In this report, a conceptual model is proposed and described for calculation of streamflow runoff arising from rainfall, snowmelt and glacier melt for the Himalayan basins. The simple structure of the model is designed keeping in view the sparse network, the availability of data and topography of the Himalayan basins. The model is based on the area-elevation characteristics of the watershed and utilizes the relationships describing the temperature lapse rates and orographic precipitation distribution.
The elevation-based structure of the snowmelt model was accompanied by sub-division of the catchment into elevation bands. Each band was assumed to be either completely snow covered or conversely snow free and homogenous with respect to snow cover. The method is so designed that a complete water balance is maintained between input, outflow and evapotranspiration, while at the same time accounting for soil moisture and groundwater.
Because there is difference in the melt rate of snow and ice under the same environment, 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 the concept of linear cascade reservoirs. Various parameters associated with melting processes are described and discussed in detail.
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