The Department of Water and Sanitation (DWS) is currently moving ahead with the implementation of the proposed conjunctive Ntabelanga–Lalini scheme, an important component of the KwaZulu-Natal-based Mzimvubu water project.
Engineering and environmental consulting company Jeffares & Green (J&G) highlights this as the first fully conjunctive scheme of its kind in South Africa which, by its nature, will ensure project sustainability and economic benefits for the region.
The project comprises two multipurpose dams, Ntabelanga and Lalini, on the Tsitsa river and a major tributary to the Mzimvubu river. The two dams will be built and operated simultaneously as one integrated scheme to make the scheme sustainable throughout its useful life. The scheme will be built as the first phase of a much broader programme for the development of the Mzimvubu river catchment, which will be phased in over time.
J&G undertook water supply yield and hydropower potential modelling for both dams, taking into account what they would yield when operated individually and when used simultaneously. The firm’s investigations considered a range of capacities, from the smallest feasible capacity to the largest possible feasible capacity within the practical imitations of the terrain. In each case, J&G took into account the allowance required for the volume of sediment that would be trapped over the operational life of the dam.
The Ntabelanga dam will be used primarily for domestic and agricultural water supply requirements, while the Lalini dam will be used for hydropower generation. A mini hydropower plant will also be built at the Ntabelanga dam to recover more energy from the ongoing environmental flow releases.
Although the Ntabelanga site scored highest with regard to the number of people who could be supplied with potable water within a viable range of the dam, it was evident that it could not generate significant hydropower when operated independently. Lalini dam, which is about 77 km downstream of the Ntabelanga site, scored high on hydropower potential but low on water requirements and irrigation potential.
Therefore, given that the objective of the project was to maximise the economic development potential of the scheme, an investigation into a second dam at Lalini was incorporated into the feasibility study conducted by J&G.
The conjunctive Ntabelanga–Lalini scheme will offer potable water supply to over 700 000 people by the year 2050 and the irrigation of up to 2 868 ha of high-potential land. It will also create about 5 000 jobs, generate some 200 000 MWh/y at an average output of 24 MW and a peak of 47.5 MW.
In addition to meeting all the operating and maintenance costs of the conjunctive scheme, surplus funds generated by green energy sales revenue could, at the discretion of the DWS and the National Treasury, also be used to repay grants or loans granted to implement the scheme, or used to finance other regional economic development initiatives.
About the Mzimvubu Water Project
South African President Jacob Zuma officiated at the Mzimvubu water project launch and sod-turning ceremony in mid-April; the project is valued at R12.5-billion.
The project, which is an integrated multi- purpose project that includes domestic and agricultural water supply, as well as power generation, transport, tourism and conservation initiatives, has been classified as a strategic integrated project to fast-track it as a priority for implementation.
Zuma commented on the multi-purpose economic benefits of the scheme, which has the potential to create thousands of job opportunities.
He also highlighted that selling hydropower to the regional grid would be a significant source of revenue for the area, and that this revenue could be used to cross-subsidise the energy, operating and maintenance costs of the potable and irrigation water supply schemes supplied by the Ntabelanga dam.
The Mzimvubu river, one of South Africa’s largest rivers, meanders through the barren countryside of the Eastern Cape for about 400 km, until it flows into an estuary at Port St Johns and finally into the Indian Ocean. These waters will help transform the province from one of the least-developed regions in the country to a place of socioeconomic opportunity.
Jeffares and Green
Following a national competitive bidding process in 2012, J&G was awarded the contract to conduct the feasibility study on the Mzimvubu river project.
J&G’s water and dams engineering, geotechnical and hydrology divisions undertook a detailed feasibility study to identify a potential site for the multipurpose dam. The first requirement – Phase 1 – was to investigate and analyse the 19 potential dam development sites that had been identified in previous studies and cut them down to the three most promising sites for meeting the specific requirements of domestic water supply, irrigated agriculture and hydropower. The three options for the dam site then underwent more detailed investigations, which included geotechnical investigations, before recommendations could be made and an agreement reached – with all relevant stakeholders – on which single dam site should undergo a detailed feasibility study in Phase 2.
J&G’s studies were comprehensive and involved various topographical surveys and geotechnical investigations, including investigations into the agricultural and domestic water supply requirements up to 2050 and beyond.
Phase 2, which began in May 2013 and was completed in April 2014, involved a detailed feasibility study of the Ntabelanga site, on the Tsitsa river, which Phase 1 findings recommended as the preferred option for the development of the multipurpose dam.