SR-40 : Rainfall runoff modelling in mountainous catchments

Abstract

The mountainous areas are source of water, food and energy for millions of peoples world over. These mountain regions are source of major rivers in the country. Past experience in harnessing of water in the mountains indicated that a scientific understanding of complex hydrological processes in the mountainous regions would be necessary to achieve the desired objectives.

Runoff estimation in mountainous areas requires thorough understanding of runoff processes in these areas. The rain and snowmelt runoff processes in mountainous catchments is relatively a complex phenomenon than that in plain areas, primarily because of rapid variation of hydrometeorological, geomorphological and other catchment characteristics in these areas. Meteorological parameters like rain, snow temperature and physiographic factors like soils, rocks and their composition in a watershed are highly variable at different elevations.

Modelling has been introduced for analysing hydrological processes influenced by multiple natural factors as well as for studying the effect of the combined factors on the process. The computer techniques have made a considerable progress and complex processes, systems and whole physical fields can be modelled using sophisticated computers and programs. No model, however, can work if it does not represent the natural conditions of the subject hydrologic process. A weak point seems to be the lack of understanding the substance of the natural processes and of the natural relations between natural phenomena.

Development of a hydrological model involves a compromise between those processes and the details the modeller would like to incorporate and those he can obtain data for and reasonably expect to control in solving the model. There have been and there are being developed a large number of models which could be applied to characterise the hydrology of various mountainous catchments.

Inspite of rapid advances in hydrology particularly in modelling, it is not always possible to make universal use of such models because local problems predominate over other factors. The last decade has seen the widespread use of watershed models for simulation and forecasting of stream flow in India. Their use in Mountainous areas have been limited party due to non availability of data and partly problems typical of the mountainous areas of the country.

As this study shows, a number of models were developed in different countries for their particular basins or need. However, most of the conceptual and physically based models as they were built on strict mathematical and physical laws, were applied satisfactorily to model eatersheds other than those for which they were developed. But care must be taken to adjust any physical model to suit particular environment.