Assessing the potential risk of glacier avalanches to hydropower infrastructure in the Himalayan region

Abstract A number of flash floods and debris flows triggered by glacier avalanches from relatively small but steep hanging glaciers over the past few years have exposed the vulnerability of infrastructures and livelihoods in the high Himalaya. As of now there are no methods to identify potentially dangerous hanging glaciers in a given catchment, and to asses the associated risk to any given infrastructure. In this paper, we propose a simple physics-based probabilistic method which attempts to provide a first-order solution to this problem. It is based on considering of a large number of hypothetical glacier avalanches and an associated flood event within a numerically-efficient Monte-Carlo framework. We assign probability weights to the chain of events involved in a flood reaching a given dam location, and assess the relative risk. We test the method in three Himalayan catchments, including two where glacier avalanche events have been reported in the recent past. The proposed method is based on a series of simplifying assumptions regarding the initiation and propagation of the events, necessitated by the complexity of the processes involved and a lack of data in these remote environments. Our method performs reasonably in two of the studied Himalayan catchments. Certain limitations in the performance of the method are apparent in one of the studied catchments. A better understanding of the underlying processes may help in coming up with more accurate paramterisations of the weights assigned to the chain of events. However, the presented method may be considered a starting point to quantify increasingly unstable ice on high and steep slopes to hydropower infrastructures in Himalayan catchments.