Page 306 - Water Loss Control

Contr olling Real Losses in the Field—Pr oactive Leak Detection 275

fiber optic cable is then connected to a data acquisition system that allows permanent
real-time acoustic monitoring.
Infrared Technology
Infrared thermography can be used as a method of testing for leaks which do not surface.
The underlying principle of this technology is that the water escaping from a leak is of a
different temperature than the surrounding ground and can therefore be detected by a
thermographic camera. The method is quite expensive and in many cases is undertaken
by flying over the areas to be tested. This method has been used successfully for testing
transmission mains in rural areas, but is not practical for dense urban areas, where inter-
ference from other underground utilities, such as sewers, would unduly complicate the
process. Some operators are using this method to detect reservoir leakage.

16.5 Leak Detection Techniques
The monetary value of water lost through leaks plays an important role in deciding
which leak detection technique or combination of techniques is most suitable for the
water utility. When deciding on the right techniques it is also important to consider age,
condition, and material of the distribution system and the skill level of water utility
personnel carrying out the leak detection effort.
District metered areas (DMAs) are used to monitor flow into discrete zones of the
distribution network in order to determine the leakage level and to monitor any rise in
inflow due to newly formed leaks. The use of DMAs in tandem with active leak detec-
tion can serve as the basis for a comprehensive leakage management strategy. A detailed
discussion of DMA technology is given later in this chapter.

16.5.1 Visual Survey
The most basic form of leak location is the visual survey. A visual survey consists of
walking the lines looking for either leaks which appear above the ground or, in very dry
countries or regions, areas that have suspicious green growth patches above the water
lines. Figure 16.13 shows a leak that could easily be located by visual survey. This par-
ticular leak is on an above-ground air valve. Other leaks, which are not quite so obvi-
ous, are also often picked up.
While the visual survey is not the most sophisticated technique but it should not be
underestimated, particularly by utilities which have suffered from lack of good and
frequent maintenance.

16.5.2 Acoustic Leak Detection Survey
The acoustic leak detection survey is probably the most common and familiar leak
detection methodology which has been around for many years. Different types of
acoustic sounding equipment are used in two distinctly different levels of detail.

General Survey
This survey method is often referred to as a hydrant survey in Canada and the United
States. This survey method generally listens only to fire hydrants and valves on distribu-
tion system mains in order to detect any leak sound, no service connections are sounded.
Fire hydrants can be found at more or less constant distances providing a good coverage
of most areas. In this survey mode geophones and leak noise correlators are generally