Acoustic technology to combat California drought

Specialised acoustic technology may help the drought-stricken state of California save millions of litres of water a year.

America's one-time Golden State is in the midst of a catastrophic water crisis, now in to its fourth year and with few signs of conditions improving any time soon. Nasa researchers have warned that reservoirs could run dry within a year and pressure is mounting on ground water supplies, which are disappearing fast.

One culprit is the underground pipe leaks. According to a 2014 analysis, the Bay Area alone loses 23 billion gallons (87 billion litres) a year from underground leaks.

Locating the leaks is the biggest obstacle: water pipes in major cities like Los Angeles and San Francisco are deep underground and many of them are over 80 years old. The San Francisco Public Utilities Commission, along with other agencies, is now responding to the problem by finding the cheapest and quickest method of locating the leaks: acoustic detection.

A number of companies around the world have recently trialled this approach, aiming to save water by monitoring the infrastructure and detecting leaks in pipes early. Israeli smart water start-up Takadu, for instance, performs the service for Thames Water, the UK utility company that brings water to Londoners.

In California, a similar firm conducting acoustic detection is the Indiana-based M.E. Simpson. The technique the firm uses relies on transducer microphones attached to hydrants or water meters or - where they can’t get direct access to a pipe - through a ground microphone. Leaks in pressurised pipes result in a characteristic hiss, which is then picked up by the microphones.

“If you put microphones on either side of the leak, the sound waves and their time delay difference allows us to mathematically calculate where the leak is,” says John Van Arsdel, the firm’s vice president.” The operator will physically measure the distance between the two microphones and enter those parameters in to the computer.”

False positives can occur due to traffic noise, make up of the soil and the height of the water table, but in San Francisco at least the pipes are made of cast-iron, having been designed to withstand earthquakes, and their higher pressure means that leak noise is easier to detect.

Transducer microphones aren’t the only weapons being deployed against leaks. Pure Technologies, a company based in Canada, uses a UK-developed sensor-based device known as Sahara. The sensor, which is attached to the surface by an unspooling cable, is pulled along by the current in the pipe using a tiny drag chute. It contains both a microphone and camera. “That’s one of the big advantages,” says Pure’s technical product lead, Mike Robertson. “You have visibility in the pipe. When you locate a leak acoustically, you can also see what part of the pipe it’s coming from.”

Sahara does not require the pipe to be shut off for it to operate, reducing the impact on water users. Robertson says that he and his team are also looking into replacing the device’s copper cable with fibre-optic, allowing them to transmit vastly more data about the leaks.

Van Arsdel says that Californian authorities have been aware of the condition of their pipes for some time and that the San Francisco project was initiated well before the drought. It has, however, become increasingly important given the lack of water in the state. The Los Angeles Department of Water and Power has allocated $1.3bn to replace old water pipes, meaning that firms like Pure and M.E. Simpson are likely to find gainful employment in the state for years to come.

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