Numerical Modeling of Sediment Transport and Its Effect on Algal Biomass Distribution in Lake Pontchartrain Due to Flood Release from Bonnet Carré Spillway

摘要

In order to protect the city of New Orleans from the Mississippi Riverflooding, the Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 todivert flood water from the river into Lake Pontchartrain and then into theGulf of Mexico. During the BCS opening for flood release, large amounts offreshwater, nutrients, sediment, etc. were discharged into Lake Pontchartrain,and caused a lot of environmental problems. To evaluate the environmentalimpacts of the flood water on lake ecosystems, a two-dimensional numericalmodel was developed based on CCHE2D and applied to simulate the flowcirculation, sediment transport and algal biomass distribution in LakePontchartrain. The effect of sediment concentration on the growth of algae wasconsidered in the model. The numerical model was calibrated using fieldmeasured data provided by USGS, and then it was validated by the BCS OpeningEvent in 1997. The simulated results were generally in good agreement withfiled data and satellite imagery. The field observation and numerical modelshow that during the spillway opening for flood release, the sedimentconcentration is very high, which greatly restricts the growth of algae, sothere is no algal bloom observed in the lake. After the closure of BCS, thesediment concentration in the lake reduces gradually, and the nutrientconcentration of the lake is still high. Under these conditions, numericalresults and satellite imagery showed that the chlorophyll concentration washigh and algal bloom might occur.