Abstract
Debris flows are a hazardous natural calamity in mountainous regions of Nepal. Torrential rainfall within a very short period of the year is the main triggering factor for instability of slopes and initiation of landslides in these regions. Furthermore, the topography of the mountains and poor land use practices are additional factors that contribute to these instabilities. In this research, a GIS model has been developed to assess the debris flow hazard in mountainous regions of Nepal. Landslide-triggering threshold rainfall frequency is related to the frequency of landslides and the debris flow hazard in these mountains. Rainfall records from 1980 to 2013 are computed for one- to seven-day cumulative annual maximum rainfall. The expected rainfall for 1 in 10 to 1 in 1000 years of return periods is analyzed. The expected threshold rainfall is modeled in the GIS environment to identify the factor of safety of mountain slopes in a study watershed. A relation between the frequency of rainfall and debris flow hazard area is derived for return periods of 25, 50, 100, and 200 years. The debris flow hazard results from the analysis are compared with a known event in the watershed and found to agree. This method can be applied to anticipated rainfall-induced debris flow from the live rainfall record to warn the hazard-prone community in these mountains.
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