A Ø630mm HDPE bulk water pipeline replacement at Courtai

A Ø630mm HDPE bulk water pipeline replacement at Courtai

Water leakage and non-revenue water are growing problems in South Africa, with many initiatives aimed at addressing the issue. Drakenstein Municipality in Paarl, Western Cape, has undertaken a 20-year master plan and had great success in reducing water loss.

With ever-increasing water losses surpassing demand growth, the municipality was forced to investigate the high water losses and find ways to mitigate these on a broader front, explains André Kowalewski, Senior Engineer: Water Services, Drakenstein Local Municipality.

In 1999, the water losses in Drakenstein stood at 34% and were increasing. The municipality began prioritising projects and introduced a 20-year project plan in an attempt to curb this. The main initiatives over the past 17 years have included pipe replacements, the replacement of bulk and domestic water meters, pressure management, leak detection and repair, public awareness and upgrading information and management tools. Reaction time to attend to burst pipes was also reduced to less than one hour.  The result of these initiatives, supported by the Drakenstein municipal council, is a significant reduction in water loss.

These initiatives have brought water losses down to an average of 16% – and 11% at its lowest. Water losses are currently at 13% for the 2015/2016 financial year. The lower losses enabled the municipality to delay the construction of reservoirs and large pipelines for several years. There was also a decrease in the occurrence of burst pipes. However, the reduction in residual pressures in various pressure zones had the biggest water saving effect, says Kowalewski.

The municipality has effectively reduced static pressures of roughly 1200kPa in the lower laying areas to around 600kPa and, at the critical point, to 280kPa. This had an immediate impact on water demand and reduced burst pipe frequencies drastically. Retention in the reservoirs increased from 48 hours to 68 hours in Paarl area alone. These savings not only delayed the construction of new reservoirs, but the reduction of pressure in the networks allowed further savings with the installation of flow controllers, which further control the flow.


Pipe rehabilitation initiative

The municipality has placed significant emphasis on replacing old asbestos pipes with new HDPE pipes. “Taking the life cycle of the HDPE pipe as a material into account, it surpasses most other pipe materials. The pipes can also handle the fluctuation in water pressure and flow characteristics within the pipe design limits better than any other flexible pipe systems. If correctly designed, and with proper installation, an HDPE system – together with the fittings – will provide the lowest maintenance compared to any other pipe material system,” Kowalewski explains.

He adds that the most attractive advantage of HDPE is a pipe system without pipe joints. In addition to this, most of the fittings used in HDPE systems are moulded out of polyethylene material. Other fittings used by the municipality include flanges and tee-pieces predominately manufactured using grade 316 stainless steel.

“The philosophy behind the use of a high-grade material is to have a total system where the pipe material and fittings, when used together, will guarantee a useful operating life that surpasses 50 years. It means that the chemical resistance and durability of the fittings must be the same as those of the pipes,” states Kowalewski.

Tests and calculations done on HDPE have shown that the pipe material’s useful lifespan runs up to 100 years. In addition to this, HDPE is the most popular pipe material to use when replacing pipes using trenchless construction methods, explains Kowalewski.


Going trenchless

Drakenstein Municipality has implemented various trenchless projects to upgrade existing pipes to larger diameters – anywhere between Ø110 mm to Ø400 mm – to provide for larger water demands. The trenchless pipe projects are all undertaken by contractors that specialise in trenchless pipe technologies, explains Kowalewski. One such contractor is Carp Civils, which has been conducting trenchless projects for Drakenstein Municipality since the company’s inception in 2003. Carp is a specialist in the rehabilitation of water and sewer pipelines using trenchless, pipe cracking methods.

The company has also been responsible for the upgrading of the smaller-diameter asbestos and cast iron reticulation pipes with HDPE piping, using trenchless technology methods, working with mainly Ø110 mm to Ø400 mm pipes in the Paarl and Wellington areas.

Pipe bursting methods are used for the replacement of existing water or sewer mains in order to minimise the excavation required. The pipe bursting methods involve pulling the new HDPE pipe through the old or existing pipe, which forces the fragments of the existing pipe outwards while a new pipe is drawn through, explains Hilton Bruyns, Dirctor, Carp Civils.

As these projects are predominately labour-intensive, the company makes use of local labour as a resource to equip the teams. Staff are trained on-site in the specialised field, with all the necessary safety and welding training, and all foremen have been developed from within the company.

“Each project brings its own challenges, many of which can be avoided with planning. However, there are unforeseen obstacles that may arise mid-project,” says Bruyns. “This is where Carp’s experience comes to the fore in working with the client for the best possible solution, ensuring satisfactory and cost-effective service delivery.”


Strawberry King bulk water pipeline replacement

One of the major projects currently under way in the Drakenstein Municipality is the replacement of the Strawberry King bulk water pipeline. The first phase of this project, which involved the replacement of a Ø560 mm pipe over a distance of 3.4 km was completed in 2015 by Strata Civils, who was also successfully awarded the contract for Phase 2 in June.

Phase 2 involves the pipe jacking of a Ø1 200 mm reinforced concrete pipe under the N1 highway and N1 off-ramps in Paarl. A section of Ø560 mm HDPE pipe is to be laid via conventional trenching and a section of thrust boring. The sections under the N1 to be pipe jacked will have the Ø560 mm HDPE pipe placed inside the concrete pipe and then grouted to secure the pipe.

It is Drakenstein Municipality’s policy to encourage contractors to use local labour and, as such, Strata Civils sourced all of its labour requirements from the Paarl area. Although no formal training was offered during the duration of the project, the local labour gained invaluable on-site experience in the backfilling of trenches, the reinstating of layer works in trenches and traffic accommodation.

“We are extremely proud to be associated with Drakenstein Municipality, whom we believe to be one of the trailblazing municipalities in providing and delivering quality water resources to its ratepayers,” says Charles Linnegar, managing director, Strata Civils. “Our team has formed a successful working relationship with Drakenstein Municipality and we hope to continue with this well into the future on some more exciting projects.”


Pioneering the way with stainless steel

“The life cycle of a pipeline must include all components of the system. Durable pipe fittings – right up to bolts and nuts – must have a similar life expectancy to the pipe used, without compromising flow properties and ease of maintenance,” Kowalewski emphasises. In this area, Drakenstein Municipality is a rare case in that it makes use of stainless steel fittings, which have an expected useful life of between 50 and 100 years.

Stainless steel material is used for all fittings where neither HDPE nor PVC are available, such as pipe saddles, tees and reducers. One of the big advantages of this is that on-site adaptions and changes to pipe fittings can be undertaken on any construction site, without special precaution taken for additional coatings. In addition, the material provides good chemical resistance against the corrosive soils and groundwater found in the area.

Both HDPE and stainless steel can be easily used in aggressive soils. Care must, however, be taken when used in areas with a salt content and where chlorine is apparent, explains Kowalewski. The use of different types of steel materials, such as mild steel together with stainless steel, must also be avoided at all times.

The downside of using this high-quality material is the price attached to it. The cost of stainless steel can easily be double the price of standard, hot-dipped mild steel materials. But, according to Kowalewski, the benefits are worth the cost. Coated steel fittings and pipes have a limited lifespan, which can be as short as 10 years, depending on the installation conditions. Stainless steel can handle the abrasive liquids and materials found in pump stations and water treatment works. “Quality workmanship and high-quality materials combine to form a recipe for a durable and low-maintenance pipe system.” The expected useful life of stainless fittings is between 50 and 100 years.

However, stainless steel cannot be utilised in all cases and so the municipality makes use of ductile iron pipes and fittings where high pressures higher than 2 000 kPa are apparent. Special care is then taken to protect these pipes and fittings against corrosion. Glass-reinforced pipes (GRP) are also used on a less frequent basis where conditions are conducive to their use. GRP pipes and fittings have good resistance to aggressive soils and water and were recently used on a new Ø400 mm bulk water pipe installation in Paarl.


Building storage capacity

Drakenstein Municipality has also placed an emphasis on the construction of new reservoirs. One such project is the construction of a new, circular 8 Mℓ reinforced concrete reservoir complete with a 1 265 m long Ø630 mm HDPE bulk supply pipeline, which ties into the existing Wemmershoek supply pipeline.

Civil engineering firm Exeo was successfully awarded this project and has a long relationship with Drakenstein Municipality, stretching as far back as 1996. The new reservoir is constructed below ground level, to minimise its visual impact, and consists of: a reinforced concrete ring beam on which a 7 m high, 400 mm thick reinforced concrete wall is constructed; a 250 mm thick reinforced concrete floor slab; 26 x 7m high Ø450 mm reinforced concrete columns; a 280 mm thick reinforced concrete roof slab; and associated reinforced concrete chambers.

One of the most challenging aspects of the project is site access, explains Kempen van Wyk of Exeo. The reservoir site is fairly congested with two existing reservoirs in close proximity. Matters are further complicated due to the fact that the site has a significant slope and that the in situ material consists of clay. This was overcome by amending one of the reservoir floor panels to the extent that it is capable of withstanding the forces of a tower crane. The position was carefully selected so as to allow the tower crane to remain in place until three-quarters of the roof slab is completed. This means the construction of the walls, columns and floor slab panels can be conducted simultaneously and without further hindering access to the different areas of the reservoir.

Construction on the project commenced early in April 2016 and is scheduled for completion in November 2017.

Another project currently under way is the construction of a 5 Mℓ reservoir and Ø400 mm HDPE connecting bulk water pipes at Welvanpas in Wellington. This is being undertaken by Vakala Construction and JVZ Construction as a joint venture. The last concrete of the reservoir deck was casted on 19 August 2016 and, with its material approach, Vakala plans to finish the contract well ahead of the deadline by targeting completion before the builder’s holiday in December 2016.

Vakala and JVZ also recently completed two 11 Mℓ reservoirs and the associated Ø600 mm bulk water pipelines for Drakenstein at Newton, Wellington. “Drakenstein Municipality is one of our preferred clients. We are proud to have offered our local municipality reliable service and quality products for almost 11 years,” says Johan van Zyl from JVZ Construction.

According to Van Zyl, the joint venture between Vakala and JVZ was established in order to ensure the strongest possible construction team that is both diverse and well-experienced. The responsibilities were shared between the parties to make use of the best competencies on each side. “Both Vakala and JVZ are well-known and experienced contractors in the reservoir field making use of proven techniques and construction methods,” says Van Zyl. This joint venture paid off in overcoming the challenge of casting the reservoir walls in three horizontal lifts, each consisting of 145 m3 concrete, which had to be casted continuously to ensure no cold joints. The pair successfully finished both of the 11 Mℓ reservoirs at Newton, Wellington before the completion dates.


Successful water savings

The answer to Drakenstein’s success lies not only in addressing infrastructure challenges but also initiatives such as stepped water tariffs and public awareness campaigns.

“Like all other local authorities, stepped water tariffs were introduced to motivate consumers to use less water. With the introduction of the stepped tariffs, a definite change in the behaviour of the consumers was observed,” says Kowalewski. The municipality also makes use of public awareness campaigns, particularly at schools, and has invited schools to visit water treatment plants as an educational process.

These projects, together with the replacement of approximately 210 km of asbestos and cast iron pipe since 1997, have resulted in an approximate 18% decrease in water losses over the past 17 years, a significant achievement for the municipality.