1978 Tropical Cyclones of the North Atlantic Ocean 1871-1977. National Oceanic Technical Report DS-78-22. and Atmospheric Admin istration, National Climatic Center, Asheville. Scholl, D. W ., F. C. Craighead, and M. Stuiver 0 Nummedal, D., s. Penland, R. Gerdes, W. Schramm, J. Kahn, and J:I· Roberts . 1969 Florida Submergence Curve Revised: Its Relation to Coastal Sedimentation 1980 Geologic Responses to Hurricane Impact on Low Profile Gulf Coast Barriers. Rates. Science 163:562-564. Transactions, Gulf Coast Association of Geological Societies 30:183-195. 0 Schoonbeck, J. B. Olsen, E. J. 1976 Land Subsidence as a Result of Gas Extraction in Gromingen, The 1982 South Plantation Beach Improvement Project. Shore and Beach Netherlands. Proceedings of the Anaheim Symposium, International 49(1):6-10. Association of Hydrological Sciences, Publication 121.

Orton, E. W. Simpson, R. H. and H. Riehl 1959 A Geological Study of Marsh Island, Iberia Parish, Louisiana. Louisiana 1981 The Hurricane and Its Impact. Louisiana State University Press, Baton of Wildlife Department and Fisheries, Technical Report, New Orleans. 28 I?P· Rouge. Otvos, E. G., Jr. Sothern, J. M. 0 1970 Develpment and Migration of Barrier Islam�, Northern Gulf of Mexico. 1980 Last Island. Cheri Publications, Houma, Louisiana. Bulletin Geological Society of America 81:241-246. Suhayda, J. N. Penland, S. and R. Boyd 1976 Wave Action Offshore of Barataria Basin. In Barataria Basin: Hydrolo�cal 0 1981 Shoreline Changes on the Louisiana Barrier Coast. '81: 209-219. and Climatologic Processes. Louisiana State University , Center for We and Resources, Baton Rouge. Technical Report LSU-T-7 6010. , D. Nummedal, and H. Roberts --1,..,9,..,8,..,1�Deltaic Barrier Development on the Louisiana Coast. Transactions, Gulf 0 Coast Association of Geologic al Societies 31. 1982 Personal communication, January 1982, Department of Civil Engineering, Louisiana State University, Baton Rouge. Penland, s. and Ritchie, W. 0 1979 Short-term Morphological Changes Along the Caminada-Moreau Coast, Swanson, R. L. and C. I. Thurlow Louisiana. Transactions, Gulf Coast Association of Geological Societies 1973 Recent Subsidence Rates Along the Texas and Louisiana as 29:342-346. Determined from Tide Measurements. Journal of Geophysical Research u 78:2665-2671. Petroleum Information Corporation (PIC) 1955- Ammann black and white controlled mosaics at 1:24,000. San Antonio. Theis, A. R. 1956 0 1969 Beach Erosion Problems at Grand Isle, Louisiana. Shore and Beach 37(1):19-22. Peyronnin, c. A., Jr. 1962 Erosion of Isles Dernieres and Timbalier Island:;. American Society of Civil Tobin Research, Inc. 0 Engineers, Journal, Waterwaysand Harbors Division 88 (W WI):57-69. 1955- Black and White Controlled Mosaics at 1:24,000. San Antonio. 1956 Price, W. A. and R. H. Parker 0 1979 Origins of Permanent Inlets Separating Barrier Islands and lnfluenc� of Todd, T. W. Valleys on Tidal Records Along Texas Gulf Coast. American Drowned 1968 Dynamic Diversion: Influence of Longshore Current-Tidal Flow Interaction on Geologists Bulletin 63(9):1610. Association of Petroleum Chenier and Barrier Island Plains. Journal of Sedimentary Petrology 0 38:734-746. Richardson, T. W. Dredging Systems for Beach Nourishment from Offshore Sources. Report 1 1976 Treadwell, R. c. Techniques. U.S. Army Engineer Waterways of Beach Nourishment 1955 Sedimentation and Ecologyof Southeast Coast of Louisiana. Coastal Studies 0 Experiment Station, Vicksburg. Technical Report H-76-13. Institute, Office of Naval Research, Technical Report 6. 78 pp.

Russell, R. J. U.S. Army Corps of Engineers (USACE) 1936 Physiography of the Lower Mississippi Delta. Louisiana Geological Survey 1961 Belle Pass to Raccoon Point, Louisiana, Beach Erosion Control Study. House Bulletin 8:3-199. document #338, 87th Congress, 2nd Session, pp. 1-31, i- x, Plates 1-6.

48 1970 Type 5 Flood Insurance Study, Louisiana Gulf Coast. Prepared for Federal Insurance Administration, New Orleans District.

1972 Grand Isle and Vicinit� Beach Erosion Hurricane Protection. New Orleans District, Revie w Re por • 68pp.

1975 Com osite Environmental Statement for 0 eration and Maintenance Dred�ing of Four Projects Located South o the GIWW in Terrebonne Parish, Louistana. New Orleans District.

0 1976 Draft Environmental Impact Statement, Calcasieu River and Pass, Coon Island, Devil's Elbow, Calcasieu River Basin, Louisiana. New Orleans Q District.

1977 Shore Protection Manual. Coastal Engineering Research Center, U.S. Government Printing Office, Washington, D. C. 3rd edition, vols. I, II, 0 III.

0 1980 Grand Isle and Vicinity, Louisiana: Beach Erosion and Hurricane Protection. New Orleans District.

van Beek, J. L. and K. J. Meyer-Arendt 0 1981 Sediment - Asset or Liability. Pages 197-215 in Proceedings of the National Symposium on Freshwater Inflow to (R. D. Cross and D. L. Q Williams, eds.). Vol. 2. Walsh, M. R. 1977 Dredged Material as a Natural Resource. American Society of Civil Q Engineers, Journal of Waterways, Ports, Coastal and Ocean Division: 309-319. Walton, T. L., Jr. and R. G. Dean 1976 Uses of Outer Bars of Inlets as Sources of Beach Nourishment Material. 0 Shore and Beach 44(2):13-19.

1 Wells, J. T. and G. P. Kemp 1981 Atchafalaya Mud Stream and Recent Mudflat Progradation: Louisiana Chenier Plain. Transactions, Gulf Coast Association of Geological Societies 31:409-416. 0

Wright, L. D., F. J. Seige, and J. M. Coleman 1970 The Effects of Hurricane Camille on the Landscape of the Breton-Chandeleur Island Chain and Eastern Portion of the Lower Mississipi Delta. Louisiana State University, Center for Wetland Resources, Coastal Studies Institute Report 76.

0 49 a Appendix 0 0 TEXAS LOUISIANA LOUISIANA MISSISSIPPI 0 0 LAFAYETTE i 1)

.. 0 0

I 0 0 v 0 Ill D 1. JOHNSONS BAYOU 11. OBAHD BAYOU DU LAilOI/BAYOU ORAND CAILLOU II 2. PBVBTO BRACH 1'1. WIIIITDN AHD CBMTRAL I8LBIDBRJOBRBS :s. HOLLY BBACH/CALCASIBU PASS 11. BA8TIIRN ISLBS IIIRBSDBRN 4. CAMBRON RAST TOROTHBRFOBD BBACH 111. CAT ISLAND PASS(WINB IBLAND) 0 5. LOWBR MBRMBMTAU RIVBR/800 BAYOU 20. 'l1MBALIBR ISLAND 6. ROCKBPBLLBR WlLDLIPH RBPUOB 11. BAST1WBAL1BR ISLAND TOBBLLB PASS 7. IIILLBR LAKB BIG CONSTAMCB BAYOU II, PORT POURCHOif/CAMINADA BBACB �·· TO •\ LOUISIANA COASTAL ZONE LIMITS 8. PLAT LAKBIROLLOVBR BAYOU IS. CHBNIBRB CAMINADA/GRAMD ISLB l 0 PllBSHWATBR BAYOU CABAL ORAND TBRRB CH.BNIBRB ROifQUILLB II. M. TO • :15. : • 10. CHBNIBRB AU 'l1GRB CH.BNIBRB ROMQUILLII TO SHBLLI8LAifD : HYDROLOGIC UNITS (H.U.) • �• 11. SOUTHWBST PASS II. OULP-BIIPIRB WATBRWAY TO IAifDY POINT • v • MOUND POINT BRBTON ISLAND 0 12. :17. 13. LAKB POIMT II. ORAlfD 008IBRISLAJm8 14. POINT AU PBR Ill, ITAKB I8LAifD8 15. OYSTBR BAYOU/PBLICAN ISLAND 10. CBMTRAL CBANDBLBUR I8LAJID8 0 III 10 11. NORTH CRANDBLBUR I8LAND8 0 ao ...... •• •�o�ne•- u Index to Plates u 0 0

.. -·

1955

e

I 0 I Match Ll•• A I

1978 0 0 0 0

\ -· 0 I j....__ \ . 101151078 Legend I 2 B.. s 1 WATERBOOIES (natural) 4 0 � 2 WATERBODIES (man-made) \ 3 5 MANGROVE (1978 only) 8 4 SPOIL DEPOSITS I 5 INTERTIDAL FLATS 0 7 I c:==J·�·'·' a BEACH 1:50,000 lliJIOiU 7 DEVELOPMENT 8II e MARSH/BEACH RIOGE VEGETATION 0 10 � II

.,. 0

1955 0 8 0

-· 8

6 I 0 0 0 0 8 0 0 7 W41' 8 I D 0 ==::: 18781 55 Legend 2 PiCBIIIiiiiiiie: • i 1 WATERBODIES (natural) II 2 WATERBODIES (man-made) i MANGROVE (1978 only) j ______. e •• 3• SPOIL DEPOSITS 7 TIIImmlllllllllllliiL______· ---� r------. 1:50,000 •• 5 INTERTIDAL FLATS ti10.1 0 • r:••••••••••••••••••••• •• Ill••• - __ :::J...... 8 BEACH l 7 DEVELOPMENT d F---i ------�__ __. 0 2 km ii!IIJiiillllllllllll__ 8 MARSH/BEACH RIDGE VEGETATION "'"S: :E3ACEAD A3:EIA ::::E::==:==3 10�• fiii 8d DRAINED MARSH e UPLAND FOREST 0 250 500 710 1000 12110 1500 1750 10 CROP AGRICULTURE AREA lacra•) PLATB 2. PBVBTO BBACH 0 � 0 27'*1' Wll' -· 1955 0 W47'30' @-1 �1

8 0 I 1 �� 8 �·� 8 \I ?"� J? I r1f I ' , � ' ' ..01 ' l' I tf \$'�� �� c!f �� , ' �� 4J �1 {51 ' r 4 8 �c:Pk I 8 � II 8 0 ' 7� Mole�r �lne 8

1978

2P47'30"

0 0 Q 0 Legend 0 1 WATERBODIES (natural) 2 WATERBODIES (man-made) MANGROVE (1978 only) ]nn.o .o3 SPOIL DEPOSITS 5 INTERTIDAL FLATS 1:50,000 8 BEACH o 1 2 ml e� =�������� ����s 1 DEVELOPMENT 0 08eceSQH�H�H�======32 km 8 MARSH/BEACH RIDGE VEGETATION 8d DRAINED MARSH

e UPLAND FOREST 0 250 500 750 1000 1250 1500 1150 2000 10 CROP AGRICULTURE 0 AREA (acr ..) PLATE 3. HOLLY BEACH/C ALCASIEU PASS 0 0 [

tJ-,o• [

1955 [ �Match Ltnec [ I I [ 0 [ H.U. e � H.U. 7

1978 [

...,-,o·

• • 1955 2 [ il Legend .. .. 1 WATERBODIES (natural) [ •.- 2 WATERBODIES (man-made) e \ 3 MANGROVE (1978 only) 7 I 4 SPOIL DEPOSITS 1:50,000 • ,l!llllllllllllllli!!ill!llllllllllllili'illl!illl!iliiiiiii'I!IIIIIIIIIIIIIIBIIIIIIIII.IIII!illillllll81llll"m;:;'Utt.t ' .. s INTERTIDAL FLATS 0 2 ml lli!ii ,.., & BEACH 0 2 km 1.7.f 1 DEVELOPMENT HWWH w e MARSH/BEACH RIDGE VEGETATION 710 � 8d DRAINED MARSH 1 UPLAND FOREST 0 zeo aoo 750 1000 1250 1500 1710 2000 10 CROP AGRICULTURE ARIA Cecr .. )

PLATE 4. CAMERON EAST TO RUTHERFORD BEACH [ J

01' -·

' 1955 ' � ' e 1 ' ' ' ' ' ' ' 8 � ' 1 ' ' _... ' 0 0 0

0 8 0 0

0 1955 Shoreline -191978511 Legend 2 1 WATERBODIES {natural) 2 WATERBOOIES {man-made)

\ 3 MANGROVE (1978 only) 5 4 SPOIL DEPOSITS 1:50,000 d 0 1 2 5 INTERTIDAL FLATS 0 ml •1 s� ==�������� ����� .. 154.1 11 BEACH • a!. �'"'· 0eeoeeoe�e�e�;;;;:=;;32 km a' 1 DEVELOPMENT 0 8d e MARSH/BEACH RIDGE VEGETATION � 8d DRAINED MARSH

9 UPLAND FOREST 0 250 500 750 1000 1250 1500 1750 2000 10 CROP AGRICULTURE AREA(acr .. ) 0

PLATE 5. LOWER MERMENTAU RNER/HOG BAYOU 0

II' -· 0 0 0

8 0 0 0 0 1-,jf::, 8 0 8 0

8 6 0 :1 0 1955 Shoreline 0 r------,·------1855 Legend -11178 2 1 WATERBODIES (natural) 0 ... 2 WATERBODJES (man-made) \ 4 •.• 3 MANGROVE (1978 only)

1:50,000 4 SPOil DEPOSITS

5 INTERTIDAL. FlATS 0

6 BEACH

7 DEVElOPMENT 8 MARSH/BEACH RIDGE VEGETATION 0 8d DRAINED MARSH

9 UPlAND FOREST 0 250 500 750 1000 1250 1500 1750 2000 CROP AGRICUlTURE AREA l•cr.. ) 10 0

PLATE 8. ROCKEFELLER WILDLIFE REFUGE 0 0 J

J ... -· .... ., ...

J ��� ., 1 J '11 � ..... 8

� I e I �� 0 I I I I 6 8 � J I ' ·� s s '-.. Matt._ Lk'leF J I I I I I I J � e �1 �, I � �� I �1 e � �� .... I I

5 ______8 ..../ J�L_s ' Match Li111af

.__._ 1955 1Shoreline J Legend 1 WATERBODIES (natural) \ z WATERBODIES (man-made) J MANGROVE (1978 only) 1:50,000 43 SPOIL DEPOSITS 0 1 2 ml s INTERTIDAL F1.ATS ce ==== �� �==� � �� ======� 6 BEACH J 7 DEVELOPMENT 8 MARSH/BEACH RIDGE VEGETATION 8d DRAINED MARSH 0 250 100 710 1000 1210 1100 1710 2000 t UPLAND FOREST J AREA (ec:rH) 10 CROP AGRICULTURE D PLATB 1. MILLER LAKE TO BIG COHSTAHCE BAYOU J J (

.. -· .... [

1\}o �� 6-1 1955 <0510..� It [ ���� t� "'-,.;# , . 8 8 .._,__,. [ ill' :IS' 8 (

II

1978

I u , , , , I I I

,�' I 8 I I I I

I I I I I Mat�h llneG

Legend [

r------��·------1851 1 WATERBODIES (natural) 1171 \ 2 WATERBODIES (man-made) [ 3 MANGROVE (1978 only)

• SPOIL DEPOSITS

5 INTERTIDAL FLATS a BEACH 0 km 7 DEVELOPMENT 0ss�e�H�H�H��======32 1 l.l ...... 8 MARSH/BEACH RIDGE VEGETATION 8d DRAINED MARSH 0 250 100 710 1000 1250 1100 1710 2000 o UPLAND FOREST

AIIIIA (acr.. ) 10 CROP AGRICULTURE u

PLATE 8. FLAT LAKB/ROLLOVBR BAYOU

0 •• -· tr'IO'

• I 8 ---- I­ \27 1955 I • I I I I • I 8 I 8 I I I I ' I 't:::!:;��=d��=s------��c=��=r====�������====�==�======�· 5 ��-===����------__j i --�}____ � ... ,.� u ..... I 5 K.U.? �K.U.el: I � I I \��� 0

1978 0 I 8

It ...... I 0 I I I I 4 4 I 8 0 I I I I I 2 8 I 0 I 1955 Shoreline 0

�---- 1.55 ---- 1·78 0 Legend

1 WA TERBODIES (natural) 5 2 WATERBODIES (man-made) 0 \ a·' 3 MANGROVE (1978 only) • 4 SPOIL DEPOSITS 1:50,000 s INTERTIDAL FLATS o 1 2 ml 0 &� �������� ����� 1 BEACH 0es�scse�w�wcs=:=::=:=a2 km 7 DEVELOPMENT ]; MARSH/BEACH RIDGE VEGETATION e 8d DRAINED MARSH o 250 5oo 750 1000 1250 1500 1750 2000 0 t UPLAND FOREST 10 CROP AGRICULTURE

PLATB 9. FRBSHWATBR BAYOU CANAL 0 0 0

17'JO. 10' 0 1955 0 I I / I I / I I 0 / I , I / I I 8 / 0 / 8 ' / 0 5 0

1978 0

I 0 8 I I I I I I 0 I I I I I 0 I I I I ·�I 0 Mele� llneK I I Legend 0

1 WATERBOD IES (natural) 2 WATERBODIES (man-made) 0 3 MANGR OVE (1978 only) I " SPOIL DEPOSITS s INTERTIDAL FLATS

e 0 )170t.t BEACH y.... .2 7 DEVELOPMENT 8 MARSH/BEACH RIDGE VEGETATION Bd DRAINED MARSH 0 9 UPLAND FOREST 1000 12150 1&00 17150 2000 10 CROP AGRICULTURE 0 PLATB 10. CHBHIBRB AU TIGRB 0 0 J

J •• -· .... ". ., ...

J 1955 J

• •

• \ \ \

e

; ' I I • I �/ \ \\ 1955 Shoreline • \ \ Wtl.. . \

Legend

' WATERBODIES (natural) Metch LlneL-.1 2 WATERBODIES (man•mlde) MANGROVE (1878 only) 4 43 SPOIL DEPOSITS ' 5 INTERTIDAL FLATS \ 7 BEACH e

1:50,000 7 DEVELOPMENT • ...... I IIIIII.IIBIIIIIIIIIBIIIIIIIIIIIIIIIIIII.IIIIIIIIIIIIIIIIII·IIIIII·IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII.JL•rn.;:;--_jl••"·• a MARSH/BEACH AtDGE VEGETATION • ...,. 0�=e��=e�BKF3F3E3F3 HM= 1���======s2 M ld DRAINED MARSH UPLAND FOREST 0 210 100 710 1000 1UO 1100 1710 2000 e CROP AGRICUl.TURE AIIIA (act.. ) 10

PLATE 11. SOUTHWEST PASS 0

17 ...... 10' 41 ... 0 I I I I I 1955 [ I I I I 8 I I 8 [ I I I I I ( I I I 0 0 0 1978 \ \ 0 \ \ \ _M•tch Lln•M \ \ 0 0

I I t--M•Ich LlneL u I 1955 Shoreline [

Legend 1 WATERBODIES (natural) [ \ 2 2 WATERBODIES (man-made) .. 3 MANGROVE (1978 only) SPOIL DEPOSITS 1:50,000 • • [ 5 INTERTIDAL FLATS 7 t1 BEACH 8 ,.,.,.,�---.�l•ou.r 7 DEVELOPMENT , .... t1 MARSH/BEACH RIDGE VEGETATION 0 0 210 100 750 1000 1280 1500 1780 2000 Bd DRAINED MARSH AREA (ecree) e UPLAND FOREST 10 CROP AGRICULTURE u PLATE 12. MOUND POINT D [ 0

0 ., ... tt•.a·

0 1955

8 0 g., 0 0

.... 0 0 0 1978 8 0 Q., 0

I 0 �1955 Shoreline wa.· 0 0 Legend 1 WAT�RBODIES (natural)

r------�------1ess 2 WATERBODIES (man-made) ----1e1a 3 MANGROVE (1978 only)

0 4 SPOIL DEPOSITS s INTERTIDAL FLATS 6 BEACH 1:50,000 0 / 1 DEVELOPMENT e MARSH/BEACH RIDGE VEGETATION soo no 1ooo uso 8d DRAINED MARSH 2km o UPLAND FOREST 0 8::eEA CEA:O AB.:13H ::::E::::======0 250 AREA (•cr.. ) 1600 1750 2000 II 10 CROP AGRICULTURE

0 PLAT8 13. LAKE POINT 0

· - 0

17'111• II'ID" 0 I I 1955 �� 0 I I 8 I I I I 0 0

Match Lrn•N

& 0

8 0 II

I 0 1978 � I 20' 8' � I 0 �� 8 I I I I Q_ I 0 ��31 8 8 � 0 Match Ll.,eN

1955 Shoreline 0

Legend

1 WATERBODIES (natural) 0 rE------��;------1955 2 WATERBODIES (man-made) 3 MANGROVE (1978 only)

4 SPOIL DEPOSITS INTERTIDAL FLATS 0 1:50,000 5 BEACH 0 1 2 mi : ::;=�-� ,.,. 6 ��==��=- 1 DEVELOPMENT a MARSH/BEACH RIDGE VEGETATION 0 DRAINED MARSH t£ 4@�!¥f§W¥*¥ 8d 9 UPLAND FOREST

10 CROP AGRICULTURE 0 250 500 750 AREA1000 (ecre•) 1250 1500 1750 2000 0 PLATE 14. POINT AU FER 0 0 J

J 10' 07'1D• ti'OI' ana·

W12'1D" J 1955 I I M•tc• l ...... I I I J I I I ) I , I I 1 I � I � I 8 � IS

6 I J I �: I I I 'I I I

J WI2'1D• 1978

I ,..,_._MitCh LineN I I I I I I I I I I I I I 6 1955 Shoreline 0

Legend

\ @'14>---� 1 WATERBODIES (natural) \ �= #jiffiW@@$ t :�: 2 WATERBOOIES (man-made) ' 2 0 ... 0 3 MANGROVE (1978 only) 1:50,000 � SPOIL DEPOSITS J 2 mi s INTERTIDAL FLATS

fi BEACH 0 1 2 km : � EL.I::.i..I::::I 7 7 DEVELOPMENT ...E!:::EEi:L-=-=:::E:;::;======3 0 . r ------,�----� ------.-• ."i"T"Juu ' 8 MARSH/BEACH RIDGE VEGETATION 8 �ifM#&MlWWW#lfWMWm mm • >t1fi%¥Wi®&&¥&1t' �lJD'i Bd DRAINED MARSH r I I I I I I I 1 0 2150 500 750 tOOO 1250 1500 1750 2000 9 UPLAND FOREST AREA (ecr .. ) 10 CROP AGRICULTURE

PLATE 15. OYSTER BAYOU/PEUCAH ISLAND 0

•••oo' 110'57'30" 56' 0

1955

.A ' ·� \ \' - ' 0 ' ' ' ' \ ' \ ' \

0 1978 8

• , .. Match l..•n•O

Shoreline [

Legend 1 WATERBODIES (natural) [ 2 WATERBODIES (man-madel 2 3 MANGROVE (1978 onlyl 4 4 SPOIL DEPOSITS \ 5 INTERTIDAL FLATS s 6 BEACH 1:50,000 6 • 7 7 DEVELOPMENT 7 •• 2 ml a MARSH/BEACH RIDGE VEGETATION 8 3" Bd DRAINED MARSH km 0 1' 2 9 UPLAND FOREST 8::e:::E HCEH:O HS::::SH::::i=::::======::3 0 250 500 750 1000 1250 1500 1750 2000 CROP AGRICULTURE AREA (acreal 10

PLATE 16. GRAND BAYOU DU LARGE/BAYOU GRAND CAILLOU

[ 0

10' 0 ... 0 1955 0 0 0 wo:�-.· + 0 0 0 1978 0 0 0 1955 Shoreline + 0

legend

0 1 WATERBODIES (nalural)

2 WATERBODIES (man-made) MANGROVE (1978 only) 0 43 SPOIL DEPOSITS s INTERTIDAL FLATS

1:50,000 6 BEACH

0 1 2 mi 1 DEVELOPMENT 0 � 8 MARSH/BEACH RIDGE VEGETATION

0 2 km 8d DRAINED MARSH S:H S:H :EH CEH3::E!:A:E H�==s=====:::3 0 250 500 750 1000 1250 11100 17110 9 UPLAND FOREST Cacree) 0 AREA 10 CROP AGRICULTURE 0 PLATE 11. WESTERN AND CENTRAL ISLES DERNIERES 0 0

... tf'ID' 0 D 1955 0 ...... lla'ID'

0 0 0 0 1978

...... 02'10' 0 0 _/ D 1955 Shoreline 0

Legend 1 WATERBODIES (natural) 0 2 WATERSODIES (man-made) 2 I 3 MANGROVE (1978 only) 4 SPOIL DEPOSITS 1:50,000 45 s INTERTIDAL FLATS 0 I BEACH 8 jlalllimillif 1 DEVELOPMENT km 7 8 MARSH/BEACH RIDGE VEGETATION 0ee�A�A�A�AcE:=:=:=:=32 �------� 0 ld DRAINED MARSH &�������,���======� 9 UPLAND FOREST 0 250 500 750 1000 1250 1500 1750 10 CROP AGRICULTURE AREA (ec:rea) 0

PL.ATE 18. EASI'ERN ISLES DERNIBRES 0 0 0

0 1978 0 .... + + + 0

0 --- 1955 Shoreline 0 Legend 1 WATERBODIES (natural)

2 WATERBODIES (man�made)

3 MANGROVE (1978 only) 1:50,000 0 4 SPOIL DEPOSITS 0 1 2 ml �� ��������� --���� 5 INTERTIDAL FLATS 6 BEACH 0 7 DEVELOPMENT a MARSH/BEACH RIDGE VEGETATION Bd DRAINED MARSH

9 UPLAND FOREST 0 10 CROP AGRICULTURE 0 PLATB 19. CAT ISLAND PASS (WIHE ISLAND) 0 0

10' Wlf'lf• 21' .... 0

\ 0 1955 0

...,.. 0

..... 0 0 0

\\ 0 ' \ 1978 ' 0 ..... 0

' n \ ' Zl'lil / \ 1955 Shoreline \ 0 \

Legend

1 WATERBODIES (natural) 0 \ WATERBODIES a (man-made)

1:50,000 3 MANGROVE (1978 only) 1 2 ml 0 4 SPOIL DEPOSITS 0 F.F.a��E3��E33C�E33C�ES�=c===:�======$ INTERTIDAL FLATS

a BEACH 7 DEVELOPMENT 0 8 MARSH/BEACH RIDGE VEGETATION 8d DRAINED MARSH 0 2110 1100 750 1000 1250 11100 17110 2000 e UPLAND FOREST AREA (ur.. ) 10 CROP AGRICULTURE 0

PLATE 20. TlMBAUBR ISLAND 0 0

0 ...... ,,...... 0 1955 0 0

0 ·-· 0

••• H.U. '

0 1978 0 0 0 ---· 1955 Shoreline

Legend .... 1 WATERBODIES (natural)

'l WATERBODIES (man-made) 2 ,._____ ---.. 3 MANGROVE (1978 only) 1:50,000 4------' 0 4 SPOIL DEPOSITS • .-IIIIIL---, 5 INTERTIDAL FLATS •'--r---....J 11 BEACH 7 DEVELOPMENT 7 0 II MARSH/BEACH RIDGE VEGETATION

114 DRAINED MARSH

0 280 100 750 1000 1UO 1500 1710 II UPLAND FOREST

10 CROP AGRICULTURE

0 PLATB 21. EAST TIMBAUBR ISLAND TO BBLLB PASS D 0

Cll'... 0

1955 D 0

WOI' 0 0

0 0 1978 0

WOI'

0 1955 Shoreline/ Legend 0 1 WATERBOOIES (natural) 2 2 WATERBOOIES (man-made) 4 MANGROVE (1978 only) 43 SPOIL DEPOSITS u 15 s INTERTIDAL FLATS 1:50,000 e e BEACH / 7 0 2 r11 7 DEVELOPMENT E3 E3 E3 E3 E3 • e MARSH/BEACH RIDGE VEGETATION 0 2 km --11":'::..=.. -=- .• ,..... DRAINED MARSH H H A AA 0 250 500 7$0 1000 1250 1500 1750 2000 8d 9 UPLAND FOREST AREA (eer.. ) 10 CROP AGRICULTUAE u

PLATE 22. PORT FOURCHONICAMINADA BEACH c 0

0 Gl' ono· WCIO' Wll'IO"

..11'10" Lafowrche � 1955 0 0

0 Goa

Mol�� Llo•P � 0

..,0'

0 ..1110" � 0 1978 0 0 1

1955 Shoreline 0 Malct. llrleP- 1

..10'

l-+---- 1ttlll Legend lilillllmll.':l+----1 1178 2 WATERBOOIES (natural)

0 21 WATERBODIES (man-made) • MANGROVE only) I ... 3 (1978 I u SPOIL DEPOSITS 1:50,000 4 0 5 INTERTIDAL FLATS e BEACH 0 1 �2km 1 DEVELOPMENT ss �HECEH�H �H LE===:=:== 8 MARSH/BEACH RIDGE VEGETATION 0 Bd DRAINED MARSH

0 210 500 7110 1000 1210 1100 1710 2000 2210 2100 9 UPLAND FOREST 0 AREA (•ere•) 10 CROP AGRICULTURE

PLATE 23. CHENIERB CAMINADA/GRAND ISLE

0 0

.,... . ICI' 0

1955 0 ... 0 0 0 0 0

1978 0

\\ \ \ .... 0 \ D ' j 1955 Shoreline D I I I 0

Legend

1 WATERBODIES (natural) 0 2 2 WATERBODIES (man-made) I 4 MANGROVE (1978 only) 43 SPOIL DEPOSITS 0 1:50,000 5 s INTERTIDAL FLATS o 1 2 mi ... s BEACH E���======� e 7 7 DEVELOPMENT 8 B MARSH/BEACH RIDGE VEGETATION 0 3 Sd DRAINED MARSH 0 250 500 750 1000 (ecre•J1250 1500 1750 2000 2250 9 UPLAND FOREST AREA 10 CROP AGRICULTURE u

PLATE 24. GRAND TERRE TO CHENIERE RONQUILLE 0

0 .,... 0 1955 0 0 0 0

Malcll LIMR---1 I 0 • 0 1978

0 .... 0 0

0 L1955 Shoreline

Legend

0 1 WATERBODIES (natural)

2 WATERBODIES (man-made) 3 MANGROVE (1978 only) 0 \ • SPOIL DEPOSITS 4 --- s INTERTIDAL FLATS 1:50,000 5 .. � 8 BEACH e t:=-J 1 DEVELOPMENT 0 0 2km e MARSH/BEACH RIDGE VEGETATION ::SH CEH:O Hs::HH::::c:::;;��:;;l B:e B:e DRAINED MARSH 500 750 1250 1750 &d 9 UPLAND FOREST ARIEA 0 (acr.. l 10 CROP AGRICULTURE 0 PLATB 25. CHENIBRE RONQUILLE TO SHELL ISLAND 0 0

•• -· .... 0

1955 0

0

......

I I 0 I I I I I I ----Motoh LIMR 0

..... 0 1978 0 0

D

•u· - 0

1955 � Legend WATERBODIES (natural) p•••u 5111.• 1 0 2 WATER60DIES (man-made) \ 1978 3 MANGROVE (1978 only) 4 SPOIL DEPOSITS 1:50,000 5 0 5 INTERTIDAL FLATS 0 1 2 mi BEACH E� ���������======� 6 DEVELOPMENT 0 2 km 1 -S:::H :S::H::EIH ::J3H ::EH �====:;� I1211A 8 MARSH/BEACH RIDGE VEGETATION 0 3 8d DRAINED MARSH 0 250 500 750 1000 1250 1500 1750 2000 g UPlAND FOREST AREA (ecre•l to CROP AGRICUl.TURE u

PLATE 26. GULF-EMPIRE WATERWAY TO SANDY POINT . . 0

0 ,...... ,... 0

..17'10' 0 1955 0 0 0 0 0

W17'10' 0 1978 D 0 �1955 Shoreline 0 Legend 0 t W ATERBODIES (natural) 2 WATERBODIES (man-made) t � 3 MANGROVE (1978 only) I SPOIL DEPOSITS 2 F-� -----. A 0 1:50,000 1!1 111111 s INTERTIDAL FLATS 1-UI!II BEACH 1!1 U78 II 7 DEVELOPMENT 7 If" •.• km 0 0eaCEecsecseceecE=:======-aa2 B MARSH/BEACH RIDGE VEGETATION Bd DRAINED MARSH

0 21!10 1!100 750 II UPLAND FOREST 0 AREA (uree) to CROP AGRICULTURE 0 PLATE 21. BRETON ISLAND 0 0

•• ...... 0 0 1955 0 0 0 t------,------�------�------l·r.· 0 0 1978

0

Shoreline 0 D

. ., ... Legend

1 WAT!RBODIES (natural) 0 2 WATERBODIES (man-made)

3 MANGROVE (1978 only) , .. . 4 SPOIL DEPOSITS I y,;;,__ 1178 0 1:50,000 INTERTIDAL FLATS / • 5 0 2 ml 1 1111111 e BEACH F3&i...... FiFH • l '1./:llo.+-3 7 DEVELOPMENT 0 1 2km MARSH/BEACH RIDGE VEGETATION AHHHH 0 210 100 a 0 DRAINED MARSH AREA (eere•) 8<1 9 UPLAND FOREST

10 CROP AGRICULTURE

PLATE 28. GRAND COSIER ISLANDS

( 0

0 ...... _. ••

0 _;!( 1955 � ....

0 Cb� ~ �. 0 0

0 1978

'\.' .... 0 ' "' ' 0 ' OdJ 0 0 1955 Shoreline

Legend

1 WATERBODIES (natural)

2 WATERBODIES (man-made) MANGROVE (1978 0 •.. 3 only) 0 • SPOIL DEPOSITS

t5 5 INTERTIDAL FLATS / 5 pa••IJ- f::=:·1�tt!!71ill _.. , 1:50,000 e BEACH 0 1 7 DEVELOPMENT • Ill! 2km MARSH/BEACH RIDGE VEGETATION uo e 0S::H :::EI HCEH:r::::JHH:EIH c:E::=;��=:I 0 500 750 8d DRAINED MARSH AREA (.creel 0 II UPLAND FOREST

1o CROP AGRICUL TUAE

PLATE 29. SfAKB ISLANDS 0

4T... ..10. -· 0

1955 D - --· 0 0 0 0

1978 0 0 0 0

Legend

' WATERBODJES (natural)

2 WATERBODIES (man-made) MANGROVE (1978 only) 11178 SPOIL. DEPOSITS -�-- 43 1:50,000 � Hl55 0 5 INTERTIDAL. FLATS

e BEACH E4 ea ea -- : o�=:liiiiii:::::Eiii:::E=-::::::EEc1 ---====--=12 ml 7 DEVELOPMENT _____ ..J) Qmo km • 0ae�H9CH�H�H�:;:;:;;;;;;;;;32 1 MARSH/BEACH RIDGE VEGETATION 0 2150 1500 7150 1000 12150 11500 17150 2000 8d DRAINED MARSH

e UPlAND FOREST \0 CROP AGRICUlTURE 0

PLATE 30. CENTRAL CHAHDELEUR ISLANDS 0

0 ...... -· 0 / 1955 0 0 0 0 w�w· �------�------�------�------�------1 0 ,. 0 1978 0 0 ·-· 0 1955 Shoreline ----' 0 Legend

1 W ATERBODIES {natural)

0 2 WATERBOOIES (man-made)

3 MANGROVE (1978 only) 5 " SPOil. DEPOSITS 0 1:50,000 • --mm-======�--� s INTERTIDAL FLATS a BEACH. 7 :.• DEVELOPMENT 8 7 0 km MARSH/BEACH RIDGE VEGETATION 2 _ 8 S:H ::J3H CEA3:J AS:::SA�::=====:3 0 0 250 500 750 1000 1250 1500 DRAINED MARSH Bd AREA (Ioree) D UPLAND FOREST 0 10 CROP AGRICULTURE

0 PLATE 31. NORTH CHANDELEUR ISLANDS 0 0 0 D 0 0 0 0 0 0 0 0 D 0 0 0 D u u 0 0 0 � l [ [ [ ( ' [ r ( I I I I - -

.. .. - I I I I I l