Distribution of suspended sediment in a partially mixed estuary, Charleston Harbor, South Carolina, U.S.A.

Abstract

A well-defined turbidity maximum zone (TMZ) exists 15–45 km upstream of the entrance to Charleston Harbor, South Carolina, on the Cooper River, where the salinity varies between 5–15 ppt. The TMZ is characterized by less than 60% light transmission over a 5 cm path-length near the bottom, as compared to 70–90% light transmission elsewhere. The TMZ oscillates along the Cooper River 3–13 km during a tidal cycle. The range of total suspended sediment (TSS) concentration is 40–100 mg l−1 in the TMZ, while 10–30 mg l−1 is the most common TSS concentration elsewhere in the estuarine portion of Charleston Harbor and the Cooper River. Transmissivity is well-correlated with TSS (r2 = 0·77) throughout the estuary. TSS concentration depends largely on tidal stage and varies significantly from spring to neap tide. Spring tide TSS concentrations are 2–3 times greater than concentrations during neap tides. The net downstream transport of suspended sediment is primarily a function of fresh water discharge, but is particularly large when flood events coincide with spring tides as was evident during the sampling of the TMZ following Hurricane Hugo (22 September 1989).