TR(BR)-2/96-97 : Development of a conceptual model for snow, glacier and rainfed catchments

Abstract

Stream flow in the rivers originating from the Himalayas comprises of the contribution from rain, snow and glaciers. A substantial contribution is derived from snow and glaciers into these rivers. Each component of streamflow plays important role in the management of water resources including reservoir operation and streamflow forecasting. There is a need to develop a hydrological model for the Himalayan basins. To understand the hydrological behaviour of the Himalayan basins, an understanding of rainfall-runoff, snowmelt and glacier melt processes is required. Topographical influence on precipitation distribution is another important problem in the Himalayan basins and further adds to the complexity of the hydrological modelling of these basins. It has been pointed out that energy balance approach cannot be adopted for the estimation of snow and glacier melt in the Himalayan basins because data required for application of such methods are not available. In the present work, keeping in view the sparse network, availability of data and topography of the Himalayan basins, a structure of a simple conceptual model is proposed. The model is based on the area-elevation characteristics of the basin and utilizes the relationship describing temperature lapse rate and orographic precipitation distribution. Because there is difference in the melt rate of snow and ice under the same environment, therefore, separate computation of snowmelt runoff and glacier melt runoff are suggested. The contribution from various sources is added together and accounting of losses is made. The routing of surface and sub-surface flow is proposed using concept of linear cascade reservoirs. The structure of the model is described and details of associated hydrological processes and parameters to be adopted for such a model are discussed.