ANALYTICAL APPROACH TO LONG-TERM COARSE SEDIMENT TRANSPORT IN ESTUARIES

Van de Kreeke and Robaczewska (1993) have nicely concluded that the long-term coarse sediment transport is only determined by three terms, i.e. the interactions (M-0 & M-2), (M-4 & M-2) and the triple interaction (M-2, M-4 & M-6). Their conclusions pertain to transport of coarse sediment by the astronomic tide including the tidal-induced negligible mean current. However, in most estuarine environment, the mean current is induced not only by the tides but also river discharges. Thus, the approximate approach by van de Kreeke and Robaczewska (1993) is verified against situations with and without residual current in the present study. The underestimation of this expression has been found when the residual current is accounted. Therefore, the approximate expression is re-derived following the approach by van de Kreeke and Robaczewska (1993) except the higher order terms included. The new expression for the long-term net coarse sediment transport by tides reveals that the interactions (M-0 & any present tidal current constituent) and the triad interactions (M-2, S-2 & MS4) and (M-2, N-2 & MN4) also contribute to the long-term net coarse sediment transport, in addition to the three terms presented by van de Kreeke and Robaczewska (1993). The underestimation of the previous expression is due to the neglecting of the higher order terms contributed by the interactions involving M-0 and any present tidal current constituents. Although these higher order terms are negligible in most time, their contribution to the long-term net coarse sediment transport can be remarkable in estuarine environment.