Hydrodynamics and freshwater diversion within Barataria Basin

Abstract

In order to understand the physical processes in the Barataria estuary, a previously developed two-dimensional, depth-integrated hydrodynamic model is applied to simulate estuarine processes. The equations for conservation of mass and momentum predict specific physical processes when forced by tidal and salinity variations at the open boundaries, wind forcing patterns, precipitation and evaporation over the model domain, and freshwater runoff as point sources. This study is focused on examining the impact of freshwater dispersion from the freshwater sources. Thus, a hydrologic model was developed to estimate runoff. Furthermore grid size was reduced, a new advective code added, and baroclinic effects included. The model was run with and without freshwater diversions from the Mississippi River. When compared to observations the correlation coefficients ( ) of model water levels are larger than 0.9 at all but one station. For the hydrologic calibration, a big flood event was tested. Agreement between observed and model results with runoff is surprisingly good. The observed agreement provides a justification for adopting 100 % coupling between the hydrologic model and hydrodynamic model, at least for this flood event. In terms of water level within the basin, the freshwater diversions seem to affect most of the Barataria Basin system water level within 3 days. Using a Hovmüller diagram, tidal phase speed was estimated within the basin as 16 hours to travel from the mouth of Barataria Bay to the top of the basin, Lac des Allemands. In terms of salinity within the basin, the impact of freshwater diversion reaches Barataria Bay within 5 and 10 days from Naomi and West Pointe à la Hache, respectively, and the Gulf of Mexico 15 to 20 days after freshwater release.