ESTIMATING RAINFALL RUN-OFF MODEL PARAMETERS BY NONLINEAR MINIMIZATION

Existing discrete, linear rainfall-run-off models generally require the effective rainfall of a given storm as the input for computing the run-off hydrograph. This paper proposes a rainfall-run-off model which uses the rainfall hyetograph as input and directly accounts for rainfall losses. The model combines an ARMA model and a modified Philip equation for rainfall losses due to infiltration. For a given watershed with measured rainfall hyetograph and the corresponding run-off hydrograph, optimal values of model parameters are estimated by using a non-linear iterative technique. Applications of the model to two different watersheds show that the computed run-off hydrographs agree well with the measurements. The proposed model is a viable alternative to the widely used unit-hydrograph method.