Auckland Water Supply

Sun (Auckland), Volume 1, Issue 73, 17 June 1927, Page 12

Auckland Water Supply

Outside Schemes Opposed Present and Impending Supplies Safe REPORT OF THE COMMISSION THAT the estimates of the Auckland City Council in regard to the present and future water supplies are safe and sound, is the opinion expressed by the commission set up to inquire into the Auckland water supply, a report of which was released by the Minister of Health, the Hon. J. A. Young, last evening. On all grounds the commission considered both the Arapuni and Taupo ' schemes .‘to be absolutely out of the question.” On the point of excessive cost a Waikato scheme is not favoured, the development of the Lower Nihotup project, following. the completion of the Upper Huia gravity scheme, being recommended. It was further conisdered that the Hunui Ranges should also be developed before the Lower Waikato was resorted to. The cost of the commission was over £1,500.

TIEALING with the question of supply the commission states that the Auckland urban area, including Papatoetoe and Manurewa, had a population of 197,242. Should the present average yearly rate of increase continue the population in 1966 would be 830,000. The commission, however, considered that there would be a material slackening in the rate of increase and based its report on «the assumption that by 1967 the population in and around Auckland city having a water supply would be 575,000. SAFE AND SOUND The consumption a head in the city area was shown to be 76 gallons a day, outside the city 22 h gallons and at North Shore 47.4 gallons. The tendency was for water consumption to increase, so the commissioners had adopted 60 gallons a head a day as the required ‘ quantity. From the Waitakere Ranges 10,000,000 gallons a day would be available by the end of the year, and 14,500,000 by 1930, when the Upper Huia works were completed. . The commissioners considered the estimate of supply safe and sound in average seasons, while restrictions would have to be made in dry seasons. In this connection the commissioners considered it important that steps should be taken at once to establish adequate rain-recording stations and run-off gauging stations. The estimates of cost of the various city schemes impending or in view had been thoroughly checked and they considered them sound. Regarding the Waikato River the commissioners found that the water as it came from Lake Taupo could, be taken as a pure water supply which would not require filtration, but at Mercer it would require filtration and probably chlorination. Subject to these two requirements the Waikato River at Mcjrcer was a pure supply, because it could by modern methods be made the safe and potable supply of the first quality. COMPARISON OF COST In the commission’s opinion it was a question of balancing the cost of supply from the Waikato, at or near Mercer, against other possible sources of supply. To effect a direct comparison of the cost of bringing a supply from Mangatawhiri and a supply from the Waikato River, the commission averaged on a supply of 11,000,000 gallons a day, that being the quantity that the Mangatawhiri was assumed to yield. On the assumption that electric current would be available at £8 10s a kilowatt a year, the commission estimated the cost, including all charges, at 7.70 d a 1,000 gallons, against 7.54 d given by the city engineer for the first stage of developing the Mangatawhiri Valley. The commission found that the cost of an emergency supply from the Waikato River for 3,000,000 gallons through a 15,000,000 gallon main to be laid from Auckland to Mercer as the first section of a 42-inch main to Taupo, would be 18d a 1,000 gallons, chiefly because of the huge capital expenditure involved. A CRUSHING BURDEN The pumping scheme at Arapuni was considered on a 11,000,000-gallon basis for purposes of comparison. The commission considered that 1,000 gallons would cose 7d more than from Lower Waikato, making the cost to Auckland City 14.7 d against 7.7 d.

The commission examined the scheme with some care and found the report referred to, in estimating the cost to provide for a supply of 15,000,000 gallons a day at £2,482,000, made important omissions and under-estimates. The value of the report was, therefore, heavily discounted. To construct a conduit to bring in a supply from Lake Taupo of 15,000,000 gallons on the lines proposed by the provisional committee, in the opinion of the commission, would cost not less than £5,250,000. As a 15,000,000-gal-lon main would be doing the full duty at 12,000,0000 gallons, the cos! would be over 19d a 1,000 gallons. The length of time that would elapse before the scheme could be utilised would in itself be a crushing burden of cost upon the district.

It was not certain either that pure water could be delivered 150 miles through pipes to Auckland in the same desirable condition, for both colour and taste might be detrimentally affected. Further, boroughs and towns in the Waikato district either had no need of supplies from Taupo, or could not afford the high cost if they did. The commission considered that on all grounds both the Arapuni and Taupo developmnts were absolutely out of the question. Possible sources of the future supply for Auckland urban areas were summarised as follows: Lower Nihotupu, pumping 6,000,000 gallons daily, 5.98 d; Lower Huia, pumping 8,000,000 gallons, 7.44 d; Mangatawhiri and Mangatangi, pumping 23,000,000 gallons daily, 7.54 d for the first stage, and 5.70 d for the complete stage; Lower Waikato, pumping an unlimited yield, 7.70 d. FUTURE DEVELOPMENT The commissioners were satisfied that following on the completion of the Upper Huia gravity scheme (now in hand), the Lower Nihotupu pumping development scheme should follow next. Final judgment could not be made, however, until more dependable figures as to the yield and the cost of the development of Mangatawhiri and Mangatangi were available and the cost of the Lower Waikato pumping had been more fully investigated in point of cost. However there would be good reasons for deferring the Lower Huia and going on with th,e Hunua Ranges development. From all the data before it the commission concluded (subject to surveys and details of ebst and yield), that the supply in the Hunua Ranges should be developed before the Lower Waikato was resorted to, the determining factor being the discharging of the sewage of towns and boroughs into the Waikato and its tributaries. The supply from Hunua would be from clean forest upland. They stressed the importance of a full investigation without loss of time into the Hunual Ranges catchments. , It w£Ss most important, also, that steps should be taken to secure the reservation of all bush-clad portions of both the Mangatangi and Mangatawhiri catchments before further bush-felling was done. The importance of this could not be over-estimated. When the Upper Huia works were completed a safe supply for 265,000 people at 60 gallons a day would be available, assuming the One Tree Hill district and the Onehunga borough continued using their underground sources of supply. Taking the fields of the Lower Nihotupu at 6,000,000 gallons daily, the Hunua Ranges, at 23,000,000, and the Lower Huia at 8,000,000, *a total of 37,000,000 gallons daily, on a basis of 60 gallons per head, would support 880,000 people.