FLUVIAL SEDIMENT DELIVERY TO A COASTAL-PLAIN ESTUARY IN THE ATLANTIC DRAINAGE OF THE UNITED-STATES

Drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries. However, significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the United States Atlantic Drainage. The limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins, and the transport-limited nature of long-term sediment yields. A sediment budget for the Pee Dee River basin and Waccamaw River/Winyah Bay estuary of the Carolinas shows that only a small proportion of gross eroded sediment within the basin (about 4%) reaches the estuary on an average-annual basis. Because the system appears to be transport-limited, it is estimated that an 88% reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary. Any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity. Estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems.