NHPC, the contracting authority for the Nachtigal site, has announced that the Sanaga River was successfully diverted on 26 September 2022, allowing the construction consortium led by NGE and its partners BESIX and SGTM, within CCN, to take a key step on this reference site for Cameroon’s hydroelectric system.
A successful tour de force has just been achieved on the Nachtigal hydroelectric development site, with the temporay diversion of Cameroon’s longest river (918 km), the Sanaga, with a flow rate four times that of the Seine. To ensure the continuity of the work on this major project serving the country’s sustainable development, it was imperative to divert the natural course of the Sanaga River through the completed works partly upstream of the development, prior to the start of the major rainy season.
“We've been in a real race against time since July. In October the Sanaga’s flow rate rises from 1,200 to more than 3,000 m³/sec. in the space of a few weeks. Without this derivation, part of the works would have had to be ‘sacrificed’ temporarily to ensure the safety of the site” explains Jean-Baptiste de Ghellinck, Deputy General Manager of BESIX International.
As a result the main flow of the Sanaga now follows the left bank, partly through the two future dam spillways with the gates open, and partly via four temporary sluices – hydraulic openings in the reinforced concrete structures – built in anticipation of this diversion phase.
“To make this diversion a success, we set up a strong task force made up of teams from the various works departments specialised in all the areas of expertise present on the site. Activities in the diversion area involved earthworks, the placing of both rolled compacted and high performance concrete, drilling, and the electromechanical installation for the gates and the electrical grounding. The placing of the bridges also needed to be completed on time to ensure logistics continuity at the dam site. All this necessarily accompanied by geological inspections, quality control and the installation of the testing system needed to guarantee the conformity of the work” continues Jean-Baptiste de Ghellinck.
This diversion will make it possible to dry out another part of the site in order to allow the main dam wall to progress towards the right bank.
“The success of this important milestone allows us to look calmly towards the continuation of work on the dam, the channel and the hydroelectric plant. Our next challenge is now to start the impoundment of the channel during the month of March 2023. A new goal for the entire team!” concludes Jean-Baptiste de Ghellinck.
With an installed capacity of 420 MW, the Nachtigal hydroelectric development will produce, once commissioned in 2024, 30% of the country's energy production capacity. Progress on the site to date is 70%.