Impacts of hydraulic releases from a hydroelectric power plant on bedload velocity and bed alteration in the Warche River (Belgium)

This study is based on the Warche River in the northern Ardennes (Belgium), on a 5 km stretch downstream of the Bütgenbach hydroelectric powerplant built in 1932. The hydroelectric powerplant releases a flow of 10 m³/s almost daily, which corresponds to the morphogenic flow (0.6 bank flow). But then, the dams play an important role in flood control and significantly reduce the number of large floods above the bankfull discharge.
A study in the 1990s showed that after the dam’s construction, a general incision of the whole 5 km stretch occured in about 30 years, followed by a doubling of the channel width in 45 years. Other changes such as a reduction in the number of riffles and pools, an increase in rocky outcrops in the channel have also taken place. The increase in the number of gravel bars and islands is the result of frequent releases which are very efficient in terms of bank erosion.
The objective is to quantify the impact of hydropeaks on bedload velocity to understand the grain-size sorting of the bed and the downstream propagation of the bed morphology’s degradation caused by the sediment deficit.
For this purpose, about 200 RFID tags were implanted in pebbles. As the morphogenic flow was reached almost daily, the surveys were accomplished directly in the days following the deployment of the PIT tags. Then, more spaced surveys were also accomplished. One of the main results is the decrease in tagged particles velocity with the duration of the hydraulic releases.