Xhora Off-Channel Storage Dam

Xhora Off-Channel Storage Dam

Xhora Off-Channel Storage Dam provides assurance of supply to the Xhora Water Supply Scheme

Amathole District Municipality | Elliotdale - Mbhashe Municipality, Eastern Cape, South Africa | 2008-2020

109local people employed over the contract.

R 5,2 millionspent 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

TheXhora Off-Channel Storage Damprovided 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

TheXhora Off-Channel Storage Damnow 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.
25mlong ogee side channel located on the right flank with a5mwide trapezoidal spillway chute, widening to9.5mbefore entering the stilling basin.
A zoned earth fill embankment dam with a29.4high crest,230 m long.
Earthworks volume –295 000 m³.
Concrete volume12 000 m³.
Total length of grouting3 500 m.