MANGAHAO WORKS

Otago Daily Times, Issue 18801, 2 March 1923, Page 4

MANGAHAO WORKS

HEAVY RAINFALL A HINDRANCE.

(Thom Oub Owm Cokbespokdeot.) WELLINGTON, March 1,

On the ranges near 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 north-west trade winds come down across the South Pacific laden with moisture, which, when 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 one for a reservoir. The heavy rainfall, however, has disadvantages in connection with the prosecution of the necessary works. In 1922 the rainfall was no less than SO inches, and there were more wet days than fine days in the year. At Maligahno there were months on which rain fell on 24 days. Judging from what has happened already 1923 may be still wetter than 1922. 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 connection with the temporary diversion of r.he Mangahao River. This flood rose to a height of 18ft. 'there has now been a second flood of the unprecedented height of 20ft. Fortunately not much had yet. been done to restore the damage of the 18ft flood, and consequently not a great deal was lost. Another source of delay has bean the necessity for deep excavation to find the solid rock on one sfdo of the bi<r dam. It was anticipated that rock would be found a few feet below the surface of the hillside. Tins was the case on one side of the gully, but not on the other. Instead of being nearer the surface, the rock was 50ft or 60ft_ down. Not only will this cause a_ largely increased expenditure for excavation, but a great outlay in addition, for the extra cement, concrete, and labour that will be necessary.