The salinity distribution in a coastal plain estuary governs the dynamic structure. In the estuaries studied, the salinity increases with depth, the salinity-depth curve having the general shape of an inverse tangent function. Though there is a layer of relatively rapid increase in salt content with depth, separating an upper less saline layer from a lower more saline layer, this halocline is still sufficiently weak to allow a downward random flux of fresh water as well as an upward random flux of salt. The longitudinal salinity gradient is approximately uniform with depth. The salinity is on the average higher on the right side of the estuary (looking downstream) than on the left....