7 minute read
The Lower Thukela Bulk Water Supply Scheme
Established by Umgeni Water, the Lower Thukela Bulk Water Supply Scheme meets the water security needs of iLembe District Municipality. Working alongside a multidisciplinary team, Zutari (formerly Aurecon) was responsible for the scheme’s design and the provision of procurement documentation on this fastpaced project worth over R1.6 billion.
The serene and majestic Tugela Falls in the Drakensberg belie the immense power and scale of the downstream river when flooding in season. A river that is clear and green in winter changes into a raging, sediment-laden torrent in summer. For this reason, the transformation of this temperamental river into a reliable water source required a highly innovative engineered solution.
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The Lower Thukela Bulk Water Supply Scheme was conceived after Umgeni Water, in 2008, became a bulk water provider to areas of iLembe District Municipality that had not previously been served by the utility (north of Stanger). At the time, the demand for potable water in these areas exceeded the available water resource.
Feasibility study The groundwork for a project of this scale is enormous and commenced in 2009 when Zutari was appointed to undertake the detailed feasibility study to identify the position for an abstraction works, water treatment works (WTW), the associated bulk pipelines and command reservoirs.
After numerous collaborative workshops and design iterations, the design team conceived a scheme capable of achieving the required 98% assurance of supply – a non-negotiable
Client
Umgeni Water
Contractors
Group Five (abstraction works) Stefanutti Stocks Coastal (water treatment works) Veolia Water Solutions (equipping of abstraction works and water treatment works) Group Five (30 Mℓ reservoir and 900 mm diameter pipelines) Esor Franki (900 mm diameter pipelines)
Professional team
Zutari (all engineering design services) Bigen (contract administration) Madan Singh & Associates (contract administration) Alex Stewart and Partners (architect) Bright Blue Designs (landscaping design)
An aerial perspective of the WTW site under construction (Credit: Group 5)
client requirement – and being constructed within a short timeframe. The design team drew on a diverse range of professionals to ensure that all aspects were considered, and all possible scenarios and options explored.
Full life-cycle costing formed part of the feasibility study and influenced the choice of location and design. Once the final scheme design had been approved by the client, the green light for implementation was received.
Project details The project involved the design and construction of a new weir, abstraction works, a 55 Mℓ/day WTW, a low- and high-lift pump station, a 30 Mℓ command reservoir plus 30 km of 900 mm diameter pipelines. To ensure effective coordination and implementation, delegation of responsibility was carefully managed. The critical risks and responsibilities were accounted for and well coordinated – from the abstraction works, which required the actual diversion of the Thukela River to the multidisciplinary WTW to the large-diameter bulk pipelines. In the end, expert project management was a major factor in ensuring that the scheme was successfully completed.
Construction started in 2013 and the WTW was finally commissioned in July 2018. The commissioning process was undertaken jointly by the contractors – Bigen Africa (contract management), Zutari (commissioning support) and Umgeni Water. Environment and community Many environmental approvals were required for different aspects of the project, and landowner negotiations were required in certain areas. Each technical lead was tasked with managing their own regulatory approvals, legal matters and landowner negotiations.
The landscaping of the site, which is naturally beautiful and culturally significant, was carefully considered. Local vegetation was propagated to ensure that the site blended with the surroundings. Furthermore, the riverine ecosystem requirements were carefully considered in the design of the weir across the river to accommodate a range of aquatic life, from crabs and fish to crocodiles.
Treated water is pumped to a 30 Mℓ command reservoir from where it is distributed through a 30 km long DN 900 steel pipeline with various offtakes along the pipeline to end-users (Credit: Group 5)
The process control building layout (Credit: Bigen)
The WTW also sits on land that was used as pasture for local livestock. The initial WTW design would have bisected the land and limited access. This was reconsidered so that local pastoralists have accessibility across the land surrounding the WTW. Wherever possible, the project team also reused in situ materials.
Apart from spending over R1.6 billion on infrastructure development, there were also social benefits in terms of skills development and local employment. During the project, numerous small contractors were used, and local labourers were employed from the nearby communities, many of whom received training and skills development. Significant expenditure on water education for the beneficiary communities was also undertaken.
More than 550 000 people are expected to benefit from the programme, with consumers ranging from the rural indigent to private developers of commercial, industrial and residential projects in this rapidly expanding northern KwaZulu-Natal region.
Operator-centric One of the distinctive features of the WTW is the operator-centric design approach adopted in collaboration with the client’s representatives. This ensured the WTW was perfected for the ultimate end-user: the plant’s operators.
The plant was laid out to simplify the route that operators would be expected to cover on scheduled rounds (as opposed to simply providing access to areas of the plant based on the immediate engineering constraints). This route was further optimised by rationalising the need to use stairs and keeping wet and hazardous chemical areas separate from a ‘clean’ dosing hall, where dose rates can be checked and controlled. The plant’s layout also gave the laboratory and the control room – the operational core of the facility – direct sight over the core processes of the treatment works.
Process flow The abstraction works from the Lower Thukela River provides a steady supply of water throughout the year, while removing as much of the sediment load from the water as possible. The abstracted water is then pumped up to the WTW. The assurance of supply is achieved by the provision of a weir across the river to direct flow to the abstraction works, even during low-flow conditions. Thanks to the purpose-built design, the water will continually scour the riverbed to maintain a channel to the abstraction works. The removal of sediment is achieved through a sequence of boulder, gravel and sand traps.
To further remove solid particles from the water, the WTW uses three stages of sedimentation. This reduces the environmental impact of disposing of large quantities of waste silt. Additionally, the flexible water treatment design accommodates seasonal variance in terms of raw water characteristics and can be optimally managed to reduce chemical consumption and associated costs.
Present-day operations and long-term demand At present, the scheme is producing and selling in the order of 28 Mℓ/day to 30 Mℓ/day of water to iLembe District Municipality. In the case of the Lower Thukela Bulk Water Supply Scheme, longer-term demand was built into the design, such that the abstraction works and WTW are readily upgradeable to 110 Mℓ/day. Umgeni Water is currently busy with the planning for the extension of the WTW to 110 Mℓ/day, with planned supply to Mandini and King Cetshwayo District Municipality to the north of the Thukela River.
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