Art. XLVII.—Artesian Wells, Wanganui, New Zealand.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 25, 1892, Page 348

Art. XLVII.—Artesian Wells, Wanganui, New Zealand. By H. Hill, B.A., F.G.S. [Read before the Hawke's Bay Philosophical Institute, 28th November, 1892.] Plate XLV. At the meeting of this society in July last I read a paper on the geology of the Wanganui district, with special reference to the possibility of Wanganui itself being situated within an artesian-water-bearing area. At that time I had no idea that the governing body in Wanganui would so soon act upon the recommendations made by me in a special report made to them; but, the test having been made and success achieved, it is with pleasure that I bring the matter once more under the notice of members. It will be remembered that a suggestion was made in my paper to the effect that two trial-bores be put down in places indicated on a plan of the district—one of the places being near the Girls' High School, the other one being near the spot marked as the “Asylum.” To test the matter, the Wanganui Borough Council decided to put down a trial-bore near the first-named place; and, tenders having been called for, Mr. Gilberd, of Taradale, obtained the contract, and on the 8th of the present month he struck a fine flow of water at a depth of 218ft. The pipe is a 4.½in. bore, and the daily flow is estimated at 100,000 gallons, with a pressure of 7.½lb. to the square inch, which is equal to a rise of about 14ft. above the surface, when friction is taken into account. At the spot where the well is situated the height above sea-level is 46ft. As the location of the second well appears to be outside the ordinary borough limits, no contract has been made for sinking the second well; but, now that artesian water is known to exist in the district, no doubt those who are interested in obtaining a water-supply at or near the place indicated will not be long in providing themselves with the inestimable boon of unlimited pure water, without which sanitation, according to hygienic laws, is impossible. The authorities in Wanganui have sent me specimens of the different strata met with during the sinking, and the beautiful section here shown, with the photograph of the well, have been prepared for me by Mr. A. Atkins, F.R.I.B.A., of Wanganui, to whom I am indebted for valuable help during my visit to the town, and who first brought the question of an artesian water-supply for Wanganui to my notice. The

To illustrate Paper by H. Hill.

different beds passed through, as shown in the drawing, correspond in many respects to those met with in the Napier-Heretaunga artesian basin; and they are similar in the main to those forming the hills over the whole of the Wanganui district, as far as seen by me. They belong to what is known as the “Kidnapper conglomerate and pumice deposits,” which are so largely developed throughout the Hawke's Bay District. From the specimens sent to me it is evident that the area forming the Wanganui artesian basin is one of depression or slow subsidence, similar to our own Heretaunga Plain; and when a few more wells shall have been put down it will be possible to do what it is possible to do now in the case of the Napier and Heretaunga wells—that is, to tell within a very small distance the depth of the sinking necessary to reach the water-bed, no matter where the locality, so long as it is situated within the basin of the water-bearing area. The following information is given concerning the beds met with in Wanganui well No. 1: (a.) 6ft. of black iron-sand, with streaks of orange-red pumice-sands. (b.) 6ft. swamp peat and sands. (c.) 18ft. pale-brown clay, somewhat tough, (d.) 15ft. of fine greyish-blue sands. (e.) 65ft. of pale-blue clay, mixed in places with very fine sand. In this bed, and at a depth of 75ft. from the surface, a pukatea log 1ft. in diameter was met with. (f.) 14ft. of dirty gravel or grit, with bits of wood. The grits are of all colours; and towards the bottom of the bed some of the grits are cemented together. An inexhaustible supply of excellent water was met with in this bed. It rose to within 6ft. of the surface, or to a height of 40ft. above sea-level. (g.) 6ft. of fine, crisp, silver-coloured sand (blown). The small black grains seen in this sand resemble pitchstone. (h.) 75ft. of blue clay, with shells. The clay is somewhat tough, but fine sand appears in places. (i.) Grey sandstone full of shells, all recent, and corresponding to most of the specimens named in my paper (Trans., vol. xxii., 1889, pp. 435–36) as occurring in the Napier wells. Mr. Gilberd, the contractor for the well, tells me that underlying the present water-bearing bed is deep-blue clay; but I am inclined to think he is mistaken in this opinion. The small specimen of clay sent to me as coming from the underlying bed corresponds in every particular with the clay in the 75ft. section; and I think it will be found that the overlying clay will slowly wear away and be brought to the surface, unless the tube-bore be driven to the bed from which the water flows. From the character of the shells, I think it very likely that another grit- and shingle-bed is below, and there is every appearance that water will be obtained from yet another underlying bed. The water now flowing corresponds to the lower middle beds as met with in the Napier 6in. sinkings;

and, should the “Asylum” well be attempted as recommended, it may be found advisable to go down at least 300ft., so as to test this point. From the specimen of the water received it appears to be admirably suited for domestic use, and with a small outlay the people of Wanganui will now be supplied with at least one inestimable blessing—viz., pure water. The diagram I exhibit (Pl. XLV.) shows in detail the character of the beds, and the locality plan shows the situation of the well, and the height of the several spots where sinkings are proposed.