UNIT HYDROGRAPH ANALYSIS OF SMALL CATCHMENTS

Abstract

Two simple conceptual models viz, those of Nash and Clark(HEC-1 approach) have been used to simulate the direct runoff hydrograph from a natural watershed. Three to nine years of storm rainfall and corresponding runoff data of six small catchments of Godavari basin subzone 3f have been analysed using the two approaches.. The model is calibrated and average parameters are estimated by taking the geometric mean of the parameters of the individual storms used in calibration. The average parameters are then used to derive the representative unit hydrograph for each catchment. The performance of these two models in reproducing the storms of respective catchments are judged by comparing the values of three error functions evaluated with the average parameters. The relation between the model parameters and catchment characteristics has also been studied to get the model parameters for ungauged catchments. The average parameters of five catch-ments are used for developing the regional relationship keeping one catchment as a test data. The performance of regional parameters estimated for all the six catchments using the regional relationship has been tested reproducing the hydrographs for different storms for the respective catchments as indicated by values of error functions. It has been found that the perfor-mance of Clark Model is better than that of the Nash Model in most of the cases.