Flow and Turbulence over an Estuarine Dune - Large-Scale Flume Experiments

Bedforms, such as dunes, are found in large parts of estuaries and coastal areas. Dunes influence hydrodynamics and sediment transport in the flowing water by causing flow resistance, whereby flow energy is dissipated. The characteristics of dune overflow are complex and vary depending on the dune shape. They have rarely been studied for estuarine dunes in particular, although a precise knowledge of the hydrodynamic processes is important, e.g. for a correct representation or parameterization in mathematical hydrodynamic models. Therefore, we conducted the first flume experiments over a typical estuarine dune. The experimental setup allowed for studying dune overflow on a large scale and in a high level of detail. High-frequency measurements using Acoustic Doppler Velocimetry (ADV) were carried out on a 1:10 scaled, fixed model dune in a closed-circuit flume. Results show that a flow separation zone with a recirculating flow cell and a turbulent wake develop which differ in their orientation and length from those reported for triangular and river dunes. The high-quality experimental dataset including the flow velocity timeseries is freely available at https://doi.org/10.48437/02.2021.K.9900.0001 (Bundesanstalt für Wasserbau 2021) and can be used for further studies, e.g. on the dissipative effect of dunes, or as validation data for laboratory experiments and mathematical models. Overall, we give indication for the need to study hydrodynamic processes related to estuarine dunes in more detail and we provide a full description of the experimental setup and the complete collected dataset to support and facilitate the needed further research.