MANGAHAO DAM.

Taranaki Daily News, 14 November 1923, Page 7

MANGAHAO DAM.

FIGHTING THE ELEMENTS. STRENUOUS EFFORTS OF MEN. 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 where the big dam is being built. This advantage, however, has its drawbacks in so far as the 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 the elements. In a special article the Wellington Post deals with this feature. The works at present, it says, present a busy scene, there being over 500 men employed. Some of the more important portions of the work are running three shifts a day for six days a week. The weather has been so uniformly bad that the men are becoming 4o 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 the dam in the Mangahao Stream. A great fight is going on against the 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 20 ft. additional, and they are not slow in rising either. Coffer dams, constructed of interlocked steel sheet piling, have been built—two rows above and two rows below. The site and the space between these double rows have been filled with concrete and other material in an endeavor to obtain a watertight wall. A duplicate outfit of motordriven lOin. centrifugal pumps has been installed, suspended on inclined ways so that they can be wound up just enough to keep ahead of the rising floods.

TOILSOME START AND PROMPT FINISH.

The building of the coffer dams was quite an undertaking, one of the difficulties being the small amount of loose material in the canyon. In other words, after the piling was driven, there was not enough lateral support for it. It was braced from side to side with heavy timbers and guyed to ring bolts let into the rock with stout wire cables. Floods have bent the piling, broken the 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 the 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 the work the river swept over the whole and filled the excavation with water and shingle. Twice during the ensuing week the river subsided to a sufficient extent to enable pumping to be 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 the work done but a few twisted steel bars which had been cemented into the rock to secure the 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 were only eightfine days and 104 inches of rain fell. September was a comparatively good month, with 14 fine days and only 8 inches of rain. $