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

Authors: CHAO, XIAOBO - University Of Mississippi; JIA, YAFEI - University Of Mississippi; HOSSAIN, AZAD - University Of Tennessee; ZHANG, YAOXIN - University Of Mississippi

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2021
Publication Date: 1/16/2021
Citation: Chao, X., Jia, Y., Hossain, A., Zhang, Y. 2021. Numerical simulation of sediment transport, phytoplankton biomass and salinity recovery processes in Lake Pontchartrain due to Bonnet Carre Spillway flood release. Ecological Engineering. 160: 106151. https://doi.org/10.1016/j.ecoleng.2021.106151.
DOI: https://doi.org/10.1016/j.ecoleng.2021.106151

Interpretive Summary: Spillway flood diversions in Lake Pontchartrain reduced salinity and increased suspended sediment without causing algal blooms. The Bonnet Carr´e Spillway was constructed to protect the city of New Orleans from Mississippi River floods over 5.18 meters of flood stage by diverting the excessive flood water into the Gulf of Mexico through Lake Pontchartrain. During these flood release events, large amounts of freshwater, sediment and nutrients are discharged into the lake and significantly affected its water quality and aquatic environment. Advanced simulation technology was developed at the National Center for Computational Hydroscience and Engineering, the University of Mississippi, to simulate the temporal and spatial distributions of sediment, salinity and phytoplankton in Lake Pontchartrain due to spillway flood release events. Results demonstrated that the effects of nutrients and suspended sediment on the growth of phytoplankton as well as the occurrence of algal bloom in the lake were minimal. This was because high suspended sediment concentration restricted the growth of phytoplankton. Results showed that it may take 6 months for salinity to recover to a normal level. This research provides useful information for analyzing the impacts of spillway flood diversions on the water quality in Lake Pontchartrain and is helpful when evaluating the environmental impacts of future spillway opening events on the aquatic ecosystems of the lake.

Technical 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 meters 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.