Tide-induced residual transport of coarse sediment; Application to the EMS estuary

For a tidal channel with water of homogeneous density, an approximate analytical expression is derived for the tidally averaged transport of coarse sediment in terms of the amplitudes and phases of the tidal-current constituents. Transport is in the form of bed load and the rate of transport is proportional to some power of the local current speed. It is assumed that the tidal current is dominated by the M2 constituent. From the analytical expression it follows that the interactions of M2 and M0 (= Eulerian mean current) and of M2 and any of its even overtides, M4, M8etc., constitute the major contribution to the tidally averaged sediment transport. A combination of the M2 tidal current and a fundamental constituent in the diurnal, semidiurnal or subsequent period bands results in a tidally averaged transport that fluctuates with the corresponding beat frequency. Therefore, for the long-term mean bed-load transport only the contributions of M2 and M0 and of M2 and its even overtides are of interest. Application to the main channel of the Ems estuary showed good agreement with transport pathways derived from the grain-size distribution pattern. The tidally averaged sediment transport is largely the result of the interaction of the M2 and M0 tidal current constituents.