Strategic approaches to sediment management for restoration of a deltaic plain

摘要

Sediment resources are essential to fulfill the State of Louisiana's commitment to implement a Coastal Master Plan (CMP) to mitigate its chronic land loss, protect more than 2 million people who live in the coastal zone, and to save Louisiana's rapidly disappearing complex and fragile ecosystem. With increasing rates of sea level rise and increased storm intensities along with continuing subsidence, the future quantity of sediment needed for ecosystem restoration will significantly increase, and at the same time, the accessibility to the sediment resources will become much more technologically challenging and cost prohibitive. These devastating environmental circumstances will compound the complexities of a sustainable ecosystem restoration in coastal Louisiana. Restoration projects must be robust enough (using adequate compatible sediment) to survive future environmental scenarios while the quantity of actively captured sediment resources available for critical restoration projects is likely to decrease, rendering the dredging and transporting of these sediment resources increasingly difficult and costly. These challenges will be an opportunity for Louisiana to utilize more sustainable, passively captured sediment (i.e. using large sediment diversions from the Mississippi River) to help offset limitations concerning actively harvesting sediment and to build and sustain wetlands in coastal Louisiana. Although any large-scale and meaningful restoration of the Louisiana coastal plain must involve sediments from the Mississippi River, the scope of this paper is restricted to offshore sediment resources. A strategic approach to optimize utilization of sediment resources includes minimizing handling and transport costs by first locating potential sediment sources and then identifying the most cost-effective way of using that sediment resource for restoration. The project cost and its success are defined by the sediment selection process. Thus, it is suggested that improvements in planning and management of multiple-use conflicts be based on regional understandings of sediment resources for an approach that maximizes benefits. The Louisiana Sediment Management Plan (LASMP) was conceptualized and formulated to improve planning and coordination of sediment utilization in Louisiana. This plan has evolved and has been adaptively managed in the absence of any prototype. Restoration activities are further complicated by competing interests and multiple uses of limited sediment resources. To maximize the availability of offshore sediment, the state is collaborating with the Bureau of Ocean Energy Management (BOEM) and engaging with other stakeholders in deciding the fate of decommissioned pipelines and to strategically plan the installation of new pipelines in offshore areas identified as significant sediment resources with the intent of protecting identified sediment resources for future use. Future offshore wind-farms may pose new challenges but simultaneously offer opportunities for conflict resolution via stakeholder engagement. For the past two decades the State of Louisiana/Coastal Protection and Restoration Authority (CPRA) of Louisiana has developed a considerable institutional knowledge base and expertise and improved the art and science of sediment management. A robust process has been adaptively developed with interagency collaboration and coordination to resolve conflicts/issues concerning obstacles to resource access. LASMP is not only a template for sediment management for coastal restoration, but also provides guidance for stakeholder engagement and conflict resolution for competing needs of sea-floor resources especially in Northern Gulf of Mexico (NGOM).