Awarded by the Nigerian FEC (Federal Executive Council) in March 2011, to Coyne et Bellier – the Hydro division of Tractebel Engineering (France), the contract for the design and works supervision of the Mambilla HPP (2600 MW) is a first step towards realising a scheme that will more than double Nigeria’s current installed hydro capacity in one go!
A long term investment of this scale needs careful thought and exceptional planning. Taking advantage of the unique topographical and hydrological characteristics of the site – about 600 km from the capital city Abuja, in a very remote part of the country on the Mambilla plateau where the Donga River flows from its source – many technical and economic design alternatives have been considered; allowing the client to review all options when making their decisions.
The concept, with the goal of achieving, at the very least, the 2600 MW target is to use the drop of +/-1000 m from the Mambilla plateau to the plain below to maximise the full potential of the Donga River…
MAMBILLA – KEY DESIGN ELEMENTS
■ A main, large rolled compact concrete (RCC) dam and reservoir (storing water and thus regulating river flow) at 1300 m above sea level – Gembu Dam.
■ Water is also diverted off the reservoir towards the western side of the plateau through 3 hydraulic tunnels totalling 33 km intercepted by 2 smaller RCC dams, both at an elevation of 1250 m – Sum Sum Dam and Nghu Dam.
■ Beyond these dams, the tunnels lead into a 1000 m drop shaft tunnelled down through the rock to a massive underground powerhouse. Via a short tunnel, the water then exits the base of the plateau and flows into a tributary river that rejoins the Donga River downstream of the plateau.
THE CORE OF THE DESIGN CHALLENGE
The design complexity is primarily the development of the underground works; viable due to the age and the stability of the plateau rock.
Sébastien Lacroix: Besides the 3 water conveyance tunnels needed due to the undulating surface of the plateau and the 1000 m drop pressure shafts, there’s the challenge of the underground powerhouse. Considering the size and space of a powerhouse (200 m x 30 m x 40 m high), this will be like excavating a small underground cathedral!
We have experience in realising such works (Dul Hasti HPP in India, Berke HPP in Turkey, Cirata HPP in Indonesia), but it often helps to see the simplicity of the final product to appreciate its workability – how it is accessed, the working conditions inside, the safety… We plan to take client representatives to see a similar underground powerhouse at Dinorwig Power Station in the UK (owned by First Hydro Company, a subsidiary of IPR-GDF SUEZ), as it also has a Pump Storage solution which could also be interesting for Mambilla.
Tractebel Engineering (France – Coyne et Bellier) has been involved in the design and construction of Hydro projects and on the rehabilitation of hydropower plants in Nigeria for almost 15 years. With the goal always being to find the best solutions possible to meet the Nigerians’ needs, a project like Mambilla not only allows us to stretch our technical creativity to the full as engineers; it also allows us to bring real added value to the project for the client.
NEW DAM FOR BRAZIL
Tractebel Engineering (Brazil) has signed recently a major contract for the Environmental studies for Belo Monte Dam in Brazil with developers Norte Energia, a consortium led by Electrobras. The Belo Monte Dam complex is on the Xingu River in the Amazonian state of Pará. The planned installed capacity will be 11,233 MW, which will make it the second-largest hydroelectric dam complex in Brazil and the world’s third-largest in installed capacity, behind the Three Gorges Dam in China and the Brazilian-Paraguayan Itaipú Dam. Construction of Belo Monte started in 2011 and will take at least 3 to 4 years to complete.
Visit Tractebel-engineering-gdfsuez.com for more references