Conceptualización específica operacional.

As described in Section 4.5, leak localisation is enabled by the use of DMAs. There are parts of the network where this cannot be achieved due to the high cost of installing (multiple) meters or due to the uncertainty over the estimates of customer use e.g. urban city centres. Within DMAs and in areas not covered by DMAs, a variety of methods are used to localise leaks. These methods are described below.

Step testing

The general principle of step testing is to isolate (turn off) sections of a DMA in turn and see what effect that has on the total (night) flow into the DMA. The expected change can be calculated based on the estimated demands of the isolated sector. This is compared to the actual change in demand from the network. Should this change be greater than expected, there is a high probability that there is a leak in the area or street that has been isolated.

Most water companies have increased the area measured in each step test to decrease the potential issues with water quality that this method can create (Dray, Loveday, Tod, & Tooms, 2010). With new data transmission technology fitted to the district meter, the flow change can be seen instantly on a hand held portable device, so that isolating individual streets for short periods is seen as an efficient and less disruptive form of step testing.

Step testing is particularly effective in areas with predominately plastic piping as step testing is less susceptible to the issues that affect other localisation technologies based on acoustic detection of leaks. However, it is best avoided on pipework in poor condition due to the potential for pressure shocks to be introduced. Finally, step testing is best carried out at night when customer demand is expected to be lowest.

Pressure testing

Pressure testing involves the pressure being raised in a controlled manner along an isolated section of network. Once a designated pressure is reached the section is completely isolated and the pressure is monitored. The rate of pressure decline is a function of the rate of leakage from the pipe. Too rapid a drop in pressure indicates serious leakage from the pipe section.

While effective, the greatest disadvantage of pressure testing is the risk of creating a burst. It is therefore not recommended for use on older pipes in the water industry, and is generally limited to new mains and trunk mains.

Acoustic loggers

A large number of water leak detection and pinpointing techniques use detection of the noise produced by the leak to identify the presence of a leak or to pin-point its location.

Acoustic loggers are units that are deployed in groups of between 6 to15 and are mounted on the pipes or fire hydrants 100-500 m apart from each other. The devices record the noise detected on the pipework. This information can then by analysed for unusual noise patterns, which can indicate potential leaks. The most sophisticated noise loggers are self-learning, which allow the filtering out of disruptive background noise.

The recorded noise can be monitored over a period of several days and weeks by either accessing them directly or in passing with a receiver to pick up their signals (Dray, Loveday, Tod, & Tooms, 2010).

Flow meters

Flow meters have also been used to localise leaks down to a sub-DMA level. This involves dividing the DMA into smaller hydraulically distinct areas and installing (temporary) flow meters on the mains feeding each sub-DMA. Some companies have a hierarchy of smaller LCAs (leakage control areas) inside DMAs which are not isolated permanently. Alternative routes into the sub-DMA can be isolated via valves on a temporary basis. The flow rate into the sub-DMA can be monitored over the course of 24 hours for unusual activity that indicates a leak, for example high flow rates or little variation in the flow rate over the course of the day (Hunaidi, Detecting Leaks in Water-Distribution Pipes, 2000).

This method has the advantage over step testing in that it will not interrupt service. In addition, due to the fact that the flow meters use telemetry to communicate information back to the office, it is less labour-intensive than step testing and pressure testing but does require access points or fittings to allow for the additional metering.

Tri-parameter systems

Tri-parameter systems measure flow, pressure (including transients) and noise. By maintaining a record of the normal pattern for a position within the network, they create a footprint from which any deviation can indicate the presence of a leak or other significant network event. These systems include Hydroguard and Trunkminder. The systems are usually permanently installed or installed for extended periods.

Typically the cost of the installations (including data connections) mean these techniques are used only on critical, large diameter trunk mains.

Photograph 5.1 Tri-parameter system in operation

Source: (Martinek Water Manafement, 2014)

Hydroguard are battery operated monitors that measure, record and transmit the flowrate, pressure and noise data from trunk mains. Trunk mains are generally large diameter mains that transfer water from one area to another. Hydroguard is designed to learn the flow and pressure profiles of the pipe it is installed on over a pre-determined length of time. Information can be sent to back to computers in the central office or to mobile phones. Should there be anomalies in the recorded data, the system can raise the alarm and increase in the frequency that it logs data.

Trunkminder is another permanently installed sensor that provides real-time data to the operator. It feeds the data it gathers (pressure, flow and vibro-acoustic) through a series of algorithms that allows it to alert operators to identify emerging problems on the pipeline and help screen out false positives allowing it to give accurate early warnings of potential leaks.

Modelling hotspots

Computer network modelling can be used to localise new leaks. Data relating to flow and pressure is gathered from an investigated DMA and is fed into the model, which in turn will predict the most likely leakage hotspots. These computer models are based on hydraulic models with algorithms to model pipe conditions and other factors.

The greatest advantage of leakage hotspot modelling is that it can localise potential leakage locations across a large area extremely quickly. It is also not labour intensive compared to traditional methods of leak localisation which are timely and costly. However, the accuracy of these models depends on the quality of the model used and the quality of the input data.

Frequently several runs are conducted for each DMA and an average taken to reduce the risk of making decisions based on one set of anomalous input data.

Leak detection models have been used by United Utilities on DMAs with historically high leakage with some success on small catchment areas (Wu, 2008).

Thames Water has recently invested in TaKaDu infrastructure monitoring systems across London in a move to help locate hotspots where leakage is most prolific. TaKaDu uses a smart grid covering the network and data gathered from the company on pressure and flow rate as well as weather and local holidays to flag potential problems.

Not all leakage modelling is used for locating leaks. The Met office has developed a model, in conjunction with Thames Water that predicts, among other things, the likelihood of increased bursts across the network due to weather conditions (heat, cold etc.) for use in management planning.