THE TRANSVERSE DISTRIBUTION OF VELOCITY IN ESTUARY FLOW

Homogeneous estuary flows and tidal models of estuaries are known to exhibit a phase shift effect. The velocity versus time curves from various positions in the transverse, z, direction (perpendicular to the long axis) may be shifted relative to one another by times of as much as 1 hour. An explanation of this phase shift is presented in terms of the magnitude of the relevant forces. A Strouhal number, proportional to fu 0 T/d, where f is the friction factor, u 0 is the longitudinal velocity, T is the tidal period and d is the depth of flow, is shown to be important in describing the amount of phase shift. Two situations which result in horizontal phase differences are analysed, and laboratory measurements of both cases are presented. In one case the phase difference results from a slow variation of depth with position z, and in the second case the phase shift results from the influence of very large sidewall roughness in a deep channel.