The report presents a hydrologic simulation model, HYSIM for modeling the daily flows of the Brahmani river at Rengali reservoir in Orissa. Considering the large catchment area of 25,250 sqkm at Rengali reservoir, for modeling purposes the basin has been divided into two sub-basins viz, Upper Sub-basin and Lower Sub-basin. The Upper Sub-basin having a catchment area of 16,900 sqkm up to Bolani gauging site is treated as a nominal sub-basin since the daily flows from this sub-basin as recorded at Bolani gauging site are available.
The Lower Sub-basin below Bolani and up to the reservoir with its catchment area of 5350 sqkm is simulated for daily flows. The recorded flows from the Upper Sub-basin are routed through the Lower Sub-basin along with the flows from local runoff from the Lower Sub-basin to the reservoir site. The model is calibrated using three years of data and is validated for its performance for a set of next three years of data.
The results of the simulation study are quite encouraging. The model has reproduced the peaks and the shape of the hydrographs reasonably accurately despite the constraint that the potential evapotranspiration (PET) values used in the study are normal monthly values and secondly, the flows at Rengali reservoir as used for comparison purposes are the average daily reservoir inflows computed from the reservoir capacity curves.
From the analysis of the results, it is concluded that the model can be effectively used for forecasting of flows at Rengali reservoir and will be useful for planned regulation of the reservoir storage during high flow periods.
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