Determination of Threshold Runoff for Flood Warning in Nepalese Rivers

The Southern Terai plain area of Nepal is exposed to recurring floods causing the loss of lives of about 300 people and damage to properties worth about 10 million USD annually. Consequently, the overall development of the country has been adversely affected. The flood risk could be significantly reduced by developing effective operational flood early warning systems. Hence, a study has been conducted to assess flood danger levels and determine the threshold runoff at forecasting stations of six major rivers of Nepal for the purpose of developing threshold-stage based operational flood early warning system. Digital elevation model data from SRTM and ASTER supplemented with measured cross-section data and HEC-RAS model was used for multiple profile analysis and inundation mapping. Different inundation scenarios were generated for a range of flood discharge at upstream boundary and flood threshold levels or runoffs have been identified for each river, thus providing the basis for developing threshold-stage based flood early warning system in these rivers.