Mississippi River - West Bay Sediment Diversion

Abstract

The project, located in Plaquemines Parish, Louisiana on the west bank of the Mississippi River at Mile 4.7 Above Head of Passes, diverts water and sediments into West Bay through a dredged conveyance channel. The objective of the project is to restore 10,000 acres of vegetated wetlands in shallow water within the Mississippi River delta over the next 20-years. The sediment diversion channel is being constructed in two phases: 1) Construction of an interim channel to accommodate a 20,000 cfs discharge at the 50% duration stage of the Mississippi River (completed November 2003), and 2) Modification of the channel to accommodate full-scale diversion of 50,000 cfs at the 50% duration stage (scheduled September 2005). The enlargement phase will be built upon completion of a period of intensive monitoring of project performance. Prior to construction of the diversion channel, a large natural gas pipeline located in the outfall channel pathway was lowered for safety reasons (completed May 2003). Contingency plans for closing the diversion channel would be implemented if hydrographic monitoring of the Mississippi River navigation channel indicates the Thalweg of the river is migrating toward the diversion channel or if river shoaling substantially increases downstream of the diversion. The project is the largest freshwater and sediment diversion ever constructed for environmental restoration purposes. Lessons learned from this project will be applied to several large-scale alternatives under development as part of a comprehensive plan to restore and sustain coastal wetland habitats in Louisiana.