Abstract
Longitudinal training dams (LTDs) have been built over a length of 10 km in the Dutch River Waal as an alternative to groyne fields, splitting the river in a fairway and a bank-connected side channel in the inner bend. Here, we study the physical mechanisms governing the three-dimensional flow and its effect on local morphology at the flow divide using a mobile bed physical model of an LTD, centred around a side channel intake. In line with previous experiments, polystyrene granules are used as a lightweight sediment that allows to achieve dynamic similarity between the model and the prototype. An Acoustic Doppler Velocimetry (ADV) profiler is used to monitor the flow characteristics, whereas a line laser scanner set-up is used to measure the morphological imprint of the flow near the bifurcation point. To study the dependence of the results on the sill height at the side channel intake, different forms and heights of the sill are used. First results show striking similarities with measurements from the field pilot in the Waal River, as well as larger sedimentation in the side channel for a uniform low sill compared to a downstream increasing sill height.
Highlights
Longitudinal training dams (LTDs) have been built over a length of 10 km in the inner bend of the Waal River near the city of Tiel, the Netherlands
Experiments are performed studying the effect of sill geometry at the entrance of an LTD side channel, using a physical scale model with movable bed
Bed level patterns around the sill in the scale model show striking similarities with the patterns observed in the field pilot in the Waal River, giving confidence in the reliability of the scale model
Summary
Longitudinal training dams (LTDs) have been built over a length of 10 km in the inner bend of the Waal River near the city of Tiel, the Netherlands (see Figure 1). Present (stretches of the LTD with lowered crest) through which interaction of fairway and side channel in terms of water and sediment is facilitated. Despite the fact that different kinds of LTD-like structures can be found in multiple rivers internationally (e.g. the Loire River near Chatillon sur Loire in France and the Main River near Karlstadt am Main in Germany), there is not yet in-depth knowledge on the way they regulate water and sediment flows. Recent work of Le et al [3] indicates that the sediment availability at the side channel intake is crucial for the two-channel stability. In the present pilot study, this is tackled by constructing a sill at the side channel entrance, being able to regulate the bed load sediment flux into the side channel [1]
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