Watershed and Estuarine Modeling of the Effects of Excess Freshwater Flows Resulting from Agricultural Land Use and Other Watershed Alterations on the Salinity Characteristics of the Lower Myakka River Estuary, Florida

Watershed and estuarine modeling were conducted in the Myakka River basin to assess the effects of watershed management plans on the salinity characteristics of the estuarine portion of the lower Myakka River. Analysis of long-term data indicate that an increase in agricultural land and water use has contributed to increasing streamflow in the upper river sub-basin which has resulted in extensive tree mortality in freshwater riparian wetlands. In order to address these adverse ecological impacts, an integrated surface water/ground water model (MIKE SHE/MIKE 11) was developed to simulate continuous streamflow in the upper river sub-basin as a function of climate and watershed characteristics. Simulations of streamflow under historic (circa 1950) and existing watershed conditions allowed for the estimation of excess flows the river currently receives due to an increase in agricultural activities and other human alterations of the river's watershed. A dynamically coupled 3D-2DV hydrodynamic model of the estuarine reach of the river was used to simulate the effects of reducing these excess flows on the salinity characteristics of the lower river. Using the existing inflow regime of the river as the baseline, reductions in the area and volume of biologically important low salinity zones were calculated to assess potential ecological changes that could result from reducing the excess flows.