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 amounts 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 restricts 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.
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