Water Quality Modeling System for Charleston Harbor, South Carolina

A three-dimensional (3-D) water quality model for the Charleston Harbor System (CHS), South Carolina, is being developed for the Berkeley-Charleston-Dorchester Council of Governments (BCD-COG) to assist in developing the dissolved oxygen Total Maximum Daily Load (TMDL). A series of linked models were developed to represent watershed flows, instream hydrodynamics, and instream water quality in the system. The ultimate goal of the 3-D water quality model is to develop a management tool to determine the TMDL and wasteload allocation strategies for the Charleston Harbor System. The water quality model will engage all stakeholders including the industries, local governments, and regulators in establishing the assimilative capacity of oxygen-consuming pollutants. 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 Moultrie, the largest contributor of freshwater flow to the Cooper River. Changing water levels, salinity, and marshes increase the complexity of the dynamics of dissolved oxygen in the system. The CHS EFDC model extends beyond the main Harbor into the Atlantic Ocean, up the Wando River just downstream of Guerins Bridge Road, up the Cooper River to Pinopolis Dam, up the East Branch of the Cooper River, up to the dam on Goose Creek, and up the Ashley River to US Hwy 17. The model was calibrated and validated using monitoring data collected in 2004 and in 1996 and several special studies.