Transport and Deposition of Sediments in Estuaries

Abstract

The dynamic processes involved in the circulation of estuarine waters are probably the most important influences on the transport and deposition of sediments in estuaries. In moderately stratified or vertically homogeneous estuaries such as the Savannah (Georgia) and Thames (England) Rivers, sediments are moved progressively landward along the bottom and they accumulate near the limit of net landward flow. In highly stratified estuaries such as Southwest Pass of the Mississippi River, coarse sediments are trapped near the toe of the salt wedge while fine sediments are carried seaward over the salt wedge with the outflowing river water. On the basis of present information, however, we cannot always distinguish between the results of natural dynamic processes and the results that are induced by the activities of man. Other possible influences on estuarine sedimentation are the inorganic and organic processes that tend to aggregate sedimentary particles, and the properties of the particles themselves. The effects of salt flocculation have been amply demonstrated by laboratory experiments, but no field evidence is available to show their importance in complex natural estuaries. The agglomeration of sediments by organisms likewise has been investigated in the laboratory, but its importance in nature needs to be evaluated. Our knowledge of the composition and size distribution of the sediment particles contributed to estuaries from different sources is seriously deficient.