Turning the tide: Estuaries and their floodplains as complex biogeomorphic systems

Estuaries often show dynamic patterns of channels, bars, tidal flats and vege tated floodplains. These aspects are important for coastal ecosystems, flood protection and navigation. How decadal and centennial development of estuarine morphology are affected by climate change and direct human interference is unclear because of the complex behavior of such estuarine systems. Current models for estuaries in morphological equilibrium, such as the exponentially convergent shape, do not predict multiple stable states. Here, a synthesis of estuarine system responses is initiated from results of numerical biogeomorphological models and landscape experiments in a 20 m long tidal flume. Both models and experiments require representation of the relevant aspects of eco-engineering species and imposed conditions, but which aspects are relevant can only be known from previous iterations between fieldwork, experiments and models. The models and the experiments show striking biogeomorphological similarities with natural landscapes despite model issues and experimental violation of the classic rules of engineering scale models. Collectively, the results illuminate effects of different mechanisms and of imposed conditions on the stable or transient states of estuaries. Similar ities and differences with nontidal river channel dynamics and their floodplain interaction shed further light on the question to what degree the concept of equilibrium or steady state is useful for application in systems with changing boundary conditions such as sea-level rise, embankment for coastal protection and land reclamation, and fairway dredging.