Medium- to long-term morphodynamic modelling in estuaries and coasts: Principles and applications

The interplay between hydrodynamics, sediment transports and geometrical constraints govern the evolution of large scale estuarine and coastal morphological features. On a long time scale (> decades) sea level rise, and changing regimes in river discharge and sediment supply may influence morphological evolution as well. Spatial gradients in tide residual sediment transport cause the morphodynamic development. Relevant mechanisms are the Stokes' drift, tidal asymmetry, wave skewness, settling and scour lag, estuarine gravitational circulation, and residual transport driven by river discharge or wind. Morphodynamic models consider these physical processes and include a feedback between hydrodynamics and morphological development. Process-based morphodynamic models may deploy process and input reduction techniques to accelerate developments focusing on major processes. An example is the morphological acceleration factor to account for the different time scales of morphodynamic evolution and hydrodynamic processes. Process-based numerical models are able to reproduce realistic morphology, such as channel-shoal patterns and delta distributary channel formation. These models are also able to hindcast historical estuarine and coastal morphodynamic evolutions and to predict morphological response to sea level rise in future. So far, limited attention has been paid to muddy systems and river flow impact thus requiring further research effort.