Numerical Modeling of Flow, Sediment, and Salinity in Lake Pontchartrain during the Bonnet Carr' Spillway Flood Release

Abstract

In order to protect the city of New Orleans from the Mississippi River flooding, the Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 to divert flood water from the river into Lake Pontchartrain and then into the Gulf of Mexico. However, a BCS opening event causes a lot of environmental problems in the lake. This paper presents the application of a two-dimensional numerical model (CCHE2D), developed at the National Center for Computational Hydroscience and Engineering, for simulating the flow circulations, sediment transport, and salinity distribution in Lake Pontchartrain during the Bonnet Carré Spillway (BCS) is opened for flood release. When the spillway is opened for flood release, large amount of fresh water and sediment discharged from the Mississippi River into Lake Pontchartrain, and then into the Gulf of Mexico, causing significant increase of lake sediment concentration and decrease of lake salinity. The aquatic environment and fish habitat in the lake are greatly affected by the opening events. CCHE2D model was applied to simulate the flow, sediment, and salinity in Lake Pontchartrain during the recent BCS flood releases in 1997, 2008, and 2011. The simulated results were compared with field measured data and satellite imageries, and good agreements were obtained. The flow patterns, sediment concentrations, and salinities in the lake due to the three flood release events were discussed. In addition, the salinity recovery processes in the lake were also simulated. The simulation results provides useful information to evaluate the environmental impacts of the flood events on lake ecosystems.