Recent Coastal Evolution and Regional Sediment Transport Dynamics in Response to Sea-Level Rise and Interior Wetland Loss:Barataria Sandy Shorelines

摘要

High rates of relative sea level rise (~0.9 cm/yr), interior wetland loss, and storm induced erosion have caused a large deficit in sediment budgets along the Mississippi River delta plain. Some of the observed impacts include increased bay tidal prism and the resulting enlargement of tidal inlets, formation of new inlets, degradation of barrier islands due to inlet widening, and finally sediment sequestration at ebb tidal deltas. We present a case study in Barataria-from Belle Pass to Sandy Point-and show the recent (~120 years) evolution of the coast. We used historical bathymetric surveys from four time periods (dating to the 1880s) to provide a series of digital elevation models (DEMs) that were used to calculate sediment volumetric changes and determine long-term erosional-depositional trends. For the most recent period (1980-2006) we separated fine (mud) and course sediment (sand) by integrating cores into the DEMs to estimate the corresponding volumes of mud and sand. Results show a net erosion of 7.7 million m3 from the backbarrier (more than 50% is mud), compared to shoreface erosion of more than 300 million m~3 (86% are fines). For sandier environments, such as ebb tidal deltas, the total volume eroded is 13.3 million m~3 (61.9% is sand), while approximately 1.27 million m3 of sand eroded from tidal inlets. Shoreface erosion dominates, with volumes that consist of more than 90% of the erosion observed in the entire study area (~311 million m~3) (14% is sand).