Practical Estimation of Inflows into Multireservoir System

Reservoir system operation requires a variety of hydrologic information, of which streamflow data are most essential. Typically, available gauged streamflows are processed to represent flows at the location of a reservoir. Rainfall-runoff models provide alternatives to estimate streamflows when gauged data are unavailable or inadequate. Reservoir inflows may also be estimated, based on water budget computation if storage levels and gauged releases are available. This study presents a series of computational procedures to estimate flows into a multiple reservoir system where storage levels and gauged releases are available at irregular intervals. The inflows are estimated by water budget computation. Then the weekly and monthly inflows are derived from cumulative mass curves of inflows at irregular intervals. The inflow to a reservoir includes releases from upstream reservoirs, which are controllable, and also the flow from the immediate watershed, which is not controllable. In order to preserve, for further analysis, the stochastic characteristics of the unregulated inflow, the flow contributed by an immediate watershed is estimated separately from the total inflow to a reservoir.