In this study, the mathematical model developed at the National Institute of Hydrology for estimation of the Clark model parameters using the geomorphological characteristics of an ungauged basin has been applied for simulation of the direct surface runoff (DSRO) hydrographs of the Ajay basin up to the Sarath gauging site of South Bihar.
Geomorphological Instantaneous Unit Hydrograph (GIUH) is one of the approaches available for simulation of flood events for ungauged catchments. Many investigators have tried to relate the parameters of the conceptual models to the geomorphological characteristics.
The geomorphological parameters of the Ajay basin have been evaluated using the Geographical Information Systems package, Integrated Land and Water Management Systems (ILWIS). The DSRO hydrographs estimated by the GIUH approach have been compared with the observed direct surface runoff hydrographs as well as with the DSRO hydrographs estimated by the Nash model and the HEC-1 package.
The performance of the GIUH model has been evaluated by employing some of the error functions viz. (i) efficiency (ii) absolute average error (iii) root mean square error (iv) average error in volume (v) percentage error in peak and (vi) percentage error in time to peak computed based on the observed and simulated DSRO hydrographs.
It is observed that the DSRO hydrographs are computed quite accurately by the GIUH based Clark model approach, which simulates the DSRO hydrographs of the basin considering it to be ungauged. Sensitivity analysis of the GIUH based Clark model shows that the peaks of the DSRO hydrographs of the various events increase in the velocity parameter of the model.
As estimation of the velocity parameter emerges to be one of the most important factors in this methodology of the GIUH derivation. Due to scarcity of data, particularly for small and medium catchments, computational and the other constraints, physically based models are very difficult to implement. Greater emphasis is now being given to the concept of models based on geomorphological characteristics.
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