Let the Land rejoice, for you have bought Louisiana for a Song.
—General Horatio Gates to President Thomas Jefferson on July 18, 1803
On August 29, 2005, Hurricane Katrina struck eastern Louisiana, Mississippi, and western Alabama, killing hundreds of local residents, displacing hundreds of thousands more, and causing an estimated $200 billion in economic damage. Less than four weeks later, Hurricane Rita struck easternmost Texas and western Louisiana. Although the loss of life from Rita was much less, significant destruction resulted, including the reflooding of some parts of New Orleans that were damaged during Katrina. The devastation wreaked by Katrina and Rita tragically demonstrated the risks that many coastal areas face from hurricanes and associ-
ated flooding. Coastal Louisiana, however, faces many unique challenges, which are the subject of this report and the proposed efforts it reviews.
The Mississippi River Delta and its associated wetlands helped to shape Louisiana’s culture and economy. In addition to being a land of natural beauty and bounty, it is also home to a rich diversity of peoples. While the unique culture of New Orleans and the bayous has been the traditional magnet drawing millions of tourists to the delta, a growing appreciation for the complex wetland systems of the area is attracting increasing numbers of tourists in search of the nature and history of the area. The long, slow mingling of freshwater and saltwater that takes place between the uplands and the Gulf of Mexico has produced a rich mosaic of wetland habitats that support rare and endangered species; great flocks of waterfowl; and commercially exploited populations of furbearers, fish, shrimp, crawfish, oysters, and crabs.
Even in the aftermath of Hurricanes Katrina and Rita, Louisiana will remain a center for oil and natural gas production, transportation, and refining, and its marine fisheries are among the most valuable in the nation. The access it provides to the Mississippi River Basin also makes it a hub for shipping and navigation. The committee recognizes that this report is being released at a time when there may be many more questions than answers. Even so, the report is provided at this difficult time in the hope that its advice on restoring and protecting coastal Louisiana can be considered as part of the nation’s strategy to rebuild the Gulf Coast and reduce the likelihood of future tragedies, such as Katrina and Rita.
HISTORY AND CAUSES OF LAND LOSS IN LOUISIANA
Coastal deposition along the southern edge of the North American continent has been taking place for tens of millions of years. However, the modern Mississippi River Delta as recognized today began to form when, at the end of the last ice age, the drainage of the mid-continent became integrated, creating the Mississippi River itself. Like other coastal deltas, the Mississippi River Delta plain is the product of sediment deposition and accumulation where waters of the river empty into the coastal ocean. During the late Wisconsian glaciation’s peak roughly 22,000 years ago, sea level was 91–106 meters (m) (300–350 feet [ft]) lower than present. When the late Wisconsian glaciers began melting 4,000 years later, an era of sea level rise known as the Holocene transgression began, and with it came dramatic changes in the basin’s hydrologic character. As the Mississippi River Basin eroded, the Mississippi River changed from a system of braided streams carrying coarse-grained sediments to a sinuous, meandering, interconnected system that carried relatively fine grain clay, silt, and sand, similar in some respects to that known today.
Earlier in its history, high rates of sediment accumulation allowed the Mississippi River Delta to build seaward, eventually forming a great accumulation of sediment that thickened dramatically to the south as it crossed the southern margin of the North American continent. The complex set of wetlands and adjacent barrier islands and levees that make up present-day coastal Louisiana represents the seaward edge of a delta plain that stretches landward onto the continent. Thus, the major source of the nutrients and sediment that sustain the natural development and maintenance of coastal Louisiana is the Mississippi River. The Holocene Mississippi River Plain is composed of six delta complexes, four of which are abandoned with transgressive barrier shorelines (Maringouin, Teche, St. Bernard, and Lafourche), and two delta complexes are active (Modern and Atchafalaya) (Penland et al., 1981; Roberts, 1998). The Chenier Plain lies west of the Mississippi River Delta where shoreline changes are linked to the complex switching process (Howe et al., 1935; Gould and McFarlan, 1959; Penland and Suter, 1989; Roberts, 1998). The Chenier Plain’s mud flats prograde when the Mississippi River discharges into the western region of its plain, and the shoreline advances seaward (Wells and Kemp, 1981). When the Mississippi River discharges into the eastern region of its plain, the Chenier Plain shoreline erodes landward, forming individual chenier ridges (Hoyt, 1969). The seaward portions of the present-day delta do not rest upon the North American continent but rather upon the tremendously thick accumulated sediment along the continent’s edge. As a consequence, the seaward portions of the Mississippi River Delta that make up coastal Louisiana, including New Orleans, naturally experience much higher subsidence rates than the vast majority of the North American continent. Until humans began to alter the flow of river water and the sediment it carried, the natural system was, on average, able to keep pace with natural subsidence and global sea level rise.
Over the last 10,000 years, the natural processes acting upon the Mississippi River Delta have created periodic changes in the course of the lower river that resulted in the building of new lobes adjacent to the new channel alignment, while the deprivation of sediments at the abandoned site brought about gradual land loss. As is the case for the entire delta, the lost land was composed predominantly of wetlands, though adjacent barrier islands and natural breaches may have been lost as well. During this time, some portions of the coast experienced land loss while others experienced land gain as the mosaic of wetlands, barrier islands, and natural levees shifted across the delta. However, in the last 200–300 years, human intervention has disrupted this natural process and caused widespread land loss along the entire Louisiana coastline. As people settled in the wetlands in the nineteenth and twentieth centuries, the Mississippi River was engineered to prevent switching course, and the occurrence of flows
and sediment transport through natural levies and the subsequent formation of crevasse splays1 have been eliminated or reduced. Wetlands were drained for agriculture, canals were dredged for navigation, forests were harvested for building materials, and levees were constructed for flood protection.
Oil and gas exploration, with its associated canal dredging, peaked in the 1960s to 1980s. Canals, and the spoil banks formed during their construction, alter local water circulation patterns and sediment depositional processes. Spoil banks impede the flow of water, causing an inundation that may be further exacerbated by sea level rise. These processes result in the drowning of fragile terrestrial vegetation. Freshwater vegetation is also adversely affected by saltwater intrusion from sea level rise or along canals that provide a route for saltwater to intrude into typically freshwater areas. Another negative effect associated with newly open water bodies includes increased wave erosion. There is also evidence that the extraction of large volumes of oil and gas has exacerbated the problems of inundation and saltwater intrusion. Finally, the introduction of nutria (a rodent that consumes marsh vegetation and thrives in Louisiana’s wetlands) has also contributed to wetland loss in many areas.
Natural causes of land loss include subsidence due to compaction of aging deltaic sediments, geologic faulting, sea level rise, and tropical storms or hurricanes. Prior to human settlement, land subsidence was naturally counterbalanced over a long period of time as the resulting low areas tended to be flooded by the Mississippi River or tidal flows, which in turn delivered sediments and nutrients that supported marsh growth. Since the channelization of the river and the construction of flood protection levees, however, these materials have been discharged near the edge of the continental shelf, far from the site where they would tend to support wetland development. Without them, the wetlands cannot keep up with all of the natural and human-caused relative sea level rises. This problem is compounded by the rise of global sea level, which may be accelerating in response to global warming. Taken together, the various natural and anthropogenic factors have resulted in a wetland loss of 62.2 square kilometers (km2) per yr (24 square miles [mi2] per yr) on the Louisiana coast over the 10-year period from 1990 to 2000 (Barras et al., 2003).
The cost to protect and restore coastal Louisiana is estimated at $14 billion over a 30-year period, not counting long-term operations and maintenance. Among the national and local policy issues associated with or
impacted by Louisiana’s coastal land loss are fisheries, oil and gas operations, navigation, water quality, sediment management, hurricane protection, flood management, and hypoxia and other issues related to nutrient pollution. While these linkages are real, it is very difficult to estimate the financial impact of future wetland loss. The public-use value has been estimated by the State of Louisiana to be in excess of $37 billion by 2050. The loss of infrastructure has been estimated at $100 billion. Hurricane Katrina caused an estimated $200 billion in damage; the degree to which this amount would have been reduced had wetland loss in Louisiana been reduced could not be determined by this committee. Development of the infrastructure impacted by Katrina contributed to the loss of wetlands; furthermore, while the existence of wetlands is known to reduce storm wave intensity, their role in reducing storm surge is less straightforward.
HISTORY OF COASTAL PROTECTION IN LOUISIANA
The challenge of slowing the loss of coastal wetlands and adjacent barrier islands and levees in Louisiana is unprecedented. The geographic extent of these wetlands2 and the range of natural and human forces that cause wetland degradation contribute to what would be one of the largest civil works projects in U.S. history. Extending from the Texas border on the west to the Mississippi state border on the east, a distance of 515 kilometers (km) (320 miles [mi]) and a north-south extent of 40.2–160.9 km (25–100 mi), this impacted region encompasses an area of more than 32,000 km2 (12,355 mi2). In the natural undisturbed state, the Louisiana coastline was subject to regions of erosion and regions of land building as the Mississippi River switched channels, which is described further in Chapter 2. The natural, but largely impractical solution, would be to allow the Mississippi River to return to this natural cycle. As the channel switches to new regions, sediments would be distributed to the shallow coastal areas rather than the edge of the continental shelf. On the scale of centuries, this would allow new areas to stabilize and become colonized by vegetation and animals. The abandoned delta lobe would gradually be lost at a rate that would depend on relative sea level rise and storm intensity. At a
smaller spatial scale, crevasse splays would create changes in the distributary channels and in local regions. To recover the entire area, massive quantities of sediment and prolific generation of organic matter through growth of vegetation would be required. There have been numerous efforts to deal with the problem since the late 1960s (Box 1.1).
Left to nature, many areas of erosion and accretion would be present as the river channel switched locations on a roughly 1,000-year cycle. The river channels would be much shallower and transient in location and dimensions and thus less reliable for navigation due to the shifting shoals. Without the levees, overbank flooding would nourish the marshes but threaten human lives and property. The fundamental problem is that human interests prefer a static landscape rather than a dynamic one that supports the natural river and deltaic systems and wetlands.
Slowing wetland loss in some areas and restoring wetlands in others raises a number of basic questions that go beyond the questions of sediment and sea level—even if the significant financial resources discussed in various studies and in this report were available. For example, to what extent can a sustainable coastal configuration be achieved with the many competing interests? How are the competing interests of various stakeholders to be balanced with the overall objective of capturing the maximum amount of sediment and delivering it to areas where it will provide the greatest benefit? In addition to the engineering and ecological challenges of sediment management, slowing wetland loss involves many stakeholders with diverse and sometimes competing interests. A physical “fix” in any one area will benefit some people but could damage the interests of others either in the same locality or in a different area.
Coastal Wetlands Planning, Protection, and Restoration Act
Initial efforts to offset catastrophic land loss have been implemented under CWPPRA, which called for the development of a comprehensive Louisiana Coastal Wetlands Restoration Plan (P.L. 101-646 §303.b). In 1993, the first plan was completed and used until the 1998 release of Coast 2050. Then, in 1994, the Governor’s Office of Coastal Activities Science Advisory Panel prepared a plan (Gagliano, 1994), constituted under Act 6 (LA RS 49:213 et seq.), for the Wetlands Conservation and Restoration Authority.
Coast 2050 (Louisiana Coastal Wetlands Conservation and Restoration Task Force and the Wetlands Conservation and Restoration Authority, 1998) was developed in partnership with the public, parish govern-
1967—The U.S. Army Corps of Engineers’ (USACE) Louisiana coastal area study evaluated options for mitigating wetland losses under a U.S. Senate resolution.
1978—The Louisiana State and Local Coastal Resources Management Act (Act 361, LA R.S. 49:213.1) established a state coastal management program that emphasized controlling activities that cause wetland loss.
1980—Coastal management efforts in Louisiana led to the Louisiana Coastal Resources Program, which became a federally approved coastal zone management program.
1981—Act 41 of the Louisiana Legislature special session established the Coastal Environment Protection Trust Fund and appropriated $35 million for projects to combat erosion, saltwater intrusion, subsidence, and wetland loss along Louisiana’s coast.
1989—Act 6 of the Louisiana Legislature passed (in the second extraordinary session) R.S. 46:213-214, and a subsequent constitutional amendment was approved by the citizens of Louisiana, establishing the Office of Coastal Restoration and Management and the state’s Coastal Wetlands Conservation and Restoration Trust Fund (also known as the Wetlands Trust Fund) to develop and implement the Coastal Wetlands Conservation and Restoration Plan for Louisiana. Income for the trust fund is a percentage of the state’s mineral revenues and varies from $13 million to $25 million annually, depending on oil and gas prices and availability.
1990—The U.S. Congress passed the Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) (also known as the Breaux Act) to contribute federal money to coastal restoration activities. This act created a partnership between the Louisiana state government and five federal agencies (USACE, the U.S. Department of Agriculture, the U.S. Department of Commerce, the U.S. Department of the Interior, and the Environmental Protection Agency).
1993—A comprehensive wetland restoration plan (Louisiana Coastal Wetlands Conservation and Restoration Task Force, 1993) was submitted to the U.S. Congress, identifying restoration projects needed to address critical wetland loss problems in Louisiana. Section 303(b) of CWPPRA directed that this plan be further developed and be consistent with the state’s existing Coastal Wetlands Conservation and Restoration Plan.
1994—As part of CWPPRA’s request for a comprehensive Louisiana Coastal Wetlands Restoration Plan (P.L. 101-646 §303.b), the Governor’s Office of Coastal Activities Science Advisory Panel released an economic plan for coastal restoration in Louisiana (Gagliano, 1994).
1995—The Barrier Island Shoreline Feasibility Study was the first large-scale feasibility study undertaken by CWPPRA to assess and quantify wetland loss problems linked to the protection provided by the barrier island formations along coastal Louisiana and to develop the most cost-effective measures to minimize future wetland loss. The study was completed in 1999 and approved by the CWPPRA Task Force in 2000.
1995—The Mississippi River Sediment, Nutrient, and Freshwater Redistribution Study was undertaken by USACE to investigate potential uses of sediment, nutrient, and freshwater resources from the Mississippi River to create, protect, and strengthen coastal wetlands. The resulting report was distributed for review in June 2000.
1997—The Louisiana Conservation Plan was approved. This plan was prepared according to Section 304 of CWPPRA and includes regulatory, nonregulatory, and educational programs the state will use to achieve no net loss of wetlands. Approval of this plan reduced Louisiana’s cost share of CWPPRA projects from 85 percent to 75 percent.
1998—Coast 2050: Toward a Sustainable Coastal Louisiana (Coast 2050) was released as the new initiative to develop a unified effort to restore and protect Louisiana’s coastal resources. This plan includes a conceptual model for achieving a sustainable coast by recommending strategies for restoration. It was developed through collaboration of federal, state, and local entities; landowners; environmentalists; wetland scientists; and the public.
1999—Investigation of the Chenier Plain is completed to develop a more holistic understanding of Chenier Plain hydrology.
1999—The 905(b) reconnaissance report (U.S. Army Corps of Engineers, 1999a) was released.
2003—Louisiana Coastal Area, LA—Ecosystem Restoration: Comprehensive Coastwide Ecosystem Restoration Study (draft LCA Comprehensive Study) was released in draft form by USACE and the Louisiana Department of Natural Resources as a possible comprehensive, long-term restoration plan.
2004—The LCA Study was released by USACE and the Louisiana Department of Natural Resources as a near-term alternative to the draft LCA Comprehensive Study.
ments, and state and federal agencies under the legislative mandates described above. The plan, which divides the Louisiana coastline into four regions based on hydrologic basins (Figure 1.1), articulates a broad vision of what the citizens of Louisiana feel should be the goals of restoration and protection efforts in Louisiana. The purpose of the plan as referenced in section 303(b)(2) of CWPPRA is to “develop a comprehensive approach to restore and prevent the loss of coastal wetlands in Louisiana. Such a plan shall coordinate and integrate coastal wetlands restoration projects in a manner that will ensure the long-term conservation of the coastal wetlands of Louisiana.” (Refer to Figure 1.2 to locate cities, geologic features, and projects discussed in this report.)
Coast 2050 incorporated three strategic goals for all regions: (1) to ensure vertical accumulation (of clastic sediment and organic material) to achieve sustainability, (2) to maintain an estuarine salinity gradient to achieve diversity, and (3) to maintain exchange and interface to achieve system linkages (Louisiana Coastal Wetlands Conservation and Restoration Task Force and the Wetlands Conservation and Restoration Authority, 1998). Detailed strategies to achieve these goals are included for each of the four coastal regions. In addition, during the course of the Coast 2050 planning initiative, programmatic strategies were developed to improve implementation efficiency of authorized restoration projects, effec-
tiveness of future restoration efforts, coordination among existing environmental resource programs, and other actions that may benefit coastal wetlands in other ways.
The draft LCA Comprehensive Study was the next step in the development of an implementation plan for Coast 2050. The goal of the draft LCA Comprehensive Study was to provide a “comprehensive program to reestablish a sustainable ecosystem along Louisiana’s coast that will support and protect the environment, economy, and culture of southern Louisiana” (U.S. Army Corps of Engineers, 2003a). After reviewing the draft LCA Comprehensive Study, the U.S. Office of Management and Budget requested a more definitive and limited scope of work (i.e., one in which construction will start in 5–10 years). The State of Louisiana agreed to this narrowed scope but firmly advocated the need for a long-term plan. Currently, the State of Louisiana and USACE are pursuing implementation of a preliminary, near-term effort, which purportedly focuses on high-priority needs in the state. This near-term effort is envisioned in the LCA Study and is expected to be used to establish the intellectual infrastructure needed to carry out the more comprehensive approach. (While a comprehensive plan is needed, this does not necessarily imply endorsement of the draft LCA Comprehensive Study.)
Based on the U.S. Office of Management and Budget’s response to the high cost and long-term elements of the draft LCA Comprehensive Study, the cooperating agencies shifted their focus to a smaller, near-term effort, which is the subject of this review. Borrowing from the plans and strategies developed in Coast 2050 and the draft LCA Comprehensive Study, the project development team narrowed the selection of near-term restoration projects to those “that can be implemented within the next 5–10 years, demonstration projects to resolve scientific and engineering uncertainty, and large-scale studies of long-range feature concepts” (U.S. Army Corps of Engineers, 2004a). The LCA Study was pulled together in a relatively short period of time as a near-term product of a much longer process that was intended to develop a comprehensive plan. As will be discussed in the following chapters, this last-minute change in focus from comprehensive strategy to near-term plan resulted in a number of disconnects between the LCA Study and the preceding efforts. Although many of the efforts proposed in the LCA Study have begun, at the date of this report, funds have not been appropriated to fully implement what is outlined in the study.
Goals and Objectives
The LCA Study encompasses the same study area and is based on essentially the same “statement of needs” as the draft LCA Comprehensive Study. However, rather than focusing on ecosystem restoration and what the end result should be, the stated objectives for the LCA Study, which focus on what needs to be done and how it will be accomplished, are as follows:
Identify the most critical human and natural ecological needs of the coastal area.
Present and evaluate conceptual alternatives for meeting the most critical needs.
Identify the kinds of restoration features that could be implemented in the near term (construction starts in 5–10 years) that address the most critical needs, and propose to address these needs through features that provide the highest return in net benefits per dollar of cost.
Establish priorities among the identified near-term restoration features.
Describe a process by which the identified priority near-term restoration features could be developed, approved, and implemented.
Identify the key scientific uncertainties and engineering challenges facing the effort to protect and restore the ecosystem, and propose a strategy for resolving them.
Identify, assess, and if appropriate, recommend feasibility studies where construction starts in 5–10 years to fully explore other potentially promising large-scale, long-term restoration concepts.
Present a strategy for addressing the long-term needs of coastal Louisiana restoration beyond the near-term focus of the [LCA Study]. (U.S. Army Corps of Engineers, 2004a)
The broad goal of Coast 2050—“to sustain a coastal ecosystem that supports and protects the environment, economy, and culture of southern Louisiana, and that contributes greatly to the economy and well-being of the nation” (Louisiana Coastal Wetlands Conservation and Restoration Task Force and the Wetlands Conservation and Restoration Authority, 1998)—has been developed into a narrower, overarching LCA Study objective “to reverse the current trend of degradation of the coastal ecosystem” (U.S. Army Corps of Engineers, 2004a). The contrast between the two goals—“sustain a coastal ecosystem that…contributes greatly to the economy and well-being of the nation” and “reverse the current trend of degradation of the coastal ecosystem”—represents a difference in view-point that ultimately influenced the planning process and selection of projects, because the LCA Study goal places greater influence on the implied economic benefits to the nation while the Coast 2050 goal places greater emphasis on environmental restoration.
Planning and the Plan Development Process
The agencies participating in the LCA Study were the same as those on the project delivery team3 for the draft LCA Comprehensive Study. The plan development process is described in six phases, and the first four phases are identical to Phases I-IV of the draft LCA Comprehensive Study (see Chapter 4). Phase V for the LCA Study is to “address completeness of coastwide restoration frameworks in a Tentative Final Array,” and Phase VI is to “identify highly cost-effective restoration features within the Final Array that address the most critical ecological needs” (U.S. Army Corps of Engineers, 2004a). This last phase essentially narrows the focus to select fewer projects that are more easily undertaken, use known technology, and can be started in 5–10 years. This selection process resulted in the following five near-term restoration projects:
Mississippi River Gulf Outlet environmental restoration features
Small diversion at Hope Canal
Barataria Basin barrier shoreline restoration (Caminada Headland and Shell Island reaches)
Small Bayou Lafourche reintroduction
Medium diversion with dedicated dredging at Myrtle Grove
These projects, a Science and Technology Program, adaptive management, and demonstration projects are discussed in more detail in Chapter 6.
Public comments on the draft programmatic environmental impact statement and draft LCA Study were collected from July 9 to August 23, 2004. During this public comment period, six public meetings were held throughout the Louisiana coastal area, and three additional meetings were conducted in Texas, Mississippi, and Tennessee. A total of 355 people attended, and a total of 77 individuals offered oral comments at the nine public meetings. USACE received 82 comment letters postmarked within the comment period. This level of public participation is far lower than that seen for either the development of Coast 2050 or the draft LCA Comprehensive Study, in part reflecting the abbreviated time during which the LCA Study was developed.
ORIGIN AND SCOPE OF THE CURRENT STUDY
In an effort to secure additional outside technical input, the State of Louisiana and USACE initially requested that the National Academies undertake a review of the objectives envisioned and the actions proposed in Coast 2050. Once funding was in place and the committee was formed, it became apparent to both the sponsors and the National Academies that greater benefit would be derived from a review of the LCA Study. (Initially drafted as a comprehensive plan in 2003, the LCA Study reviewed by the committee was rescoped and released by USACE in November 2004.) The change in focus was approved by both the sponsors and the National Academies and is reflected in the committee’s formal statement of task (Box 1.2).
The Committee’s Approach
The nature of the questions comprising the statement of task places emphasis on understanding the strategic value of various components of the LCA Study. Rather than a detailed technical review of the LCA Study and its supporting documents, the committee was charged with commenting on the appropriateness of the effort in terms of broad approaches, scale of effort, and timeliness of action. In order to address the questions
This study will evaluate the near-term plan for the restoration of coastal Louisiana (released by the U.S. Army Corps of Engineers as the Draft Louisiana Coastal Area [LCA], Louisiana—Ecosystem Restoration Study in July 2004). The overall committee approach will be to examine the LCA Study and all of its components in detail. This examination will then serve as a basis for evaluating the usefulness of the LCA Study for developing and implementing a long-term comprehensive program consistent with the broad vision articulated in Coast 2050: Toward a Sustainable Coastal Louisiana (appended to the U.S. Army Corps of Engineers’ Louisiana Coastal Area 905(b) reconnaissance report in May 1999). Specifically, the committee will address the following questions:
framed by the statement of task, the committee had to understand the challenges facing existing efforts to restore and protect coastal Louisiana as well as efforts proposed in the LCA Study. This report has benefited considerably from the many informative presentations made by individuals with substantial knowledge of the history and processes associated with the Louisiana coastal area. Interaction with the National Technical Review Committee (see Chapter 4 for additional detail), including the opportunities to participate in two of its meetings and access its reports and findings, has been extremely valuable. This considerable body of
work raises many overarching issues that are described and discussed in this report.
Existing commercial interests, recreational opportunities, social activities, and infrastructure needs place constraints on the remedial measures that can be carried out, thereby reducing the scope of the overall restoration that can be accomplished. For example, many existing communities are located on the relatively high ground formed by natural levees. These areas are now subsiding, becoming more vulnerable to flooding, but the prospect of future intentional sediment-laden water diversions to these areas is quite unlikely. This essentially rules out a natural approach to maintaining land areas in such locations and leaves constructed levees around the developments as the most probable future approach for flood protection. Another example is that the municipal and industrial water supply for New Orleans is obtained from the Mississippi River. With the present deep navigation channel, saltwater encroaches upstream during periods of low flow to a point where, twice in the past, consideration was given to constructing a sill to block saltwater intrusion. However, municipal and industrial water supply needs must be a factor in any proposal to divert upstream river water to carry sediments into marshes. Also, while a new Third Delta is considered a possible long-range project, it is clear that the effort to prevent the Mississippi River from following its natural, historic pattern of shifting will continue as long as such a change would jeopardize New Orleans or the viability of the port.
The size of the affected system is also an important physical constraint. In some areas close to existing waterways, sediment can be delivered via gravity by diverting sediment-laden water through spillways and siphons. Unfortunately, existing waterways do not reach much of the vast affected area, which leaves two possibilities. The first is to deliver sediment via pipeline, and the second is to accept that many of the wetlands will continue to subside with attendant wetland loss. In the latter case, as the area subsides over the years, wetlands will be replaced by more contiguous areas of open water.
A logical approach to the planning of restorative actions commences with a clear understanding of the dynamic nature of the natural system and the natural processes that create and sustain the system. Some of the natural processes are constrained by actions outside the control of efforts in Louisiana (sediment deposition in upstream reservoirs and contributions to the heavy concentrations of nutrients in river waters), and others will be unacceptable to the existing web of commercial, recreational, and societal activities and interests. Thus, there are limitations to what can be accomplished, and successful execution of the program rests as much on the recognition of these limits as on the engineering and construction of projects selected for implementation.
In summary, there are stabilized elements of the modern system of coastal Louisiana that are of critical importance to society, including the water supply for New Orleans, navigation, and a relative permanence of the present landscape and its urban and industrial infrastructure. It is worthwhile noting that the LCA Study seeks to maintain, more or less, the current landscape; however, many diverse natural landscapes have existed in the past. An example is that at one time the Mississippi River with its natural levees ended at the current Head of Passes. Were all of these past landscapes less desirable than the one that these efforts are designed to preserve?
This brief discussion illustrates the complexities facing the planners, engineers, scientists, and decision makers involved in designing and implementing the LCA Study. Broad and strong political support at the state level for the LCA Study is evident, but this can be maintained only through effective management and the achievement of early successes.
Structure of This Report
This document represents the cumulative efforts of the committee to provide answers to the questions in the statement of task. The report contains seven additional chapters (brief overviews can be found at the beginning of each chapter). Chapter 2 offers an overview of Louisiana’s past and present coastal system to provide an understanding of the limitations the physical and biological systems place on restoration efforts. Chapter 3 discusses present-day conflicts and the sociopolitical limitations to efforts to return the delta to a desirable condition. Chapter 4 describes previous and ongoing efforts, such as CWPPRA, to protect and restore coastal Louisiana. Chapter 5 focuses on the planning process used to develop the LCA Study, while Chapter 6 discusses the LCA Study itself. Chapter 7 discusses knowledge gaps identified during the review of the LCA Study, which merit attention through an adaptive management process as efforts move forward. Finally, Chapter 8 provides an integrated discussion of the findings and recommended actions that should be taken by USACE and the State of Louisiana to strengthen the efforts laid out in the LCA Study to protect and restore coastal Louisiana.