Analysis on residual coarse sediment transport in estuaries

•Interactions M2 & M0, M2 & M4 and M2, M4 & M6 lead to most residual sediment flux.•Interaction of M0 and any tidal constituent enhances residual sediment transport.•Triad interaction M2, S2(N2) & MS4(MN4) also yields residual sediment transport.•A single representative tide is insufficient for estuarine morphodynamic models.

The analytical expression for residual coarse sediment transport of Van de Kreeke and Robaczewska (1993) is extended for estuaries. The major extension concerns the contribution to sediment transport by residual current, which is ignored by Van de Kreeke and Robaczewska (1993). Tidal constituents M0, M2, S2, N2, M4, MS4, MN4, M6, K1 and O1 are used to represent the collinear tidal current. It is shown that interactions of M0 and all tidal constituents contribute to residual sediment transport when M0 is not negligible. Thus, a representative tide based on M2 and its overtides only is not sufficient to drive morphodynamic models in this case. The present analysis also reveals that triad interactions of compound tides with their basic constituents, i.e. MS4 with M2 & S2 and MN4 with M2 & N2, contribute to residual sediment transport, besides interactions of M0 and M2, and of M2 and its even overtides M4 and M6. The extended analytical expression is applied to determine residual sediment transport in the Yangtze Estuary. It is demonstrated that a single representative tide does not exist for morphodynamic models in this case. This conclusion is likely to also apply to other estuaries in which residual flow is not negligible.