A Comprehensive Hydrodynamics-Salinity-pH Model for Analyzing the Effects of Freshwater Withdrawals in Calcasieu Lake and Surrounding Water Systems

Abstract

The study is a continuation of the authors' previous works on hydrodynamics and sediment transport modeling for Calcasieu Lake area (located in southwest Louisiana) (Zhang, N., Zheng, Z. C., and Yadagiri, S., 2011, “A Hydrodynamic Simulation for the Circulation and Transport in Coastal Watersheds,” Comput. Fluids, 47(1), pp. 178–88; Zhang, N., Kee, D., and Li, P., 2013, “Investigation of the Impacts of Gulf Sediments on Calcasieu Ship Channel and Surrounding Water Systems,” Comput. Fluids, 77, pp. 125–133; Yadav, P. K., Thapa, S., Han, X., Richmond, C., and Zhang, N., 2015, “Investigation of the Effects of Wetland Vegetation on Coastal Flood Reduction Using Hydrodynamic Simulation,” ASME Paper No. AJKFluids2015-3044). The major purposes of the study are: (1) to demonstrate the new model features and validate the model results, (2) to disclose the effects of Gulf Intracoastal Waterway (GIWW) and determine the boundary conditions for GIWW in the model, and (3) to use the model to analyze the effects of excessive freshwater withdrawals on the changes of hydrodynamics and salinity in the Calcasieu Lake system. Several new model features were added to the existing model framework, including the extension of modeling domain, vegetation model, salinity transport model, and pH calculation. Measurement data from NOAA and USGS are used as boundary conditions for the model. Simulation results were compared with measurement data from NOAA, USGS and other sources for validation. Due to lack of measured data for GIWW in the target area, the effect of GIWW flow conditions on the modeling results was investigated and appropriate GIWW boundary condition was determined based on numerical tests. Numerous petrochemical plants in the area use tremendous amount of fresh surface water. Recent industry expansions may further increase the demands of freshwater withdrawals. One of the purposes of the study is to use developed model to test and analyze the effects of increased freshwater withdrawal from Calcasieu River at the north boundary of the study area on the hydrodynamics and salinity in the downstream Calcasieu Lake system.