WATER & WASTEWATER Mpolweni pump station
Laying the 700 mm diameter steel pipe
Dalton and Wartburg integration A prestressed concrete structure with a flat concrete roof slab, the 10 Mℓ Dalton Reservoir was constructed adjacent to an existing 0.8 Mℓ reservoir that currently supplies the town of Dalton. The 8 Mℓ Wartburg Reservoir was constructed adjacent to an existing 1.5 Mℓ reservoir under a separate contract. The integration of the Dalton Reservoir, the Wartburg Reservoir and the existing 1.5 Mℓ reservoir was added to the scope of the Phase 2 project during the course of construction and required the construction of new chambers, pipework and control systems on the Wartburg site. The development of a complex design and control philosophy allows the three reservoirs to be filled via the Mpolweni pump station in any
combination of one, two or three concurrently. This was achieved by using programmable logic control systems that were configured based on predetermined (but adjustable) settings that allow for the operation of either one or two pumps, and for the speed of the pumps to be varied according to the preset rates – made possible due to the upfront design of VSDs at the pump station.
Steel pipeline The buried pipeline (15.1 km long) comprises a continuously welded 700 mm diameter steel pipe with a 6 mm wall thickness and 3LPE anticorrosion coating. This pipeline connects the new 8 Mℓ reservoir in the town of Wartburg (part of Phase 1) to the 10 Mℓ Dalton Reservoir. During the design phase, a net present value
Pipe jacking in progress
PHASES OF THE UMSHWATHI REGIONAL BULK WATER SUPPLY SCHEME Phase 1: 850 mm diameter steel pipeline (including the new Mpolweni booster pump station) from the existing Claridge Reservoir to Wartburg Phase 2: 700 mm diameter steel pipeline from Wartburg to a new 10 Mℓ reservoir at Dalton, including the new Dingle pump station Phase 3: Bulk pipeline from the Dalton Reservoir, which supplies water through a series of trunk mains to the Nadi and Ozwathini reservoirs, from which Phases 4 and 5 will be supplied
analysis was conducted to determine the optimal pipe diameter, considering the power, capital and maintenance costs of the various diameters and associated pumps. Through this analysis, it was determined that a 700 mm diameter pipeline would offer the best rate of return to the client. When crossing provincial roads and Transnet railways lines, the pipeline construction required the driving of five separate 2 130 mm diameter pipe jacks. Soil testing at the design stage revealed the need for cathodic protection, and this was installed through a specialist subcontractor, with temporary protection being provided during the construction phase. This necessitated the installation of two transformer/rectifier units, as well as test posts and current isolating flanges, along the pipeline route. Regular monitoring of the pipeline during construction and after commissioning of the system ensures that it performs as designed and the pipeline is fully protected. When steel pipelines are located near high-voltage overhead power lines, there is the danger of stray currents from the pipeline earthing through personnel working in the chambers. During the course of construction, following the recommendations of the cathodic protection specialist consultants, a decision was made to retrofit alternating current mitigation (ACM) measures on all chambers on the Phase 2 pipeline. This involved the construction of internal and external earth mats and monitoring points, and cross-bonding the systems to the pipeline and chamber reinforcing. Following the success of the Phase 2 work, a variation order was issued to further retrofit ACM measures on identified chambers on the Phase 1 pipeline. The communities of Mpolweni, Wartburg and Bruynshill can now benefit from an improved, reliable water supply while the vital supply of water to communities in Efaye, Ozwathini and Southern iLembe is now possible.
IMIESA July 2021
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