Tidal Response of Two-Layer Flow at a River Mouth

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 throretical 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 λ and θ. The former parameter λ is given by λ = A_o/U_oT_o, in which T_o is the tidal period, A_o is the tidal amplitude of the sea level, and U_o is the temporal mean velocity of the fresh water at the river mouth. The latter parameter θ 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.