WATER PRESSURE MANAGEMENT
Over 2 000 PRVs in the Valley of a Thousand Hills EThekwini is unlike SA's other metros. Approximately 60% of its population lives in rural areas, with over 560 informal settlements. It also operates across a varied topography – from 0 m to 1 000 m above mean sea level. By Kirsten Kelly
O
ur metro has one of the biggest pressure management programmes in the country. Between R30 million and R40 million has been invested annually over the past 12 years in pressure management. The programme cuts across a number of departments and teams within the municipality and is highly complex, given our hilly terrain and large rural areas,” says Bhavna Soni, department deputy head, eThekwini Water and Sanitation (EWS). Consulting engineering teams are appointed to actively review the existing water distribution systems – with the aim of having a minimum 250 kPa and a maximum 600 kPa supply pressure to customers. If there are any places that breach the 600 kPa measurement, steps are taken to install a pressure-reducing valve (PRV). “However, EWS is starting to reach a
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saturation point with the retrofitting of PRVs, and we are now focusing on the pressure management of new reticulation systems. These are constructed according to design guidelines where, according to pressures, control valves are installed at key points,” explains Nischal Nundlall, acting senior manager: Water Design and Non-Revenue Water at EWS.
Asset management “Asset management and pressure management go hand in hand. EWS has established a prioritisation model when it comes to pipe replacement that is purely based on the performance of the system. We are currently conducting a case study in Chatsworth, where an entire pipe network (including the service connections) up to a metering point will be replaced. This area has experienced a high number of water leaks. The performance of the new system will be benchmarked against the old system. The new system will need to meet certain parameters regarding leakages in order for the contractor to receive full payment. It is a performance-based contract,” adds Nundlall. The operations team engages with EWS Planning and Design teams whenever pipes repeatedly burst in a supply area. Before pipes are replaced, the existing supply pressure is measured. If pressure exceeds 600 kPa, steps are taken to reduce that pressure in the area, which will then, as a consequence, lessen the frequency of burst pipes.
Retrofitting PRVs Nundlall adds that a works contractor is
currently retrofitting the distribution system with PRVs or control valve installations. This involves installing pipework and building chambers/kiosks to house the PRVs. To date, over 130 sites have been handed over to eThekwini Municipality.” The municipality’s water distribution system is divided into roughly 300 reservoir supply zones, with over 12 500 km of distribution mains. Each reservoir zone is evaluated based on the level of the reservoir and the extent to which that reservoir feeds into an area. The reservoir zones are further broken down into district metered areas that comprise a maximum of 2 000 households. These district metered areas are then divided into pressure management zones. The pressure management zones cover approximately 40% of EWS’s total distribution system. Serving no more than a couple hundred households each, the pressure management zones do not have multiple feeds – there is a distinct supply point where a PRV is installed. This makes it easier to operate and maintain control.
ETHEKWINI MUNICIPALITY STATS • 1 050 Mℓ/day water in the system • Population: 3.6 million people • Non-revenue water: 49.2% • Pressure-reducing valves: 2 341 • Control valves: 265 • Break pressure tanks: 94
