Engineering Geology for the Snowy Mountains Scheme
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Fig 11.—Kosciusko Dam Site, Spencer—s Creek
Kosciusko Dam Sites.
—The sites being investigated for the proposed Kosciusko Dam on Spencer’s Creek, a tributary of the upper Snowy River, are in considerable contrast to those already described. This region, above 5,600 feet above sea-level, is within the area affected by the first and second stages of the Pleistocene glaciations. Upper Spencer’s Creek and tributaries occupy broad flat-bottomed valleys shaped by valley glaciers of the second stage of glaciation. A large terminal moraine, the David Moraine, lies across the valley of Spencer’s Creek, rising 150 feet above creek level near where the road to the Kosciusko summit crosses the creek. This moraine dammed the creek which eventually broke through at one end of the moraine, through a comparatively narrow gap.
This constriction in the otherwise wide valley of Spencer's Creek appears on surface topography to be an attractive site for a dam to the height of about 90 feet, with a good storage basin in the wide glaciated valleys upstream. Conditions at the site (Site 2) as shown by geological mapping, exploration by seismic refraction, drilling and trenching, are shown on Fig. 11. The right abutment consists of granite in situ weathered to shallow depths. The granite bedrock slopes gradually downwards under the creek bed to a maximum depth of about 300 feet under the centre of the David Moraine, which forms the left abutment of the site, before rising. The granite represents the glaciated valley floor later buried under moraine.
