River Flood modeling of Amochu River using GIS and HEC-RAS: A case study in Phuntsholing city, Chukha, Bhutan

Abstract

The study area, Phuntsholing, commercial hub of Bhutan, is exposed to major threat to the flood as it is located at the proximity of the giant river, Amochu. Thus, the flood modeling of Amochu River was carried out to generate the flood inundation map to locate sites vulnerable to flooding and to obtained the impact of flood on the settlements of present and future plan city. Log Normal and Log-Pearson III techniques were used to find out the affected areas on both present and future city. However, it is observed that Log Normal technique will have the heavy impact on the city with the rapid time period than the Log-Pearson III technique. One-dimensional model in HEC-RAS was used to find the flood inundation map using the information from the observed peak discharge to get the depth of flood. The result showed that in the current Phuentsholing city, the major vulnerable regions by flood from 25 years till 1000 years will be the flood plain and shrub areas and the least affected areas will be agriculture and forest land. The study also displayed that in the upcoming city plan, Zone B, Zone E, Zone C will be the most vulnerable places and the least will be LAP and Zone A. The study also found that the depth of the river will be estimated to increase with increasing in time. The map also showed that inundated area will be increased with increasing in time especially at the riverine areas of the river. Thus, this study not only provides an identification of flood risk zones to serve as emergency services but also provides potential area for town planning by reclaiming the land to certain height. These findings can be replicated to other flood prone regions for similar flood mapping.

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