Downstream Flood Forecasting During Dam Breaching

The heavy thunderstorm as equivalent to PMF (Probable Maximum Flood) was occurred in 2012 at 12MW Jhimruk small hydropower project located in Pyuthan District, Lumbini Province no 5 of Nepal. Three radial gates were operated to evacuate the reservoir level in dam. About 10kM far downstream of the existing Jhimruk, the flood level was marked and the peak flow was validated for the flood event. The land and properties of downstream communities were damaged by the flood during operation of the gates. There was no early warning system installed beforehand to protect the life and property of the downstream communities. After this event the early warning system is installed and the mechanism to predict the flood damage during the operation of gates was established. The article intends to discuss the various methods for solving unsteady surge wave problems of by the use of Dam Break equations. The HEC-RAS 2D flow equations were implemented to a wide rectangular channel by correlating the kinematic surge wave propagation to downstream with respect to time and space. The travel time of the peaks has been evaluated from upstream to downstream for the implication of early warning flood forecasting