Impact of potential flood on riverbanks in extreme hydro-climatic events, NW Himalaya

Floods are becoming more frequent in Himalaya, particularly in the NW Himalaya, and have been related to the increasing impact of changing climate. Uttarakhand in the NW Himalaya has witnessed 2 major flood events in the last decade that killed more than 6000 people. This study is an attempt to explore the impact of potential flood on a riverbank slope in Uttarakhand, NW Himalaya. The response of this riverbank slope during extreme rainfall is also explored in terms of stability and debris flow runout. Therefore, we evaluated the riverbank slope stability and the runout extent of its material to understand the slope response during extreme rainfall. Flood simulation was also performed to determine the potential flood impact on the riverbank slope. Results revealed that the slope material at the exposed fluvial sequence and slope toe might displace forward ~0.12–0.4 m. The potential debris flow from the slope may impact the retaining wall supporting the slope with a pressure up to 150 k Pa. The potential flood may strike the riverbank with a velocity and stream power of 10 ± 2 m/s and 0.2 ± 0.1 M N/m-s, respectively, which is about three times higher than the approximated resistance of the retaining wall.