FDEP Caloosahatchee River Basin and San Carlos Bay, Hydrologic, Hydrodynamic and WQ Modeling, FL, USA

The Caloosahatchee River Basin , extending from Lake Okeechobee to San Carlos Bay on Florida’s west coast, has several Waterbody Identification units (WBIDs) included in the State of Florida’s 2004 list of impaired water bodies because of nutrient enrichment and low levels of dissolved oxygen. The tidal estuary of the Caloosahatchee River is characterized by freshwater inflow from Lake Okeechobee along the non-tidal portion of the river that receives agricultural wastewater discharge and run-off from the urbanized and developing areas around Ft Myers. As part of FDEP’s TMDL development process, DSI/Dynamic Solutions, LLC developed a linked HSPF watershed and EFDC hydrodynamic/water quality model of the 1,400 square mile Caloosahatchee watershed, river and estuary. A large database was developed from local, state, and federal sources integrated with ArcMap GIS.  Historic and baseline data including land use, streams, tributary gauging, point sources, water quality and meteorological (rainfall) were used  to develop the watershed loading  model. The watershed model was then linked to a 3-dimensional hydrodynamic, sediment transport and water quality model (EFDC) of the tidal portion of river and estuary. The EFDC model is being used to simulate water quality, sediment oxygen demand, sediment diagenesis and eutrophication kinetics. The linked models were used to simulate and compare historic and existing conditions and the effects of load reduction scenarios on water quality, sediment chemistry and clarity in identified existing and potential sea grass habitat.

Submerged aquatic vegetation (SAV), such as sea grass, is seen by many as an indicator of the overall ecosystem health of coastal waters. DSI/Dynamic Solutions, LLC has recently added the capability to EFDC_Explorer to post-process EFDC simulation results to characterize the attenuation of sunlight in the water column.  When applied to areas of a water body whose depth is within the growing range of SAV the simulation can provide insight on the effectiveness of alternative water quality management options for improving water clarity to sustain, or restore, the establishment of SAV beds.

A separate large-scale EFDC model was also developed to simulate the tidal and water quality inputs to the system from the open-ocean Gulf of Mexico.