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‘Detecting mechanism’ for water leaks

August 25, 2012

CHRONIC drinking water shortages have been the hallmark of the KWSB’s water management over the decades. The rapid growth of Karachi with increasing population and expanding service areas further magnifies the impact of drinking-water shortages.

Good water management practices, like metered water supply and water conservation, have the potential to save enormous quantities of water, but the KWSB is in no mood to adopt these good practices. Karachi water supply is riddled with problems like intermittent supply, low average water pressure, poor drinking-water quality at consumers’ end (e.g., the recent episode of primary amebic meningoencephalitis infection caused by naegleria fowleri) and, a two-hour water supply time daily.

A major problem the KWSB is facing is the water leakages from the distribution system, also called as unaccounted-for water (UFW).

According to the published data, in Karachi the UFW is as high as 30 per cent of the water supplied. This shows the KWSB’s poor efficiency. This means a loss of about 200mgd, which is equal to water supplied to Saddar, Gulshan-i-Iqbal, Korangi, North Nazimabad and North Karachi, collectively. In financial terms, the cost of water lost through leakages is estimated at Rs 30 million, at current prices.

Current leakage location techniques depend on acoustic sensing, employing devices such as listening posts and correlators, using the noise generated by water escaping from a pipe under pressure. Acoustic-based techniques perform poorly in situations where the noise created by a leak is small or attenuates rapidly.

On Karachi streets one can some time see KWSB or DHA operators patrolling networks with devices such as listening sticks and correlators and attempting to pinpointing leaks. Piping materials may, at times, interfere with detection process. A reliable, nonacoustic-based location technique would be more helpful in such difficult situations.

Researchers at the University of Sheffield, UK, have developed a more accurate ‘cepstrum-based signal processing technique’ which locates leaks by sending a pressure wave along the pipe that sends back a signal if it passes any glitch and abnormality in the pipe’s surface.

The method follows the well-known concept of ‘water hammer’ in water engineering. Any sudden change in flow, such as sudden closure of a valve, produces a pressure transient that travels along the pipeline with a wave speed that depends on the pipe material and condition.

This is commonly known as a water hammer. When this wave encounters a feature such as a junction or a leak, some of it is reflected back and some continues. The pressure history of the outgoing and reflected waves can be captured and this gives information of the features in a network.

The system, which can be fitted to a standard water hydrant, consists of a valve that is opened and closed rapidly to generate a pressure wave that is sent down the pipe. When this wave encounters any unexpected features, such as a leak or crack in the pipe’s surface, it sends back a reflection that can be analysed to reveal the location and size of the leak.

The researchers conducted trials at the Yorkshire Water’s field operators training site in Bradford. The prototype device was able to locate leaks in cast iron pipes with accuracy to within one metre, while leaks in plastic pipes were located to within 20 centimetres.

F. H. MUGHAL Karachi