Regional Flow-Duration Models for Large Number of Ungauged Himalayan Catchments for Planning Microhydro Projects

In the Himalayan region of India, most prospective sites for microhydro projects are ungauged and there are insignificant data for analysis. Design flow estimates are made using a regional flow-duration curve. Regional studies on Himalayan watersheds do not appear to have been reported in the literature. Therefore, models are developed for 1,200 ungauged watersheds of the Lower Himalayas. To this end, the region, comparatively larger in size than the catchment, is assumed to be hydrometeorologically homogeneous in its behavior. Formulation of models is based on data transfer between gauged watersheds of the same region, statistical normalization, and empirical regional relation. The performance of a specific model developed for Himachal Pradesh (Region C) is evaluated using the data of 13 watersheds in calibration and 4 watersheds in validation. It is found that the statistical approach of quantile estimation (nondimensional) performs satisfactorily in calibration as well as in validation. The simple power relation for mean flow-estimation, as well as the complete model, performs well in calibration and less satisfactorily in validation because of the short length of data.