MANGAHAO HYDROELECTRIC WORKS.

Press, Volume LIX, Issue 17702, 2 March 1923, Page 6

MANGAHAO HYDROELECTRIC WORKS.

FLOODS CAUSE DAMAGE (skoal to "the rues.") WELLINGTON, March 1. On the ranged west of Shannon, amidst which are situated the dams and tunnels that will provide the water for Wellington's electric power supply, a great deal of rain falls. The northwest trade winds eomo i down across the South Pacifio laden with moisture, which, whenj it strikes the cooler air of" the mountain tops, is precipitated in rain. The heavy rainfall may be taken as an indication of the wisdom of the engineers in pitching upon this locality as a satisfactory ono for a reservoir. The heavy rainfall, however, lias disadvantages in connexion with, the prosecution of the necessary works. In 1922 the rainfall was no less than "80 inches, and there were more wet days than tine days in the year. At Mangahao there were months on which rain fell on 24 days. Judging from what has happened already, 1923 may be still wetter than 1&22. Already there have been two heavy floods, the first of which destroyed the whole result of three months' work of a large number of men in connexion with the temporary diversion of the Manga hao river. This flood, rose to a height of 18 feet. There has now been a second flood of the ui.prec-edent-ed height of 20 feet. Fortunately, not much had been done to restore the dnniage of the IS feet flood, and consequently not a great deal was lost. Another source of delay has been the necessity for deep excavation to find the solid rock. On one side of tho big dam it was anticipatedMh.it rock would be found n few feet celow the surface of the hillside. This was th-3 case on one side of the gully, but not on the other! • Instead of being near the surface, the rock was 50, feet or <X) ieet down. Not only will this cause- a. largely increased expenditure for excavation, but a great outlay in addition fur the extra cement, concrete, and lahour that will be necessary.