The upcoming maintenance of the Lesotho Highlands transfer system is a routine operation, not a crisis. Jay Bhagwan and Ronnie Mckenzie demystifiy the process and reassure that Gauteng’s water supply remains secure and sustainable.
The recent announcement of the planned shutdown of the Lesotho Highlands transfer system and tunnels for maintenance has generated a fury of media attention, fueled by several alarmist opinions from various experts and panic among communities, and intertwined in this narrative is the conflation of issues.
It is true that Gauteng Province has several challenges with the sustainable supply of drinking water, related to the effectiveness of the several municipal supply systems. Compounded by power outages, that disrupt pumping and treatment of water, an integral part of the water supply systems throughout South Africa. These problems are, however, different from the management of the resource.
READ | ‘Don’t panic, but prepare,’ says Rand Water ahead of extended maintenance
Gauteng receives most of its water from the Integrated Vaal River System (IVRS), which is a complicated network of reservoirs, pipelines, and tunnels. This system is augmented by a number of large inter-basin transfer schemes, which take water from adjacent catchment areas and transfer it into various parts of the Vaal River catchment, where it is used to support the ever-growing domestic and industrial water users in the industrial powerhouse of South Africa. The largest of these is the Lesotho Highlands Water Project (LHWP).
Shutdown normal part of operations
One of the most complex and integrated water resource systems in the world, the IVRS has been owned and operated by the Department of Water and Sanitation (DWS) for the past 40 years. Rarely are the facts and science provided on this marvel to alleviate concerns, fears and ensure water supply assurance (security) at the bulk resource level.
READ | Lesotho Highlands Water Project tunnel closure: Maintenance will not affect users – water department
Looking at the proposed six-month maintenance shutdown of the tunnel from Lesotho to South Africa, members of the public need not panic. Maintenance of bulk infrastructure is normal as part of operations in the management and supply of water, and must be welcomed as a critical part of ensuring the sustainability and life span of the infrastructure.
The proposed routine maintenance has been carefully evaluated and planned by DWS to minimise disruptions and ensure that the tunnel is in good shape to accommodate the increased flow rates from Lesotho that will be brought online when the new Polihali Dam (to be built as phase 2 of the LHWP) is fully commissioned in the near future. The support of the public and users goes a long way not to elevate such normal situations to a crisis.
To alleviate some concerns, it is helpful to look at a few facts and figures on this subject.
Where does Gauteng’s water come from?
The overall net water demands from the IVRS (mainly for Gauteng) are in the order of 3 200 million m3 per annum (or approximately 8 760ml/day). These demands are supported by 14 medium to large reservoirs which operate as the IVRS, with the Vaal Dam as the main storage dam.
Based on the actual measured storage as of April 2024 (data from DWS website), the current IVRS total live storage is 10 500 million m3 (or in laymen’s terms 10 500 000ml of water) and representing 86% full capacity of which 85% comes from the five largest dams (Sterkfontein, Vaal, Katse, Bloemhof and Mohale).
The main recipient of this water, Rand Water, currently supplies approximately 1 860 million m3/year of which 780 million m3/year is supplied through the network of tunnels from Lesotho to South Africa.
READ | PROFILE: Rand Water CEO Sipho Mosai: The unheard voice amid water turmoil
It is important to note that the Lesotho transfer tunnel is able to supply around 1 200 million m3/year (around 3 300ml/day). This means that even if it is shut for six months, it will be able to transfer the full annual allocation if needed in the following eight months.
The water that would have been transferred when the tunnel is closed will not be lost, and simply held in the Katse Dam ready to be transferred as soon as the maintenance is concluded. It should be noted that the second phase of the LHWP will increase the transfer volume from Lesotho to around 1 200 million m3/year (3 280ml/day), which will be about a third of the total IVRS demand.
For the purpose of this discussion piece, it is important to note that as part of the IIVRS, inflows to Vaal Dam from which Rand Water abstracts its supply include:
- The 2 500 million m3 average natural inflow from the Vaal River;
- The 630 million m3 transfer from Woodstock Dam via Sterkfontein Dam in KwaZulu Natal which has a storage capacity of around 2 600 million m3; and
- The transfer from Lesotho.
Another popular misconception relates to the operation of the IVRS whereby water in the Vaal Dam is used before the water in Sterkfontein Dam and, to some extent, also the water from Lesotho.
The reservoirs created by the dams in Lesotho and Sterkfontein are very deep with small surface areas (about 30km2 and 70km2 respectively) and in areas of relatively high rainfall and low evaporation.
High evaporation at the Vaal Dam
In contrast, the Vaal Dam is a shallow water body with a huge surface area (over 300km2 when full), with high evaporation. To minimise evaporation losses, the DWS prioritises abstractions from Vaal Dam where possible and tries to hold the water in the Lesotho and Sterkfontein dams.
It is for this reason that Vaal Dam is often at or close to its lowest drawdown level of around 18%. At the time of writing, the live storage of the supporting dams (Katse, Mohale and Sterkfontein) were 92%, 97% and 100%, respectively, which can provide the water demand for Gauteng far beyond the scheduled six-months’ maintenance.
The current situation in the Vaal River System is healthy, in that the available live storage is around 86% of full capacity. Obviously, the situation can change depending on future rainfall and reservoir inflows. However, the system is being operated to ensure that risk of failure of water supply is minimised and restrictions will be introduced should the situation change or when we move into a severe drought.
The DWS has a responsibility to ensure that the LHWP is reliable and fit for purpose, and this includes conducting the necessary maintenance. It is expected that the current storage in Vaal Dam will be sufficient to meet demands, and any shortfall will be covered by releases from Sterkfontein Dam.
During the tunnel maintenance period, water will continue to build up in Katse and Mohale dams and will not be lost. After completion of the maintenance, it should be possible to transfer the full year’s allocation from Lesotho if required.
– Jay Bhagwan works for the Water Research Commission and Dr Ronnie Mckenzie is an Independent Consultant.
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Jay Bhagwan and Ronnie Mckenzie
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