An experimental study of salt wedges

Abstract

The objective of the estuary studies being conducted at this Institution is to attempt an understanding of tidal flushing. Two theories have been developed, that of Ketchum employing an extension of the tidal prism technique, and that of Arons and Stommel who treat the flushing problem through the diffusion theory. An experimental program has been established to determine the validity of these theories so that model laws may be established for tidal flushing. At the beginning of this program, the phenomenon of the salt water wedge was observed in the experimental apparatus over a wide range of flow conditions. To produce salinity distributions other than this, it was necessary to stimulate diffusion of the salt water with turbulence created by added roughness. In view of the apparent importance of the salt wedge, it was decided that an investigation of the factors that influence its shape and length would be of particular value to the future work. An empirical equation has been developed which describes the salt water wedges formed in the laboratory. This equation, how ever, does not describe well the salt wedge as found in the Mississippi River. It is of particular interest that the equation appears to describe the mean horizontal distribution of salinity in estuaries where the fresh and salt water are well mixed and not stratified as in the wedge.