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Stortemelk Hydropower Station

Civil and Mechanical Erection 4,2MW

For a video overview of this project, courtesy of Aurecon, click here

Project Value: R 54,850,491.00

Client: Stortemelk Hydro

Completion Date: 2016

Consulting Engineer: Aurecon

Developer: REH Project Development

Main Contractor: Eigenbau (Pty) Ltd



The Stortemelk hydro power plant has been developed as a greenfield project by REH Project Development (formerly NuPlanet Project Development). The plant has an installed capacity of 4.5 MW and operates as a run-of-river power station with an annual output of 28GWh.

A single vertical Kaplan turbine is installed in a powerhouse alongside the existing Botterkloof Dam, situated on the As river in the Free State province of South Africa. The design provides a compact solution for the turbine, optimising the short penstock route while avoiding any adverse impact on existing structures, as the power station was constructed between two existing dams without affecting their operations and stability.

The project was awarded Preferred Bidder status under Bid Window 2 of the South African Renewable Energy Independent Power Producer Procurement (REIPPP) Programme and commenced construction in August 2014.

The project was implemented under an engineering, procurement and construction management (EPCM) structure with contracts being awarded to:

  • Andritz Hydro GmbH and Indar Electrical SL for the plant’s turbine, generator and switchgear.
  • Aurecon South Africa (Pty) Ltd for engineering, procurement and construction management (EPCM) services.
  • Eigenbau (Pty) Ltd for civil works construction including
    • All civil and building works including access roads.
    • Installing the hydro-mechanical equipment.
    • Electrical in the power in the power station.
    • Water filtration plant.



Arial view of the construction of Stortemelk


The power station had to be constructed between the spillway of the existing Botterkloof dam wall and spillway and the Boston A Dam spillway without affecting their operations and stability. This required deep excavations in very difficult working conditions.

The sides of the excavation had to be stabilised with soil nails and gunite to ensure that the works could be constructed safely.

Deep excavation of the power station

Outlet draft tube installation


The power station is of conventional design and was constructed in reinforced concrete with a structural steel superstructure. The walls were cast directly against the sides of the excavation anchoring the power station and ensuring that floods will not cause flotation of the structure. The transition section from square to round of the draft tube upstream of the turbine was formed with a purpose made shutter. The draft tube downstream of the turbine was fabricated by the turbine supplier and placed and cast in position by Eigenbau. The steel was later sandblasted to specification and the corrosion protection coating applied.

The superstructure supports two 30 ton overhead cranes. The roof is cromadek IBR sheeting and the side walls are clad with clear polycarbonate sheets and covered with an outer skin of corten (rusted steel) sheeting. This allows the structure to blend in to the surroundings to create a non-traditional power plant that blends in with its environment and causes minimum visual impact. The project was recently honored with an architectural design award.

Construction on the project started in September 2014, and it has been contributing energy to the grid since 28 July 2016.

The smooth start-up and successful operations of the Stortemelk plant is testimony to a project well executed. The team from Eigenbau are proud of their achievement.