SA engineering firm wins Nacala dam rehabilitation contract - Engineering News , 26 June 2009
Consulting engineering company Jeffares & Green (J&G) has signed a $2,7- million contract with the government of Mozambique to carry out rehabilitation on Nacala dam, the main source of water for Nampula province.
The contract includes augmentation of the capacity of the dam to 21-million cubic metres, benefiting around 70% of the population in the Nacala area. At this time, the dam has a capacity of 14-million cubic metres of water and supplies only 20% of the population.
State of Disrepair
The Nacala dam is in a state of disrepair, and the reduction of the water level since 2005 has seen a portion of the local population relying on cisterns.
Work on the dam is expected to cost $11,7- million, expanding the Nacala water supply system will cost a further $10-million and reconstruction of the wastewater collection system will cost another $17,2-million.
J&G will be assisted on the project by two main subcontractors, Lamont (Zimbabwe) and Conseng (Mozambique). The hydrology, geotechnical engineering and environmental services will be undertaken by Terratest, a specialist associated company of J&G.
“The project will investigate several key aspects and the first will be to determine the current condition of the dam to check its safety factors,” says J&G director Andy Pepperell.
The second will be to raise the dam capacity so as to increase its yield and to provide additional water for environmental purposes, and the third will be to redesign and reconstruct the dam spillway to ensure that it is fully compliant with international dam safety requirements.
The feasibility study starts this month and construction is expected to begin at the end of 2010.
Meanwhile, the company reports that an important milestone has been reached in the construction of the Dikgathlong dam, a project of the Botswana Department of Water Affairs, for diversion of the flow of the Shashe river so that the dam wall can be built through the dry riverbed during the winter season. The dam has been under construction for just under a year.
J&G is also the design and technical consul- tant on the Dikgathlong dam project, in a joint venture with Bergstan & Gauff.
“A core trench excavation through a section of the Shashe river started at the beginning of May. A diversion conduit has been successfully installed and runs parallel to, but bypasses, the river channel. This carries the dry-weather flow around the dam wall excavation,” says J&G site representative Tom Spiers.
The diversion has now been put into use by closing the upstream and downstream coffer dams, and the contractor is excavating the core trench through the now dry riverbed section. The aim is to bring the main clay core up to riverbed level by the end of the dry season, after which it will be suitably protected to allow the river to again flow along its natural course during the wet season.
At a cost of two-billion Botswana pula (about $300-million), provided by the Botswana govern- ment, the dam will not only be the largest source of water supply in Botswana but will also be used to establish and operate a new coal mine and a 3 600-MW power station at Mmamabula, about 130 km north of Gaborone.
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