Surficial sediment distribution maps for sustainability and ecosystem restoration of coastal Louisiana

摘要

Louisiana's coastline, especially the Mississippi River Deltaic Plain (MRDP), is experiencing some of the most extreme erosion rates in the nation and needs urgent mitigative measures to re-establish a sustainable coastal ecosystem via large-scale restoration. Sedimentological restoration is one of the strategies currently being used to achieve this goal. Sediment management plays a vital role in implementing this strategy. The Louisiana Sediment Management Plan (LASMP) facilitates sediment management for restoration by providing an inventory of potential sediment resources and tracking sediment needs, both of which are crucial to the development of regional strategies for restoration. To aid in the development of Louisiana's coastal master plan and to help fulfill the goals of the LASMP, first-order surficial sediment distribution maps for offshore and the Lower Mississippi River were developed based on existing geophysical and sedimentological data residing in the Louisiana Sand Resources Database (LASARD). LASARD was initially developed by the state of Louisiana to manage geological, geophysical, geotechnical and other related data pertaining to offshore sand searches. However, with time the scope of LASARD has expanded and it is no longer limited to data related to sand searches only. Keeping the needs of coastal restoration in mind, the sediment deposits that were mapped were broadly classified as surficial sand, surficial mixed sediment, and surficial fines and digitally archived. However, a large portion of offshore areas were classified as "unknown" due to a lack of sufficient reliable data. Based on these maps, first-order total and available (by excluding sediment impacted by oil and gas infrastructure) volume estimates were calculated for sand, mixed sediment, and fine-grained sediment. Based on the 2017 Coastal Master Plan an estimated 5,000 to 11,000 million cubic meters (MCM) of sediment is required to meet coastal Louisiana's needs. Volume estimates based on the surficial sediment maps indicate that this volume of sediment may be available but dredging all of these sediment resources is not necessarily feasible or technically sound even with sufficient resources. It is important to emphasize that these volumes are first-order estimates as these calculations are based on various geoscientific information with varying degrees of confidence. The development of such maps is a painstakingly intensive effort. These maps are living documents and are updated as new data become available. As such, the mapping is updated periodically and the volumes are updated accordingly. Ultimately the results of the mapping will be available as a digital database. These maps are basic but important tools for resource planning and play a critical role in the management of sediment resources at a regional level. Additionally, these maps are good indicators of presence as well as absence of sufficient geoscientific data. As such, they are a useful tool for conducting data gap analyses, which are typically conducted at planning stages of various investigations. These maps also form templates and/or base maps for development of comprehensive biotic and abiotic habitat maps. Most important, they play a vital role in the enforcement of federal and state regulations related to removal of decommissioned pipelines and coastal zone management. The utility of these maps is not limited to the Louisiana coastal area. Similar maps could be compiled for the entire northern Gulf of Mexico, helping not only the remaining four Gulf states but also supporting Gulf-wide efforts such as the GOMAs (Gulf of Mexico Alliance) Gulf of Mexico Master Mapping Plan (GMMMP) and RESTORE (Resources and Ecosystem Sustainability, Tourist Opportunities, and Revived Economies) Councils Coastal Monitoring and Assessment Program (CMAP).