Are riverine sediment discharges sufficient to offset the sinking coast of Louisiana?

摘要

The Mississippi River and four other major rivers along Louisiana's coast (USA) discharge a combined total of 620 km3 of water annually into the Gulf of Mexico. In addition to the vast quantity of freshwater, these river systems carry substantial sediments that affect physical, biological and human domains in the northern Gulf of Mexico. In the past century, river engineering and land use practices in the river basins have changed dramatically. A large number of locks and dams were built along the major tributary rivers including the Upper Mississippi River, Illinois River, Missouri River, Ohio River, Tennessee River, Arkansas River, and Red River, which has greatly contributed to the reduction in sediment yield to the continental shelf of the northern Gulf of Mexico. Concurrently, Louisiana's coast has experienced the highest rate of relative sea-level rise of any region in the USA. In the past 50 years land loss rates along Louisiana's coast have exceeded over 60 km~2 year~(-1), and in the 1990s the rate has been estimated to be between 40 and 56 km~2 year~(-1). This change represents 80% of the coastal wetland loss annually in the entire continental USA. The highest relative sea-level rise is 17.7 mm year~(-1) at Calumet, Louisiana, compared to 6.3 mm year~(-1) at Galveston, Texas, 1.5 mm year~(-1) at Biloxi, Mississippi, and 2.3 mm year~(-1) at Pensacola, Florida. Riverine sediments are precious resources to coastal Louisiana, and their effective management is of long-term strategic importance. This paper reports combined sediment yields from two major distributaries of the Mississippi River and four major coastal rivers in Louisiana for the most recent three decades, and discusses the actual availability of sediment and a new diversion approach - controlled overbank flow - that mimics the natural process of sediment replenishment over large areas.