Copeton Dam
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Copeton Dam is a 113 metres high, earth and rock fill embankment dam on the Gwydir River near Inverell, New South Wales, Australia. The dam was built by the New South Wales Department of Water Resources to supply water for irrigation and was completed in 1976. Unexpected erosion of hard, sound, unweathered granite in the unlined spillway discharge channel was caused by rock failure under high in-situ compressive stress. This type of erosion due to high in-situ stress has not been reported elsewhere in the world.
Remedial works involved building a training wall to separate the original single spillway into a service spillway and a secondary (emergency) spillway. A concrete slab, anchored to the underlying rock was constructed in the floor of the main scour channel to provide some additional protection on those rare occasions when the secondary spillway will discharge water over this area. The smaller, more frequent flood events will be discharged through the service spillway onto more scour resistant rock which has performed satisfactorily to date. The secondary spillway will operate very infrequently and will only discharge when the capacity of the service spillway is exceeded.
Geological investigations for the design of these remedial works included surface stress measurements in the unlined spillway discharge channel as well as geological mapping and diamond core drilling.
