Reservoirs and other hydropower infrastructure in mountainous areas have to deal with various natural hazards. Ice- and rockfalls, landslides as well as rock and snow avalanches may impinge the reservoir, generating impulse waves that may overtop dams. Due to climate change and the rise of the permafrost base, the landslide and rockfall hazard is likely to increase in the future. A reliable risk analysis regarding potential impulse waves is therefore inevitable for the hazard assessment of hydropower infrastructure. The existing computational procedures to calculate wave heights and run-up are mostly based on small-scale model tests and may therefore exhibit scale effects. In addition, the uncertainty of the calculated wave height and run-up is still high. Therefore, new data on impulse wave characteristics were collected using large-scale field tests. A test site was established in a 30 m deep gravel pit. The artificial reservoir was 15 m wide, 55 m long and had a still water depth of 1.5 m. A 40 m long steel ramp along the pit slope (37°) provided a sliding surface. The sliding mass was represented by a steel sledge (3 to 7 tons). The sledge could be released from different ramp positions to vary the impact velocity between 6 and 17 m/s. The resulting wave heights along the wave propagation path and the wave run-up were visually determined using gauge poles. The results help to (1) improve existing computational procedures, (2) determine possible scale effects; and (3) serve as calibration and validation data for numerical modelling of impulse waves.