Abstract
Himalayan region is highly susceptible to natural hazards particularly those that are triggered by the action of water. Due to the vast topographical diversity, events of ‘peak runoff’ pose various risks to small villages located at the watershed’s foot area. In this study, for the purpose to estimate flash flood risk along the Gagas River in Kumaun lesser Himalaya, high-resolution Digital Elevation Model (DEM) coupled with Geographical Information Systems (GIS) were utilised. The region experiences frequent storm events especially in the monsoon season. The river basin is also an evolving HELP basin endorsed by UNESCO as part of its global efforts for restoration of languishing river systems. Variability in the climatic conditions has imposed undue pressure on the livelihoods for survival. Relevant morphometric, topographic parameters and maximum runoff of the sub-watersheds of Gagas river watershed were computed in the GIS environment and were analysed to understand the drainage basins susceptibility to the flash flood hazards. These measurements allowed prioritising the sub watersheds in the presence of a series of rainstorms that generate unusual runoff volumes. Map representing hazard zones of sub-watersheds were identified and classified into four susceptibility groups (very high, high, moderate and low). The knowledge of flash flood susceptibility is important in mitigating the losses incurred to agriculture, irrigation systems, watermills, and recreational activities; and in the proper management of water resources.
Highlights
In complex mountainous environment such as Himalayas, due to their high susceptibility to natural hazards such as debris flows, debris floods, and flash floods, hydric analysis is very important, so that appropriate risk management could be initiated
In complex mountainous environment such as Himalayas, along with the topography having a major role in seasonal flooding, the effects of climate change render the region vulnerable to the natural hazards
As the primary determinants of running water systems functioning at the watershed scale, the physical and climatic attributes were evaluated using remotely sensed data (ASTER-Digital Elevation Model (DEM)) and Geographical Information System (GIS) based approach
Summary
In complex mountainous environment such as Himalayas, due to their high susceptibility to natural hazards such as debris flows, debris floods, and flash floods, hydric analysis is very important, so that appropriate risk management could be initiated. Various morphometrical parameters including linear, areal and relief aspects are used worldwide for the characterisation of fluvial originated drainage basin (Chalam et al, 1996) and due to its perspective view Remote Sensing (RS) and Geographical Information System (GIS) applications has been useful for monitoring and management of watersheds. It outplays conventional studies since these techniques coupled with high-resolution Digital Elevation Model (DEM) measure a number of terrain and morphometric parameters efficiently, precisely and rapidly to characterise the stream network and watersheds (Vijith and Satheesh, 2006). Stream properties, basin characteristics and maximum stream discharge of the Gagas watershed and its sub watersheds have been analysed for their risk of flash floods and for prioritisation
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