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, pr ojects are ungauged and there are insignificant data for analysis. Design f low estimates are made using a regional flow-duration curve. Regional studi es on Himalayan watersheds do not appear to have been reported in the liter ature. Therefore, models are developed for 1,200 ungauged watersheds of the Lower Himalayas. To this end, the region, comparatively larger in size tha n the catchment, is assumed to be hydrometeorologically homogeneous in its behavior. Formulation of models is based on data transfer between gauged wa tersheds of the same region, statistical normalization, and empirical regio nal relation. The performance of a specific model developed for Himachal Pr adesh (Region C) is evaluated using the data of 13 watersheds in calibratio n and 4 watersheds in validation. It is found that the statistical approach of quantile estimation (nondimensional) performs satisfactorily in calibra tion as well as in validation. The simple power relation for mean flow-esti mation, as well as the complete model, performs well in calibration and les s satisfactorily in validation because of the short length of data.