CHAPTER 3: REVIEW OF EWS NRW AND OPERATIONAL METHODOLOGIES
3.4 ACTIVE LEAK DETECTION
In some areas, the residents are not prone to report leaks and therefore the Department has to go out and actively find and repair them. In some cases, the leaks are not visible and sophisticated equipment is used to survey and pinpoint these leaks. This work focuses on the location and repair of visible and non-visible leaks on mains, service connections and fittings, examples of which have been presented in Figure 3.13.
Figure 3.13: Examples of Typical Leaks within eThekwini Municipality Conventional Leak Detection and Repair
The main factors that influence leakage are the condition of the infrastructure, the static and dynamic pressure, the number of service connections, the length of mains, the annual number of new leaks (reported and unreported) and the average run-time of reported and unreported leaks.
Visible leaks are usually reported by the public and other staff such as maintenance teams and meter readers. Unreported leaks are usually non-visible, ring fractures, splits and corrosion holes on mains, mains fittings, service connections and pipes or on meter installations.
Analysis shows (Brothers, 2003) that in well managed networks, reported bursts account for less than 10% of the annual real losses volume. The largest components of real losses come from
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long-running unreported leaks and bursts, from background leakage, and from long-running reported leaks which the Water Utility is slow to repair.
Conventional leak detection and repair is carried out by EWS through external contracts procured through a public competitive bidding process. This comprises of leak detection using mechanical or electronic equipment and conducted on 5 different levels:
• Level 1 leak detection comprises of a visual survey (Figure 3.14)
• Level 2 leak detection comprises of a mechanical and electronic survey using listening sticks, ground microphones and leak noise correlators (Figure 3.15-3.17)
• Level 3 leak detection comprises of leak noise correlators only (Figure 3.18)
• Level 4 leak detection comprises the deployment of leak noise loggers (Figure 3.19-3.20)
• Level 5 leak detection allows for leak detection surveys to be undertaken on trunk mains using ground microphones (Figure 3.21) or intrusive methods such as Sahara (Figure 3.22) or Smartball (Figure 3.23-3.25).
Figure 3.14: Visual Leak Detection. (Photo courtesy of Mr Chris Otto, 2010)
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Figure 3.15: Traditional Mechanical Listening Stick. (Photo courtesy of Mr Julian Thornton, 2010)
Figure 3.16: Mechanical Leak Detection using amplified listening stick. (Photo courtesy of Mr Chris Otto, 2010)
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Figure 3.17: Leak detection using a ground microphone. (Photo courtesy of Mr Chris Otto, 2010)
Figure 3.18: Leak Detection Using Leak Noise Correlators Showing an Indication of a Leak.
(Photo courtesy of Mr Chris Otto, 2010)
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Figure 3.19: Leak Detection Using Leak Noise Loggers. (Photo courtesy of Mr Chris Otto, 2010)
Figure 3.20: Correlating Radio Noise Logger with Alarm System. (Graphic courtesy Guttermann, 2012)
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Figure 3.21: Trunk Main Leak Detection with Amplified Listening Stick. (Photo courtesy of Mr Chris Otto, 2010)
The figures 3.22 and 3.23 show an internal tethered pipe technology from SSIS (Pty) Ltd which can survey pipes up to 2000m in length with one deployment. With this system, a head attached to a cable is inserted into a live water main through a fire hydrant or air valve. This head consists of a location sonde, a camera and a hydrophone. The head is thus able to see, hear and pin point the position of a leak. This technology is also useful for showing the internal condition of the pipe and revealing blockages, unknown laterals, tuberculation and many other problems.
The downside of this technology is that the preparation and deployment is costly and time consuming. The cable cannot be deployed through too many pipe bends as the accumulated frictional resistance can snap the cable when trying to retrieve the head.
Figure 3.22: Sahara SSIS Leak Detection (Photo courtesy SSIS Consulting Engineers, 2010)
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Figure 3.23: An example of In-pipe Acoustic Technology (SSIS Consulting Engineers, 2010) Non tethered devices consist for example of a ball that rolls down the main which locates leaks as it passes them in the pipe. The ball is captured by a net installed downstream in the pipe and then recovered but this technology is only suitable for pipes 300mm diameter and above. When testing this system in a 450mm steel main in the Durban CBD, the ball failed to arrive in the net.
Figure 3.24: Smart Ball Internal Noise/Leak Technology (SSIS Consulting Engineers, 2010)
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Figure 3.25: Smartball Leak Detection (SSIS Consulting Engineers, 2010) There are a few other methods that can be used to help locate leaks in transmission mains:
• Ground penetrating radar
• Step testing
• Pressure testing
• Aerial photography
• Satellite photography
• Thermography
• Using a helicopter to survey trunk main routes from the air in winter and compare flora and ground conditions.
Alternative Leak Detection and Repair
An alternative leak detection and repair strategy was adopted by EWS in January 2011 that allowed quicker leak repair times and surveys to be undertaken in high density low income areas. This involved the use of Category B plumbing teams sourced from the EWS Plumber Roster on a two-week shift basis. These plumbers are allowed to work on live mains up to 54mm diameter.
The plumbers are deployed into areas previously identified and assessed by Non-Revenue Water (NRW) Engineers. The plumbing teams are briefed, provided with repair fittings and then targeted with identifying and repairing all visible leaks (Figure 3.26). Quality control is undertaken through GPS coordinates, digital photographs and sample field inspections.
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Figure 3.26: Category B Plumbing Leak Detection and Repair. (Photo courtesy of Mr Chris Otto, 2010)