Abstract
Basin geomorphology is a complete system of landforms and topographic features that play a crucial role in the basin-scale flood risk evaluation. Nepal is a country characterized by several rivers and under the influence of frequent floods. Therefore, identifying flood risk areas is of paramount importance. The East Rapti River, a tributary of the Ganga River, is one of the flood-affected basins, where two major cities are located, making it crucial to assess and mitigate flood risk in this river basin. A morphometric calculation was made based on the Shuttle Radar Topographic Mission (SRTM) 30-m Digital Elevation Model (DEM) in the Geographic Information System (GIS) environment. The watershed, covering 3037.29 km2 of the area has 14 sub-basins (named as basin A up to N), where twenty morphometric parameters were used to identify flash flood potential sub-basins. The resulting flash flood potential maps were categorized into five classes ranging from very low to very high-risk. The result shows that the drainage density, topographic relief, and rainfall intensity have mainly contributed to flash floods in the study area. Hence, flood risk was analyzed pixel-wise based on slope, drainage density, and precipitation. Existing landcover types extracted from the potential risk area indicated that flash flood is more frequent along the major Tribhuvan Rajpath highway. The landcover data shows that human activities are highly concentrated along the west (Eastern part of Bharatpur) and the east (Hetauda) sections. The study concludes that the high human concentrated sub-basin “B” has been categorized as a high flood risk sub-basin; hence, a flood-resilient city planning should be prioritized in the basin.
Highlights
Flood is one of the major disasters that threaten human lives and causes property losses worldwide
This paper highlights geomorphological approaches based on the satellite remote sensing data to identify flash flood potential areas in the East Rapti River basin
In addition to index modelling, flash flood risk was estimated by hazard degree calculation linear interpolation techniques [59], where if the value of the morphometric parameter is positively correlated with flash flood occurrence, we used Equation (1); otherwise, we used Equation (2)
Summary
Flood is one of the major disasters that threaten human lives and causes property losses worldwide. Given that watershed geomorphology is essentially important when the basin undergoes heavy rainfalls, we considered several morphometric parameters in this study to identify flash flood potential areas [21,33,37]. During the last few decades, the empirical studies on flash flood forecasting [40,41], and flood risk management [34,42] in Nepal have been accumulated, but surprisingly, there is limited attention to morphometric analysis identify flood potential at the basin level Against this backdrop, this paper highlights geomorphological approaches based on the satellite remote sensing data to identify flash flood potential areas in the East Rapti River basin. This study aims to (1) examine the relationship between morphometric parameters with a flash flood in East Rapti River basin; and (2) develop a complete flood susceptibility map for the study area
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