Runoff prediction dynamic model based on transfer function for a small watershed

In this study, a variable storage coefficient conceptual model based on unit-step and transfer functions approach for Karkara watershed of Tilaiya dam catchment in Upper Damodar Valley of Jharkhand State, India was developed for estimating direct runoff hydrographs on storm basis. The rainfall data in blocks of finite duration are represented by the unit-step function in this model. Outflow hydrograph is obtained by taking inverse Laplace transform of product of Laplace transforms of Instantaneous Unit Hydrograph (IUH) and the input (effective rainfall). The ordinates of direct runoff hydrograph are computed by lagging the ordinates of outflow hydrographs by the effective rainfall block duration. The parameters i.e. storage coefficient and geometric ratio were estimated using the methods suggested by Sabol and method of moments using rainfall and runoff data of the watershed. The performance of the model was tested by comparing the computed direct runoff hydrographs with the observed runoff hydrographs. The model was calibrated for nine storm events and validated for three storm events. Based on the performance evaluation criteria model was found to be working well for the study area.