Numerical simulation of sediment transport, phytoplankton biomass and salinity recovery processes in Lake Pontchartrain due to Bonnet Carré Spillway flood release

Abstract

The Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 to protect the city of New Orleans from the Mississippi River floods. When the water stage of the Mississippi River is over 5.18 m of flood stage, BCS will be opened to divert the excessive flood water into the Gulf of Mexico through Lake Pontchartrain. During these flood release events, large amounts of freshwater, sediment and nutrients were discharged into the lake and significantly affected its water quality and aquatic environment. A numerical model (CCHE2D) developed at the National Center for Computational Hydroscience and Engineering (NCCHE), the University of Mississippi, was applied to simulate the dynamic process of hydrodynamics and associated temporal and spatial distributions of sediment, salinity and phytoplankton in Lake Pontchartrain due to the BCS flood release events. Three events occurred in 1997, 2008 and 2011, representing the median, low, and high flood discharge cases, were selected for this study. The simulated results were compared with field measured data and satellite imageries obtained from USGS, US Army Crop of Engineers and NOAA, and good agreements were obtained. The effects of nutrients and suspended sediment on the growth of phytoplankton as well as the occurrence of algal bloom in the lake were analyzed. The processes of salinity recovery in the lake were also discussed. The results obtained from this research provide useful information for analyzing the impacts of flood release event on the aquatic ecosystems in Lake Pontchartrain.