Impulse Waves due to Avalanche Impact into Kuhtai Reservoir

The Tyrolean Hydropower Company TIWAG-Tiroler Wasserkraft AG plans the Kuhtai reservoir as an addition to the existing pump-storage scheme Sellrain-Silz. Two relevant natural hazards potentially affecting the dam were identified: an avalanche near the dam axis and a rockslide further upstream, both possibly impinging the reservoir at full supply level and thereby generating impulse waves. A preliminary analysis based on literature led to the conclusion that dam overtopping cannot be excluded. The Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich was therefore assigned to perform related hydraulic model tests. However, no overtopping occurred in these model tests, such that no measures as breakwater or increase of the freeboard were required. The article discusses the effect of avalanche generated impulse waves and compares an analytical estimation with results derived from the model tests.