Calculating Uncertainty In The Supply Demand Balance

Management of water resources requires prudent decision making in the face of both short and long term uncertainties. 

Probabilistic outage and headroom methodologies have been developed by United Kingdom Water Industry Research to quantify short and long term uncertainties respectively. Outage represents an allowance for a reduction in source or treatment capacity. Headroom represents uncertainty of either the yield that sources can supply, or the demand that is forecast. These concepts therefore provide a framework for considering risk and uncertainty in the water supply-demand balance in a clear and transparent manner. 

This paper summarises the application of outage and headroom methodologies the metropolitan Auckland water supply and a small town outside of the main network. The output of each of these assessments is a probability distribution, from which the water provider, Watercare, can select a value that reflects the exposure to uncertainty that it can accept and that is also acceptable to customers. One key benefit highlighted by this study is that the outcome can be a single value of a reasonable buffer, or uncertainty allowance, for each part of the planning period. This makes communication with non-technical stakeholders more straightforward.