LaBranche Wetlands Storm Water Drainage and Watershed Management Master Plan

U.S. Army Corps of Engineers (USACE)

The US Army Corps of Engineers (USACE) in partnership with the Pontchartrain Levee District (PLD) retained ILSI Engineering to develop Watershed Management Master Planning for the LaBranche Wetland with the primary goal of reducing habitat loss due to salt water intrusion into the marsh.  The LaBranche Wetlands consist of approximately 19,300 acres of intermediate and fresh marsh in northern St. Charles Parish.  For this planning effort we reviewed and collected field data that was used to develop a numerical model to study water circulation patterns in the wetland in order to develop a better understanding of the hydrodynamics and salinity of the wetland.   This hydraulic model aided in the watershed management decisions and planning that were aimed at improving the over-all health of the wetlands.  The model was also used to simulate the implementation of various projects designed to conserve and help restore the wetland.  The model was then used to evaluate multiple scenarios to determine the wetland response to a salinity inundation event and varying freshwater inputs.  The results of the modeling effort showed that freshening of the LaBranche Wetland after a salinity inundation event is directly related to the volume of freshwater discharged into the wetland and not just the flow rate at which the freshwater was discharged.  The model showed that the proper freshening could be achieved by discharging approximately 420 million cubic feet of freshwater into the wetland.