uMshwathi Regional Bulk Water Supply Scheme Phase 2

uMshwathi Regional Bulk Water Supply Scheme Phase 2

The Dalton Reservoir site

Umgeni Water appointed Hatch to design and manage the construction of the uMshwathi Regional Bulk Water Supply Scheme Phase 2. This comprised a 15 km, 700 mm diameter steel pipeline between Wartburg and Dalton, two booster pump stations, and a 10 Mℓ reservoir.

The project was located in the uMshwathi Local Municipality north-east of Pietermaritzburg in KwaZulu-Natal. The municipality falls within the uMgungundlovu District Municipality, which is responsible for the supply of water to consumers within this region.

Booster pump stations

The 58 Mℓ/day Mpolweni pump station was designed and constructed at km 19.3 on the 27.7 km long 850 mm diameter pipeline built in Phase 1. The pipeline had been constructed under a separate contract and was practically complete at the time of commencement of the construction of the pump station. The Mpolweni pump station consists of three pumpsets in parallel with a combined installed capacity of 900 kW, with future upgrading planned to 2.25 MW. The pumpsets installed for the initial two duty points were designed to run at 860 rpm and 1 065 rpm, respectively, using variable-speed drive (VSD) technology – allowing for flows rates from 1 620 m3/h to 2 180 m3/h. The pump station has been configured to operate with a single duty pump when required.

Consisting of two pumpsets with a combined installed capacity of 1.5 MW, the 41 Mℓ/day Dingle pump station operates with one pump on duty and one pump on standby. These pumpsets are designed to run at 1 350 rpm and 1 450 rpm, respectively, using VSD technology. This allows for flow rates from 980 m3/h to 1 320 m3/h. A future third pump was allowed for in the design, where two pumps will operate as duty with a third pump on standby. The Dingle pump station was constructed about two thirds down the Phase 2 pipeline route to boost pressure in order to supply the Dalton Reservoir.

Using the VSDs, these pump stations can meet projected system demands to 2035 using the same mechanical and civil infrastructure (including pumps). In order to achieve the ultimate 40-year demands, only the motors and the electrical switchgear would need to be upgraded, which will be necessary due to their design life in any event.

PROJECT TEAM

Client: Umgeni Water

Principal design consultant and

construction manager: Hatch

Electrical consultant:

Adamastor Consulting

Cathodic protection consultant:

Paradigm Projects Environmental consultant: Afzelia Health and safety agent: ORM Principal contractor: Icon Construction

Mechanical and electrical

subcontractor: Oro Projects / Electron

Mpolweni pump station

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

Pipe jacking in progress 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

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

Laying the 700 mm diameter steel pipe

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.