TR(BR)-113 : Excess rainfall and direct surface runoff modelling using geo-morphological characteristics

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 madels 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 analysing 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.

In this study a hybrid approach is developed integrating the Clark model and the geomorphological instantaneous unit hydrograph approach. This approach enables the estimation of Clark model parameters using the geomorphological characteristics and storm pattern. It avoids the use of extensive rainfall-runoff records, which are many times not available, for the calibration of the Clark models parameters. Various event based conceptual models and the models for ungauged catchments have been reviewed. The developed approach is illustrated by applying it for the simulation of the historical flood events of Kolar sub-basin of river Narmada located in Madhya Pradesh state. The description of the study area along with the availability of the data for the present study has also been presented. The methodology is also presented in full detail. Analysis has been carried out by using the computer software developed for this approach. In general, the reproduction of observed flood events using this approach is good for all the events considered in the study. Further investigations and field applications are needed to improve upon the present form of the model structure by incorporating the latest developments in the field of fluvial geomorphology.