Hydrodynamic and Environmental Impact of Edisto Beach Causeway on the Scott Creek Estuary, South Carolina

The Scott Creek estuary is a long system of meander tidal creeks and salt marsh between Edisto Island and Edisto Beach, South Carolina. A causeway for South Carolina Highway 174 (Edisto Beach Causeway) divides the estuary into two nearly equal-length basins that drain, east through Jeremy Inlet and west through Big Bay Creek, into the Atlantic Ocean. The disruptions of the natural flow through Scott Creek and rapid resort development on Edisto Beach are believed to have accelerated sedimentation and sedimentation related water quality problems. The creeks are well-mixed and strongly influenced by semi-diurnal tides. The creeks nearby the causeway undergo wetting and drying under normal tide range. A numerical flow and particle-tracking model was employed to study water levels, flow and circulation details of the Scott Creek and to evaluate the potential causeway-induced environmental stresses in terms of residence time of a conservative substance. The model is based on the general 2D shallow water equations in strong conservation form. The equations are discretized using the Total Variation Diminishing (TVD) finite volume method. The model accounts for flooding and drying of intermittently wetted areas. The numerical model was calibrated with available measured water surface levels and currents. Model prediction of residence time distribution shows that under present condition, portions of the creek near the causeway require more than ten days to flush. On the other hand, this preliminary study shows that the reconnection of the causeway will greatly improve the flushing rate as compared to the existing condition.