Flash flood dynamics in the foothills of NW Himalaya: Insights into hydrological and geological controls

Abstract

Himalaya experiences several cloudbursts because of its physiography, geomorphology, and geology. Uttarakhand is one of the Indian states circumscribed mostly by Himalayan hills and has experienced a rise in number of cloudburst catastrophes in the last few decades. These catastrophes produce substantial loss of lives and property, still, very less studies are available that characterize these unpredictable cloudburst-flash floods in different regions of Uttarakhand. The present study discusses the geological and hydrological factors associated with the Raipur-Kumalda cloud burst in Uttarakhand's Dehradun district. The flash flood associated with this cloud burst during 20-21st August 2022 significantly damaged roads, bridges, and settlements throughout the valley. This study intends to the geological and geomorphological controls of this event by determining the peak discharge during the flood and assessing the reasons behind this. The basin geomorphometry reveals poor drainage, steep slopes, rapid peak flows, a sharp peak hydrograph, and a short concentration time worsening the impact of the flood. Different flood indices such as rising curve gradient (K), flood magnitude ratio (M), and flood response time (TP) implicitly 50 to 100 times higher discharge during the event when compared with the usual monsoonal discharge. The role of mountain topography, climate, the geology of the region, and irreversible changes of land use–land cover (LULC) associated with urbanization in the intensification of the destruction is also discussed.