Book Description

One purpose of the diversion is to reduce salinities in the Biloxi Marshes by 2 to 8 parts per thousand (ppt) in order to improve oyster productivity. A range of monthly salinities has been identified as the desired product of the project. Those salinities, called the Chatry salinities in this report, consist of a narrow band of 'optimum' salinities and a somewhat wider band of 'range limits.' A time varying, three dimensional numerical model of the estuary was constructed using the U.S. Army Corps of Engineers TABS-MD modeling system. The modeled area included Lakes Maurepas, Pontchartrain, and Borgne, Biloxi Marshes, and a portion of Chandeleur Sound plus connecting waterways of Mississippi River Gulf Outlet (MRGO), Inner Harbor Navigation Canal, Gulf Intracoastal Waterway, Chef Menteur, and The Rigolets. All major tributary freshwater flows were simulated, as were tides at the Gulf of Mexico boundary and winds. The model computed instantaneous water levels and current velocities and salinities in three spatial dimensions throughout the area modeled. The model was verified to satisfactory reproduce hydrodynamic behavior observed in the natural system in 1982 and 1994. Four conditions were modeled for April through August of a typical year: a Base condition with no diversion, Plan RT with freshwater diversions up to 20,000 cfs, Plan MBP5 with freshwater diversions up to 8,500 cfs, and Plan LBCl, with no freshwater diversions but with the connections between the MRGO and Lake Borgue closed. The numerical model results were used to construct a simple regression equation that relates Biloxi Marsh salinities at a point to freshwater flows from the natural tributaries plus the diversions. The equation was then used to develop other diversion schedules that offered various salinity reduction scenarios.