PROTECTING THE CAHORA BASSA HYDROPOWER PLANT
Learn how Bolina’s LSB600 is protecting the Cahora Bassa Hydropower Plant in Mozambique.
Hidroeléctrica de Cahora Bassa (HCB) is Mozambique’s pre-eminent hydropower generation company, and it is a major contributor to the country’s socio-economic growth and development. Its main focus is in extending the electricity potential of the Cahora Bassa dam – Africa’s fourth-largest artificial lake.
Located in the Tete Province of Mozambique, the lake started in the 1960s as a project of the Portuguese, with the intention of building and operating a hydroelectric generating station, along with a high-voltage direct current transmission system.
The Hidroélectrica de Cahora Bassa operated hydropower plant provides much of the power to the national grid in Mozambique and as such is a critical installation, being the largest hydroelectric scheme in Southern Africa. The water impounded behind the 170-metre-high reinforced concrete dam (which was constructed in the 1970’s) stretches an incredible 280km upstream and is subject to severe fluctuations in levels due to rainfall and other weather conditions.
As a result, the plant had been experiencing ongoing operational problems with waterborne debris overwhelming the existing boom which had been in place for a number of years and couldn’t hold the debris back. In order to overcome these issues and to increase the reliability of the installation, a new solution was urgently needed.
Therefore, the Bolina Team was approached by the client to find a solution that would benefit all stakeholders. The team initially spent time discussing the requirements with the client and analysing conditions on the lake, especially around the plant. They then proposed that a robust and reliable custom Bolina LSB600 be installed, as it would provide much better protection to the plant than the existing boom.
The LSB600 is Bolina’s Log Screen Boom developed from their highly successful Traffic Control Booms tested to over 60-tonnes. It incorporates a subsurface mesh joined together to provide a seamless barrier for logs and debris with full articulation provided between units.
The unique tubular backbone of this boom system and the Bolina lug connections make the boom immensely strong without stressing the floats, which are fully demountable with the booms designed for continuous motion and heavy loads.
A total of 380 metres of boom were shipped from the United Kingdom (UK) in containers to Cahora Bassa together with an impressive gate assembly designed by the Bolina team to match the strength of the LSB600. The gate was included to allow the passage of maintenance boats either side of the boom and was the largest that Bolina had constructed to date.
Shipping in itself was a logistical challenge to arrange the safe delivery of all the materials and fixings required to construct the boom, as spare parts would not be available locally if any were missing on arrival – it was critical that every single part arrived safely and in the shipment.
In order to ensure that assembly and installation went smoothly, one of the Bolina Field Engineers travelled to site to assist with the assembly and construction of the boom. The work was undertaken by local workers employed by the power company using readily available hand tools. The complete construction of the boom on site only took two weeks and it was then simply floated into place and secured in position, utilising the end connections from the previous boom.
The installed boom works as designed, and captures and diverts much more debris than the existing boom. This has both increased the operational efficiency of the plant and reduced the need for the maintenance team to clear debris from around the intakes.