CONCEPTUAL MODELLING OF EXCESS-RAINFALL DIRECT RUNOFF PROCESS

Abstract

Direct runoff hydrograph from a natural watershed is simulated using a conceptual model instead of 'Cho traditional unit hydrograph approach. The Nath model is taken as the basis of this study. Two approaches have boon considered for this purpose. In the first approach the Nash model is used with nonuniform areal distribution of rainfall considering the.catchmont as one unit. In the second approach, the catchment is divided into three subareas on the basis of tributary drainage boundaries. Each subarea is then represented by the Nash model. Then the combined flow from the two tributary subareas are taken through a linear channel to join the flow from the third subarea and the direct runoff hydrograph is reconstructed. The performance of the two approaches is evaluated using rainfall runoff data from catchment Bridge No.566 of Indian Railways. The model efficiency for both the cases are found to be quite pro-mising, though the subarea typo model gave . better performance in dealing with the rainfall data with nonuniform aroatdistribution of rainfall. The sensitivity of the subarea type model to timo distribution of excess rainfall is tasted with assumed values of model parameters and typical rainfall excess distributions. The results show good response sensitivity as indicated by the variation 'of hydrograph peak.