Observation- and Modelling of Morphodynamics in Sandy Coastal Environments

The topic of sandy coast morphodynamics involves the mutual influences of coastal topography, local sedimentology, the driving meteorological and hydrodynamic boundary conditions, flora and fauna, and the activities of human beings: The latter as direct actors through coastal constructions and other interventions, as indirect actors through possible contributions to global change, but also as receiving agents - as living individuals confronted with the forces of the sea. The general aim of coastal research is to gain an as comprehensive as possible understanding of the different systems and their interaction in order to be able to evaluate their current state, assess their stability, explain past changes (in the geological record), and predict future developments under different conditions. Such systems dynamics involve a large bandwidth of spatial and temporal scales: from the microscopic interaction of turbulent fluid motions with single particles to meso-scale tidal dynamics of subaqueous bedforms to macro-scale seasonal adaptations of beach profiles or the meandering of tidal channels, to the mega-scale evolution of shorelines and shelf systems over decades to centuries. The process of understanding involves a continuous feedback of observations, abstractions, mathematical formulations, model development (ranging from conceptual models to mathematical formulations of processes, and to complex, process-based numerical modelling systems), and the testing of models on the basis of observations, new abstractions, and so forth. In the case of the morphodynamics of sandy coasts, the interaction of the physical processes involved in hydrodynamics, sediment dynamics, and their mutual adjustment to changing bed topographies seem most relevant, although biogeochemical processes play a (commonly underrated) additional role. This discourse presents an extended summary of the current state in the continuous process of gaining knowledge on coastal morphodynamics. It focuses on the dynamics of tidal channels and their main roughness elements: subaqueous compound bedforms. Methodological approaches involved are field measurements and numerical modelling, which are introduced and discussed.