Lesotho Highlands Water Project

Lesotho Highlands Water Project Phase 2, Kingdom of Lesotho

Double

breakthrough

for

Polihali

Dam

Diversion

Tunnel

The Lesotho Highlands Water Project (LHWP) comprises a system of several large dams and tunnels throughout Lesotho, which delivers water to the Gauteng region of South Africa via the Vaal River System. It is the largest water transfer scheme in Africa.

SMEC South Africa is a member of the Metsi a Senqu-Khubelu Consultants Joint Venture, appointed to design the tunnels for Phase II and lead construction supervision. Phase II will increase the current water transfer rate of 780 million cubic metres per annum incrementally to more than 1,270 million cubic metres per annum. At the same time, the quantity of electricity generated at the Muela hydropower station will exceed 500GWh per year and is a further step in the process of securing an independent electricity source to meet Lesotho’s domestic requirements.

Polihali Dam

In August 2021, Lesotho Highlands Development Authority (LHDA) celebrated a significant milestone in the construction of Phase II of LHWP with the double breakthrough of the projects two diversion tunnels. The breakthrough marked the completion of 1,870m of tunnel excavation. The 7m and 9m diameter tunnels were excavated by both drill and blast method and achieved the breakthrough on the same day.

The diversion tunnels will enable dry zones for the construction of the Polihali Dam, to ensure the site is uninterrupted by the river flow. The construction methodology incorporated concrete intake structures and a range of concrete lining methods. The team used shotcrete, in-situ reinforced concrete and invert concrete lining to optimise the process. The delivery team overcame challenges such as the COVID-19 pandemic, harsh weather conditions and flooding of the Senqu River which affected the construction site in January 2021.

Katse Dam

SMEC is also working on the Polihali Transfer Tunnel contract, which involves the design and construction supervision of the 38km long water transfer tunnel from the planned Polihali Dam to the existing Katse Dam. The tunnel is to be largely excavated by tunnel boring machine but also includes significant lengths of drill and blast tunnelling. The scope incorporates two gate shafts which will be used to manage future operations. Each gate shaft will include stoplogs, gates, dewatering pumps and filling valves. A notable technical feature of the project is the Katse lake tap, where the tunnel is designed to be excavated into a dam basin below water level. Construction of the 38km section of tunnel is expected to commence mid-2022.

Client

Lesotho Highlands Development Authority (LHDA)

Location

Kingdom of Lesotho

Expertise

Tunnels Water Resources Hydropower & Dams Construction Phase Services

1870

of tunnel excavation

1270

million

cubic metres per annum

500