Fry, V. and D.G. Aubrey
Estuarine, Coastal and Shelf Science, Vol. 30, pp. 453-473, 1990 WHOI-R-90-008
Tidal circulation can cause a net transport of sediment when the tidal velocity is asymmetric about a zero mean (flood or ebb dominant) and the sediment transport rate is related nonlinearly to velocity. The relationship between tidal elevation and velocity is elucidated here to permit determination from tide gauge data and sediment transport relations whether tidal asymmetry needs to be considered as a mechanism for net sediment transport in the embayment of interest. A relationship between elevation and velocity in a shallow water, nonlinear system is derived through the continuity equation and shown to be significantly different than the linear relation. Finite difference numerical solutions of the one-dimensional, shallow water nonlinear equations are compared to the continuity relation and are in agreement especially toward the landward end of the channel. Tide gauge data collected at the landward end of the embayment are most useful for predicting velocity asymmetries throughout a major portion of the embayment channel. The ratio of flood-to-ebb bedload transport and its relation to an asymmetric tidal elevation has been determined for both the linear relation between elevation and velocity and the nonlinear relation. Results show that the ratio of flood-to-ebb bedload transport as calculated from the nonlinear relation between elevation and velocity is similar to the flood-to-ebb ratio calculated from the linear relation because of offsetting effects.