Clarrie Hall Dam
Clarrie Hall Dam is located on Doon Doon Creek - a tributary of the South Arm of the Tweed River, some 15 kilometres south-west of Murwillumbah. The dam was designed and constructed by the then NSW Department of Public Works for Tweed Shire Council and was completed in 1983.
The primary function of the dam it to provide storage of water for Tweed Shire's drinking water supply. The dam has a catchment area of 60 square kilometres and a usable storage capacity of 15,000ML. When required, water is released from the Dam’s intake tower and flows down the Tweed River. From there water for the Tweed region’s drinking water supply is drawn off and treated at Bray Park water treatment plant.
Clarrie Hall Dam consists of a concrete faced rockfill embankment, a concrete lined spillway, intake and outlet works constructed on a foundation of very hard/strong rhyolite rock (of volcanic origin).
The rockfill embankment has a height of 43 metres, crest length of 175 metres and a volume of about 160,000 cubic metres. The crest width is 6 metres, the upstream and downstream slopes 1V to 1.3H. The upstream slope is covered by a 300mm thick concrete face slab which connects at the top to a wave wall along the embankment crest. The bottom of the face slab is tied to the embankment's upstream concrete toe slab which also acts as the grout cap. A grout curtain comprising a single line of holes is located under the slab.
The embankment is constructed from hard rhyolite rockfill which is free draining except for a 4m wide semi-permeable zone located immediately underneath the upstream face. Seepage through the embankment is measured by a weir located at the downstream toe.
The present full supply level (i.e. top water level) of the dam is RL61.5m (AHD) which is 7 metres below the embankment wave wall crest level (i.e. the top of the wave wall on the dam crest).
The spillway is an ungated concrete chute with ogee weir and flip bucket located on the left abutment. The spillway chute, and approach area between the dam toe slab and spillway crest, are fully lined and have 6 to 8m high walls. The spillway chute is 110m long. The spillway crest is 22m wide and the chute width narrows to 12m for much of its length. The spillway was designed to pass the original probable maximum discharge of 590 cumecs.
The intake/outlet system consists of a 34m high, 4m outside diameter reinforced concrete tower of the wet well type situated on a tower base structure at the head of the outlet tunnel which is located under the right abutment.
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