AN ENVIRONMENTAL-ECONOMIC BLUEPRINT FOR RESTORING THE

LOUISIANA COASTAL ZONE: THE STATE PLAN

REPORT OF THE GOVERNOR’S OFFICE OF COASTAL ACTIVITIES SCIENCE ADVISORY PANEL WORKSHOP

AUGUST 1994

1994

AN ENVIRONMENTAL-ECONOMIC BLUEPRINT

FOR RESTORING THE LOUSIANA COASTAL ZONE: THE STATE PLAN

REPORT OF THE GOVERNOR’S OFFICE OF COASTAL ACTIVITIES SCIENCE ADVISORY PANEL WORKSHOP

Report Prepared by Sherwood Gagliano

Coastal Environments, Inc.

Prepared for Governor Edwin W. Edwards, the Governor’s Office of Coastal Activities, and the

Wetland Conservation and Restoration Task Force

August 1994

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TABLE OF CONTENTS LIST OF FIGURES ........................................................................................................6-iii SUMMARY..................................................................................................................... 6-1 THE COASTAL EROSION PROBLEM ........................................................................ 6-7

Causes of Deterioration................................................................................................ 6-7 LOUISIANA’S COASTAL PROGRAM...................................................................... 6-11

Striving for “No Net Loss” ........................................................................................ 6-12 Economically Sustainable Development ................................................................... 6-16 I. DEFENSIVE MEASURES ................................................................................... 6-20

A. STOP MARINE TIDAL INVASION.............................................................. 6-20 1. Restore Barrier Islands- ................................................................................ 6-20 2. Establish “Critical Defense Line” (CDL)-.................................................... 6-23 3. Stop Marine Invasion in Navigation Channels-............................................ 6-25

B. PREVENTIVE MAINTENANCE................................................................... 6-26 1. Maintain Fresh Water Basins........................................................................ 6-26 2. Enhance Estuarine Areas- ............................................................................. 6-29

II. OFFENSIVE MEASURES.................................................................................. 6-30 A. RESTORE LAND BUILDING PROCESSES ................................................ 6-30

1. Reallocate Distribution of Mississippi-Atchafalaya River System Flow-.... 6-30 2. Manage Zone of Subdeltas- .......................................................................... 6-35 3. Build Land With Dredge Material-............................................................... 6-37

RECOMMENDATIONS FOR CWPPRA FEASIBILITY STUDIES.......................... 6-39 APPENDIX.................................................................................................................... 6-41

LIST OF FIGURES

Figure 6-1. Natural and man-made ridges form the skeletal framework to which the coastal wetlands are attached. They form hydrologic basin divides and are major elements in the overall planning process (After S. M. Gagliano and J. L. Van Beek, 1993). .......................................................................................... 6-8

Figure 6-2. Most of the landmass of the Deltaic Plain consists of wetlands lying between finger-like natural levee ridges and fringing barrier islands. The landmass of the Chenier Plain is also mostly wetlands between the edge of the uplands and the chenier ridges and Gulf beach (After S. M. Gagliano and J. L. Van Beek, 1993). .................................................................................. 6-8

Figure 6-3. Subsidence causes ridges to sink and marine tidal processes to invade fragile swamps and marshes. The fresh wetland basins (A-G) will be predictable lost to marine tidal invasion without remedial action (After S. M. Gagliano and J. L. Van Beek, 1993). .......................................................................................... 6-9

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Figure 6-4. Without an effective program, in some areas the shore of the Gulf will move inland 30 miles (After S. M. Gagliano and J. L. Van Beek, 1993)............................................................................... 6-9

Figure 6-5. Comparison of measurements of coastal land loss rates as determined by the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers. The curves indicate that the losses began prior to 1910 and peaked during the 1960’s. The difference in most recent rates (25.3 and 34.9) is attributed to measurement techniques (After National Biological Survey, National Wetlands Research Center, 1994). .................................................................................................. 6-13

Figure 6-6. Trends of coastal land loss (1978-1990). Most of the recent loss has occurred in the Terrebonne and Barataria hydroigic basin (Data from National Biological Survey, National Wetland Research Center, 1994). ....................................................... 6-13

Figure 6-7. Measured and predicted land loss/gain for Louisiana coastal area. The Gross Annual Loss curve is projected to meet goals for further reduction of the annual loss rate. The “no net loss” condition is reached at the end of Phase II of the program in 2043.................................................................................. 6-14

Figure 6-8. The "no net loss" condition will be attained in 2043. At that time a dynamic equilibrium will be restored to the coastal system and land will be added to the coast each year......................... 6-14

Figure 6-9. Measured and predicted land loss/gain for the Deltaic Plain area...................................................................................................... 6-17

Figure 6-10. Measured and predicted land loss/gain for the Chenier Plain area...................................................................................................... 6-17

Figure 6-11. Outline of the coastal restoration plan. ............................................... 6-19 Figure 6-12. Defensive measures of the restoration plan. ....................................... 6-21 Figure 6-13. Ship Shoal provides a potential source of sand for restoration

of the critical barrier islands along the Louisiana coast (After l. Ll van Heerdon, 1994). .................................................................... 6-23

Figure 6-14. Typical components of a shore zone management project (After S. M. Gagliano, et al., 1994). ................................................... 6-30

Figure 6-15. Offensive measures of the restoration plan......................................... 6-31 Figure 6-16. Conceptual interpretation of the Breton delta and Mississippi

birdfoot delta approximately 20 years after the diversion into Breton Sound (After l. Ll. van Heerden, 1994). ................................. 6-36

Figure 6-17. South Central Louisiana coastal areas presently benefiting from Atchafalaya River fresh water and transported sediment (After l. Ll. Van Heerden 1994).......................................................... 6-38

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SUMMARY

The state of Louisiana, through its own coastal restoration program, and in conjunction with a task force of federal agencies under the Coastal Wetland Planning, Protection and Restoration Act (CWPPRA), has launched a major effort to restore its eroded and deteriorated coastal zone. A long-term trend of natural land building along the coast was reversed about a hundred years ago by natural changes and acts of man and a cycle of rapid erosion and deterioration was initiated. Approximately one million acres of land has been lost. The erosion rates peaked in the 1960’s and have declined to an annual loss rate of 25 to 35 mi² per year. The land in the coastal zone continues to subside and the sea continues to erode barrier islands and to invade fragile wetlands at an alarming rate. The coastal restoration program supplements a regulatory program that has been effective in reducing loss rates. The restoration program has two major goals: 1) to reach a “no net loss” condition in the coastal wetlands, and; 2) to achieve conservation management of the wetlands and estuarine areas in a way that restores a dynamic equilibrium to the natural systems and that is compatible with, and contributes to, sustainable economic development. Strategies for achieving these goals include further reduction of loss rate, reestablishing the delta system’s ability to build and maintain wetlands, restoring barrier islands, and building wetlands with dredge material. Target goals for reduction of land loss rates and for land building are established and evaluated. The no net loss condition will be achieved in 50 years. A plan consisting of defensive and offensive measures has been devised to provide guidance in developing and evaluating projects designed to achieve the goals of the program. Defensive measures include restoration of barrier islands, establishment of a critical defense line (to maintain a separation of fresh water wetlands from marine influences), measures to stop marine invasion along navigation channels, preventive maintenance in fresh water basins, and fish and wildlife habitat enhancement of estuarine areas. Offensive measures include reallocation of Mississippi River flow and transported sediment (through the Lower Mississippi River, the Atchafalaya River, a new conveyance channel parallel to historic Bayou Lafourche, and a new conveyance channel in the St. Bernard area), a zone of managed subdeltas, and land building with dredge material. The program will be implemented in three phases, each of which will require 25 years. The target for reaching the no net loss condition is the end of Phase II, or about the year 2043, after which new wetlands will be added to the coast each year. Recommendations for feasibility studies to be conducted under the CWPPRA program have also been developed. These include investigations of the feasibility for: 1) increasing the share of Mississippi River borne sediments sent down the Atchafalaya River; 2) re-establishment of the barrier island systems along the seaward perimeter of the Barataria and Terrebonne Basins; 3) modification of major navigation channels to offset marine transgressions of historically fresh and intermediate coastal wetlands and to reallocate flow and sediment for diversions and sub-delta building, and; 4) a Mississippi diversion plan which includes upper basin fresh water diversions and major conveyance

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channels in the Bayou Lafourche corridor, lower Mississippi diversions below New Orleans, and lower Atchafalaya diversions. Socioeconomic issues are of paramount importance and should be considered in conjunction with the feasibility studies. At a minimum this should include consideration for flood protection for critical development corridors and phased relocation of coastal interests, where necessary, with fair compensation. Natural system management and multiple use planning is a dynamic, ongoing process. The plan presented in this report should be regarded as an incremental plan, which hopefully will serve as a point of departure and will undergo further testing and refinement.

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THE COASTAL RESTORATION PLAN WORKSHOP

The plan presented in this document represents a compilation and refinement of several prior-planning efforts. The first comprehensive proposal for environmental restoration of the deltaic area of the Louisiana coast was proposed by Sherwood M. Gagliano and Johannes L. van Beek in 1975. The proposal was the culmination of a six year study effort initiated in 1969, various components of which were funded by the New Orleans District, U.S. Army Corp of Engineers; the Office of Sea Grant, National Oceanic and Atmospheric Administration; and the Ecological Studies and Assessments Branch, Implemented Research Division, of the U.S. Environmental Protection Agency. The 1975 plan recognized deterioration and land loss and its causes. It also presented proposals for: 1) barrier islands, reef and Gulf shore areas; 2) estuarine nursery and fresh to brackish marsh areas; 3) fresh water basins, and; 4) development corridors. The plan called for fresh water diversions and controlled subdelta building. It proposed a new navigation entrance into the Mississippi River in the vicinity of Empire, Louisiana and illustrated an approach to shore zone management. In 1987 a report entitled “Coastal Louisiana Here Today and Gone Tomorrow?” was produced by the Coalition to Restore Coastal Louisiana. This report was a synthesis of the technical literature concerning environmental problems in coastal Louisiana, and the report also proposed solutions. The report laid out an action program which included regulatory and legislative changes as well as active environmental management. The report was widely circulated and was instrumental in raising public awareness of the magnitude and urgency of the problems and the critical need for restoration. Beginning in about 1991 several serious efforts were initiated to develop a comprehensive plan for the preservation, restoration and management of Louisiana’s coastal wetlands. One effort was undertaken by a task force of federal agencies under the Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA). A plan was developed over a two year period and completed in November, 1993. Simultaneously, a companion wetland plan was developed under contract by Coastal Environments, Inc. (CEI) for the Louisiana Department of Natural Resources (DNR) in conjunction with the state’s Coastal Wetland Conservation and Restoration program and was completed in December, 1993. The CEI/DNR plan was reviewed by the State’s Wetland Conservation Tack Force (WCTF). An outline of a restoration plan was developed by the Governor’s Office of Coastal Activities (GOCA) in June 1993 and an independent report on a long-term comprehensive management plan was written by Ivor Ll. van Heerden and completed in January 1994. Paul Templet has also prepared a water and sediment diversion plan (1994). In addition a number of position papers and recommendations prepared by individual scientists and interested citizens related to planning for the coastal wetlands have been prepared and circulated for comment. These have been incorporated into an appendix volume of this report. The thrusts of the major plans and recommendation were generally parallel and in agreement, but there were significant differences in conclusions and approaches.

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The CWPPRA plan delineates a 20 year program made up of individual projects and organized according to nine hydrologic basins. The GOCA, CEI/DNR, van Heerden, and Templet plans take a long view (50 years or more) and place much emphasis on river diversions. The CWPPRA plan approaches management at a hydrologic basin level. The other plans referred to above, and the plan presented in this report, view management at a major natural system or province level. The coastal restoration plan, which is finally adopted by the federal government and the state, will have far-reaching implications for the future of coastal Louisiana. Billions of dollars of public funds will ultimately be spent in implementing the plan. The plan will determine the future configuration of the vast coastal zone and will influence not only wetlands, but also infrastructure for human use and development (flood protection and drainage works, highways, navigation canals, ports, urban and industrial water supply, etc.). For these reasons it became important to make a serious effort to critically review the various proposed plans and recommendations and to glean from them the best concepts. These could then be included in a consolidated plan. The GOCA has undertaken this important step. To assist the GOCA in developing a consolidated plan for restoration of Louisiana’s coastal zone a panel of invited experts was convened. A series of panel workshops was held by the GOCA in conjunction with the Wetland Conservation Task Force. The first workshop was held in the Louisiana Wildlife and Fisheries building in Baton Rouge on November 17 and 18, 1993. The panelists were provided with copies of the various draft plans and recommendations prior to the workshop. Summaries were presented and the panelists conducted a systematic evaluation of the major aspects of each plan and proposal. Emphasis was placed on validity of the concepts and feasibility of major aspects. This report constitutes a summary of the evaluation and recommendations compiled during the workshop and provides the basis for a report of findings and an consolidated plan. Several follow-up meeting were held to develop recommendation for CWPPRA feasibility studies and to review general recommendations of the advisory panel. The plan presented in this report is a snapshot of a very dynamic and ongoing planning process. The plan represents a point of departure and will undoubtedly be refined and revised as the process continues.

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THE COASTAL EROSION PROBLEM

The coastal restoration approached recommended in this plan are based upon recognizing and reversing the processes that have contributed to coastal erosion in the past. The coastal lowlands of Louisiana are a product of natural progradation and aggradation in two dynamic natural systems over a period of about 5000 years (since sea level reached its present level at the end of the Holocene rise). The two systems are the Deltaic Plain of the Mississippi River, which occupies the southeastern part of the state, and the Chenier Plain, which dominates the western coastal zone (Figure 1). The coastal wetlands are a direct product of, and an integral part of these two systems (Figure 2). Most of the fault bounded geological blocks that make up coastal Louisiana are sinking. The rate of sinking has increased during the last 40 years. The land is no longer built up fast enough by annual overflow of the Mississippi River, by aggradation of living wetland surfaces, or by delta building processes at the river’s mouth to offset the sinking. The sea is invading the land. The marine invasion has been accelerated by a maze of channels dug for navigation, and in conjunction with activities related necessary to offshore and onshore subsurface mineral extraction. The barrier islands and wetlands are eroding away and the cities and communities of the coastal area are increasingly threatened (Figures 3 and 4). The rates of coastal erosion and deterioration were identified more that 20 years ago, as were the basic approaches to management of these two natural systems to offset the effects of massive system collapse and resulting transgression (Gagliano and van Beek, 1970, 1975). The approaches have been refined through some pilot projects and innovative methods continue to be developed. Initial response to the problem was in the form of state and federal regulatory programs, aimed at reducing wetland loss resulting from dredge and fill activities and hydrological modification. These programs have been moderately successful and the loss rate is decreasing. The loss rate peaked between 1960 and 1965 when it was 39 to 42 square miles per year. Since then it has declined, however, the coastal zone land loss rate remains at 25 to 35 square miles per year (Figure 5). Areas of most intensive loss have shifted through time, however during the most recent interval of comparison the highest rates have occurred in the Terrebonne and Barataria hydrologic basins (Figure 6). Causes of Deterioration The natural dynamic equilibrium of Louisiana’s coastal system has been upset by human activities. Massive coastal erosion, which began approximately 100 years ago and peaked during the 1960’s, has resulted in loss and deterioration of wetlands, barrier islands and ridgelands. Approximately one million acres of land has been lost during the last 100 years. Both the Deltaic and Chenier Plains systems are badly degraded and approaching collapse.

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Figure 6-1. Natural and man-made ridges form the skeletal framework to which the coastal wetlands are attached. They form hydrologic basin divides and are major elements in the overall planning process (After S. M. Gagliano and J. L. Van Beek, 1993).

Figure 6-2. Most of the landmass of the Deltaic Plain consists of wetlands lying between finger-like natural levee ridges and fringing barrier islands. The landmass of the Chenier Plain is also mostly wetlands between the edge of the uplands and the chenier ridges and Gulf beach (After S. M. Gagliano and J. L. Van Beek, 1993).

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Figure 6-3. Subsidence causes ridges to sink and marine tidal processes to invade fragile swamps and marshes. The fresh wetland basins (A-G) will be predictable lost to marine tidal invasion without remedial action (After S. M. Gagliano and J. L. Van Beek, 1993).

Figure 6-4. Without an effective program, in some areas the shore of the Gulf will move inland 30 miles (After S. M. Gagliano and J. L. Van Beek, 1993).

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Causes of wetland loss are well documented and include the following: Natural Processes - Shifting of river courses, storm waves and surge, fires, and destruction of marsh plants by animals (herbivory) cause erosion of barrier islands and loss of wetlands. Under natural conditions damage from these processes was often only temporary or local, the systems were self-healing, and land loss was offset by land building elsewhere. Flood Protection and Navigation Works - Construction of flood protection levees and navigation improvements along the Mississippi River and its principal distributaries have stopped overbank flooding, the natural process for building up the land and nourishing the wetlands. Active distributary channels, such as Bayou Lafourche, were blocked at their confluence with the Mississippi, thus cutting off vast wetland areas of the Deltaic Plain from their life sustaining supply of fresh water and transported sediment. Jetties and navigation channels at the mouths of active distributaries direct sediment into the deep waters of the Gulf and prevent delta-building processes. Reduction in Transported Sediment - Changes in management of the river and its tributaries have caused the amount of sediment transported by the Mississippi River to decrease during recent decades. This in turn reduces the river’s capacity to build new deltaic lands. Land Sinking - Land subsidence (relative sea level rise) is a natural long-term process, the rate of which has accelerated in recent decades. The sinking rate in vast areas is presently 2 to 4 feet per century (Figure 3), whereas during the preceding 2,000-year period it was only 0.5 to 0.7 feet per century. Sediment Deficit - If land sinking is not offset by upward build up (aggradation), inundation occurs and the land reverts to open water. Aggradation results from deposition of mineral sediment (introduced mainly from river overbank flow and tidal movement) and/or accumulations of organic deposits (derived from marsh and swamp plants). The difference between the amount of sediment required to maintain land above inundation level and the amount presently accumulating is the sediment deficit. The sediment deficit has been determined in some areas by comparing the difference between controlled measurements of accumulation rates and sinking rates. Marine Tidal Invasion - The combined result of accelerated subsidence and an extensive man-made canal network, has caused massive wetland die-back, expansion of tidal channel networks, and erosion of poorly consolidated organic soils. In many areas intrusion of water from the Gulf of Mexico containing salt and sulfide has killed fresh water vegetation which is capable of building and maintaining living mats and organic soils (Figure 3). Accelerated tidal processes have then removed the fragile unvegetated organic soils, causing land to revert to open water.

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The bottom line is that the lowlands are sinking, land building is at a stand-still, and the sea is rushing in.

LOUISIANA’S COASTAL PROGRAM

The goals of the Louisiana coastal wetland conservation and restoration program are: 1) “no net loss” of coastal wetlands, and; 2) conservation management of the wetlands and estuarine acres. Both goals are to be accomplished in a way that restores a dynamic equilibrium to the natural systems of the coastal zone and that is compatible with, and contributes to, sustainable economic development. The goals will be achieved through continuation of the regulatory program, which has proven effective in reducing loss, and in further development and implementation of comprehensive restoration program to be carried out by the state in partnership with the federal CWPPRA program and private initiatives. Another fundamental part of the restoration progam is the development of scientifically sound, flexible, long-term plan that is equal to the magnitude of the task and that will provide the principles, creditability, and inspiration that guide this effort. Scientifically sound means that the plan is predictable, coordinated, and works with natural processes and systems. A well documented record of past efforts at mitigation and restoration clearly indicates that anything less will result in wasted time and money, unsatisfactory results, and in general will be predestined to failure. The program must be based on a scientifically sound method and theory for natural-system management. The systematic study of natural systems is a specialized branch of science, which draws upon a number of related disciplines. Natural-system management decisions must be based on proven conceptual and quantitative models, which inter-relate process-form responses, energy flow, faunal and floral successions, and principles of hydrology and sedimentary processes, to human uses and societal needs. The models must be accompanied by a comprehensive data base related to indicator parameters. Each proposed action must be tested by conducting a systematic impact analyses, which utilizes the models and the data base. In order to maintain creditability, participating research scientists must play a leadership role in this effort working alongside agency field manager. The approach must recognize that coastal Louisiana is occupied by two major systems, the Deltaic Plain and the Chenier Plain. Each has a unique history and each is characterized by quite different processes and landscapes. Much of the natural productivity of the two coastal systems is due to their dynamic, ever changing character, ranging from the twice-daily fluctuation of the tide, to the seasonal pulses of the rivers, on to the millennial shiftings of the mouth of the Mississippi. Delta processes are cyclic and this cylcic nature drives a succession of environmental change. Some are predictable, like the sequence of wetland deterioration that follows sub-delta abandonment, but many are as unpredictable as the weather that leads to a major flood one year or the landfall of a hurricane in the next. It follows that arresting the dynamic nature of the system would reduce renewable resource values, and this has in fact been one of the major effects of modern activities. The plan developed for

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the program must allow for a continuation of dynamic change; establishing a dynamic equilibrium. Human intervention in the processes will, however, continue to be necessary and can be useful in manipulating the natural systems to prolong favorable parts of their dynamic cycles. Specific ways for doing this include: 1) redirecting and phasing subdelta development so that new actively growing subdeltas are in place to keep the system going when the current deltas reach senescence; 2) re-establishment of more natural hydrologic processes (controlled fresh water diversions, controlled delta building, hydrologic management of marshes, etc.); 3) supplemental sedimentation (restoring and nourishing barrier islands, building marshes with dredge materials, etc.), and; 4) intervention in biological processes (control of herbivores, vegetation plantings, etc.). The program must also ultimately deal with multiple uses. An expanded multiple use program done within the context of natural systems management must provide the basis for restructuring coastal Louisiana for the future. The blueprint for the program is a comprehensive plan. This plan must become the yardstick for evaluating individual restoration and conservation projects, which are the building blocks of the plan. Evaluation of projects must ultimately follow the process prescribed by the National Environmental Policy Act. Striving for “No Net Loss” Land loss/gain is a useful index of the health or status of the coastal natural systems. It indicates whether the system is expanding, contracting, or stable. Generally net gain indicates expansion of the system boundaries, while net loss indicates a condition of overwhelming decay. Land loss curves developed through systematic comparison of maps and aerial photographs show the history of change during the past century (Figures 5 and 6). Tends in change of the rate of annual loss/gain also provide some basis for predicting conditions 25, 50, and 75 years from now (Figures 7 and 8). The curves are useful devices for setting goals for the coastal conservation and restoration program. The condition of “no net loss” can be reached by reducing the rate of loss, and by building new land along the coast. The numbers indicate that no net loss could conceivably be achieved by reducing loss rates alone, without any net gain. Thus it makes sense to absolutely reduce loss rates as much as is possible without destroying the fundamental dynamism of the system (upon which its productivity depends). The remaining areas that are most vulnerable should be identified and measures developed for preventing their loss. Loss prevention is accomplished through protective measures, including a continuation of a strong regulatory program, and through effective nourishment and maintenance of existing wetlands. New land can be added to the coast through natural processes and through artificial land building. Maximum land gain can be achieved through natural and controlled subdelta building. Directing the total flow and transported sediment of the

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Figure 6-5. Comparison of measurements of coastal land loss rates as determined by the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers. The curves indicate that the losses began prior to 1910 and peaked during the 1960’s. The difference in most recent rates (25.3 and 34.9) is attributed to measurement techniques (After National Biological Survey, National Wetlands Research Center, 1994).

Figure 6-6. Trends of coastal land loss (1978-1990). Most of the recent loss has occurred in the Terrebonne and Barataria hydroigic basin (Data from National Biological Survey, National Wetland Research Center, 1994).

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Figure 6-7. Measured and predicted land loss/gain for Louisiana coastal area. The Gross Annual Loss curve is projected to meet goals for further reduction of the annual loss rate. The “no net loss” condition is reached at the end of Phase II of the program in 2043.

Figure 6-8. The "no net loss" condition will be attained in 2043. At that time a dynamic equilibrium will be restored to the coastal system and land will be added to the coast each year.

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Mississippi and Atchafalaya Rivers into shallow water subdeltas would result in approximately 8.5 mi²/yr of new land being added to the coast of the Deltaic Plain. The principal land building process along the Chenier Plain coast is mudflat development, resulting from an east to west flow of the longshore mudstream derived from the Atchafalaya River subdeltas. The sediment transport capacity of the smaller rivers that cross the Chenier Plain is relatively low, but these streams do contribute to the land building process. The influence of these coastal plain rivers on land building has not been quantified. The present annual loss “benchmark” rate for the entire Louisiana coastal area is 25 mi².1 Other estimates are higher, but indicate the dependence of the numbers on the methods used to derive them. The important thing in determining trends is to compare sequential estimates derived in the same way. Reduction of the gross annual loss rate to 17 mi² in 25 years, and to 11 mi² in 50 years is an achievable goal based on the remaining acres of wetlands (the erodible base) and the success in reducing the loss rate through regulations during recent decades (Figure 7). These rates could be further reduced by more active intervention, for example slurried sediment conveyance (Suhayda, et al., 1991). Land can be built artificially by filling shallow water areas with dredge material derived from both maintenance dredging and dedicated dredging. Dedicated dredging is the removal of material from a borrow area for the specific purpose of land building or beach nourishment. Dredge material can be used to fill shallow water bodies and restore barrier islands and beaches, thus partially offsetting the annual loss rate. Lesser amounts of dredged material can be broadcast over the marsh to spur productivity and offset subsidence. Using these approaches, a goal believed to be attainable 25 years from now (2018 A.D.) is to reduce the net annual loss rate to 12 mi². This would be achieved by reducing the gross annual loss to 17 mi² per year by preventive maintenance and regulations, by building subdeltas at a rate of 4 mi² per year, and by artificially building land at a rate of 1 mi² per year (Figure 7). In 50 years the goal would be the targeted no net loss or balanced condition. Under the proposed scenario there would be further reduction of the gross loss rate to 11 mi². This would be offset by 8.5 mi² of subdelta land building and 2.5 mi² of artificial land building, thus achieving the goal of no annual loss in the coastal zone by the end of Phase II of the plan or by about the year 2043.

1 There is a difference in loss rates as measured by the U.S. Army Corps of Engineers and the U.S. Fish and Wildlife Service. Measurements made by the Fish and Wildlife Service indicate that the present annual loss is approximately 35 mi²/yr, while the Corps measurements show approximately 25 mi² (Figure 5). This is a significant difference, which needs to be resolved. The more conservative Corps measurements will be generally used for the purpose of this discussion.

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After the no net loss condition is reached, further refinement of the program could result in a condition of annual land gain. The natural systems would then begin to build new land each year, and the extent of coastal lowlands would gradually increase. The rate at which this happens will be based largely on our ability to further reduce the annual loss rate and to increase the annual rate of artificial land building, as the Mississippi-Atchafalaya River system has a finite amount of sediment that can be used to build new land. The land building capacity of the river system can only be increased by directing sediment into shallow near shore water instead of shunting it into deep water and by making the rate of sediment retention in subdelta areas higher. Separating the land loss curves into a Deltaic Plain component (Figure 9) and a Chenier Plain component (Figure 10) provides further insight into the problems and the solutions. Most of the present loss and the future loss will be in the Deltaic Plain. However, there is potential for offsetting much of this loss through restoring natural hydrologic and sedimentary processes. Reduction of loss in the Chenier Plain must be based largely on prevention of predictable loss, mudflat building, and artificial land building because there is no possibility for subdelta building west of the Atchafalaya River. The influence of the Atchafalaya could, however, be extended westward through fresh water diversions routed along the GIWW and utilizing pipelines for sediment conveyance from the coastal mudstream. Restoration of sediment transport down the Sabine River (blocked by the Toledo Bend Dam) could also contribute to land building, but the amount that could be introduced from this source is not known. Annual loss is part of the dynamic of the systems and should continue at a reduced rate even after the no not loss goal is achieved. Thus, a coastal restoration program cannot be entirely defensive and directed only toward reducing the rate of predictable loss (with no new land building). If the program focused entirely on reducing the rate of predictable loss, approximately 760,000 acres would still be lost during the next 50 years, and annual loss would continue indefinitely. A plan that does not include land building would not realistically ever lead to “no net loss.” If subdelta building and artificial land building were also implemented, the loss during the next 50 years would be reduced to approximately 610,000 acres and the no net loss goal would be achieved. After stopping annual loss the system would be restored to a condition of annual growth (see Figures 7, 8, year 2068). Economically Sustainable Development Directing surface water and transported sediment to achieve a dynamic equilibrium in the natural systems of coastal Louisiana is cost effective, because it utilizes natural energy to drive renewable resource producing systems. Utilizing natural systems management as the basis for a long-term plan will avoid the necessity for costly “quick fixes” to address crises that arise from projects based on maintaining “brute force” opposition to the processes and tendencies of nature. The plan presented in this report will ultimately save billions of dollars of public money that can be directed to more productive uses, such as education and improving the infrastructure necessary to support

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Figure 6-9. Measured and predicted land loss/gain for the Deltaic Plain area.

Figure 6-10. Measured and predicted land loss/gain for the Chenier Plain area.

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economic activities. It will also foster the development of a new ecological engineering technology with considerable potential for export around the world. Subdelta cycles drive changes that are responsible for the natural resources wealth of the Deltaic Plain. The single or, at least double purpose historic plan to “harness the Mississippi River” for flood control and navigation improvement has greatly curtailed the natural subdelta process that builds and sustains the land and has slowed development of more broadly useful and less expensive technologies. A system of ten proposed subdelta lobes extended along a broad arc around the deltaic coast with each operated according to phased or sequenced schedule will not only rebuild eroded wetlands, but will also restore a dynamic equilibrium to the system and ensure future continuity of the fish and wildlife and other renewable resources. Implementation of the plan will yield other economic benefits. The construction projects required represent a major public works undertaking, and will result in planning, construction, operation, and maintenance jobs. The changes required for reallocation of Mississippi and Atchafalaya River water represent a monumental renovation of the plumbing system of coastal Louisiana. This renovation will create new opportunities for ports, navigation, and flood control as well as opportunities for revitalizing the traditional renewable resource based industries. Clearly, the restoration planning process should be expanded to include these and other economic development infrastructure elements. COMPOSITE LONG-TERM PLAN FOR LOUISIAN’S COASTAL WETLANDS2

It is beyond the present resources and capabilities of the state and the nation to restore coastal Louisiana to the way that it was. The magnitude of the damage is too great. The increased sinking rates and reduced sediment load of the Mississippi River will prevent maintaining the area in its historic configuration even if it could be restored. An achievable goal is to stop losses and to re-establish equilibrium in a smaller delta system. This can be accomplished by carrying out two basic strategies (Figure 11). The first is defensive, and it is simply to stop the loss. A past of the defensive strategy is preventive maintenance, which will utilize management to prevent deterioration and to enhance existing functional wetlands and estuaries, and to optimize conditions in areas undergoing unavoidable change. The second strategy is offensive, and it is to restore a dynamic equilibrium (a balance between the natural environmental processes and the natural deterioration processes) in the Deltaic and Chenier Plain systems that make up the coast and to enhance them through management. The plan should be carried out in three phases, each of which will require 25 years to implement. Natural system management and multiple use planning is a dynamic, on-going process. The plan presented in this report should be regarded as an incremental plan, which hopefully will serve as a point of departure and will undergo further testing and refinement. Discussion of key elements and phases follow.

2 Recommendations from the Advisory Panel have been incorporated into the “Long-Term Plan for Louisiana’s Coastal Wetlands” originally prepared by S.M. Gagliano and J.L. van Beek, 1993, for the Coastal Management Division, Louisiana Department of Natural Resources.

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ELEMENTS OF THE PLAN I. DEFENSIVE MEASURES -

A. STOP MARINE TIDAL INVASION 1. RESTORE BARRIER ISLANDS 2. ESTABLISH CRITICAL DEFENSE LINE 3. STOP MARINE INVASION IN NAVIGATION CHANNELS

a. CLOSE MRGO (N7) b. CONTROL TIDAL MOVEMENT IN HOUMA NAV. CANAL (N4),

BARATARIA WW (N5), CALCASIEU SHIP CHANNEL (N2), & SABINE SHIP CHANNEL

B. PREVENTIVE MAINTENANCE

1. MAINTAIN FRESHWATER BASIN a. FRESHWATER DIVERSIONS (D1-D5) b. SUCCESSION MANAGEMENT

2. ENHANCE ESTUARINE AREAS a. DEVELOP REEF ZONE b. MANAGE SHORE ZONE

II. OFFENSIVE MEASURES -

A. RESTORE LAND BUILDING PROCESSES 1. REALLOCATE MISSISSIPPI RIVER FLOW

a. INCREASE ATCHAFALAYA RIVER FLOW b. CHANGE NAVIGATION CHANNELS

(1) ESTABLISH CRITICAL DEFENSE LINE (2) REALIGN LOWER ATCHAFALAYA R. (N3)

c. BUILD CONVEYANCE CHANNELS (1) LAFOURCHE (2) ST. BERNARD (VIOLET TO MRGO)

2. MANAGE ZONE OF SUBDELTAS

a. LAFOURCHE (M1 & M2) b. LOWER MISSISSIPPI DELTA (M3-M6) c. ST. BERNARD (M7) d. ATCHAFALAYA OUTLETS (A1-A3)

3. BUILD LAND WITH DREDGE MATERIAL Note: Refer to maps for locations of features referenced in parenthesis above.

Figure 6-11. Outline of the coastal restoration plan.

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I. DEFENSIVE MEASURES (Figure 12)

A. STOP MARINE TIDAL INVASION

1. Restore Barrier Islands-

Barrier islands are key elements in the geometry of the lower Pontchartrain (St. Bernard area), Barataria, and Terrebonne basins (see Figure 1). The barrier islands and the tidal passes between them control the hydrology of the estuarine basins. Historically, the estuaries landward of the barrier island chains have been protected from the destructive forces of high wave energy, storm surges, and saltwater intrusion. In recent decades the islands are experiencing landward migration, island narrowing, segmentation, and area loss. These changes are a consequence of a complex interaction among global sea level rise, subsidence, wave and storm processes, inadequate sediment supply, and intensive human disturbance. The continued loss of these barrier islands will result in the collapse of the estuaries and wetlands that protect and will severely disrupt coastal fisheries. Moreover, a large portion of the petroleum and natural gas infrastructure located in the state’s shallow bays is relatively old and not designed for open-ocean conditions. Exposure of these structures to open-ocean forces sets the stage for chronic oil spills. In addition barrier islands have significant habitat value in themselves, particularly for migratory songbirds, breeding shorebirds, and turtles, many of which are experiencing sever population decreases at the present time. Shoals, reefs, and tidal passes adjacent to the islands provide fish habitat of immeasurable value. The short-term goal for barrier islands is restoration and maintenance of islands that play a critical role in hydrologic control of estuaries and reduction of hurricane induced impact. Critical barrier islands are those chains extending from Shell Island in Plaquemines Parish to Racoon Point in Terrebonne Parish (Figure 12). These are the barrier islands along the seaward edge of the Barataria and Terrebonne estuarine basins. Restoration is proposed for the most important segment of the critical barrier islands. This should be accomplished by dredging sand from buried offshore and onshore deposits and by using material from maintenance dredging neighboring navigation channels. Two priorities for restoration are recognized. The highest priority if for those islands that are nearest to, or attached to, a headland. The second priority is for islands on the distal ends of the island chains and which are more subject to rapid shifts, changes, and loss of sand. Computer model studies of the consequences of restoring the Terrebonne barrier islands to their 1870’s configuration indicate a number of benefits (van Heerden, Kemp, and Suhayda, 1993). Island restoration would decrease the tidal prism (69%), with a corresponding decrease in marsh surface inundation periods. There would be an average salinity decrease to 1/3 of present conditions. The average area of tidal flooding would be reduced (about 30,00 acres of Terrebonne wetlands). Tidal currents and shoreline erosion rates would be reduced. In addition wetland salinity would be changed, resulting in a reduction in the area of saline and brackish marshes, and an increase in the area of fresh and intermediate wetlands. The Terrebonne model indicates that restoring the

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Figure 12. Defensive measures of the restoration plan.

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barrier islands to their 1870’s configuration would protect 117,000 acres of wetlands and that there would be a total long-term gain of 147,000 acres. Restoring the barrier islands also would substantially decrease communities landward of the inlands. By using the uninhabited barrier islands as a component in the regional hurricane protection strategy, it is possible that hurricane protection levees presently being planned could be reduced in size resulting in savings in cost for construction and maintenance. Deltaic barrier islands and associated tidal inlets are mobile and can be effectively managed as such. The shift positions through time, generally migrating both in the direction of longshore drift and inland. Efforts to stabilize barrier islands and inlets with rocks or other rigid structures may be justified to protect homes, businesses, roads, and other infrastructure, but have generally proven to be costly and futile. The most satisfactory solution is to restore and maintain sand beached along the seaward sides of the islands. The technology to accomplish barrier island restoration through various nourishment approached has already been demonstrated on Grand Isle (Louisiana’s only inhabited barrier island), on East Island in the Isles Derniers chains, and on Wine Island immediately to the east. Approximately 20 to 25 million cubic yards of material will be required to restore the Terrebonne Basin’s Isle Derniers land bridge and associated barrier island chain. The barrier islands along the seaward side of the Barataria estuarine basin will probably require a similar amount of sand. Ship Shoal, an offshore sand body that lies approximately 11 miles south of Isles Derniers, contains an estimated 1.5 billion cubic yards of borrow material, ranging from very fine to medium sand (Figure 13). This material constitutes an excellent source for barrier island restoration. Long-term concepts for barrier island restoration may call for the mining of sediment from Ship Shoal and utilizing of this sand for large-scale barrier island restoration. Restoration and maintenance of barrier islands requires more than a one-time pumping of sediment onto the island. There must be a ribbon of mobile, granular material on the seaward side of the island to absorb wave energy. Proper design of such a program requires quantitative data in response to a number of critical questions. How much sand is needed to restore each island? How much sand must be added to maintain the budget? How frequently must sand be added? What particle sizes and sorting of sand are required in reference to the wave energy and longshore currents active on the island? The long-term goal is to maintain dynamic chains of barrier islands around the perimeter of the Deltaic Plain. Some new barrier islands will develop as existing land masses continue to deteriorate (notably in the active Mississippi delta area and in the lower Pontchartrain basin between Lake Borgne and Chandeleur Sound). New barrier island chains will eventually form during the waning phases of subdelta lobes developed under this program.

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Figure 13. Ship Shoal provides a potential source of sand for restoration of the critical barrier

islands along the Louisiana coast (After l. Ll van Heerdon, 1994). Because of the important function which barrier islands play, it is proposed that new islands be constructed with dredge material at some locations. Maximum benefits occur when the islands are situated across the lower ends of sub-basins, where they will perform important functions in controlling the hydrology of those units and will prolong the life expectancy of the wetlands within the units. They will also improve conditions for finfish, shellfish, and shorebirds. Priority for barrier island restoration and/or building must be based on the island’s overall functional value to the natural system. Evaluation factors include hydrological benefits, overall estuarine geometry (long-term), critical habitat conservation, marsh protection, and the costs relative to other types of projects that accomplish similar objectives. 2. Establish “Critical Defense Line” (CDL)-

A line has been delineated across the coastal zone where the destructive invasion of marine tidal processes must be halted (Figure 12). The trace of the line is based upon a number of factors that control hydrology, including: 1) present location of the leading

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edge of marine tidal processes; 2) location of fault zones bounding high subsidence areas, and; 3) location of critical ridgelines and land bridges. Landward of the CDL the wetlands that constitute the estuarine headwater catchment areas are largely freshwater terrestrial in character. Their soils are highly organic, they have low hydrologic energy conditions, and they are little influenced by ebb and flow of daily tides. If the CDL boundary is penetrated by hydrologically efficient or enlarging channels that increase the rate of exchange with the lower estuary, large fresh water wetland areas will be subject to fluctuations in salinity, sulfides, and energy conditions that give rise to rapid degradation and erosion. There must be a strong resolve to prevent uncontrolled tidal ebb and flow from progressing inland of this line. The nature of CDL boundary is variable. Along some segments it is delineated by existing flood protection levees. These are located primarily along coastal corridors and in other places where agriculture and various other kinds of developmental land use are in place.3 Along other segments the line is delineated by low-lying natural levee and chenier beach ridges, which form natural hydrologic boundaries. Along some segments the boundary is not well delineated, but rather is a transitional zone from fresh or brackish low-energy conditions, with no more saline higher-energy conditions, with no distinguishing features in the marsh or shallow water bodies. Long-term maintenance of the boundary likewise takes a number of forms. These include maintaining critical land bridges and ridges, use of maintenance and dedicated dredging material to restore wetlands, hydrologic management, and reef and shore zone management. Where natural levees and cheniers provide a boundary they should be maintained, and reinforced. Specific measures should be taken to prevent them from being breached. In those segments where artificial levees presently exist, or where they may be required in the future, the boundary is a rigid structural feature. Where the boundary crosses an interdistributary basin, it should be maintained as a “leaky hydrologic barrier.” A leaky barrier is one where water exchange is permitted across the boundary, but precautions are taken to prevent the volume of water exchange from increasing. In some instances it may be desirable to reduce the existing volume of water exchange without unnecessarily interfering with estuarine functions. This is achieved by strengthening, through restoration and management, land bridges and ridges and preventing expansion of natural and artificial tidal and backswamp drainage channels. The leaky barrier concept depends in part upon sufficient fresh water outflow for the upper basin through the barrier t offset saltwater intrusion. In basins where fresh water outflow is deficient it should be supplemented through fresh water diversions. Important advantages of the leaky barrier are that it does not prevent ingress and egress

3 Coastal corridors are agriculture and development areas that usually follow natural ridge features through the wetlands of the coastal zone. In many instances the development has been extended beyond the natural ridges through land reclamation accomplished with levees and forced drainage systems. Such areas surrounded by levees and subjected to forced drainage are called fastlands. Structures and development along unleveed segments of the corridors are subject to flooding.

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of estuarine organisms and does not block the export of organic nutrients from the upper ends of the estuarine basins. As subsidence continues it may be necessary to construct additional artificial levees and hard structural shore zone management features along additional segments of the CDL. These features will have to be designed to withstand open water wave energies and storm surges. It will require most of the financial resources that can be marshalled during the next 25 years to establish the critical defense line. Vast fresh water wetland areas and low ridge lands landward of the line will be subject to deterioration and lost to erosion if this goal is not achieved. Failure to establish and maintain the CDL will also endanger many coastal cities and communities. 3. Stop Marine Invasion in Navigation Channels-

Marine tidal invasion presents a problem along most navigation channels and waterways that cut through the coastal zone (Figure 12, N1-N5, N7 and N8). There are three alternative treatments: 1) construct locks on the waterways to prevent saltwater intrusion and to reduce tidal effects (an example is found today on Freshwater Bayou); 2) completely isolate the banks of the channels form adjacent wetlands and waterways (there is no example where this has been successfully done in Louisiana); 3) supply supplemental fresh water to offset tidal intrusion (the proposed Davis Pond Fresh Water Diversion will partially offset tidal intrusion in the Barataria Waterway), or; 4) replace particularly damaging channels with less destructive alternative. The banks of most navigation canals and natural waterways used for navigation are subject to rapid erosion and bank slumping. Boats throw up wakes and cause suction as large vessels pass through channels with narrow cross-sectional areas. Bank erosion and slumping rates are highest where channels have been constructed through wetland areas with deep organic soils. In addition, a zone of marsh breakup usually occurs adjacent to the channels in such high organic soil areas. A variety of bioengineering, and in some instances structural techniques will be utilized to stabilize fragile techniques will be utilized to stabilize fragile banks. A comprehensive program of bank stabilization in environmentally fragile areas is proposed, although it is recognized that existing technologies will require considerable adaptation and development to achieve these goals. Any future navigation channels must be compatibility with the plan for natural system management. a). Phase-out the Mississippi River-Gulf Outlet (MRGO)- The MRGO has been, and continues to be, a major cause of wetland loss in Louisiana (Figure 12, N-7). It is a man-made arm of the sea that allows marine processes to intrude deeply into the Deltaic Plain. It breaches a major hydrologic boundary, goes

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through areas of highly organic soil, had a large and expanding cross-sectional area, and because of the size of the ships that use it, the channel is subject to bow suction effects. Detrimental impact of the MRGO is ongoing and cumulative. The only effective way to curtail these destructive processes is to close the channel. The most favorable place for a closure is where the channel cuts through the natural levee ridges of Bayou Lafourche. Here soil conditions are favorable for a closure structure and the closure will restore the integrity of an important natural ridge system which formerly divided two hydrologic basins (before the ridge was breached by the MRGO). It is proposed that the channel be left open both landward and seaward of the point of closure to accommodate local fishing and navigation interests. Phase-out of the MRGO should be done in conjunction with a re-evaluation of the long-term plans for port development along the Mississippi from Baton Rouge to the Gulf. New ship locks in the Inner Harbor Navigation Channel could provide access to existing facilities in the Centraport plan, which is the tidewater component of the Port of New Orleans, should be re-evaluated in light of the far-reaching channel and flow allocation changes which will be required for coastal restoration.

b). Control Tidal Movement in Houma Navigation Channel, Barataria Waterway, Calcasieu Ship Channel, and Sabine Ship Channel-

There are relatively few remaining fresh water wetlands along the Houma Navigation Channel (Figure 12, N-4). However, the channel provides a pathway for storm generated surge and should be fitted with a flood gate. Because its cross-sectional area is relatively small, tidal intrusion along the Barataria Waterway (Figure 12, N-5) may be offset by introducing supplemental fresh water into the Barataria Basin through the Davis Pond Fresh Water Diversion. The Sabine Ship Channel and the Calcasieu Ship Channel are also corridors for marine tidal invasion (Figure 12, N-1 and N-2). The present plan (as well as the CWPPRA plan) calls for protecting affected wetlands by isolation them from the channels. If this approach does not work, locks at the seaward ends of these two channels may ultimately be required. B. PREVENTIVE MAINTENANCE 1. Maintain Fresh Water Basins Restoration of overbank flooding through fresh water diversions will be the principle preventive maintenance technique for the remaining fresh water basins identified as A-G in Figure 3.

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a). Fresh Water Diversions- From 12 to 15% of the total Mississippi-Atchafalaya system flow on an annual basis should be dedicated to fresh water diversions into the upper and middle estuarine basins to compensate for loss of overbank flow (Templet, 1944). These features provide a method for restoring overbank flooding in a way that is compatible with present land use, flood protection, and drainage patterns (Figure 12, D1-D11). Many small diversions may be better than a few large ones. A few sediment diversions may be added, however to initiate crevasse splays and lacustrine delta building. These are necessary sedimentary episodes that drive environmental succession in fresh water basins. The spring flood pulse of the rivers should be used to inundate deltaic wetlands to provide a short period sedimentation and wetland maintenance each year. It should be distributed during the six high water months (December-June) through as decentralized a network as possible. Flow should be regulated through the diversions to maximize sediment dispersal, vegetation and fauna enhancement and minimize damage to human activities. The present plan supports implementation of the authorized and planned U.S. Army Corps of Engineers diversions, however they should be redesigned, where feasible, to maximize sediment introduction, improve wetland maintenance, and maximize water quality. Lower sills, higher flows, removal of sediment traps and placement for sediment capture will improve their effectiveness. Mississippi River at Davis Pond - The proposed 10,650 cfs fresh water diversions at Davis Pond is compatible with the present plan and should be implemented (Figure 12, D3). This would be the largest fresh water diversion. Outfall would benefit the middle Barataria Waterway. This will be an important element in maintaining a leaky barrier segment of the critical defense line. Mississippi River at Bonner Carre - A large fresh water diversion has been proposed at the Bonnet Carre location (Figure 12, D2). This would allow a maximum of 30,000 cfs of Mississippi flow to be introduced into Lake Pontchartrain. This volume of river water could cause high turbidity and pollution, which may be incompatible with recreational uses of Lake Pontchartrain. A current re-design effort is underway, which would shunt as much of this water as possible through existing wetlands before it enters the open waters of the lake. This would trap some suspended sediment, and reduce excessive nutrients. Under the revised plan the diversion would only be operated during high stage conditions. Mississippi River at Blind River - This plan proposes a fresh water diversion into the upper Pontchartrain Basin in the vicinity of Romeville or Lutcher (Figure 12, D1). This would be smaller diversion (5,000 to 10,000 cfs) and could be accomplished with a multi-barreled siphon structure. A conveyance channel would direct flow into the upper reaches of the Blind River drainage basin. The vast Cypress-Tupelo Gum swamps

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around Lake Maurepas would benefit from the introduction and would absorb turbidity and pollutants. East of Lafourche Conveyance Channel - Overbank flooding into the upper Barataria Basin could be accomplished by leaving low spots or gaps along the confining bank of the major conveyance channel as proposed for the Lafourche corridor in a subsequent section of this report (Figure 12, D8 and D9). West of the Atchafalaya via the GIWW - An opportunity exists to extend the influence of Atchafalaya River water and sediment further west into the Chenier Plain area via the GIWW (Figure 12, D10 and Figure 15). The main constraint is the navigation locks on the waterway, which maintain water levels within the Mermentau Basin. b). Succession Management of Fresh Water Basins- A variety of landforms, habitats and conditions occurs in the fresh basins which lie landward of the critical defense line (Figure 12). While conditions in some areas area so well balanced that change in some areas are so well balanced that change is almost imperceptible for hundreds of years, alterations in hydrology, sediment supply or biological factors often trigger rapid and dynamic landscape changes. Cause and effect relationships are reasonably well known, as are the sequences of change or successions, which may unfold when balances are upset. The understanding of cause and effect relationships and natural or induced sequential change provides the basis for long-term management of these areas. Fresh water vegetation has the remarkable ability to build and maintain living surfaces. Under natural conditions vegetation growth and accumulation of plant materials were the dominant geomorphic processes in vast areas of the upper Deltaic Plain and mush of the Chenier Plain. The plants are able to maintain living surfaces in high subsidence areas through accumulation of peat deposits and development of floating marsh root mats (flotant). Living swamp and marsh surfaces persisted for thousand of years. Fresh water habitats may persist with or without overbank sediment input. Flotant development may be initiated or accelerated in selected areas that are distant from overbank sediment sources. Terracing and fencing are effective techniques for providing a skeletal framework essential to flotant development. These are techniques for reducing wave action and inducing sedimentation in shallow marsh ponds and lakes. In other areas it may be more desirable to increase the number of streams and water bodies in the fresh water basin. This may be accomplished by increasing the hydroperiod (induced flooding) and/or by dredging channels and lakes. Succession may be accelerated or altered through hydrologic management and/or induced sedimentation. An example of an induced sedimentary event would be the initiation of a lacustrine delta by constructing an artificial crevasse distributary. Sedimentary events may also be induced by directing hydraulic dredge material into fresh water basins.

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It is the natural course of events for some swamps to open up, while others fill in. Continuity of productive wetland habitats in fresh water basins depends upon predictability, monitoring, and hydrologic measurement. However, some areas require only regulatory management and sound land use practices. The temptation to overuse structural measures should be resisted. “If it’s not broke don’t fix it.” 2. Enhance Estuarine Areas-

The vast area lying south of the critical defense line will continue to revert from land to open water (Figure 12). In addition the ridges and barrier islands will continue to sink. Where major ridges are at or near the surface, they may be reworked into barrier islands and shoals as coastal retreat progresses. Thus, this area will gradually change to mostly shallow, open water with scattered islands shoals. In this zone emphasis of both the state and federal programs should be placed upon managed deterioration and retreat of wetlands, barrier islands and Gulf shore. Emphasis should be shifted from management of emergent wetlands to management of shallow estuarine water bodies. The extensive shallow bays, remnant salt marsh islands, barrier islands, shoals and reefs will continue to be an exceptionally resource rich estuarine area. The CWPPRA should be amended to provide for management and enhancement of shallow water fisheries habitat of this zone.

Coastal communities seaward of the CDL will be increasingly affected by

flooding as a result of subsidence and will become more vulnerable to hurricane and storms. It will be necessary to relocate some coastal communities.

a) Develop Reef Zone-

It is proposed that a series of oyster reefs be artificially initiated in each of the deltaic estuaries. The lining reefs will produce large volumes of oyster shells, some of which will wash onto the shore to form beaches. The reefs and beaches are resistant to erosion and reduce storm surge. These reefs should be formed along broad arcs, and along the shorelines of lakes and bays in critical areas (Figure 12).

b) Manage Shore Zone-

Along bays and lakes where shoreline erosion rates are excessive and/or where

fragile wetlands and land bridges are threatened, structural measures to reduce shoreline erosion may be appropriate. However, in such instances the structural measures should be designed, not only to protect against erosion, but also to enhance and diversify fish and wildlife habitats of the shore zone. Features should include segmented barriers, granular beaches, tidal inlets, shallow flats, grass beds and reefs (Figure 14). A shore zone management project of this type is proposed for the Lake Borgne area, where it would extend along the lake shore from the Rigolets in Orleans Parish to Bayou St. Malo in St. Bernard Parish (Figure 12).

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Figure 6-14. Typical components of a shore zone management project (After S. M. Gagliano, et al., 1994).

II. OFFENSIVE MEASURES (Figure 15) A. RESTORE LAND BUILDING PROCESSES 1. Reallocate Distribution of Mississippi-Atchafalaya River System Flow-

Long-term maintenance of the coastal area (25 to 50 years and beyond) depends upon reallocation of Mississippi River flow and transported sediment. As indicated previously, 12 to 15% of the river system flow should be directed into the upper and middle basins through fresh water diversions to compensate for blockage of overbank flows by flood protection levees and closure of historic distributaries. A zone of subdeltas must be established along the seaward side of the critical defense line. This can only be accomplished by discontinuing wasteful practices of discharging river water and transported sediment into areas where the delta building process does not occur, or where land building is inefficient because of deep water or high subsidence rates. Poor delta building conditions presently exist at the major outlets of the Mississippi River in the active delta and the Lower Atchafalaya River Navigation channel. This wasted water and sediment must be redirected into the zone of subdeltas. Reallocation of flow and sediment may necessitate construction of new navigation entrance channels into the Mississippi River and the Lower Atchafalaya River. It will

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Figure 15. Offensive measures of the restoration plan.

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also include the construction of the planned Davis Pond diversion, as well as major new distributary conveyance channels. Existing waterways, such as the GIWW should be used as lateral channels to move water across and between basins. This is presently occurring through the GIWW in the vicinity of the Lower Atchafalaya River and Wax Lake Outlet (Figure 16). This plan involves major changes in water distribution not only for environmental management purposes but will also necessitate equally major changes for navigation and flood control. Developing and implementing an comprehensive plan for reallocation of flow and overhauling the present plumbing system is beyond the scope of the existing state coastal restoration program and/or the federal CWPPRA program and will require congressional authorization. Relocation of navigation channels must be achieved within the next 25 years. a). Increase Atchafalaya River Flow- Implement a phased diversion of Mississippi River waters into the Atchafalaya River (Figure 15) on an estimated 2%/yr basis until 40% is reaches and carefully monitor the results. Increase percentage flow to the Atchafalaya River if results are positive. This will partially reinstate the long period sedimentation event. Flow should be dispersed through natural channels and canals into the coastal marshes as widely as possible. b). Change Navigation Channels- Ports and navigation channels are vital to the economy of Louisiana and the state’s coastal waterways provide a gateway to the country. However, the present navigation system was designed prior to the recognition of the importance of wetland and estuarine environments and prior to a full understanding of how the natural systems functioned. The river water distribution system, including navigation channels and flood control structures, must be renovated to make it compatible with current water resource needs. New Mississippi River Entrance (Empire-Gulf) - At present, the Southwest Pass channel is maintained at a depth of 45 feet as the major navigation entrance to the Mississippi River. The operational depth through Southwest Pass is scheduled to be increased to 55 feet within the near future. The Mississippi can only support a diminutive delta. Land building in the lower delta is inefficient because of high subsidence rates. It is a matter of budgeting the available sediment load of the river system to build and maintain the largest wetland area possible. The lower delta can only be maintained at the expense of losing larger acreage elsewhere. Reallocation of low from the lower delta into other areas will result in unavoidable losses of wetland in the lower delta. These will be replaced by new subdelta lobes, but in different places.

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A new navigation entrance channel into the Mississippi River should be constructed and it should be designed to minimize the flow of sediment charged waters into the depths of the Gulf of Mexico. Two alternative locations are: 1) on the west bank from the vicinity of Empire to the 60 foot contour in the Gulf (Figure 12, N6), or; 2) on the east side of the river south of Point a la Hache, eastward to the MRGO, and then to the deep waters of the Gulf. The west bank location is preferred. Design and construction of the new navigation entrance into the Mississippi River will be done during Phase I. By Phase II the new channel will be completed and opened. In effect, the “Head of Passes” will be relocated in the vicinity of Empire, Louisiana. Maintenance dredging of Southwest Pass will be discontinued. The lower delta will be cut off from active flow and transported sediment and will begin to deteriorate. Barrier islands will form as the old deltaic landmass begins to erode back and deteriorate. Realign Lower Atchafalaya River - For the past decade outflow from the Lower Atchafalaya River has been utilized to reduce dredging requirements in the navigation channel. This was achieved through a rock weir that was constructed at the upper end of the Wax Lake Outlet. This sill limited the amount of flow and bedload passing through the Wax Lake Outlet and forced most of the flow and sediment through the Lower Atchafalaya channel. As flow left the confined channel velocities decrease and sediment was deposited to form bars and shoals. Since these block navigation, an extensive dredging program has been required to keep the channel open. The channel passes through Atchafalaya Bay to Eugene Island and then extends 11 miles offshore from Eugene Island until it reaches the 18-foot contour in the Gulf. However, unlike the situation in the lower Mississippi Delta, where jetties are effective because deep water is located a short distance from the channel outlets, the Gulf bottom is gently sloping beyond the offshore entrance to the Lower Atchafalaya Navigation Channel. The 30 foot contour lies another 20 miles seaward of the present channel entrance. Thus, as long as a significant amount of the river’s bedload passes through the navigation channel it will require a perpetual commitment to maintenance dredging. As fast as sediment is removed from the channel, new bars will accumulate. The Corps of Engineers is now in the process of removing the rock weir located at the head of the Wax Lake Outlet and is considering deepening the channel in the vicinity of the weir by dredging.4 If this plan is carried out, it is predictable that the Wax Lake Outlet will gradually capture most of the flow of the Atchafalaya River. This should result in accelerated growth of the Wax Lake Outlet subdelta and should reduce the dredging requirements to maintain navigation in the Lower Atchafalaya Navigation Channel. These changes being made by the Corps are completely consistent with the state plan presented in this report. In addition this plan recommends that the navigation channel be realigned so that it passes between the Wax Lake and Lower Atchafalaya subdelta lobes in its alignment through Atchafalaya Bay (Figure 12, N3 and Figure 15).

4 Removal of the rock weir began in May 1994. Current plans of the New Orleans District Corps of Engineers call for complete removal of the weir and supplemental dredging to restore the cross-sectional area to pre-weir conditions. The work is scheduled for completion during the fall of 1994.

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c). Build Conveyance Channels- Conveyance channels are open conduits leading to subdeltas (Figure 15). They can deliver flow and sediment to areas of the coast where subdelta building is needed to offset erosion. Each channel should be approximately 1/3 the size of the Atchafalaya River. The channels should be confined by levees for much of their length. Some conveyance channels will require a number of major highway and railroad bridges and numerous pipeline crossings will also be necessary. Special hydrologic design problems will be encountered where the conveyance channels cross the GIWW. A zone of phased subdelta extending around the seaward perimeter of the Deltaic Plain is a keystone element of this plan. Multi-distributary outlets must be initiated and maintained across a broad arc around the seaward margin of the Deltaic Plain (natural outlets and diversions through conveyance channels). Each will lead to a strategically located subdelta. The subdeltas will be initiated sequentially to optimize diversity and resources yield. Each subdelta will be allowed to develop through a sequence of phases. The phases will drive an environmental succession in the subdelta area. Lafourche Conveyance Channel - A major conveyance channel is needed along, or parallel to, Bayou Lafourche (Figure 15). There are two options for this channel: 1) dredge out the old channel of Bayou Lafourche or; 2) construct a new channel following the backslope of the natural levee ridge of Bayou Lafourche. In the first option, to accommodate the required discharge portions of the bayou will have to dredged. Dredge material would be disposed of to create or restore wetlands adjacent to the bayou. An interim project utilizing a siphon at Donaldsonville could provide up to 2000 cfs of Mississippi River water into the existing channel of Bayou Lafourche. In the second option the channel would leave the Mississippi River in the vicinity of Aben or Lauderdale, Louisiana and follow the eastern swamp side of the sugar cane fields along Bayou Lafourche to the area between St. Charles to Raceland, Louisiana, where it would turn south and cross Bayou Lafourche. One branch of the channel would feed a subdelta lobe in the southwestern part of the Barataria Basin. A second would supply flow and sediment to a subdelta in the upper Terrebonne-Timbalier Bay area of the Terrebonne Basin. Under either option, approximately 10 - 12% of the Mississippi River flow and transported sediment would be directed down the channel to feed two subdelta areas. Overbank flooding into the Barataria Basin would be a feature of the project. Communities along the bayou are experiencing a shortage of drinking water, which is obtained from the bayou. This problem would be alleviated by either alternative. The oil industry job pool is rapidly disappearing in this area; restoring the bayou to a navigable waterway and associated marsh creation could open up many opportunities for job creation, including the development of an ecotourism industry.

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St. Bernard (Violet to MRGO) - Wetland areas in the lower Pontchartrain Basin (St. Bernard marshes) will continue to deteriorate during the next 25 years. This will leave the New Orleans metropolitan area and satellite cities of southeastern Louisiana (i.e. Chalmette, Metairie, Slidell, Mandeville) much more exposed to open conditions of the Gulf. In order to re-establish a deltaic land mass to the southeast, a major conveyance channel is recommended. The channel would be located in the vicinity of existing Violet Canal in St. Bernard parish and would connect with a segment of the existing channel of the MRGO (above the point of closure recommended in section C.1. of this report, see Figure 15). The conveyance channel would then branch to the east, where it would provide water and sediment to a subdelta lobe along the southern side of Lake Borgne. Planning, design, and right-of-way acquisitions would be done during Phase I, and the channel would be built during Phase II. 2. Manage Zone of Subdeltas-

A zone made up of ten subdelta lobes would be created and maintained extending across the Deltaic Plain and lying on the seaward side of the critical defense line. These subdeltas would be supplied by existing Mississippi and Atchafalaya channels and the proposed Lafourche and St. Bernard conveyance channels. Their development and management would be phased. Some are already in existence and growing (Figure 15, A1 and A2). Others could be developed during Phases II and III. The subdeltas should be brought on line at intervals, so that while some are maturing others would be in their initial stages of development. This would result in maximum diversity of habitat conditions across the Deltaic Plain, with a constant dynamic renewal.

a). Lafourche (M1 &M2)- The subdeltas supplied by the Lafourche Conveyance channel will be directed into the highest erosion area along the Louisiana coast. One subdelta will build into the upper reaches of Terrebonne and Timbalier Bays (Lakes Barre, Felicity, and Raccourci) and the second into the Barataria Basin in the vicinity of Little Lake. b). Lower Mississippi Delta (M3-M6)- A cluster of three subdelta lobes will be maintained along the lowermost reaches of the Mississippi River. Mississippi River below Bohemia - The largest of the three lower delta lobes will be on the east side where the Mississippi River will be diverted into Breton and Chandeleur Sounds through the Bohemia Wildlife Management area (Figure 16). Approximately 5,000 acres of new wetland will be created in this stable basin every year. Increased sediment and fresh water input will greatly aid the St. Bernard marsh complex

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Figure 6-16. Conceptual interpretation of the Breton delta and Mississippi birdfoot delta

approximately 20 years after the diversion into Breton Sound (After l. Ll. van Heerden, 1994).

and freshen Lake Pontchartrain. The wrap-around geometry of the resulting subdelta would also protect existing wetlands. Mississippi River at Empire - A controlled diversion will be initiated on the west bank of the river in the vicinity of Empire, Louisiana, which will initiate a subdelta lobe in the Adams Bay and Bastion Bay areas. After the subdelta landmass has been allowed to grow for 25 to 50 years, the new navigation entrance from the Gulf of the Mississippi River will be cut through the land mass. The subdelta will occupy an area that has historically been a major oyster producing area. However, changing conditions will make the area increasingly less favorable for oyster growth and thus, an excellent candidate site for a controlled subdelta. Mississippi River at Venice - The historic area of active delta building below Venice, Louisiana will gradually deteriorate, but a subdelta lobe will be maintained in part of the lower delta area. The lobe will extend into parts of the old West Bay and Cubits Gap subdelta areas.

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Mississippi River at Myrtle Grove - A conveyance channel at Myrtle Grove will lead into a subdelta area in the vicinity of the southeastern Barataria Basin. This is an area of remnant marsh island in extensive shallow bays. c). St. Bernard (M-7)- A controlled subdelta lobe will be initiated in the St. Bernard marshes along the eastern shore of Lake Borgne and in the vicinity of Bayou St. Malo and the Biloxi Wildlife Management Area. d). Atchafalaya River Outlets (A1-A3)- Outflow and sediments from the Atchafalaya outlets dominates a large segment of the Louisiana coast (Figure 17). Changing conditions in this area it will necessitate fine-tuning of flow allocation into the existing subdelta at the outlet of Wax Lake Outlet and the Lower Atchafalaya River, and a third subdelta proposed in this report, as well as though lesser distributary channels to optimize delta growth and productivity. Wax Lake Outlet Subdelta - This is presently the area of greatest subdelta growth, and it will continue to be the fastest area of subdelta growth during Phase I of the program. Lower Atchafalaya River Subdelta - Growth of the subdelta into Atchafalaya Bay will continue during Phase I, but the rate of growth will decrease during Phases II and III. Atchafalaya Channel Training to Four League Bay - A branch training channel should be dredged on the east side of the Lower Atchafalaya River Channel. This will direct subdelta growth into Four League Bay. A wrap-around subdelta lobe would develop in the bay which would provide long-term protection to the large area of fresh and fresh-floating marshes of western Terrebonne Parish (the Bayou Penchant Basin). 3. Build Land With Dredge Material-

Bucket dredges, draglines, hydraulic dredges and spray dredges are basic restoration tools. They must be used to supplement natural depositional processes if a goal of no net loss is to be achieved. However, because dredging represents an intervention into natural processes and because it is costly, it must be used judiciously. The success of the restoration program depends upon redirecting fresh water and sediment from the Mississippi and Atchafalaya River system to areas along the coast. Many areas are too distant from the river channels to receive direct benefits from diversions. Utilizing pipelines to direct sediment to these areas may be the solution. Hydraulic dredging has long been utilized in Louisiana and other areas a technique for land filling and beach nourishment. The distance from the dredging location to the

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Figure 6-17. South Central Louisiana coastal areas presently benefiting from Atchafalaya River

fresh water and transported sediment (After l. Ll. Van Heerden 1994). dredge material discharge point can be extended through the use of booster pumps. Major advances have been made in the use of dredge material to create and enhance functioning wetlands. These advances must be expanded and integrated into cost-effective approaches that are workable at the scales required to rebuild Louisiana’s wetlands. Dedicated dredging could be performed year round and with reductions in the costs of transport and placement. This technique could have widespread application. Slurry pipelines should be considered as modern surrogates for natural distributary channels in a system tightly managed for navigation, flood control, fisheries, and energy development. Slurry pipelines can transport water with sediment concentrations of 100,000 to 600,000 mg/l. At about 15 percent solids, the lower limit of slurry transport, a single 24 inch slurry pipeline could theoretically transport sediment at nearly 30 times the rate of an open channel passing more than 100 times the water at normal surface river water concentration of 150 mg/l. Pipelines may have a more general applicability if they can be directed to the relatively small interior marsh “hot spot” where wetland loss is concentrated. Use of

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long-distance pipelines and hybrid sediment transport systems, that could include barge transportation links, should be used to aggressively build and maintain wetlands and barrier islands. Sediment mined from the Mississippi and Atchafalaya Rivers could be stored and prepared at depots to be shunted into a temporary pipeline network for transport to nearby land-building locations, or, alternatively, loaded on barges and sent to more distant sites. At each wetland restoration site, a distribution network would be set up with a booster pump brought in to do the final material placement. Once the terminal distribution system was installed; it could be used whenever an opportunity arose, or for regular maintenance as required. Other approaches might rely on sediments dredged from offshore or from hopper dredging operations at the rivers mouths. Pipelines used might be newly laid or refurbished natural gas pipelines already in place. All of these options call for tapping into essentially limitless sources of material that can be economically mined and transported in slurry form. All available, non-toxic dredge material generated by maintenance dredging should be used to nourish and create wetlands and/or barrier islands. Other sources of non-toxic materials (e.g., spent bauxite) should also be used.

RECOMMENDATIONS FOR CWPPRA FEASIBILITY STUDIES

Re-establishing large scale sedimentation processes and hydrologic “buffers” are the principal long-term solutions to Louisiana’s coastal wetlands loss. A strategy to reverse the loss calls for initiating feasibility studies on the following four major project concepts.5 This list reflects the state’s desired order of initiation and does not imply their relative importance:

1) Increasing the share of Mississippi River borne sediments sent down the Atchafalaya River on an annual basis in accordance with P.L. 101-646, Section 307 (b) to maximize delta development without creating new flooding;

2) The re-establishment of the barrier island systems along the seaward

perimeters of the Barataria and Terrebonne Basins, to an extent sufficient to ameliorate negative effects on estuarine wetland hydrology;

5 Two feasibility studies, as recommended to the CWPPRA Task Force by Governor Edwin Edwards, and which were a direct result of the OCA Workshop, were approved by the CWPPRA Task Force on July 14, 1994. There will be an evaluation of large scale Mississippi and Atchafalaya River diversion, which will be conducted under the direction of the New Orleans District, Corps of Engineers and an evaluation of barrier island restoration and maintenance conducted under the direction of the Louisiana Department of Natural Resources.

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3) Modifications to major navigation channels sufficient to offset marine transgressions of historically fresh and intermediate coastal wetlands and to reallocate flow and sediment for diversions and subdelta building in other areas. Channels to be studied, at a minimum, include the MRGO, Barataria Waterway, Houma, Calcasieu, GIWW, Sabine, lower Atchafalaya, and the lower Mississippi;

4) A Mississippi River diversion plan including: upper basin diversions, Bayou

Lafourche corridor diversion, lower Mississippi diversions below New Orleans, and lower Atchafalaya diversions; in order to maximize the wetland conservation and creation potential of the water and sediment resources of the lower Mississippi River system.

To insure that the appropriate large-scale projects are implemented within a

reasonable time, the feasibility studies should begin immediately (January 1994) and should have achieved most major objectives by 1996. This date coincides with the three year statutory deadline for the evaluation of the comprehensive plan called for in P.L. 101-646 (Section 303, b,7). Socioeconomic issues are of paramount importance and should be considered in conjunction with the feasibility studies. At a minimum this should include consideration for flood protection for critical development corridors and phased relocation of coastal interests, where necessary, with fair compensation. In order to save time and reduce cost, the feasibility studies should, to the maximum extent possible, incorporate existing data that have been published in scientific papers and technical reports. The studies should also take advantage of the technical expertise available in state agencies, academic institutions and the private sector.

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APPENDIX

Letters of Recommendation from Governor Edwin W. Edwards to Colonel Michael Diffley, District Engineer, New Orleans District Corps of Engineers, regarding recommendations for the Coastal Wetlands Planning, Protection, and Restoration Act program.

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ADVISORY PANEL

Convenors - Dr. L. Bahr and Dr. J. Stone Governor’s Office of Coastal Activities Facilitator - Dr. S.M. Gagliano Panel - Dr. I. Ll. van Heerden, LSU; Dr. G.P. Kemp, LSU; Dr. J. Suhayda, LSU;

Dr. P.H. Templet, LSU; and Dr. J.L. van Beek, Coastal Environments, Inc. Wetland Conservation and Restoration Task Force Members - Department of Environmental Quality

Department of Natural Resources Department of Transportation and Development Department of Wildlife and Fisheries Division of Administration State Soil and Water Conservation Committee

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