Understanding the role of topography, climate, and sediment transport dynamics in flash flood hazards along the Dhauli Ganga River of northwest Himalaya, India

The present work focuses on the role of topographic factors, sediment sources, and their connectivity in determining the flash flood hazard in mountain terrain. The study highlights the climatic and topographic configuration of the Dhauli Ganga Valley of the NW Himalaya that have contributed to the vulnerability of the area. We employed the digital elevation model, satellite data, and field observations to produce the stream profile, stream power index, land use land cover map, and connectivity index to better understand the interaction between topographic parameters and sediment transport dynamics in the high-altitude region. Furthermore, the 2D hydrodynamic model in HAC-RAS software was used to analyze the risk of flash flooding caused by a potential glacier lake outburst. The sedimentary landforms of the valley show evidence of high-magnitude paleo-flood, suggesting enormous potential for the valley to generate high-magnitude floods during extreme events and climate change. The analyses show that the channel slope and sediment availability vary from the headwater glaciated region to the trunk river. These factors, along with connectivity, determine the nature of the hazards associated with the flash flood. The upper reaches have considerable sediment availability, but due to low stream power, the sediments reside there for a considerable time. The middle section has high stream power because of the optimization of the slope and stream discharge, which plays a significant role in sediment entrainment. The trunk river in the lower reaches works like the local sink and, accordingly, leads to sedimentation during flood events. The study highlights the need for a quaternary geological approach in assessing long-term hazard potential and risk reduction in the Himalayan terrain. Research highlights Quaternary geological methods offer valuable insights into long-term flash flood hazards. The valley has a large quantity of sediments in the paraglacial zones. Sediment availability and transport dynamics dictate damage patterns in the higher Himalayas. The Dhauli Ganga Valley faces increased glacial hazards due to the growing number and size of glacial lakes. Sediment connectivity and stream power provide an account of sediment dynamics and hazards.