MANGAHAO DAM.

Otago Daily Times, Issue 19009, 3 November 1923, Page 15

MANGAHAO DAM.

FIGHTING THE ELEMENTS. STRENUOUS EFFORTS OF PUBLIC WORKS MEN. (From Our Own Correspondent.) WELLINGTON, November 2. There is one excellent feature about the country chosen for the water supply of the station that is to provide Wellington and a portion of Hawke’s Bay with electric current for power and light. It is the copious and almost continual rainfall in the high hills whore the big dam is being built. Tins advantage, however, has its drawbacks in so far as tho construction of the works is concerned. Some incompetent critics have complained of the delay in regard to these works. They have made little allowance for the continuous battle that has been going on between man and tho elements. ' In a special article to-night’s Post deals with this feature. The works at present, it says, present a busy scene, there being oyer 500 men employed. Some of the more important portions of tho work are runningthree shifts for six days a week. The weather has been so uniformly bad that the men are becoming to some extent amphibious, and on days when it is hardly fit for a dog to be out the motors hum and the crushers grind away at tho dam in the Mangahao Stream. A great fight is going on against tho forces of Nature. The dam has to be placed in a canyon which, when the river is low, has 12ft of water in it, and in the canyon floods rise as much as 20ft additional, and they arc not slow in rising cither. Coffer dams, constructed of interlocked steel sheet piling, have been built—two rows above and two rows below. Tho site and the space between these double rows have been filled with concrete and other material in an endeavour to obtain a watertight wall. A duplicate outfit of motor driven lOin centrifugal pumps has been installed, suspended on inclined ways so that they can be wound up fast enough to keep ahead of the rising floods. TOILSOME START AND PROMPT FINISH. Tho building of tho goffer darns was quite an undertaking, one of the difficulties being tho small amount of loose material in the canyon. In other words, after the piling was driven, there was not enough lateral support fol it. It was braced from side to side with heavy timbers and guyed to ring bolts let into tho rock with stout wire cables. Floods have bent the piling, broken tho timbers and the wire ropes, and generally upset matters, ‘ but the dam builders simply set their teeth and built it again. Finally the pumps unwatered the hole, and every man available was put into the excavation, from which tho spoil was hoisted and carried away with the aid of tramlines, electric cranes, etc. Last Saturday week rock was exposed and the first concrete was put in. Within 10 minutes of the completion of tho work the river swept over tho whole and filled tho excavation with water and shingle. Twice during the ensuing week the river subsided to a sufficient extent to enable pumning to bo resumed, but not long, enough for the hole to be cleared and any work to be done. When the excavation was finally unwatered on Tuesday nothing was left of tho work dono but a few twisted steel bars which had been cemented into the rock to secure tho first of the concrete. BUILDERS BUILD ANEW. Still the staff are not discouraged. These difficulties have to be met in all such works, and it is expected that before very long the concrete will be up to such a level as will enable the dam-builders to laugh at all except the most stupendous floods. During October there wore only eight fine days and inches of rain fell. ' September was a comparatively good month, with 14 fine days and only 8 inches of rain.