Flood routing with real-time stage correction method for flash flood forecasting in the Tanshui River, Taiwan

Based on the dynamic wave theory of unsteady flow in open channels, a four-point implicit finite-difference method is employed to develop a flash flood routing model for the Tanshui River in Taiwan. The real-time observed river stages are specified as the internal boundary conditions for the routing model in order to adjust the computed real-time flow. The number of discritized equations for the conservations of mass and momentum, plus the internal boundary conditions, is more than that of flow variables to be solved for. The least-squares method is used to solve the over-determined problem. The model is calibrated and verified with the field records of several typhoon flood events. There is a reasonable good agreement between measured and computed river stages. Four typhoon flood events are simulated to confirm the accuracy of the forecasting method. The results reveal that the present model can provide accurate river stage for flood forecasting in the Tanshui River.