The Lomati and Komati Rivers in the eastern lowveld of the southern African region fall under the Komati Basin Water Authority, a bi-national agency created by South Africa and Swaziland. This agency regulates the supply of water to the adjacent communities and extensive agricultural lands of both countries. Maguga Dam is the largest component in the system, located in a mountainous area 12 km south of Piggs Peak on the Komati River.
The structure is a 115 m high clay-core rockfill embankment dam, constructed between 1998 to 2002 with a hydropower development following shortly thereafter.
Three separate tender designs were prepared by the consultant JV, in which Aurecon assumed a leading role in both design and project management.
Furthermore, a detailed geotechnical site investigation was undertaken by Aurecon to supplement data from feasibility studies. After consideration of technical and cost factors, a rockfill embankment was selected as the most suitable construction method.
An innovative design feature included a curved ungated labyrinth spillway (one of the largest of its type in the world) that enabled the full width of the spillway to be reduced from 460 m to 181 m. From there, a 310 m long concrete-lined chute ends in a 100 m wide deflector bucket discharging into a 40 m deep plunge pool. A physical model study proved that the PMF of 15 000 m3/s can be accommodated within its 8.3 m freeboard.
Materials for the 3 million m3 embankment were obtained from quarry and borrow areas within the reservoir basin and from essential spillway excavations.
A full environmental impact assessment (EIA) was carried out and a comprehensive mitigation plan (CMP) was strictly followed to minimise the adverse effects of construction on the surrounding physical and social environment.