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-cu rrent constituents. Transport is in the term 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 M(2) constit uent. From the analytical expression it follows that the interactions of M(2) and M(0) (= Eulerian mean current) and of M(2) and any of its even overtides, M(4), M(8) etc., constitute the major contribution to the tidally averaged sediment transport. A combination of the M(2) tid al current and a fundamental constituent in the diurnal, semidiurnal o r 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 M(2) and M (0) and of M(2) and its even overtides are of interest. Application to the main channel of the Ems estuary showed good agreement with transp ort pathways derived from the grain-size distribution pattern. The tid ally averaged sediment transport is largely the result of the interact ion of the M(2) and M(0) tidal current constituents.