CITY WATER

New Zealand Herald, Volume LXXV, Issue 23178, 26 October 1938, Page 16

CITY WATER

SUPPLIES FOR FUTURE RESERVES AT HUNUA VAST RESOURCES AVAILABLE COUNCIL ACQUIRING AREAS For some years the Auckland City Council has been carrying out a policy of acquiring hush-clad areas in the Hunua Ranges for water conservation purposes, looking forward to the day when the growth of the city will provide a demand for water well beyond the present and potential resources of the reserves in the Waitakere Ranges. Si) far the council has acquired 8310 acres in the watersheds of tho Mangatangi and Mangatawhiri Stream?, and the recent offer of tho Lands Department to transfer 1619 acres of Crown reserves in the Mangatawhiri watershed to the council will bring its holding in the Hunua area to just on 10,000 acres.

The storage capacity ,of the four reservoirs in the Waitakere Ranges is 1,569.000,000 gallons, so that with a daily average, consumption of approximately 11,000,000 gallons there is sufficient water to supply Auckland over a dry 'weather period of between four and five months. However, the increasing demand for water in recent years, particularly for the growing industrial plants in and around the city, makes it necessary*to plan beyond the capacity of these ranges.

Estimated Capacity Investigations already made by the waterworks staff of the City Council * in the Hunua Ranges show that tht-rc is an area Of 8400 acres in the Mangatangi catchment area and 6700 acres in the Mangatawhiri watershed. The minimum daily dry weather flow in these two elevated valleys is estimated at 14,250,000 gallons, and it is considered that it will be practicable, by the erection of two dams, to store 5,030,QP0,000 gallons, with a possible dailv draw-off of 36,800,000 gallons. Tlie Hunua Ranges cover an area of 100 square miles, lying between the Wairoa River and the Firth of Thames, and rise to a maximum height of 2200 ft. at Kohukohunui, 28 miles from Blount Eden. There are five main streams in the area and, while there will be ample water for the future large city, the lovrer courses of these streams offer facilities for the supply of water to the farming districts and townships on the lower country surrounding the ranges. Storage Possibilities Present calculations place the prospective dam sites at about 400 ft. above sea level. An extremely favourable site for a dam on the Mangatangi Stream has already been located. This ■would require a concrete wall lolft. tigh containing considerably less concrete than was used in the Nihotupu dam, but it would form a lake capable of storing 3,260,000,000 gallons, or six times that of Nihotupu. On the Mangatawhiri Stream a dam 80ft. high would be necessary, and here it would be possible to store 1,770.000,000 gallons. The main to the city will have a length of approximately 35 miles.