Projects

Project output

Insights on the erosion and deposition effects of the longitudinal training dams, as well as on the detailed flow patterns at the side channel intake.

Challenge

More extreme river conditions will likely occur in The Netherlands, for instance, longer dry periods and more extreme discharge peaks. To mitigate these effects, longitudinal training dams have been implemented in the inner bend of a 10 km river stretch in the Waal River (see Figure). The purpose of these dams is to increase the flow depth in the navigation channel during low water levels and to decrease high water levels. Despite the fact that longitudinal dams can be found in different forms in multiple rivers internationally (e.g. the Loire river in France and the Main River in Germany), there is not yet in-depth knowledge on how these structures regulate water and sediment flows. Erosion and deposition patterns in both the navigation and side channel are important for river managers, as they might increase the need for dredging on the main channel or limit the suitability of the side channel to be used by recreational boaters.

To optimize longitudinal training dam design, we focused on the local effect of the geometry of the sill at the side channel intake. Therefore, we carried out experiments with four inlet geometries (see Figure): A) uniform low sill, B) sill with downstream increasing height, C) sill with downstream decreasing height and D) uniform high sill.

An existing dataset of bed level measurements in the Waal River is analyzed to study the effect of the longitudinal training dam on the river bed dynamics.  The resulting bed level data is not only used to verify the results of the laboratory experiments but also to study the effect of longitudinal training dams on bedforms on different spatial scales (dunes, bars).

In order to understand the flow patterns at a side channel intake, measurements were carried out with ADCPs (acoustic Doppler current profilers). Measurements with vertical ADCPs were carried out at different water levels to capture the spatial variation in flow velocities. Continuous measurements with two horizontal ADCPs on the upstream sill were carried out for over a year to capture the temporal variation of the flow over the sill.

For whom and where?

The general results can be used by river managers on the river reach scale. Laboratory methods like the line laser scanner can be used in hydraulic laboratory studies with the movable bed. Advisors studying the classical situation of flow and bedload transport over an oblique weir can also benefit from the results for this specific setting.