2D Bedload Modelling at the Run-of-river Power Plant Klingnau

The Run-of-River hydropower plant Klingnau is the last power plant at the Aare River before the confluence in the Rhine River. According to the Swiss water protection act (Gewässerschutzgesetz, GSchG), measures must be taken to restore sediment continuity. In future, an annual bedload yield of 8000 m³ is assumed in the case of fully recovered bedload continuity in the upstream reach. The present feasibility study on behalf of the Aarekraftwerk Klingnau AG is investigating whether under certain reservoir operation scenarios (water level lowering rate, duration of flushing, discharge) the bedload material can be transported through the reservoir. For the present project, we perform 2D simulations using the 2D hydrodynamic module BASEplane of the software BASEMENT [1].

The topography of the river bed and reservoir derived from multibeam echo sounder survey in 2018 serves as basis for the numerical model. Based on bed material samples downstream of the powerplant Beznau (upstream of Klingnau), the grain size distribution was discretized using 5 grain classes. First, a sensitivity analysis was performed to determine and validate the model configuration. Based on the cross-section surveys from 2006 and after the flood event in 2007, the amount of bedload deposition was estimated for this period. In the scope of the sensitivity analysis, the grain size distribution and the bedload transport formula were found to be the most sensitive model parameters. Finally, the deposition and morphological pattern were best reproduced with the extented bedload formula of Meyer-Peter-Mueller for non-uniform bedload transport (MPM-Multi) [1] using the corrected form of Wong and Parker [2].

The bedload transport through the reservoir was investigated using single flushing events and long term simulations (26 and 39 years) with periodic flushing events. This feasability study provides an important basis for the power plant operator (Aarekraftwerk Klingnau AG) to decide whether lowering the reservoir water level during flood events is a feasible, efficient and economic measure for restoring bedload continuity.

[1] BASEMENT - Basic Simulation Environment for Computation of Environmental Flow and Natural Hazard Simulation. Version 2.8. (c) ETH Zurich, VAW, 2006-2018.

[2] Wong, M., Parker, G. (2006). Reanalysis and correction of bedload relation of Meyer-Peter and Mueller using their own database. Journal of Hydraulic Engineering, 132(11): 1159-1168