Reservoir capacity yield reliability analysis

Storage yield reliability analysis is used to determine the volume of water that should be stored in order to provide a specified water demand with a stated reliability. Storage depends on the volume of demand D, reliability R and the hydrology of the catchment supplying the reservoir. The effect of hydrology of the catchment on the required storage volume depends upon the temporal uniformity, or lack of it, of the streamflow and the causal rainfall4. For a given D and R, a reservoir on a catchment having substantially variable wet and dry season rainfall, needs to be larger than if the rainfall is more or less uniformly distributed throughout the year. The reliability gives a measure of certainty that a given yield can be met without failure. Failure in this context was considered as the interval during which the reservoir is empty. The reliability is an index between 0 and 1 and can be expressed in one of three ways (annual, time based and volumetric). In this study the time-based reliability was used.