PIPELINES & LEAK DE TEC TION
Damp areas on the ground or very green grass patches surrounded by dry grass are visual indications of a leak
Leak detection in the Mother City
One of the leak detection methods used by the CoCT is a mechanical listening stick
Leak detection has been identified by the Water Conservation and Water Demand Management (WC&WDM) Strategy of the City of Cape Town (CoCT) as one of the best methods to minimise water losses in its reticulation network. By Kirsten Kelly
T
he City concentrates on detecting both visible and non-visible leaks, supporting reticulation depots to pinpoint the location of existing leaks, and improving the leak repair response
Unathi Noludwe, senior technician: Water Demand Management Division, CoCT
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time to a maximum of 48 hours,” says Unathi Noludwe, senior technician: Water Demand Management Division, CoCT.
Non-visible leaks
Different types of equipment are used by the CoCT to detect non-visible leaks: • Mechanical listening stick – used at all contact points (meters, valves, fire hydrants). • Noise loggers – deployed on pipe fittings and programmed over a period of time (recordings are usually taken at 02:00). • Leak noise correlators – this needs accurate information around the pipe material and diameter. Then the exact location of certain noise profiles (such as hissing leak sound) on the pipe is determined by correlating the noises that reach both sensors and measuring the difference it takes to travel on the pipe from the leak location to each sensor. • Data loggers – measures the flow and pressure of water in order to analyse the minimum night flow. • Ground-penetrating radar – locate the pipe direction and depth.
Methods
The CoCT uses four leak detection methods: • Visual leak detection – drive or walk on streets to inspect reticulation networks for obvious ground leaks. There is a 3 km target per team per day. • Localise – conduct leak noise surveys by using a listening stick and noise loggers. • Locate – identify a leak location by using a leak noise correlator. • Pinpoint and confirm – find the exact leak location by using a ground microphone. “We also use step testing as a leak detection method. Step testing is the process of localising leakage into specific pipe segments of the distribution system for subsequent replacement or repair. It is conducted at night when there is low demand, as we often shut off certain valves. A leak is usually found in an area with a disproportionate drop in flow,” adds Noludwe.
Non-discrete zones
Leak detection in non-discrete areas can be challenging, as it is difficult to
