Effect of riverbed morphology on lateral sediment distribution in estuaries

An idealized model is applied to a set of eight estuaries with various transverse depth cross-sections to examine the effect of riverbed morphology on suspended sediment concentration (SSC) distribution. Five estuaries consist of a single deep channel, and three estuaries consist of double deep channels. All estuaries share a set of boundary conditions, including tidal flow, density gradient, river discharge, in an attempt to represent a typical estuary. Under these conditions, model results suggest that both tidal and residual flow fields vary significantly among eight estuaries, resulting in significant differences on SSC distribution, e.g., maximum mean SSC , location of , and space uniformity of mean SSC. In most estuaries, the SSC is higher over the left channel than that over the right channel mainly due to the lateral density gradient-generated residual flow . However, the space distribution of mean SSC is more uniform over the estuaries with a rightward deep channel than those estuaries with a leftward deep channel. Furthermore, the former estuaries get a higher value of , which is mainly caused by the decreasing lateral density gradient across the estuary. Lateral residual flow generated by nonlinearities would transport sediment from two sides of the estuary to the central channel (convergent transport). This transport component would play an important role in a narrow deep estuary, and would shift the location of to the central orientation. On the contrary, a much lower value of is examined in the broad wide estuary because of the extreme weak nonlinearity. Sensitivity analysis of tidal asymmetry indicates that both the amplitude and phase of M4 tidal flow would affect the transverse sediment distribution though the M4 tidal transport and the influence of M4 tidal flow on the M2 tidal transport , resulting in a significant variance of and over estuaries.