Methodology for leak detection

Water utility saving water

Identifying leaks quickly and cost-effectively is a key issue in South East Water’s commitment to water conservation. Solving the problem of thousands of litres of water literally going down the drain each year is crucial for the sustainability of community, the environment and the water industry.

New pipelines and, in particular, existing mains and service lines can start to leak due to bad joints, deterioration, stress in the soil and corrosion. This could lead to more extensive damage and loss of precious water. Finding a leak and pin-pointing the location will have an impact on the extent of rectification works, environmental burden and investment.

‘us’ — Utility Services has many years of experience in undertaking proactive leak detection of water mains and service pipes in South East Water’s and other Regional Utility networks, to identify and pin-point the location of hidden water leaks.

The initial survey of water mains is carried out by using electronic listening sticks that will analyse unusual noise from a water main fitting or a water meter to determine the likely location of leakage. The operator will eliminate operational noise generated by normal usage.

Once a potential leak is evident, the specialist leak detection technician determines the exact location of the leak through data evaluation.

The preferred method of finding water is a system called Soundsens that was developed in the UK. The system combines noise logging and leakage noise correlation into a single process.

The Soundsens approach is based on the deployment of highly sensitive and accurate loggers, called pods. The pods, which are time synchronised, record sound in short bursts lasting a few seconds. This recording is repeated multiple times to separate genuine use from suspected leakage. The duration of recording, the number of recordings and the dwell time between each data block is programmable and depends on the pipe material in question, or whether the test is taking place during the day or night.

The pods have an advanced digitally amplified accelerometer which is capable of detecting lower levels of sound than can be expected from conventional designs, which simply correlate sound velocity between two points.

The data from each pod is transferred to a laptop where a layout of the pipe work is graphically drawn using either GIS data or as a simple sketch. The layout enables the software to both link and take into account the spatial relationship between the pods.

Once the layout is complete, the software uses proprietary algorithms to amplify the sound and filter out anomalites. Correlation takes place between each pod in the array and all of the others. The cross-correlation is unique to the Soundsens and enables greater certainty in pin-pointing leaks, as it discerns leak noise profiles from other water sounds.

All leaks are pinned on the pipe layout diagram, tabulated and ranked in order of probability. The software will also show any correlations that should be subjected to further investigation. To help with this, the operator can listen to the sound using the software’s audio feature. The data files can be stored on a PC to make additional analysis or be used at a later date for reporting and tracking purposes.

As the loggers don’t require a transmitter like the conventional correlator, traffic management is less onerous as no transmitter is left in the road, requiring no traffic diversion during the correlation process. ‘us’ has identified and repaired 104 leaks during 2007/08, which has saved approximately 124 million litres of water, and has investigated more than 2000 km of water mains for South East Water this financial year in the search of ‘hidden’ leaking water pipes.

The recent example was located in Wonthaggi-Victoria, where a cast-iron, flanged dog leg on a 1000 mm AC water main was the reason for leakage. As a 200 mm concrete stormwater drain was in the near vicinity, the water was flowing directly into the stormwater system (with no water coming to surface). It was apparent that the leak had been flowing for many months with a flow rate of 70 L/min.

The development of the web-based consumption monitoring platform ‘HydroShare’ is also playing a vital role to identify leakage on the user site (after the water meter). Any sudden increase of continuous flow is immediately alarmed via exception reporting to email or phone SMS. Everything is clearly visible by just accessing the secure, customised website. This has resulted in massive savings or cost avoidance for users.