On line to meet leak reduction targets

In recent years, UK water companies have been highly successful in combating leakage. The figures from the industry regulator, Ofwat, show a fall in leakage levels across England and Wales of almost 35% since 1994, equivalent to a daily saving of over 2,000 megalitres. However, this achievement means that many companies are now close to the point at which the cost of finding and repairing new leaks is greater than the cost of the water saved.

If this target is to be met, the process of finding and fixing leaks must be made more economical. The traditional practice of ‘stop-tap bashing’ with listening sticks is labour-intensive, time-consuming and expensive. The obvious solution is to have this task carried out by automatic listening equipment.

Permanent monitoring

Many companies are already conducting unmanned, short-term surveys using electronic noise loggers. Palmer Environmental’s Permalog® developed for permanent installation, allows water companies to respond immediately to every leak because the distribution network is monitored continuously from the moment the system is deployed.

Attached to pipe fittings by powerful built-in magnets, compact Permalog® noise loggers can be left in place to operate continuously and without maintenance for up to ten years. Immersion-tested to IP68, they work even in flooded chambers.

Unlike conventional loggers which are removed from their positions for data analysis, each Permalog® unit transmits its data in the form of a radio signal to a Patroller receiver module, which can be carried by hand or in a vehicle. Now an area that would take weeks to cover with listening sticks – and days with other logging systems – can be surveyed in a matter of hours. Since a single operator can cover several DMAs (District Metered Areas) in a day, survey costs can be cut by over 90% when Permalog® is used in place of stop-tap bashing.

Each intelligent logger unit adapts itself automatically to its environment. If no leak is present a signal is transmitted to indicate normal background conditions. However, as soon as a possible leak is detected, the unit enters an alarm state and transmits a ‘leak’ signal.

Surveys with the Patroller can be carried out in response to an unexpected rise in apparent water consumption or at standard intervals as part of a routine leakage control programme. The Patroller lists all loggers in ‘leak’ mode, so identifying the approximate position of the leaks. An audible signal confirms that a leak has been detected. Data transmitted by the logger are displayed on an LCD screen and stored in the Patroller’s memory.

At the end of the survey, information from those loggers in ‘leak’ mode can be printed out or downloaded to a PC. Free to concentrate solely on suspect areas, engineers using correlators can then pinpoint the exact location of the leaks. As an option, Permalog® data can also be enhanced with data from GPS (Global Positioning System) and GIS (Geographical Information System) equipment to provide a comprehensive picture of current leakage.

UK case study

The UK’s South East Water supplies water to 1.5 million users in Sussex, Kent, Surrey, Hampshire and Berkshire. Its distribution network covers over 3,600 km2 and includes over 9,000kms of high pressure mains. South East Water introduced Permalog® to its network last year as part of a major investment in leak control technology. All in-house leak detection is now carried out using noise loggers, where previously the company relied on a combination of listening sticks and correlators.

According to Leakage Strategist Ruth Jolley, the Permalog® system is particularly effective in areas where naturally low resources make it imperative to keep leakage to a minimum. One such area, in East Sussex, includes South East Water’s leakage control centre at Barcombe, near Lewes. Over one weekend in July last year, the telemetry system at Barcombe recorded a steady increase in the nightline (nightly minimum flow rate) for the Forest Row DMA (see below). On the Monday morning, the water company’s leakage control inspector David Partridge observed the nightline had surged from its typical 5 or 6 l/s to 14.4 l/s. He immediately set out to survey the area using the Permalog® Patroller.

At Forest Row, natural subsidence had caused a plastic water main to sink until it was touching a clay drain. Under the weight of the soil, the water main had distorted and burst, causing water to fill the cavity to a depth of four feet.

Due to their limited propagation of sound when compared to iron, plastic pipes have traditionally represented a tough challenge for acoustic location equipment. Despite this, the Permalog® logger was able to locate the leak, which was then pinpointed, and repairs got underway in the afternoon.

Environmental bonus

The speed with which the leak was found benefited not only South East Water and its customers, but also the UK’s Environment Agency. Coincidentally, an EA officer was investigating an unexplained discharge from a rainwater drain into the River Medway, some 1.5 miles from the site of the leak, which was stirring up the river bed.

Seeing South East Water at work on the burst main, he asked whether the discharge into the river was connected to the repair work. It was discovered that the downward pressure of the soil on the water pipe had dislodged a section of drain from its joints. Water from the main was flowing directly into the drain, causing large quantities of nothing more harmful than fresh water – to the relief of the EA officer – to flow into the river.

As well as identifying this major leak, the Permalog® survey revealed a number of smaller leaks in the area which were repaired on the same day. The total effect of these repairs was a reduction of the nightline to 5.6 l/s, nearly 9 l/s lower than it had been twenty-four hours earlier.