Charleston Harbor System 3-Dimensional Modeling, Charleston, SC

A three-dimensional (3-D) hydrodynamic model for the Charleston Harbor System (CHS), South Carolina, has been developed for the Berkeley-Charleston-Dorchester Council of Governments (BCD-COG) to assist in developing the dissolved oxygen Total Maximum Daily Load (TMDL). The hydrodynamics of the CHS are largely influenced by incoming tides, salinity, and vegetated marshes. The CHS drains over 1,200 square miles directly, with a larger area contributing freshwater flow to Lake Moultre, the largest contributor of freshwater flow to the Cooper River. The Environmental Fluid Dynamics Code (EFDC) was used for the hydrodynamic simulation. The CHS EFDC model extends beyond the main Harbor into the Atlantic Ocean and it includes the Ashley River, Wando River, and Cooper River including both east and west Cooper River branches. Both instream flows and lateral overland flows generated by the watershed model, the Loading Simulation Program in C++ (LSPC), were input to the EFDC model. Effluent discharges received from facilities and the State were also input as lateral flows to represent point source inflows to the system. The CHS marshes were delineated from landuse maps. Wetting and drying grid cells, equal in area to the delineated marsh area, were initially simulated in the model. Using continuous monitoring data collected 1996 and 2004 and several special studies the hydrodynamic model was calibrated and validated. Measured water levels, flows, salinity, and temperature at several stations in the CHS were compared with simulated model results.