MODELING OF THE PRECIPITATION INDUCED FLASH FLOOD IN SARPANG, BHUTAN USING HEC-RAS.

Flood is define as a natural disaster that causes loss of life and property damages. Flash flood is an overflow of water that submerge lands and properties affecting lives and habitats all around the world due to climate change and heavy rainfalls. It is impossible to avoid risk or prevent their occurrence but we can reduce their effects by various engineering techniques. Incessant monsoon rains in the month of July 2016, triggered flash floods in several southern districts of Bhutan including Sarpang town affecting hundreds of people. The town was also wiped out after an overnight flash flood in 1996 and several minor flash flood kept on occurring particularly during monsoon. Hence, the present study aims to model the flash flood with respect to rainfall at Sarpang, Bhutan and to understand the suitability of methods in mountain terrain. Modelling was done by integrating ArcGIS and HEC-RAS modelling software. SRTM DEM and Landsat 8 OLI satellite image were used as base data. Meteorological data from Department of Hydro Met Services, Bhutan has been used to calculate average discharge of the river outlet. The model was validated with the recent flash flood event and also study shows that the methods and procedures adopted in this paper are suitable for carrying out similar kind of studies in mountain terrain like Sarpang where flash floods are very frequent and most common. [ABSTRACT FROM AUTHOR]