Optimal water resources allocation for the lowveld of Zimbabwe: a case study of Runde catchment

The optimum management of multi-reservoir systems becomes increasingly complex when competing and often conflicting uses of water exist. The sugar plantations in the South-Eastern Lowveld of Zimbabwe are important to the economy of Zimbabwe. They are supplied with irrigation water from a number of reservoirs on different river systems but experiencing water shortage due to challenges in operation of the reservoirs. Thus the aim of this research was to develop an optimal operating policy model for a multi-reservoir system that could be used to allocate water. Two trend tests were used to assess the variability of historic monthly rainfall and inflows of Runde catchment. The WEAP water allocation model was set up to come up with a reference scenario. Stochastic Dynamic Programming was used for optimisation of the multi-reservoirs releases. There was no significant trend in the rainfall but a significantly decreasing trend in the inflows time series. The water allocation model (WEAP) showed significant deficits (~ 40%) in irrigation water allocation in the reference scenario. The optimal rule curves obtained were considered to be a proper guideline for solving multi- reservoir management problems within Runde catchment.