Incorporating drought management planning into the determination of yield

Abstract

The definition of system yield has undergone somewhat of a revolution in recent years with it no longer being acceptable to simply consider yield in terms of acceptability limits on the frequency and severity of restrictions. The reason for this change is it is “now expected that water utilities manage their water resources so that communities never run out of water” (Erlanger & Neal, 2005). The system therefore consists not only of the demands and infrastructure that exist, but also the emergency infrastructure and restriction strategy, referred to as a drought management plan (DMP), that must also exist to ensure an ongoing supply of water should a drought continue. The calculation of yield must now take into account the acceptability of reaching the various triggers in the DMP in addition to the previously used acceptability criteria relating to the severity and frequency of restrictions. A new methodology is presented in this paper to integrate performance of the DMP with a classical storage risk analysis to determine system yield, including an approach to present these two fundamentally different aspects of yield versus demand on a single diagram. The new methodology thereby allows users to simultaneously identify interactions between demand and the frequency and severity of restrictions, demand and the risks of activating drought management measures, and demand and the manageability of the DMP itself. Application of the new methodology is presented by way of a case study of the Hunter Water Corporation headworks system.