Author(s): Jakob Siedersleben; Stefan Achleitner; Markus Aufleger; Marco Schuster

Linked Author(s): Jakob Siedersleben, Stefan Achleitner, Markus Aufleger

Keywords: Sediment transport; Sediment management; Reservoir; Physical modelling; Hydropower

Abstract: The presented work is part of the optimization of the sediment management plan at the hydroelectric powerplant in Reutte/Höfen in Tyrol/Austria. The runoff power plant is situated in an alpine environment and exploits water of the river Lech which transports high rates of coarse material. The lateral water intake is equipped with a flushing channel located in front of horizontal bar screens. Thereby, sediments cannot enter the turbine intake and the retained sediments must be flushed frequently. Due to the shallow water situation and a given preferential flow path (initiated by 15 m³/s turbine capacity), frequent sedimentation is the case. The overall objective of the study is, to optimize the sediment management by means of (i) avoiding sediment deposition near the lateral intake or (ii) flush settled sediments frequently. The focus lies on the second aspect, the optimization of the flushing process once the sediments have entered the flushing channel. The physical experiments on a model with a scale of 1:15 and an extent covering half of the reservoir/weir system, was used to test different flushing options. The experiments were conducted with a movable bed mixed according to the downscaled particle size distribution of the river Lech. In order to prevent cohesion, the minimum particle size was limited to 0.5 mm. At first, the ability of the model to mimic initial conditions of sediment depositions in the flushing channel was tested. The sediment deposition, generated by upstream hydraulic forcing, matched well with field conditions. Still, sediment deposition bodies were implemented artificially for the subsequent routine testing of different construction options. In general, flushing of the channel is conducted by opening the sluice gate, which is located at the downstream end of the channel. However, this works only partially since the channel is fed along its side as well. Thus, only in the downstream part of the channel an effective flushing is observed. Flushing the upstream half can only be realized by lowering the normal water level and thereby stopping the energy production over longer periods. For easier flushing of the upstream part of the channel, deep seated pressurized culverts have been introduced. In the simplest case, neighbouring culverts with varying lengths are installed in the flushing channel. Sediment can enter from the top at the upstream ends where the hydraulics are still operated by opening and closing the existing sluice gate. Since the affected flushing area is limited around the upstream openings, different geometric variations were considered. In the optimization several configurations with regard to arrangements of the openings, size of the channels, number of openings, etc. were tested. Besides the efficient flushing behaviour of the pressurized culvert system, the normal water level can be maintained avoiding operational interruptions.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022514

Year: 2022