Mud bottom evolution at open coasts.

摘要

Nearshore evolution of muddy coasts by waves and weak-current forcing has been examined. A mud transport model, which takes into account relevant physical processes in the open coast environment, is developed. The model simulates the time-evolution of the bathymetry due to sea forcing.; The model couples a sediment transport sub-model with a hydrodynamic sub-model. A finite difference scheme over a staggered spatial grid is used. The sediment transport sub-model solves for the bottom change in each grid cell for each time-step due to changes in cross-shore and alongshore sediment fluxes. The hydrodynamic sub-model, which drives sediment transport, includes wave damping by fluid mud, wave shoaling and refraction, as well as an imposed weak current in the alongshore direction. A depth of closure relevant to mud profile response to waves is introduced. Deep water waves and alongshore current are considered as input for each time step.; The model is used to explain mud profile changes due to a variety of erosional and accretional conditions at muddy coasts. Several field examples of such conditions and the resulting bottom changes are presented. It is shown that accurate simulation of these changes is sensitive to the hydrodynamic and sedimentary boundary conditions. Also, whereas in analogous models for sandy profile evolution conservation of sediment mass within the modeled domain is commonly assumed, such an assumption does not always apply in cases involving fine sediments. This is because of the low settling velocities and long travel distances associated with suspended fine sediment. For these reasons, synoptic and synchronous data on hydrodynamic forcing and sediment fluxes are critical for simulating profile evolution at muddy coasts.