Full Description

The Halifax Regional Water Commission (HRWC) has documented success in water losscontrol through adoption of the methodology promoted by the Water Loss Task Force ofthe International Water Association (IWA). HRWC put the methodology into action in1999 and formally adopted it as a best practice in April, 2000. By March 31, 2006, HRWCreduced leakage in the distribution system by 34 million liters/day with a correspondingplant output reduction from 168 to 134 million liters/day. The total leakage reduction of 34million liters/day is reflected in an Infrastructure Leakage Index (ILI) reduction from 9.0 to3.0 and annual savings of $550,000. In addition to direct savings, the customers ofHRWC see increased public health protection (a leaking system has more potential forcontamination), less service disruption and reduced property damage, as leaks are nowfound in a proactive manner through early intervention. Water loss control at HRWC isholistic in nature and benefits greatly from a distribution network that is subdivided intopermanent district metered areas (DMAs). The HRWC has over 65 DMAs and a robustsupervisory control and data acquisition (SCADA) system. These tools are used intandem for night flow analysis for leakage assessment and to determine best achievablebenchmarks in system flows. A typical DMA incorporates a zone in the distribution systemwith a maximum pipe length of 30 km, 150 hydrants or approximately 2500 customerconnections. Building on thesuccessful installation of DMAs, flow modulated pressure control was installed in a typicalsector in Dartmouth to further control and manage leakage. The Dartmouth Central DMAwas selected to evaluate advanced pressure management as aleakage management tool for AwwaRF Project 2928, "Leakage ManagementTechnologies". By reducing system pressures during periods of low demand, flow ratesthrough background and active leaks were expected to be reduced. Improved control ofsystem pressures would also reduce or eliminate pressure surges that can occur withinthe DMA. The HRWC chose the Dartmouth Central DMA for several reasons; the DMA issupplied by two recently constructed in-ground pressure reducing and metering chambers,providing new control valves and accurate metering. Dual supplies into the DMA offeredthe challenge of modulating two control valves in geographically differing locations, to achieve the desired system pressure in response to the changing demand. Finally,following regular active leakage detection, the minimum night flow was considered to besignificantly higher than it should be, providing the opportunity to demonstrate andmeasure a reduction in real losses through pressure management, and additionally,through advanced pressure management.To be considered successful, reductions in real losses through advanced pressuremanagement had to be achieved without degrading minimum system requirements.Adequate minimum residual pressures had to be maintained during peak hourly flow ormaximum day demand plus fire flows. Water quality was also a concern, with possiblerapid changes in velocity, flow reversal between supply points or excessive water age.Other concerns included customer complaints from low supply pressure, and a loss ofmetered sales offsetting the savings gained from reductions in real losses. Includes 3 references, table, figures.

Product Details

Edition: Vol. - No. Published: 09/01/2007 Number of Pages: 8 File Size: 1 file , 2.1 MB