THE CHRISTCHURCH ARTESIANS AND THE CITY WATER SUPPLY.

Star (Christchurch), Issue 17346, 10 May 1924, Page 8

THE CHRISTCHURCH ARTESIANS AND THE CITY WATER SUPPLY.

BY CHAS. CHILTON (Rector and Professor of Biology, Canterbury College, X.Z.) XXVII. THE 1907 PROPOSALS AND THE PERFORMANCE OF 1908. Though thr City Council, in carrying out the works in 1908 for the high pressure supply after the loan had been authorised in 1907, abandoned their twelve-foot cylinder well, presumably because they found on reflection that the objections raised to it were sound, they did not profit by the advice offered by their critics on other points. They took no precautions to avoid interference of their wells with one another. In the writer’s article, published on June 7, 1907, separate copies of which were widely distributed at the time, there is the following passage:— " It this were done (i.e., taking over the deep stratum for municipal purposes) and a number of wells sunk at reasonable distances from one another, there would still be enough water supplied from these wells for our whole requirements. It is important that these wells should be scattered. If we attempt to draw the whole from one single large well, too great a drain is made on the district immediately surrounding the wells, and both the pressure and the quantity of water may be seriously lessened. With a number ot wells at sufficient distances, the risk of this is very materially lessened, and the supply is proportionallv greater.” The question of interference was of course dealt with in the ordinary books on artesians, and particularly in Slichter’s report published in 1902, and had been guarded against in the water supply of Madison, Wisconsin, E.S.A., particulars of which are given in his report, and the map of which was exhibited as a lantern slide at the lectures given in opposition to the Council’s proposals. These facts were also brought prominently before the notice of the public in a letter by Professor Speight in the “Press” of June 18. 1907. He says:— “ This town is supplied from artesian wells sunk in the neighbourhood of a water tower to which the water is pumped. The total available supply from ten 8-inch wells is over three million gallons per day, and the following facts are noteworthy in the present connection. One well at th« pumping station yields half a million gallons per day, but the supply obtained by pumping from four is only one million gallons. If we apply the same principle to the local conditions we shall probably be correct in saying that a greater supply would be obtained from four 8-inch wells sunk at a little distance from one another, than from the Council’s proposed cylinder, and that at far less cost even allowing for an underground reservoir There would he no danger of the supply running short, and if wells were put down to a deeper stratum there would be no interference whatever with those already in existence. This interference would undoubtedly occur in the case of wells near others pumped from continuously, and the more porous the beds are the greater the area that would be affected.” Notwithstanding all this advice the Council, when abandoning the cylinder well and sinking a small number of 6in. and Bin. bores, put them all close together in the ground at the Cashmere Pumping Station. Mr J. M. Stewart, in his report dated June 13, 1922, says There exists at present a cluster of bores—two (jin., five Bin., and one 9in. They are situated within an area of approximately five chains in length by two chains in width.” That is, they are all within one acre of ground. And yet the City Council’s engineers knew all about the risk of interference for, hi their report to the Mayor, dated June 22, 1907, in giving reasons whv the pumping station was to be placed near the foot of the Port Hills, they related the serious effects produced by interference on surrounding wells when they had tried to pump from the City’s well in Market Square in 1902. Apparently the present advisers of the City Council are more alive to the danger of interference for, from information kindlv supplied to me by the City Surveyor, the three 6in. “ test wells ” that have been, or are being sunk, since the defeat of the proposed loan at the poll in January last, are situated as far from the “ cluster of bores ” and from one another as the limits of the space offered by the pumping grounds and the neighbouring towing path along the hanks of the river Heathcote will allow. Whether these distances are sufficient for 6in. wells and for the 14in. well that has been sunk at the position of one of them is a question on which it is to be presumed careful investigations were made before the expense of sinking the wells was authorised by the Council. Another matter on which the City Council, in 1907, might have listened to their critics, but did not, was that of the amount of water to be supplied per head of the population. The following figures were quoted for the consumption in other New Zealand cities, viz:—Auckland, 18.4 gallons; Wellington, o/ gallons, and Dunedin, 71 gallons. Vet for Christchurch, with its people demanding baths, its beautiful gardens asking each summer for moisture, and its streets crying aloud for water to lav the dust, the Council based their scheme on a supply of onlv 20 gallons per head, and their reservoir was planned to hold 1 200.000 gallons, or one day’s supply, for a population of 00,000 people It is no wonder that a scheme devised with so little, provision for future growth of population and of increased use of water has had to be augmented since, and that a further greatly increased supply is now urgently called for. (The next article will appear on W ednesday. May 14, 1924.)