Envisioning the Future of the Louisiana Gulf Coast DONALD F. BOESCH President-Emeritus, University of Maryland Center for Environmental Science Fellow, Walton Family Foundation CONTENTS SUMMARY..................................................................3 INTRODUCTION.............................................................5 Why Another Vision? . 5 Why My Vision? . 6 How Did I Develop This Vision? . 7 ADDRESSING LOUISIANA’S COASTAL CRISIS ....................................9 A Challenge of Immense Scale and Gravity . 9 Evolution of Comprehensive Planning . 11 AN OVERARCHING VISION . 13 KEY CONSIDERATIONS ......................................................15 Building on the Coastal Master Plan . 15 Subsidence . 17 Sea-Level Rise, Critical Determinant of the Future Coast . 20 Storm Frequency and Intensity . 26 Precipitation and Runoff . 27 Actions to Reduce Shelf Hypoxia . 29 Biological Productivity and Value . 31 Projections of the Future Coast . 32 Broad and Profound Consequences of Limiting Climate Change . 33 VISIONS FOR THE COASTAL BASINS...........................................35 Pontchartrain Basin: The Eastern Flank of Louisiana’s Most Populous Region . 35 Birdsfoot Delta: Maintaining Global Access to the Heartland . 44 Barataria Basin: Lafitte’s Backdoor . 53 Terrebonne Basin: The Dilemma between Two Rivers . 61 Greater Atchafalaya: Keeping It Building . 67 Chenier Plain: Plainly Stranded . 72 AN ACHIEVABLE COAST OVER FIFTY YEARS ....................................78 REFERENCES ...............................................................82 ENVISIONING THE FUTURE OF THE LOUISIANA GULF COAST | DONALD F. BOESCH 2 SUMMARY This vision of the future of the Louisiana Gulf Commendably, Louisiana’s Coastal Master Plan has Coast over the next fifty years was developed taken into account environmental changes that could from the perspective of an environmental scientist occur in the future . The three scenarios used in the with nearly a half-century of experience in the 2017 plan are examined with regard to how they diagnosis and treatment of coastal environmental might affect achievable futures. Numerical and spatial deterioration in various parts of the world . It modeling of land changes under these scenarios with and without component restoration projects is used was developed with the empathy of a native, the to provide a basis to envision outcomes . Because it knowledge drawn from extensive experience on is built on thick layers of unconsolidated sediments the Louisiana coast, an objectivity afforded by deposited over just the last 7,000 years, the Louisiana having lived outside of the state for nearly three coast is subsiding faster than any place along the U .S . decades, and a perspective based on engagement coast. Controversies remain over the effective rates in addressing environmental change at the regional of subsidence in wetlands and the extent to which scale. Within the bounds of scientific reality, it is subsidence may have slowed with reduced oil and a purposely optimistic vision, one that assumes gas withdrawals. Substantial effort is being expended that humankind did all the right things including to provide more reliable subsidence rates for use in environmental restoration in Louisiana, better project planning and in the next Coastal Master Plan . management of the Mississippi-Atchafalaya River The other environmental changes assumed in the Basin, and limiting climate change . It seeks to scenarios are affected by human-influenced climate describe a plausible best case for the future, one change, including precipitation and runoff, storm frequencies and intensities, and the rise in the levels in which Louisiana’s coastal environments can be of the Gulf of Mexico . The degree to which the Gulf more productive and valuable than they are today . sea-level rise accelerates will be the predominant factor governing the extent of coastal changes later The vision builds on decades of analysis and in the century . planning for the rehabilitation of rapidly deteriorating landforms and ecosystems, the The amount of sea-level rise experienced in protection of residents in the Mississippi Deltaic the Gulf of Mexico will be determined by how Plains, and the adjacent Chenier Plains that much Earth’s temperature warms and on the together comprise the Louisiana coast . The vision amount of greenhouse gases humans emit . The starts with the Louisiana’s 2017 Coastal Master scientific consensus, as reflected in the most Plan, elements from which are already being recent projections of global sea-level rise by the implemented . While written for a broad audience, Intergovernmental Panel on Climate Change, offers including those who have influence on decisions, an some good news and some bad news for coastal important objective for the vision is to inform and Louisiana . It is unlikely that sea level will rise over the next fifty years as much as predicted under the inspire the development of the 2023 Coastal Master lowest assumption used in the 2017 Coastal Master Plan that is already underway . Plan, thus affording an opportunity for restoration measures to work more effectively. Continued ENVISIONING THE FUTURE OF THE LOUISIANA GULF COAST | DONALD F. BOESCH 3 If global emissions are reduced sufficiently to keep During this same fifty-year period, there will be a global warming well under 2°C, consistent with massive global transition in the sources and uses the goal of the Paris Climate Agreement, sea-level of energy that will involve Louisiana . Indeed, the rise should be relatively manageable well into future of its coast over the subsequent fifty-year the next century . On the other hand, if emissions interval will depend on how quickly and completely of greenhouse gases continue to grow at recent this transition is effected. The transition requires rates, Gulf levels could likely rise by over 6 feet that Louisiana adapt its economy and society as over the next hundred years, ultimately inundating fossil-fuel production and manufacture declines or the coast Louisiana is working to restore and the changes at the same time during which the state communities it is trying to protect . is working to restore its coast . The nature of the work in this Working Coast will change with less oil A fifty-year vision is outlined for each of six basins and gas production and constraints on the use of comprising the Louisiana coast: Pontchartrain diesel engines for transportation and restoration, (including the Breton Basin), the Birdsfoot Delta, but increase opportunities for renewable energy Barataria, Terrebonne, Atchafalaya (including production and carbon sequestration, global the Teche/Vermilion Basin) and the Chenier Plain leadership in coastal sustainability, and for more (comprised of the Mermentau and Calcasieu/ productive and profitable cultivation of the state’s Sabine basins) . For each basin, the particular bountiful living resources . The critical role played setting and trends of coastal land loss are reviewed, as the global commercial gateway to the American the restoration accomplished and planned are Heartland continues even as shipping adapts, assessed using the modeling framework of the placing urgency on planning for a sustainable river 2017 Coastal Master Plan, and a vision is developed entrance and the lower Mississippi infrastructure that offers further considerations for protection needed for the future . This provides more and restoration . These considerations are not impetus for working on a national scale for the necessarily novel, in fact, many are already being comprehensive management of the Mississippi- evaluated by the Coastal Protection and Restoration Atchafalaya River Basin to address flooding, Authority . Treatment by basin allows the integration upstream pollution, sediment transport, of various restoration measures, such as sediment and navigation . diversions, maintenance of barrier islands, and marsh creations within a place-specific context. Assuming work along the coast will remain the same while we restore and sustain its landscape, From a higher altitude, Louisiana’s coastal planning it is just not realistic . Rather, Louisiana should and implementation must fundamentally involve embrace this new future with all its threats along the effective distribution of freshwater and with its abundant opportunities . sediment flows together with adjustments to maintain a reasonably stable boundary with the Gulf of Mexico, important landscape features, and to enhance the longevity of intertidal wetlands . Net land loss will continue over most regions of coastal Louisiana over the next fifty years. With the rise in sea level likely over this time, it is possible to maintain the basic integrity of Louisiana’s coastal landscapes, take steps that will help sustain it over a longer term, and enhance its biological productivity and value. Prudent and effective choices will require sound technical guidance, appropriate resources, and strong societal and political will . ENVISIONING THE FUTURE OF THE LOUISIANA GULF COAST | DONALD F. BOESCH 4 INTRODUCTION Why Another Vision? Why, the reader might ask, yet another vision of the future of the Louisiana Gulf Coast? Surely, there have been many other books, reports, and plans that describe the challenges faced in stemming the alarming loss of coastal lands, the degradation of productive and diverse ecosystems, and the increasing vulnerability of its human residents and their distinctive cultures . After all, Louisiana already has a Comprehensive