Author(s): Carolyn Cload; Laura Quick; Elizabeth Dingle; Maggie Creed
Linked Author(s):
Keywords: Rivers; Instability; Remote sensing; Monsoon flooding
Abstract: Flooding during the monsoon season has a devastating effect on communities and land in Nepal, displacing thousands of people, and costing millions each year in damages. Rising temperatures are causing glaciers in the Tibetan Plateau to melt, resulting in increasing seasonal discharge and sediment loading in Himalayan rivers (Li et al., 2021). Flood patterns are changing due to the increasing frequency and intensity of monsoonal rainfall events. Dynamic gravel-bed river systems in the Nepali Terai plains have historically experienced frequent changes in river course and flow distribution, which can alter the location and extent of flooding. However, current flood risk mapping of these rivers does not consider channel bed movement, and there has been limited research into the drivers of change. The Karnali River in western Nepal is used as the case study for this work. As it exits the Himalayan mountain front, the Karnali exhibits a long bifurcation, where the river splits into two channels that rejoin 40 km downstream. The location of the main bifurcation point is known to be unstable, and the dominant channel (branch conveying the larger flow) is reported to have switched sides in the past. With a 1 in 1-year peak discharge of 4300 m3/s, changes to the flow regime have a significant impact on livelihoods, habitats and infrastructure in the region (Dingle et al., 2020). The aims of this research are to test whether variations in monsoon flood patterns could cause instability in dynamic gravel-bed river systems, and to develop a method of quantifying and modelling the key areas of instability within a river corridor.
Year: 2024