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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #343605
Title: Numerical modeling of sediment transport and its effect on algal biomass distribution in Lake Pontchartrain due to flood release from Bonnet Carré Spillway

Author
item CHAO, XIAOBO - University Of Mississippi
item JIA, YAFEI - University Of Mississippi
item AZAD, HOSSAIN - University Of Mississippi

Submitted to: International Journal of Geosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2016
Publication Date: 10/1/2016
Citation: Chao, X., Jia, Y., Azad, H. 2016. Numerical modeling of sediment transport and its effect on algal biomass distribution in Lake Pontchartrain due to flood release from Bonnet Carré Spillway. International Journal of Geosciences. 4:64-79.

Interpretive Summary: A 2D numerical model was developed and applied to simulate the wind and tide induced flow fields, sediment transport and algal biomass distribution in Lake Pontchartrain. The model was first calibrated using measured water surface elevation and velocity in Lake Pontchartrain, and then it was applied to simulate the flow fields, sediment transport and algal biomass distributions due to the BCS opening for flood release. The simulated results were generally in good agreement with field observations provided by USGS and satellite imagery obtained from NASA. In general, during the period of BCS opening, the light attenuation coefficient increases due to the high sediment concentration of the lake. Therefore, the algae growth rate is very low and there is no algal bloom observed. After the BCS closure, the suspended sediment gradually settles down to the bed, and the light attenuation coefficient decreases. The algal growth rate could increase due to the high nutrient concentration and low sediment concentration. The algal bloom may occur potentially. For 1997 BCS opening event, the field observation data and simulation results showed after one and half month of the BCS closure, the algal bloom started to occur at the end of May and last for about one month. The research has positively demonstrated that the developed model is capable of predicting flow fields, sediment transport and algal biomass distribution in Lake Pontchartrain due to BCS opening for flood release. The model results provide useful information to analyze and evaluate environmental impacts of spillway opening events on the lake.

Technical 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. During the BCS opening for flood release, large amount of freshwater, nutrients, sediment, etc. were discharged into Lake Pontchartrain, and caused a lot of environmental problems. To evaluate the environmental impacts of the flood water on lake ecosystems, a two-dimensional numerical model was developed based on CCHE2D and applied to simulate the flow circulation, sediment transport and algal biomass distribution in Lake Pontchartrain. The effect of sediment concentration on the growth of algae was considered in the model. The numerical model was calibrated using field measured data provided by USGS, and then it was validated by the BCS Opening Event in 1997. The simulated results were generally in good agreement with filed data and satellite imagery. The field observation and numerical model show that during the spillway opening for flood release, the sediment concentration is very high, which greatly restrict the growth of algae, so there is no algal bloom observed in the lake. After the closure of BCS, the sediment concentration in the lake reduces gradually, and the nutrient concentration of the lake is still high. Under these conditions, numerical results and satellite imagery showed that the chlorophyll concentration was high and algal bloom might occur.