An Evaluation of the Robustness of the Sample UK Water Distribution System Configurations to Operational Stresses

Abstract

In England and Wales, water companies are required to report to OFWAT annually on the performance of their networks to demonstrate the current and future level of serviceability to customers. In support of this, a Common Framework has been adopted for the necessary capital maintenance planning, which focuses on the asset condition assessment and risks associated with the probability and consequence of failure. Unfortunately conventional water distribution analysis, supported by computer packages such as EPANET-2, may not easily quantify the actual severity of such failures as most adopt Demand Driven Analysis (DDA) in that the water withdrawal from the system is predetermined and independent of the local pressure available to achieve it, hence the need for Pressure or Head Driven Analysis (HDA) routines. In this study a simple iterative approach known as the Sequential Solution Seeking DDA based HDA (or `SSS' hereafter) routine is employed to compute the actual outflows according to the chosen head outflow relationship(s), within the pressure deficient zones. A range of asset failure scenarios are run on a number of representative UK water distribution network configurations, of special interest being the consequential Zone Of Deficiency (ZOD). Both pipe (link) isolations and bursts incidents have been investigated, in an attempt to appraise the `robustness' of these real systems. ZOD size and the internal Demand Satisfaction Ratio (DSR) are quantified and the security of supply to sensitive customers such as hospitals has also been considered, as a precursor to the formal reliability estimation and the `consequence of failure' appraisal necessary for `risk' based system management. Finally, over the past decade or so UK companies have favoured pressure management schemes to reduce leakage and relieve stress on networks. This, however, reduces the residual head on the system which acts as a buffer when partial failure occurs. The consequences of asset failure before and after Pressure Reducing Valve (PRV) installation on a set of representative UK networks are also compared to evaluate the potential repercussions of this strategy. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).