Current and Historical Sediment Loads in the Lower Mississippi River

Questions concerning past, present, and future temporal trends in the sediment load of the Lower Mississippi River are of great importance because the redistribution of available Mississippi River sediment is vital to on-going efforts to reduce land loss and restore coastal marshes and wetlands in Louisiana. This document reports the results of a 1-yr study performed by Nottingham University, Halcrow and the Biedenharn Group in collaboration with the Waterways Experiment Station, Engineer Research Development Center (ERDC), Vicksburg, Mississippi, that was aimed at assembling available data on sediment loads in the river, assessing its reliability and temporal variability, and exploring the implications for sediment diversions. The lower Mississippi River, extending from Cairo, Illinois, to the Gulf of Mexico, currently transports approximately 150 million tons of sediment annually. Historically, the quantity and caliber of sediment derived from catchment erosion have been affected by changes in land-use and river management; increasing in the 19th and early-20th Centuries, before decreasing due to soil conservation and improved land management. The supply of sediment from tributaries is also believed to have decreased markedly as a result of river engineering and management. However, there is no consensus on the degree of reduction as a proportion of the previous natural or undisturbed load, the time distribution of the reduction or how the trajectory of past and present trends may change in the future. Cumulative land loss in Louisiana over a 50-yr period represents on the order of 80% of the coastal land loss in the United States. The Louisiana Coastal Area (LCA) was released by the United States Army Corps of Engineers (USACE) in 2004 and included the consideration of approximately twenty-three diversions of water and sediment from the Mississippi River, with a total diversion capacity in the range of 150,000 to 200,000 cfs. The original document contains color images.