Simulation of Monasavu Reservoir, Fiji

Monasavu is a 4.8 km2 reservoir situated in the high plateau of Viti Levu, Fiji. The reservoir stores the summer rains to provide water for the 80 MW Wailoa power station, Fiji's major source of electricity and its only large hydro station. Up until 1991, Monasavu has always had adequate storage to provide the full electrical load over the dry season from June to December. However, in 1991 a combination of low inflows, possibly caused by an El Nino condition which started in March 1991, and rising power consumption has meant that careful management of the reservoir is required. Simple hydrological models provide the tools to enable the best management decisions to be made. One model calculates the historical inflows so that the current inflows can be compared with those that have occurred in previous years and future inflows can be estimated. A second model uses these inflows, along with projected power demand, to forecast the resulting reservoir levels. From these forecasts, managers can decide what mix of hydro and diesel generation is required to make up the demand, but still leave adequate storage in the reservoir for later in the dry season.