My focus is on the coupled system of flow, sediment transport and channel morphology in rivers, estuaries and lowland delta settings. Over the past decades, I have collaborated with hydrologists, physical oceanographers, geologists and ecologists in projects on river and delta restoration, river training and environmental monitoring. I am particularly interested in the physical interactions between river discharge and tides in the fluvial to tidal transition zone, where the impacts of sea level rise, land use change and engineering works culminate.
From field analyses and model simulations representing deltas in the Netherlands, Bangladesh, Indonesia and China, my coworkers and I have quantified how tides modulate the river discharge in delta channels, and how the river discharge in turn influences tidal propagation in branching channels. We explained why natural delta channels are comparatively stable. We showed that human impacts on tides overwhelm the effect of sea level rise on extreme water levels in the Rhine-Meuse delta. We demonstrated that after river restoration projects, there is an initial system response that differs from the gradual trends in channel morphological adaptation afterwards.
I have led projects focussed on field and laboratory techniques to monitor flow and sediment transport from the fine timescales of turbulence to the seasonal scale of river discharge variation. This has resulted in new techniques for improved processing of acoustic Doppler current profiler data collected during standard river discharge surveys. The new processing methods have revealed the causes of scour in rivers, and allow to detect subtle changes in sedimentary regimes.