TR(BR)-132 : Derivation of GIUH for small catchments of Upper Narmada and Tapi sub zone ( Subzone 3C part I)

Abstract

The computations of flood hydrographs have always been one of the major concerns of the water resources engineers and scientists. For the purpose of rainfall-runoff process simulation, mathematical modelling is often resorted to. Continued research in this field has resulted in numerous types of rainfall-runoff models. For simulation and design flood evaluation, conceptual models and physically based models are widely used. The linearity principle of unit hydrograph theory has been widely applied for the simulation of rainfall-runoff process, particularly for small and medium sized catchments. Derivation of unit hydrograph has been extensively investigated by many researchers since Sherman gave the principle of unit graph in 1932. For the gauged catchments the unit hydrographs can be derived by analyzing the historical rainfall-runoff records. However, for ungauged catchments some indirect approaches have been used for the derivation of the unit hydrographs. Due to scarcity of data, particularly for small and medium sized catchments, physically based models are very difficult to be implemented. Greater emphasis is now being given to the concept of models based on geomorphological characteristics. Geomorphological instantaneous unit hydrograph is one among the various approaches available for the simulation of Flood events, especially for the ungauged catchments. Many investigators have tried to relate the parameters of the conceptual models to the geomorphological characteristics of the catchments.

A mathematical model has been developed at the National Institute of Hydrology which enables the evaluation of the Clark model parameters using geomorphological characteristics of the basin. Earlier, this model was successfully implemented on the Kolar sub-basin of river Narmada. In the present study, this model has beer applied for deriving the instantaneous unit hydrograph and thereby for simulation of flood events in the small catchments of Upper Narmada and Tapi Sub-zone. Three catchments of this sub-zone have been taken for this part of the study and the remaining catchments would be taken in the next part.

Various event based conceptual models and the models for ungauged catchments have been reviewed. The description of the study area along with the availability of the data for the present study has also been presented. The methodology is fully explained. Analysis has been carried out by using the computer software developed for this approach. The results of the application of the proposed model for the simulation of the historical flood events of selected three small bridge catchments are discussed. In general reproduction of observed flood events using this approach is good. The necessity of extensive observed runoff data for the calibration of the Clark model parameters is avoided. Various conclusions drawn have been presented along with the suggestion for further work in the direction of improvement of the methodology.