Assessing flood susceptibility and frequency analysis in himalayan river basins: A GIS-based multi-criteria approach

Abstract

Flooding is a recurrent issue in Nepal during the monsoon season. This study assesses flood susceptibility zones in Himalayan River basins, specifically Tamakoshi and Indrawati River Basin, Nepal utilizing Geographic Information Systems (GIS) and multi-criteria analysis. Additionally, it employs Gumbel’s distribution method for flood frequency analysis, estimating potential flood discharges for different return periods (2, 5, 10, 50, and 100 years). The critical flood causative factors like slope, elevation, land use/land cover, rainfall intensity, and river proximity are analyzed in this study using weighted multi-criteria overlay methods to produce flood-prone areas. Because the study areas are part of mountainous catchment areas, these regions have steep slopes, meaning surface runoff velocity is increased, ground infiltration of water decreases, and flood risks increase. GIS-based weighted overlay analysis identified approximately 26.6% of the Indrawati Basin and 25.4% of the Tamakoshi Basin as highly flood susceptible zones. The predicted flood discharges for a 100-year return period are 1566.59 m³/s for Indrawati River Basin and 1821.87 m³/s for Tamakoshi River Basin. The findings will support regional flood hazard management strategies and contribute to disaster risk reduction efforts in Nepal.