TIDAL RESPONSE OF TWO-LAYER FLOW AT A RIVER MOUTH

Abstract

This paper describes various features of tidal effects on the behavior of a salt wedge and on the mechanism of mixing between the salt water and the fresh water in the vicinity of a river mouth. The studies have been performed through experiments, field observations and theoretical considerations. The condition upon which the fresh water begins to show an intermittent flow-pattern owing to an increase of the tidal action, and the criterion of a transition of the mixing type from negligible into intense, were obtained, with two dimensionless parameters X and 6. The former parameter X is given by A = A0/U0T0, in which T0 is the tidal period, A0 is the tidal amplitude of the sea level, and U0 is the temporal mean velocity of the fresh water at the river mouth. The latter parameter 9 is the so-called Keulegan number. Besides, it came evident that a tidal motion of the salt wedge couldn't be understood without a consideration of the internal wave inside the mouth, which were induced by the tide, in addition to a direct effect of the tide.