Lesotho Highlands Water Project

The Lesotho Highlands Water Project is a water and electrical power supply project implemented by the governments of Lesotho and South Africa to find new sources of supply to support development in both countries. This major undertaking is the largest water-transfer project ever launched in Africa. Our consortium was in charge of part of the project. Our work package included building hydraulic conduits 65 kilometres in total length and 5 metres in diameter, two water intake structures with siphons, and several shafts and installing a surge chamber.

Background

Since the early 1950s, the governments of the ten Basotuland and Union of South Africa protectorates had studied the possibility of diverting the waters of the Orange River in Lesotho into the Vaal River nearby. Subsequently, the growth of metropolitan centres in the area caused a sharp increase in the demand for water. In 1978, both countries decided to launch a joint feasibility study. The study, which assessed more than 2,000 variants for several alternative options, recommended a four-phase, 25-year construction project to keep pace with the rising need for water in South Africa.
This development project in the Lesotho Highlands included the construction of five dams and a dual tunnel more than 200 kilometres long designed to supply 70 m3/s of water to the Vaal River in South Africa. Our consortium was entrusted with several activities in the initial phase of this major project.

Technical overview

In the first phase of the Lesotho Highlands Water Project, we were in charge of building the Katse Dam. This initial structure was designed to deliver 18 m3/s of water and produce 72 megawatts of electrical power.
To be more specific, our achievements on this project include the construction of an intake tower in the Katse Dam reservoir that is 25 metres in diameter and 90 metres high, a 120-metre access bridge, a 45-kilometre transfer tunnel 5 metres in diameter built in three segments (Katse, Lotse and Muela), a 13-kilometre distribution tunnel 5 metres in diameter, with two siphon passageways under the Hololo and Ngoajane Rivers.
In addition, we were in charge of building seven access galleries to the main tunnels (lengths ranging from 200 to 2,000 metres, sections from 26 to 39 square metres) and ten ventilation shafts including five ventilation shafts for the transfer tunnel of an excavation diameter of 2.13 metres and depths ranging from 90 to 315 metres, excavated using a raise borer, and five ventilation shafts for the distribution tunnel of an excavation diameter of 30 centimetres and depths ranging from 58 to 118 metres, also excavated with a raise borer.

The south and north transfer tunnels convey water from the Katse Dam to the hydroelectric power plant in Muela. The water restored by the Muela plant is then sent to the border with South Africa through the south distribution tunnel.

IMPACT

Lesotho is a mountainous country landlocked within South Africa that receives abundant rainfall: more than 1,000 millimetres in the Highlands, resulting in a flow of about 150 m3/s in the Senqu River.
Despite this level of precipitation, neighbouring areas in South Africa face water shortages. Since the Pretoria-Wiwaterstand-Vareeniging (PWV) complex accounts for about 60% of South Africa industrial production, the people in this region were compelled to find other sources of water to support regional development.
We were in charge of part of the hydraulic project that will allow Lesotho to develop water-supply and irrigation programs as well as regional development schemes. The project will allow the country to make strides toward self-sufficiency since it imports 98% of its energy from South Africa. Furthermore, hydroelectric power production in Lesotho is considered to be the most appropriate energy source for this country.

Project participants

Client
Lesotho Highlands Development Authority

Project management
Lesotho Highlands Development Authority

Key figures

Implementation dates
February 1991 to October 1997    

Underground excavations
1.5 million m3

Concrete
358,650 m3

Improving the supply of drinking water

Faisalabad

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