Commenced in March 1968, commissioned in 1973, and completed in 1976, the Copeton Dam is a major dam on the Gwydir River, a tributary of the Barwon River, and is located approximately southwest of Inverell, between Bingara and Bundarra. The dam was built by the New South WalesWater Conservation & Irrigation Commission and the Department of Water Resources to supply water for irrigation. Water from the dam is now released directly into the Gwydir River which is used by irrigators downstream of the dam including for pecan nut farming, and for producing cotton, wheat, lucerne, vegetables, fruit trees, oil seeds and fodder as well as pastures for sheep and cattle. The dam wall comprises of rock fill and is high and is long. The maximum water depth is and at 100% capacity the dam wall holds back of water at AHD. The surface area of Lake Copeton is and the catchment area is. The gate-controlled concrete chute spillway is capable of discharging of water per day. Together with a series of diversionary weirs and regulatory works downstream from the dam, Copeton is able to provide a reliable flow of water to of land. This amount is much less than the originally planned because of higher rates of absorption and evaporation along some of the irrigation channels. Despite these overestimates irrigated agriculture in the Gwydir Valley saw the area become Australia's major cotton-producing region.
Upgrade of facilities
In 2007, it was decided the dam would need an upgrade for safety reasons. The 70 million upgrade is expected to be completed during 2013 and Stage One involves the construction of a four-bay, -wide, fuse plug spillway at Diamond Bay to enable the dam to safely pass extreme floods. Once the fuse plug is installed the dam wall will be raised and the spillway gate modified.
Spillway
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 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.
Copeton Dam offers sailing, windsurfing, boating, water skiing, fishing and swimming while bushwalkers can enjoy unusual geological formations, lake and mountain views and a wide variety of plant life.
