Construction of Phases 1 and 2 of the Swartland Bulk Water Pipeline in Gouda, Western Cape, commenced in May last year and has reached the final stages with an estimated completion date of mid-2013, Ehrane Holderness, UWP Consulting principal engineer, recently told Chantelle Mattheus.

According to Holderness, the project’s background is fairly simple. A 525 mm Nominal Diameter (ND) steel pipeline currently runs between the Swartland Water Treatment Works at Voëlvlei Dam and the Kasteelberg Reservoirs at Riebeek West. “The pipeline was constructed in the 1970s and is the main bulk water supply line for seven towns in the Swartland municipal area. The West Coast District Municipality’s 2010 Water Master Plan identified the need for an additional parallel pipeline to meet future water requirements, mitigate the risk associated with having a single bulk supply line and to allow downtime for maintenance work on the existing pipeline,” says Holderness.

The five municipalities falling under the West
Coast District Municipality are:

• Swartland Municipality with Malmesbury as administrative centre
• Bergrivier Municipality with Piketberg as administrative centre
• Matzikama Municipality with Vredendal as administrative centre
• Cederberg Municipality with Clanwilliam as administrative centre
• Saldanha Bay Municipality with Vredenburg as administrative centre.

The Swartland Regional Water Supply Scheme supplies Yzerfontein, Malmesbury, Darling, Riebeek West, Riebeek-Kasteel, Gouda and farms along the route with water it abstracts from the Voelvlei Dam, where it is treated as well. The allocation from the dam to the Swartland Regional Water Supply Scheme is 4.2 million m³/year. Additionally, barring a few of the small towns that are heavily reliant on fishing, the majority of the economy is bolstered by agricultural endeavours in the region, for which a continued sustained supply is a necessity.

Therefore the impact of the project on the local water supply network and the surrounding communities’ continued ability to access good quality drinking water cannot be underestimated, with the project set to ensure that the district is able to meet water requirements of the current supply area until 2040.

Project outline

The project, with an estimated cost of R70 million, involves the construction of a new 600 mm ND bulk water pumping main between the Swartland Water Treatment Works at Voëlvlei Dam and the Kasteelberg Reservoirs, explains Holderness. “The new pipeline must be constructed in parallel with the existing pipeline and be located in the existing 10 m wide servitude.”

The 17-km-long pipeline is a rising main with a static elevation difference of 225 m. A surge analysis was conducted during the design stage in order to determine the type and extent of surge mitigation measures required, as well as the class of pipes to be used. The high-pressure section of the pipeline will be constructed of continuously welded steel pipes and the low pressure section with ductile iron pipes. Four tie-ins must be provided between the old and new pipeline for maintenance purposes.

“The pipeline incorporates surge mitigation measures such as air valves and check valves. The upgrading of the pump station to meet future water requirements and the provision of surge protection measures at the pump station do not fall within UWP’s scope of work,” explains Holderness.

Phased approach

Construction of Phase 2 commenced in winter in order to optimise the use of funding in the applicable financial year, says Holderness. She adds that above-average rainfall over a three-month period hampered construction progress and the works were therefore temporarily suspended for a one-month period. “This was necessitated by concerns over quality control as well as problematic access to site owing to the wet conditions.”

Additionally, the pipeline route runs mainly across private agricultural land and construction access had to be negotiated with land owners. “Although affected parties were very forthcoming in this regard, careful planning around the movement of construction vehicles was required during harvesting periods,” says Holderness.

At the project’s peak, approximately 35 workers were on-site, including of operators and supervisory staff.

Differentiating factors

According to Holderness, what makes this project different is the use of ductile iron pipes for the low-pressure zones and continuously welded steel pipes in the high-pressure zones. “Ductile iron was the preferred material from a financial point of view.  However, continuously welded steel pipe was used in the high pressure zones as insufficient space was available in the servitude for the thrust blocks associated with ductile iron pipes.”

In addition, phasing of the project was required in line with the availability of municipal funds. “During Phase 1, 8 450 m of standard 600 mm ND Class K9 ductile iron pipes were ordered in advance. Phase 2, which will be completed in June 2013, entails the construction of 2 650 m of continuously welded 600 mm ND steel pipe and 9 050 m of 600 mm ND ductile iron pipe, of which 600 m was manufactured with restraining joints,” adds Holderness.

Phase 3 of the project will commence in 2014 and will entail the supply and construction of 2 600 m of 600 mm ND steel pipe and 1 900 m of 600 mm ND Class 30 ductile iron pipe.

However, the design for the entire project was completed prior to Phase 2 commencing, says Holderness.

Challenging context

Although the civil engineering aspects of the project are fairly straightforward, with no new technologies, processes or procedures really being implemented, this does not mean the project has been without its challenges.

According to Holderness, these included difficult accessibility to the site via informal dirt roads, which is exacerbated by wet conditions during the Western Cape rainy season. In addition, all construction activities such as stringing of pipes, excavation and storing of the topsoil for reuse had to be accommodated on a narrow servitude, and commercial bedding and ready-mix concrete had to be transported through private farmlands.

“The highlight will be the successful completion of the interconnecting chambers and successful hydrostatic pressure testing of all the installations,” concludes Holderness.