Hydraulic modelling of flood of pochu river

Abstract

This paper focuses on the upper watershed of Pochu River in Bhutan, which comes under Punakha District. Pochu is a main tributary of Punatshangchu, which receives an enormous amount of discharge throughout the year, either by rainfall or by melting glaciers at the sources of the river Pochu. On October 7, 1994, a glacial lake outburst flood (GLOF) occurred on the Glacial Lake of Luggye in the Kingdom of Bhutan, sending a flood wave down the Phochhu and Punatsangchu Rivers, claiming 22 lives and causing massive property and livestock damage. Although major flooding had occurred in the past, the 1994 GLOF was the catalyst for the government of Bhutan to establish an Early Warning System, giving downstream inhabitants sufficient time for evacuation. Similarly, another Rapteng lake is located, which is expected to be outburst at some point in time. The study is carried out over a stretch of 20 km of the Pochu River, modeling the discharge from the Rapteng lake to see the water profile if this Rapteng lake were to outburst. River analysis and steady flow water surface profiles were calculated using HEC-RAS.