MASS OF CONCRETE

Timaru Herald, Volume CXXXVIII, Issue 19941, 27 October 1934, Page 10

MASS OF CONCRETE

EXCAVATION OF TAILRACE

Altogether about 500,000 tons of concrete have been used in the construction, made from shingle taken from the river bed, and 48,000 tons of cement from Dunedin, valued at about £200,000. The concrete in the dam far exceeds in strength and weight that generally used in New Zealand, owing to the excellence of the cement and of the local supplies of gravel and shingle. Between the tailrace from the Power House drought tubes and the main river stream is a wing dam. This is designed to prevent the water surging back and forming a vortex at the outlets. Another less obvious feature is the upward slope of the bed of the tail race after it leaves the Power House. The top of this slope is at a height of ten feet above the bottoms of the draught tubes and the crest is 100 feet distant from the mouth of the tubes. The idea is to provide a constant seal of water over the exit of the draught tubes, so that full suction will be maintained. The huge excavation for the tailrace has left a big island in midstream. This will gradually be worn away by attrition, but in the meantime will help'"in the same function as that of the wing-dam above-mentioned. At the northern downstream end of the dam is a vast concrete “apron,” or sloping area, its highest slope being at the extreme Canterbury side, gradually falling to river level. This will tend to keep the water in its proper course and prevent erosion of the north bank, which is a high cliff.