Effect of the proposed Cooper River rediversion on sedimentation in Charleston Harbor, South Carolina

The rates of sedimentation and of resultant maintenance dredging in Charleston Harbor increased dramatically in the 1940s, following two major modifications to the harbor. One modification, the Santee-Cooper diversion project, caused a twentyfold increase in freshwater inflow to the harbor. The other modification was deepening of the navigation channels in the harbor from 30 to 35 feet below mean low water. After field and model studies indicated that the diversion was the major cause of the increase in the sedimentation rate, plans were made to redivert most of the Santee River water back to its former channel. This report documents a review of existing data and literature that was made to evaluate rediversion as a means of reducing the rate of maintenance dredging. The postrediversion decrease in the rate of maintenance dredging can be estimated only within broad limits because some important questions lack reliable answers. Analysis of available information indicates that rediversion will eventually reduce the rate of maintenance dredging by about 40 to 75 percent. The reduction in the rate of maintenance dredging may be delayed for a decade or more by the gradual removal of accumulated sediment and may be partially offset by the effects of future channel deepening.