Analytical approach to long-term coarse sediment transport in estuaries.

Ao Chu, Jia'ai Tai

Wednesday 1 july 2015

9:00 - 9:15h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 8A. Sediment - Transport

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 of tidal current constituents M0 & M2, M4 & M2 and the triple interaction of M2, M4 & M6. In their approach, M2 is assumed to the dominant harmonic and the coarse sediment transport is proportional to some power of the local depth averaged velocity. Their conclusions pertain to transport of coarse sediment by the astronomic tide including the tidal-induced 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 interaction of M0 & any present tidal current constituent and the triple interactions of M2, S2 & MS4 and of M2, N2 & 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 interaction of M0 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.