Active Leakage Control
Active leakage control (ALC), or sometimes known as active leak detection, is vital to cost-effective and efficient leakage management in water utilities and cities.
The concept of monitoring flows into zones, or district meter areas (DMAs), where bursts and leaks are unreported is an internationally accepted and established method to determine where leak location activities should be prioritized. The faster the utility operator can analyze DMA flow data, the quicker bursts or leaks can be located. This, together with speedy repair, limits the total volume of water lost and drives down non-revenue water.
There are many points in a distribution network where leakages can occur and where they are best monitored.
Modern flow monitoring and data capture techniques play a major role in the identification of bursts and in estimating the gradual growth of smaller leaks. Many water utilities integrate data from DMAs, via communication devices, into their supervisory control and data acquisition (SCADA) or data collection systems. This approach is particularly effective when implemented together with a data analytics package that helps the utility manager identify DMAs that requiring leak location work.
Leak Localizing and Pinpointing
Utility managers need to ensure a detailed process is undertaken to locate leaks:
Use flow monitoring data to identify DMAs that contain unreported bursts or growing background levels of smaller leaks
Narrow down the area of leakage within the DMA through activities such as step-testing
Pinpoint the exact (or nearly exact) position of the leak using more advanced electronic equipment
This process requires reasonable accuracy at each step to avoid high excavation costs and ‘dry holes’ (excavations at suspected leak locations but where nothing exists). The basic method of detecting and locating a leak is to listen for the noise of the water being released from the pipe under pressure. The pressure differential between the environment inside and outside the pipeline causes a pressure differential that creates a unique acoustic signature. The effectiveness of this activity is dependent on the system pressure, the size and shape of the leakage defect in the pipe wall and the pipe material.
Skilled operators who detect leaks on water pipelines use a range of acoustic equipment to pinpoint leaks. Some examples include acoustic sounding sticks, leak noise loggers, leak noise correlators, ground microphones, and more advanced internal acoustic techniques. Although these tools are extremely helpful for leak detection, utility managers must understand the correct applications and maintenance requirements of each tool to maximize results.
Leak Noise Loggers
Leak noise loggers narrow down areas of specific DMA, or network, that contain suspected bursts or leaks. A cluster of loggers is usually deployed in the survey area, with each logger placed on a hydrant, meter, or other surface fittings. Noises that are suspected of being caused by leaks can be confirmed, and the leak is located using other location equipment as described below. In more recent times, and aligned with advancements with cellular communication technologies, permanent deployments of leak noise loggers have become more common. The cost, accuracy and battery life of these devices have improved considerably in recent years and can form a key component of a 'smart water network'.
Leak Noise Correlators
Rather than locating a leak based on the noise level, a leak noise correlator uses the speed of sound from the leak location to the location of a sensitive acoustic microphone (accelerometer or hydrophone) placed on the pipeline. Typically two acoustic microphones are placed on the pipeline - either side of the leak location. The leak noise correlator will automatically calculate the speed of sound through that specific pipeline (based on material and diameter) and determine the time-delay between each acoustic microphone. The effectiveness leak noise correlation is dependent on the strength of the leak noise and the sound conductivity of the pipe material (e.g. non-metallic pipes have poor sound propagation).
Accelerometers are attached to fittings along the pipe and listen to the leak sound. These are very effective on metallic pipes; particularly cast iron, ductile iron, and steel.
Hydrophones placed in the water column can also enhance the leak sounds in plastic or large pipes and other pipes where the noise conductivity is known to be poor. These hydrophones work by listening to the leak noise travelling through the water, which is a better conductor, than most pipe materials, of sound.
The more advanced leak noise correlators have the capability of frequency selection and filtering, to quickly locate leaks to within 0.5 metres in most sizes of pipe, provided there are sufficient contact points along the line of the main. There are many brands of leak noise correlators, including Gutermann, Echologics, Primayer, HWM and vonRoll Hydro.
The ground microphone electronically amplifies the sound of a leak in a below-ground pipe. It is used by placing the microphone on the ground at intervals along the line of the pipe, usually where a correlator or leak noise logger indicates a leak, with a skilled operator noting changes in sound amplification as the microphone nears the leak position. The sound of water escaping from the pipe under pressure attenuates through the soil and to the surface covering (usually concrete, asphalt or soil).
Acoustic Sounding Sticks
The acoustic sounding stick can be an inexpensive, simple rod made of wood or metal with an earpiece attached to amplify sounds. It can also be an amplified electronic version that allows greater sensitivity. These are typically used in a survey mode as a team of leak detection operators moves through a DMA or network zone.
In addition to having a range of tools and technologies, it is important to have a team of experienced and skilled operators who are well trained in leak detection activities.