Big savings on weir

Press, 28 October 1981, Page 10

Big savings on weir

■ Almost $1 million has been saved on the Upper Waitaki power development by innovative design and rapid construction of a big concrete weir. The weir is on the left bank of the Ohau C canal, 1600 m downstream from the Ohau B power station. Each wall on the weir is 18.6 m long and 2.5 m high and the entire structure occupies a length of 75m. In total it has used 6100 cubic metres of concrete. The cost savings come in two forms. The zig-zag design means that the weir occupies only a small length of canal. A conventional design would have involved a structure longer than 400 metres, and would have involved more than $850,000 worth of extra concrete alone. The rapid construction pushed the completion date almost a year ahead of schedule. The labyrinth weir, which

was designed by the Ministry of Works, is the largest weir in the Southern Hemisphere. It will be brought into use -in October next year when the first of four 53-megawatt generators is commissioned on Ohau B. and because the Ohau C station will not be ready for a further two years the water discharged from Ohau B will have to be splitvia the weir into the Ohau River, where it will travel to Lake Benmore. The intake structure for the Ohau C. station at the end of the canal will act as a dam, and water will build up until it starts spilling over the weir. The intake is designed to pass a full flow of about 525 cubic metres of water a second. The intake is designed to pass a full flow of about 525 cubic metres of water a second. Construction on the project began last November, and involved 17 men.