Acoustical discrimination of estuarine turbidity structure

Abstract

The distribution of suspended sediment in estuaries is often concentrated in turbidity maxima which, because of the association of many contaminants with fine-grained sediment particles, can be important in determining the overall water quality. Acoustic investigations of the turbidity in the Hudson River estuary were done with a 200-kHz transducer and a 600-kHz broadband acoustic Doppler current profiler. (Water temperature and salinity were also measured and samples of suspended sediment were collected.) High turbidity here was found to be associated with tidally modulated and geomorphically controlled salinity intrusions. A salinity front is arrested at the bottom by the ebbing tide. As the tide turns, the front migrates upestuary producing an intense, local turbidity maximum. The re-establishment of a front in the original position on the next ebb can leave high turbidity pockets stranded upestuary. This is a novel mechanism for the generation of estuarine turbidity maxima but probably not unique to the Hudson River estuary; it may prove to be of widespread importance. [Work supported by the Hudson River Foundation, New York, NY.]