Use of GIS to rationalise pressure in water supply systems

Abstract

Water is a valuable resource needing conservation. Excessive water pressure in water distribution systems causes leakages leading to substantial losses of treated water. It also places additional strain on networks reducing their efficiency and increasing annual maintenance costs. Conversely, too low a water pressure can be an inconvenient annoyance to the user and, more importantly, mean inadequate conditions to meet fire fighting requirements. The North Shore City Council (NSCC) in Auckland, is not free from the aforementioned pressure-related problems.

This paper summarises the outcome of a study undertaken, using GIS technology, to identify areas with potential pressure problems and suggest options for consideration to resolve pressure issues with the intension of (a) reducing water losses, (b) providing customer satisfaction, (c) ensuring fire-fighting readiness, and (d) making long term savings by strategic capital investment in the water supply network of the NSCC.

First, the clusters of properties with potential pressure problems were identified. A sensitivity analysis was carried out to determine the optimum pressure for the key zones to minimise the number of properties affected by either low or high pressure issues. Then, the optimum pressure for each user was determined while ensuring (a) a minimum supply head of 30m for each property, (b) a maximum static head of 90m, (b) no property experiences a reduction in pressure exceeding 30m as a result of the implementation of the remedial measures suggested, and (c) a minimum residual pressure of 10m at fire hydrants during fire-fighting. Finally, a range of suggestions ranging from pressure zone boundary adjustments to sample designs that can eventually lead to potential capital expenditure are made.