Engineering Precision In Hawea Control Gates

Press, Volume XCV, Issue 28263, 29 April 1957, Page 14

Engineering Precision In Hawea Control Gates

[By a Special Correspondent}

Construction of the four sluice gates which will control the level of Lake Hawea has been completed and delivery to the site is taking place progressively as shipping and road transport can be arranged. Part of the control equipment was made in Christchurch and has already been installed. The first gates to arrive should be ready for unpacking within the next few days. “These gates are a fine achievement and a first-class example of constructional engineering calling for precision and skill of a very high order, exploiting both modern methods and modern materials,” said the engineer-in-chief for the Ministry of Works (Mr C. W. O. Turner). “They arc of the radial type, a kind already in use here for hydraulic control work in certain cases, but in several ways they are unique. Used as we intend to use them at Hawea, they will provide a highly efficient method of controlling a considerable head of water —a method quite new to this country, but one which wo hope to apply more widely on future hydro-electric construction tasks. “Unlike control gates such as those at the Roxburgh dam, which, once used to fill the lake, normally remain closed, these radial gates will probably be adjusted several times a week to control the flow of water from Lake Hawea to the generators at Roxburgh in accordance with varying demands,” said Mr Turner. Frames Installed The frames have already been installed, set in concrete under stringent control conditions to ensure the highest degree of accuracy, but the gates themselves are unlikely to be in position until concrete work on the vertical gate shafts is almost completed, probably about next July. In the meantime the gates will be thoroughly treated by painting with anti-corrosive materials, and later any necessary final adjustments will be made. Because of the essential painstaking attention to detail,. installation will take some time —three months or more. All four gates were built in the department’s central plant zone workshops at Gracefield, near Wellington, and the “pictureframe” type of gate frames mounted with rubber seals, to which they must be mated with an accuracy of better than one sixty-fourth of an inch, were made in Christchurch by private contractors, as was the hydraulic-ally-operated lifting equipment. Work on Gate Chamber Work on the gate chamber, which is to be at the bottom of the great mass of A rocky spoil which will constitute the dam, and about 120 feet downstream from the inlet to the sluices, is now going rapidly ahead and part of the roofing is complete, but tall concrete shafts reaching to the crest of the dam have yet to be built.

When in place the gates will be 80 feet below the highest possible flood level of the lake, and each will bear a maximum water load of 308 tons distributed over a stainless steel-clad face plate 10 feet wide and 14 feet high. This plate, rolled by the railway workshops at Woburn, is in shape a segment of a circle and the designed margin for variation in its radius is only one-sixteenth of an inch.