HYDRO-ELECTRIC POWER

Star (Christchurch), Issue 17029, 1 May 1923, Page 7

HYDRO-ELECTRIC POWER

THE ARAPUNI SCHEME. Tlie specifications and conditions for the heachvork:« contract of the Arapuni electric power supply have been issued by the Public Works Department. The contract comprises the construction of rhe diversion tunnel, the main concrete dam, the excavation of the headrace from the dam to the spillway, the construction of the latter, and the penstock intake and other necessary work. The contract is to be completed within forty-eight calender months from the date of acceptance of the tender. The scheme is explained in the specifications. They state that on the •western side of the Waikato River, at Arapuni, there is an old river bed of the Waikato, roughly parallel to, but 130 ft above, the existing river bed, and separated from it by a low ridge. It is proposed to divert the Waikato into the old river bed by the erection of a dam. the crest of which will be_about 150 ft above the present, water lelel. The old channel will have to be deepened, and will then form the headrace for about sixty chaine. The power house site is at the bottom of the present gorge and opposite to it a weir will be constructed across the headrace to divert the water into penstocks. ’Hie construction of the twelve pipe linos to the power house and the erection and equipment of the latter are beyond the scope of the No. 1 contract. The diversion tunnel, which will be required to carry the waters of the river round the dam during the construction of tbe headworks and to regulate the level of the lake behind the dam by taking off the extra flow in floods, will be about thirteen chains long. Details of this work are left to tenderers but the tunnel is to be at least twenty-five feet in diameter. The magnitude of this undertaking is apparent f r om a comparison with the Rianda.rd tunnel on r.he New Zealand railways, which is loft 3in in height in the oentre and 14ft in width. In mid-stream, the height of the dam to the crest of the parapet will be 193 ft 9in ; its length along the orest 150 ft, with a width of 20ft, comprising a road surface 17ft 6in wide, enclosed by parapets 3ft 9in high. The structure will be slightly sloped on the upstream face ; downstream it will extend steeply, so that the width at bottom will be 177 ft 6in.