Water Quality Reliability Based Design of Water Distribution Networks

The performance of a water distribution network is affected by several factors, pipe failure being a major one of them. Several methodologies have been suggested for optimal design of water distribution networks (WDNs) to meet reliability criteria regarding supply of adequate quantity of water in the events of pipe failure. A two-phase methodology is proposed for least-cost design of WDNs to achieve desired levels of both hydraulic as well as water quality reliability (WQR). The WQR is defined as the ratio of total quantity of water supplied with desired quality in the period of analysis to the total quantity of water of the desired quality required in the period of analysis. In the first phase, an iterative methodology based on trade-off between hydraulic reliability and cost is used to design network with desired level of hydraulic reliability. In the second phase, optimal number and locations of booster chlorination (BC) stations along with required chlorine dosage are determined to achieve desired WQR. Initially, booster stations are located considering only normal working condition of pipes. The WQR is obtained with the proposed number of BC stations, and a methodology is proposed to improve the WQR considering options of increasing more number of stations and/or temporarily changing the chlorine dose at already selected BC stations during pipe failure conditions. The application of methodology is illustrated with an example network taken from literature.