A vital part of any water-loss strategy: pressure management

As a water services authority, the City of Cape Town (CoCT) is expected to implement water conservation and water demand management interventions to deliver water as efficiently as possible. Pressure management is an integral part of this commitment.

By Kirsten Kelly

We immediately see the benefits of pressure management by reduced pipe bursts, which limits operational costs for repairs and, most importantly, limits water leaks. We also extend the infrastructure lifespan, postponing costly upgrades,” explains Ivy Maisela, senior professional officer, Water Demand Management Division, CoCT.

She adds that through Cape Town’s drought period, 70 Mℓ/day of water was saved by pressure management alone. As water restrictions eased and water pressure increased, the savings have reduced to 20 Mℓ/day.

As an ISO 9001 certified organisation, CoCT follows a process-based approach with regard to pressure management, where there is an increased focus on standard operating procedures and documenting all water pressure management activities. “Recordkeeping and documentation play a key role in water demand management. Data integrity is very important,” states Maisela. A 10-year plan has been formulated on how CoCT will implement its pressure management strategy, prioritise areas in need of pressure management, analyse pipe burst statistics, evaluate different pipe materials, and look into average system pressures.

Pipe distribution network A pipe distribution network can fail due to: • ageing infrastructure • failure of the joints of the pipeline (corrosion or age) • poor workmanship (poor flushing/air in pipes) • high network distribution pressure (faulty valves). CoCT therefore focuses on reducing the pressure of its pipelines to acceptable parameters. “Ironically, our pipelines often fail as a result of routine maintenance and daily operations. For example, when a burst pipe has been repaired, and there are air pockets in the mains, there are often additional burst pipes. Pressure management plays a vital part in pipe replacement programmes,” adds Maisela.

Zone management CoCT’s water distribution network is divided into four regions that are further divided into pressure management zones.

Zone management for non-complex areas is managed internally by CoCT, while complex areas are outsourced. Implementing zone management

infrastructure (like pressure-reducing valves [PRVs], zone meters, strainers, chambers, isolation valves, spool pieces, bends and thrust blocks) is also managed in-house, as is analysing the viability of controllers. Close-out reports and as-built drawings are also created.

All zone information captured while working in the field is shared with the Geographic Information Systems (GIS) team, the Engineering team, and the Asset Management team responsible for capturing and maintaining asset registers. Dates are also recorded for proactive maintenance plans.

“Confirming or verifying the discreteness of a zone is a critical part of our zone management design, even after the zone has been designed. We use the information on the design report as well as logging data (inside and outside of the zone) and pressure zero tests where we isolate the zone,” explains Maisela.

Zones are monitored remotely for their discreteness. There are alarm settings to notify a reticulation operator if there are changes (outside set parameters) in the operation of the zones. Monthly formal reports on the performance of zones are produced and distributed to operations. They contain information about a zone’s upstream pressure, downstream pressure and flow profile of each zone. Also known as record drawings and red-line drawings, as-built drawings are documents that allow one to compare between the designed versus final specifications, and provide a detailed blueprint of the land around the zone. “CoCT now combines as much information about a zone as possible on the as-built drawings, such as number of properties, length of mains, static inlet pressure, inlet elevation at PRV, supply reservoir, critical point elevation, and the coordinates of where the valves are placed. These drawings are invaluable when zones are breached,” states Maisela.

Time-modulated pressure control (TMPC) She adds that CoCT has adopted the TMPC approach, whereby pressure is reduced at night and in the afternoons and increased in the morning when water is used the most. This has reduced incidents of pipe bursts. The critical point is monitored to ensure that the minimum pressure requirement is supplied.

The TMPC approach offers greater flexibility in pressure adjustment at specific times of the day, achieved with the help of the controller. The controller is low in cost and relatively easy to set up. A notable limitation of TMPC is that of its poor response to water demand requirements, such as the demand for firefighting. During the firefighting demand period, full pressure is usually required to tackle a fire outbreak. A higher level of expertise is required to operate and maintain the installation of the devices used in this approach compared to the fixed-outlet pressure control approach.

Non-revenue water CoCT is currently sitting at a 34% non-revenue water (NRW) figure and implementing measures to reduce this further.

“An NRW steering committee has been created to provide an integrated approach with implementing methods to reduce NRW,” says Maisela. Some of the key focus areas include: • bulk meter audits and a meter replacement programme • pipe replacement programme • water network leak detection and repair programme • pressure management and district meter areas programme • zonal water balance for discrete zones (bottom-up approach where water balances are produced for the individual zone) • water infrastructure asset management • education and awareness areas. Maisela adds that CoCT experiences a number of challenges (that they are working to overcome) with regard to reducing NRW:

CAPE TOWN’S WATER SUPPLY AND DISTRIBUTION SYSTEM

Population served Number of connections Total length of mains (excluding bulk) Total length of mains under PRV control Total length of mains under booster zones Total length of mains under DMA Pressure management mains coverage Total number of zones established to date 4.7 million 673 789 10 977 km 7 698 km 63 km 92 km 70% 236

• reporting inaccuracies, especially when dealing with meters • zones being breached • the licences belonging to remote pressure controllers and zone monitoring platforms are owned by third parties – creating red tape within the procurement process • long turnaround time when repairing PRVs • in the procurement process, brand names cannot be specified, resulting in many different PRVs in the field – requiring additional training for operators as they need to make use of multiple different types of PRVs • low availability of spares • ageing infrastructure • loss of skills and institutional knowledge through resignations and retirement • quality of workmanship • lack of an in-house meter maintenance capability • oversized meters.

Future plans “CoCT plans to implement pressure management measures across the entire city by 2028, where all areas will be zoned with a clear idea of the positions of all boundary valves. In the near future, we will be implementing meters and monitoring systems at reservoir outlets, as well as creating reservoir water balances. CoCT also aims to increase the visibility on 70% of the pipe distribution network that can be monitored for performance. There are also plans to install meters at all PRV zones,” says Maisela.

She adds that there will be a focus on creating district metered areas in industrial regions to monitor leakage levels. CoCT will also pilot new technologies for leak detection and pressure management.

“CoCT has initiated an integrated approach to water supply. Reducing NRW is approached from a holistic point of view – from bulk water supply to the customer. We have found that the effectiveness of any pressure management strategy relies on the skills and experience of the zone operators, and they need to be constantly upskilled,” concludes Maisela.

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