Xhora Off-Channel Storage Dam
Xhora Off-Channel Storage Dam provides assurance of supply to the Xhora Water Supply Scheme
Amathole District Municipality
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Elliotdale - Mbhashe Municipality, Eastern Cape, South Africa
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2008-2020
109 local people employed over the contract.
R 5,2 million spent on local wages and local contractors.
Earthworks volume
295 000 m3.
Concrete volume
12 000 m3.
Challenges
- The Xhora Off-Channel Storage Dam provides assurance of supply to the Xhora Water Supply Scheme which is intended to provide potable water to 70 000 people.
- Environmental impacts on the surrounding rivers and streams were to be minimised.
- A shortage of suitable embankment materials required innovative solutions.
- The water in the dam is expensive as it was pumped so minimum leakage was required.
Solutions
- The Xhora Off-Channel Storage Dam provided the required assurance of supply with the minimum impact on the environment.
- The in stream flow requirements of both the stream below the off-channel storage dam and the Xhora River required care in the design of the raw water abstraction to provide for the maintenance of the low flows.
- Maximum use was made of the materials from the basin, which required a project specific density test method to be developed.
- To reduce leakage a low permeability grout curtain was required, which required an innovative approach.
Highlights
- The Xhora Off-Channel Storage Dam now provides the assurance of water supply to 70 000 people who have never previously had potable water.
- This solution was able to minimize the environmental impacts of a new dam.
- To ensure a low permeability foundation, grouting of the shales and mudstones below the core to 2 lugeon reduced the dam leakage.
- A novel grouting approach was utilized to increase the grouting pressure.
The project has been awarded a commendation in the Technical Excellence Project category at the SANRAL SAICE National Awards 2021 in South Africa.
Project numbers
R 112 million, excl VAT - Capital value of the project.25m long ogee side channel located on the right flank with a 5m wide trapezoidal spillway chute, widening to 9.5m before entering the stilling basin.
A zoned earth fill embankment dam with a 29.4 high crest, 230 m long.
Earthworks volume – 295 000 m3.
Concrete volume 12 000 m3.
Total length of grouting 3 500 m.