Salinity intrusion models

Abstract

In many cases, the salinity intrusion processes of estuaries are dominantly governed by the amount of fresh water discharge, the density difference between fresh water and sea water, and the tidal amplitude. The time for reaching periodic tidal conditions is of the order of one day, while the time for reaching equilibrium conditions for the salinity distribution is of the order of several weeks. Due to this fact, a time averaging over the tidal motions can be performed in order to study the salinity intrusion processes separately. The stream velocities of the tidal motion are often of the order of 1 m/s, while the stream velocities of the fresh water discharge is of the order of 1 cm/s. The deviations in the vertical velocity profiles from the usual logarithmic shape which are essential for the salinity intrusion process, are caused by the horizontal density gradients; these deviations are of the order of 1 cm/s too [1]. So, if one is only interested in the tidal dynamics of an estuary, the barotropic assumption of constant density is well justified. Furthermore, if the salinity distribution in an estuary at a certain time is known, the variations in salinity due to the tidal motions can be calculated to a good degree of accuracy for a few tidal cycles under the barotropic assumption, because the tidal and salinity time scales are so different.