Improving Energy Dissipation of a Spillway with Structural Modifications

The stilling basin of Rusfors spillway comprised a concrete frame with two supporting plates and a cover, which was probably constructed for timber floating but was not in use anymore. Abrasion damages occurred in the basin bottom due to the sediment carried by the bottom current. To safely discharge the updated design flood, removal of the structure was suggested to avoid further deterioration of the operation conditions. Physical model tests and CFD modelling were performed to help understand the flow behaviors in the basin. The studies show that, due to the concrete frame, strong surface currents prevail in the basin, with inefficient energy dissipation and accordingly large water-level fluctuations downstream. The supporting plates also lead to skewed bottom currents, which are the cause of the bottom damages. Together with the detruncation of the spillway crest, the removal of the frame results favorably in a typical hydraulic jump. As shown from both the physical and numbering modelling, the basin flow pattern and energy dissipation become satisfactory at the design flood.