April 2021 Vol. 76 No. 4
Features
Pandemic Puts Hold on Southern Africa’s Water Tunnel Projects
By Shem Oirere, Contributing Editor
As the COVID-19 pandemic’s unpredictable trend causes cancellation or delay of infrastructure projects globally, South Africa and its neighbor Lesotho are grappling with disruption of the second phase of the $1.5-billion Lesotho Highlands Water Project (LHWP), Africa’s largest water transfer scheme.
The project is diverting water from the Senqu River system in Lesotho to South Africa’s Vaal River system, which supports 50 to 60 percent of South Africa’s economy. LWHP entails the construction of at least five dams and nearly 125 miles of water transfer and delivery tunnels in five phases.
The bi-national, inter-basin water transfer project, which is being implemented by Lesotho Highlands Development Authority (LHDA) and Trans-Caledon Tunnel Authority (TCTA) in South Africa, was set to enter its second phase in 2020. Advance works were launched during the first quarter, just as the COVID-19 pandemic broke out.
According to TCTA’s CEO Percy Sechemane, “agreements on funding still need to be concluded” for the project and he warns “the advent of COVID-19 in the current and future years are likely to prove even more challenging.”
Phase II of LHWP entails construction of the 540-foot high concrete faced rock fill Polihali Dam, with a capacity of 2.2 billion cubic meters of water.
The dam is to be connected with the 27.3-mile water transfer tunnel to Katse Dam that was completed under Phase 1A in 1998. It has a height of 607 feet, storage capacity of 1,950 million cubic meters of water and spillway discharge of 6,252 cubic meters per second.
However, before the construction of the Polihali Dam, two water tunnels have to be excavated to divert the waters of Senqu River, where the dam is located, away from the natural riverbed.
“This will create a dry foundation to facilitate the construction of the Polihali Dam,” said a project brief by LHDA. The two tunnels will increase the capacity to carry floods and provide flexibility to work in one tunnel while the river flows in the other one.
Tunnel specs
The first tunnel is about 0.6 miles long with a diameter of almost 23 feet, while the second also runs for 3,281 feet and is 29.5 feet wide. Both tunnels run parallel to each other from the intake point upstream to the outlet downstream of the Polihali Dam.
Although concrete casting and reinforcement of the diversion tunnels, initially slated to take 18 months from contract signing date, was scheduled to start in the first quarter of 2020, LHDA reported in June 2020 the works were disrupted by the COVID-19 outbreak.
“Full resumption of the Phase II advance infrastructure construction works and the Project’s social and environmental programmes will be incremental as consultants and contractors meet their Covid-19 mitigation obligations and travel restrictions are lifted,” said LHDA CEO Tente Tente in a June 2020 statement.
No further updates have been given on new deadlines for the diversion tunnels. However, LHDA had earlier said such construction “usually goes along with the building of cofferdam, one upstream and one downstream of the proposed dam, which together allow the river flow to bypass the dam foundation area.”
Construction of both river diversion tunnels will use the drilling and blasting method “supported by rock bolts and shotcrete as required,” according to LHDA.
In April 2019, the SCLC Polihali Diversion Tunnel Joint Venture had been awarded the $34-million contract for the construction of the tunnels. JV members include Salini Impregilo SpA (South Africa), Cooperative Muratori Cementristri CMC di Ravenna (South Africa), LSP Construction (Pty) Ltd (Lesotho) and CML Infrastructure Ltd (South Africa).
The two tunnels have been designed and will be supervised during construction by Metsi Senqu Khubelu Consultants JV comprising South African firms Aurecon, Knight Piesold, Hatch Goba, SMEC and FM Associates of Lesoth. They are part of a long network of water transfer and diversion tunnels meant to deliver nearly 70 cubic meters of water per a second to South Africa’s water-stressed areas, such as Gauteng province.
During Phase 1A of the LWHP, a 30-mile long tunnel was constructed to transfer water from the Katse Dam. It was during Phase 1A that the underground Muela Hydropower Station in Lesotho was constructed. Water being transferred to South Africa is used to power the Muela station.
Furthermore, another 23-mile long tunnel was constructed to deliver water from the Muela reservoir to South Africa’s Ash River that flows into Vaal Dam.
Feasibility
According to a previous feasibility study by Lesotho Highlands Water Commission, which monitors the implementation of LWHP, the Muela reservoir transfer tunnel “has sufficient capacity to transfer the required water until at least 2048.
“The Muela Dam will not require any modification but raising the dam and upgrading the delivery tunnel are future options that will increase the hydraulic capacity of the delivery tunnel required,” said the study.
An additional 20 miles of interconnecting concrete transfer tunnel, with an 11-foot diameter, was constructed during Phase 1B to move water from the Mohale rockfill dam on the Senqunyane River to Katse Dam.
In the delayed Phase II of LHWP, a 23.7-mile gravity water transfer tunnel will be constructed to connect the new Polihali Dam. According to an initial project schedule by LHDA, its design commenced in mid-January 2018 and was set for completion in 2019, before construction commences in 2020 for at least six years. The schedule is most likely disrupted by the COVID-19 outbreak.
When Phase II is successfully completed, the water supply to South Africa from Lesotho will incrementally rise from 780 cubic meters annually to 1270 cubic meters. No specific time has been given as to when this target would be achieved.
The additional phases III and IV involve construction of the Tsoelike Dam at the confluence of Tsoelike and Senqu Rivers, with storage capacity of 2,223 million cubic meters of water, and the Ntoahae Dam, nearly 25 miles downstream of Tsoelike Dam.
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