Determining operating rules for the Letaba river system in South Africa using three models

An increasing importance is being placed on the operation of reservoirs and water resource systems in South Africa. Since 1985 the water resources yield model (WRYM) and the water resources planning model (WRPM) have been applied to support decisions concerning the operations of water supply to the Gauteng region. Other models such as the Reservoir Operating Model and the Rationing Model have been developed for application on less complicated systems. In this study the WRYM/WRPM modeling system, the Mike Basin and the Water Resources Modeling Platform (WReMP), are applied on the Letaba River System. The general approach on operational analysis is explained. An attempt is made to have the same set-up on all three models. The results show that the relative advantages of each model depend on user experience with a specific model and their preferred way of presenting results. The selection of a model also depends on the nature of the problem being investigated, preferred conceptual representation and availability of data. The format for presentation of results tends to vary between modelers. However, the link to a GIS interface on the Mike Basin means that preparation of schematics is easier and relates better to real operation of water resources in a catchment than the other two models. This paper also discusses possible use of the output to support operational decisions and presents tabulated data which could be useful to a system or reservoir operator. Recommendations are given on possible future research.