Impact of Demand Management on Peak Demand
Abstract
In recent years, average daily water consumption across Melbourne has been reducing. This reduced consumption has been driven in part by the target set by the Victorian Government in late 2002 as part of the Water Resources Strategy for Melbourne. With the aim of reducing Melbourne’s drinking water use per capita by 15 per cent by 2010, the Melbourne retail water companies undertook a substantial program of demand management. In the intervening time, Melbourne has experienced a drought requiring stage 2 restrictions, which has resulted in high public awareness of water issues. In addition, the implementation of permanent water saving measures has resulted in a greater than expected reduction in annual demand of 22% for 2005. Whilst this is a significant reduction in average annual demand, the impact on peak instantaneous demand has not previously been assessed. This paper examines the impact of demand management reductions on peak instantaneous (“peak hourly”) demand, and the potential resultant savings in infrastructure, within the network managed by South East Water, one of the Melbourne retail water companies.
Instantaneous peak demand is the key design unit for sizing urban water distribution networks. The peak instantaneous demand is related to the number of properties connected to the network, and the land use of those properties. Most commonly, the peak demand depends on the number of residential property connections, and this is the basis of South East Water’s urban network design standards. Reduction of this standard could result in significant capital infrastructure savings.
The true peak instantaneous demand is difficult to estimate. In Melbourne, the residential peak hourly demand with an annual exceedance probability (AEP) of 5% (or 1 in 20) is adopted as the design standard measure for sizing water infrastructure. Typically, this peak hourly demand can be estimated by gauging the flow at the outlet of a major service basin or at the top of a major network branch, and using the gauged flow to predict the 1 in 20 AEP peak hourly demand. If the number of residential connections downstream of the gauge is also known, then the peak hourly demand per property can also be determined. Currently, South East Water have adopted a value of 0.08 litres per second per residential connection as the design peak hourly demand.
In this paper a statistical analysis of water demands within the South East Water supply network was undertaken to quantify the 1 in 20 AEP peak hourly flow rate and test whether this design flow rate has reduced in recent years.
Authors
Robert Morden, Andrew Chapman, Emily Payne & Phillip Jordan