SONAR technology designed for detecting submarines could soon be used to find
leaks. Water squeezing through small holes or cracks makes a telltale noise, and
one of Britain鈥檚 water companies, Yorkshire Water, hopes to exploit this to
pinpoint faults.
鈥淭he water companies lose about 30 per cent of their treated water through
leaks,鈥� says Simon Tanner, a sonar expert at the Defence Evaluation and Research
Agency in Winfrith, Dorset, who was asked to look at the problem by Yorkshire
Water.
Water engineers already rely heavily on sound, holding hollow metal rods
against suspect pipes to listen for the noise of a leak. 鈥淚f you鈥檙e skilled, you
can pick up a leak, but it鈥檚 very subjective,鈥� says Tanner.
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But neither this method nor the sonar detectors used in the past decade are
good at spotting leaks in mains pipes, which cause the largest water losses, or
in plastic pipes, which are becoming common. Tanner鈥檚 findings, presented to
journalists in London last week, suggest how existing detection methods can be
improved, and which new ones might be needed.
He focused on improving the systems that measure how long it takes a sound to
reach two sensors placed on either side of the source. Processors can calculate
the sound鈥檚 origin from the times of arrival of the two signals. 鈥淚f the leak is
bang in the middle, it arrives at both sensors at the same time,鈥� says
Tanner.
Tanner says the sonar system works well with metal pipes less than 200
millimetres in diameter. 鈥淭he pipe acts as a waveguide, like an optical fibre,
and the noise can be detected as much as four kilometres away.鈥�
But in the large trunk mains, which can be up to a metre across, the noise
propagates in all directions, and so dissipates quickly. Plastic pipes tend to
lose the signal into surrounding soil and transmit sound more faintly.
For these pipes, Tanner says, the best bet is to listen out for faint
lower-frequency sounds transmitted through the water itself, rather than through
the material from which the pipe is made, as previous systems did. Many existing
detectors can be adapted to do this, Tanner says. But the larger trunk mains
might need new equipment installed inside the pipes. This could include
fibreoptic cables linked to piezoelectric transducers, which convert sound waves
into electrical signals, but DERA won鈥檛 reveal the precise details. 鈥淲e have
some ideas, but it鈥檚 commercially sensitive at the moment,鈥� says Tanner.