TR-8 : Water balance of a reservoir

Abstract

The water accounting of reservoirs is necessary for their proper management. The purpose of water balance of a reservoir is to estimate the various components representing inflows, outflows and change in storage. Once these are determined, the continuity equation can be used to either test whether the components tend to balance out or to estimate an element of water balance which could not be determined. Although all the components of a water balance equation should balance themselves theoretically, a residual term is obtained in practice. This happens because the related measurements are susceptible to various sources of errors.

The water flows into the reservoir through stream flow, surface runoff, direct precipitation and ground water inflow. The main components of outflow are evaporation, discharge through spillway and outlets, turbines and seepage. Various techniques which can he used for determination of each of these individuals terms and change in reservoir storage are described in the report. As far as possible, independent methods should be used to determine the individual components so that the errors are not, propagated.