Charleston Harbor, SC, Regional Sediment Management study; beneficial use of dredged material through nearshore placement

Abstract

Abstract : The 2015 Charleston Harbor, SC, final feasibility study (USACE 2015) presents results of analyses of proposed modifications to the existing navigation system. The improvements would deepen the Entrance Channel from -47 feet (ft) mean lower low water (mllw) to -54 ft mllw. The dredged material is estimated to be 80% sand and does not meet U.S. Army Corps of Engineers guidelines for beach placement. Instead of disposing in the Ocean Dredged Material Disposal Site, nearshore placement is considered as a beneficial use. The U.S. Army Engineer Research and Development Center CMS-Flow and CMS-Wave numerical models were utilized to estimate benefits from nearshore placement of 400,000 cubic meters (523,000 cubic yards) of new work in three areas south of the Harbor south jetty. The least sediment erosion occurred where the material was placed in Area 1, the location nearest the shoreface. This resulted in maximum deposition along the Morris Island southern shoreline and least deposition inside the Entrance Channel and in the ebb-tide delta of Lighthouse Inlet. As more details of the new work dredge material become available, this analysis will be re-evaluated with longer simulations to better understand morphology changes along Morris Island and the northern portion of Folly Island.