Designing-out network leakages

30 August 2007, 12:30pm

Reduced network leakage is one of the many benefits being enjoyed by South West Water as updating of its GIS goes hand-in-hand with a re-design of its District Metering Areas

To keep tabs on their liquid assets, Britain’s water suppliers define a number of local District Metering Areas or DMAs across their distribution networks. Within each DMA, metered flows are captured using data loggers feeding back flow rates (sometimes remotely using SMS) for leakage assessment and to plan maintenance activities or justify network expansion.

Clearly, the design of a DMA is crucial in identifying and targeting leakage points. DMAs with a high property count and/or excessive numbers of meters become increasingly difficult to monitor, while long-established DMAs may no longer fit the purpose for which they were designed.

Three key considerations in such a design or re-design is that it should (1) separate trunk mains from subsidiary networks (2) limit the number of recording meters (ideally single-feed) and (3) limit the number of properties, residential and commercial, to help target leakage more accurately.

Other factors to be considered are many and varied, ranging from regulatory exposure to seasonal demand, and from water quality issues to the re-use of existing assets as a means of containing capital expenditure.

A case in point

There are also factors specific to individual suppliers, not least South West Water Ltd, (SWW) which identified the need to improve the accuracy of leakage reporting. When addressing Torquay DMAs, this reporting was hampered by a combination of factors:

 Complex design of the Water Into Supply (WIS) Zones
 High burst frequency
 High percentage of brought-forward DMAs
 Lack of confidence in DMA boundaries
 Lack of confidence in the corporate Geographic Information System (GIS)
 ‘Patchy' local knowledge
 Average of five import/export meters per DMA
 High property count per DMA (six with more than 2,500 properties and one with more than 5,000 properties)

Due to substantial rehab work having been undertaken throughout the WIS Zone the first step in tackling these issues was to undertake a sluice valve survey … one that would help verify the accuracy of existing asset records and which, as a by-product, would address any hydraulic anomalies. Specialist water industry service provider Exwater UK Ltd of Axminster was tasked with co-ordinating the project whose three phases included a Survey Pilot Study, the Valve Survey itself, and a DMA Redesign.

The Pilot Study was based on a survey of 30 per cent of all sluice valves within a 14 sq/km area. This investigated the level of anomalies in a mix of rural and urban districts and determined whether there was a need to survey the whole WIS Zone. The sample of 1,000 valves revealed a high level of anomalies (>35%) and necessitated a survey of the remaining sluice valves across an area of 33 sq/km in total.

The Phase 2 survey was undertaken by two teams which completed a physical inspection of approximately 2500 sluice valves. All anomalies were noted such as incorrect records of size, position, orientation (open/closed/throttled) and whether or not valves were recorded in the STRUMAP GIS. The findings were as follows:

 Total number of Valves Surveyed: 3433
 No. of valves shown on GIS: 2948
 No. of valves not shown on GIS: 487
 No. of GIS & hydraulic anomalies: 1229
 Anomalies as a percentage of total: 41.69 per cent

All anomalies were addressed with the local Distribution and Leakage Inspector and records amended as necessary. Once this has been done, all valve data were collated and presented to the GIS for re-digitising and, once updated, Quality Assured as a final check for accuracy.

With GIS records updated, the DMA re-design could be conducted with a high level of confidence. The designs were conceived jointly by Exwater UK Ltd and SWW’s Distribution and Leakage departments. Leakage benefited from Distribution's specific knowledge of Torquay while Distribution gained a better understanding of Leakage requirements and constraints. As the dialogue ensued, other departments offered valuable support to the project (O&M, Rehab, GIS, Developer Services, Asset Planning and Engineering Services).

Bespoke STRUMAP modelling packages were used to enact a number of design scenarios, with parting valves closed and the various options trialled prior to the commencement of any ‘civils’ work. Each DMA was closely monitored and, where meters existed, flow data was collected and analysed.

Once designs were proven and following successful completion of Zero Pressure Tests (ZPT), any outstanding civils work was completed and the new DMAs commissioned. The new DMAs were signed over to Leakage Control and committed to the corporate reporting system. Finally WIS Zone Management Plans were compiled along with schematics for all the new DMAs.

Results

The figures below gives a snapshot of the reported leakage immediately following design and implementation of the new DMAs.

WIS Zones Pre-design: 2
WIS Zones Post-design 3

No. of DMAs Pre-design: 16
No. of DMAs Post-design 28

Total WIS leakage
Pre-design: 5.40 ml/day
Total WIS leakage
Post-design: 3.46 ml/day

Properties brought
forward Pre-design: 76%
Properties brought
forward Post-design: 5%

DMAs brought
forward Pre-design: 10
DMAs brought
forward Post-design: 2

Since completing the project, South West Water has benefited from reduced leakage, improved targeting for leak detection, robust data for reporting and, with the introduction of “remote logging”, greater transparency in day-to-day operation of DMAs.

Many more benefits were derived from the project and SWW has extended the same design ethos to other WIS Zones. To date Exwater UK Ltd has undertaken further DMA re-designs in Brixham and Paignton, with another (Newton Abbot) nearing completion.

More information:

Exwater UK Ltd: www.exwateruk.com
South West Water: www.southwestwater.co.uk
STRUMAP: www.strumapgis.co.uk

www.exwateruk.com

Simon Harris, Exwater UK Ltd

simon.harris@exwateruk.com