Water Supply.

Finally I wish to add to this chapter some observations on the artesian water supply, either already obtained in and near Christchurch or highly desirable, over the greater portions of the Canterbury plains, and some other districts:—

page 469

To this subject of great practical importance I have already alluded on page 58, when speaking of my report, written in 1863, on the possibility of obtaining a supply of artesian water for the City of Christchurch, and in my report on the Formation of the Canterbury Plains in 1864, when the borings had been crowned by suck excellent results, I offered further observations on the natural process by which such ample supply of pure water has been stored up. There have been several causes in operation to form in the Christchurch district inclined porous beds, enclosed between impermeable strata, by which the water is retained—if not stored in a basin—and is compelled to flow downwards until it finds means of escaping. It is evident that for Christchurch and its neighbourhood, the bottom of the former greater extension of Lake Ellesmere, filled up by silt, sands, fluviatile and turbary deposits, underlying that city, is the source from which the greatest portion of the artesian water supply is derived. Part of these beds have therefore been deposited in the form of a basin, in which artesian water is generally obtained with some degree of certainty. For those artesian wells however situated to the east of the former eastern shore of that late, the water can only be derived from gently inclined littoral beds, having been formed below the surface of the sea. That this is the case is conclusively shown by the depth the borer has to go before reaching the water retaining stratum, lying near Riccarton at 54 feet, whilst near the sea-coast it is only reached at 136 feet. It is natural that the deposits filling up such a considerable portion of the former Lake Ellesmere extension, according to the seasons or the advance of the deltas of rivers, or having been formed on the bottom or along its shore, must all be of a very different character.

Moreover, below the lacustrine beds, there also exist a number of layers formed in an arm of the sea, once surrounding an island (now Banks' Peninsula), formed of shingle, sand, _ clay and ooze; these in their turn would offer the necessary conditions for the formation of water retaining beds. It has been successfully demonstrated that below the stratum from which in Christchurch the usual flow of artesian water is obtained, one or more of these beds exist, containing also an abundance of water, which when tapped, rises to a higher level than the former. Thus, to give a few instances, at the North Town Belt water was first obtained at a depth of 76 feet, having only a surface flow; the same well continued to 136 feet, gave a splendid supply rising six feet hight. At the Whately road public well the water was reached at 74 feet, with scarcely a surface flow, but when page 470the same well was sunk to 166 feet the water gained 9 feet in height. The numerous borings all over Christchurch and its neighbourhood have given us a clear insight into the nature of the deposits by which the Lake Ellesmere extension was filled up. The bottom of the water-bearing stratum consists invariably of a bed of shingle, mostly of small size, upon which a deposit of sandy clay reposes. Above this the character of the beds changes incessantly, and often within very short distances from each other.

In some places the deltaic deposits of rivers reach from near the surface to the water-bearing stratum, as for instance, in Upper Riccarton, where after passing through 76 feet of shingle, water is obtained. It rises however, only within six feet of the surface. Near the foot of Banks' Peninsula, near Waltham, the shingle continues for about 100 feet till water is reached. At Middle Riccarton the shingle begins at only 50 to 60 feet below the surface.

In some parts of the district deposits of shingle are only near the surface, as in Cathedral square, and in Cashel street west, in others it forms only the central portion of the deposits passed through. Thus in Armagh and Chester streets east, shingle begins at 27 to 33 feet below the surface, continuing for about four feet, when it is underlaid by sandy deposits continuing to the bottom, about 98 feet. In some other portions of the city, as for instance in Hereford street east, there are deposits of silt, peat and sand for about 33 feet, after which the remaining 60 to 65 feet are formed by well cemented shingle, before the water is reached. In other places again, only sands, greyish, yellowish, or blackish, with occasional deposits of peat, driftwood, and silt have been passed by the well-borer. We have also good evidence of the character of the deposits in the Lower Heathcote district, in a brick well sunk a few years ago for obtaining a water supply for Lyttelton, and of which the details were kindly furnished by Mr. H. B. Huddleston C.E. This well reaches a depth of 40 feet, the whole consisting of sandy silt, such as is now being formed in the estuary of the Heathcote. At depths of 6½ and 25 feet from the sarface, two layers of Estuary shells were passed through, each about six inches in thickness, consisting mostly of specimens of Chione Stuchburyi and Amphibola avellana, still now living in the Heathcote estuary. Also a great deal of driftwood was met with.

To give a few more examples, I shall here offer the details of two artesian wells sunk to the east of Christchurch, in order to show the page 471nature of the ground passed through. An artesian well bored a quarter of a mile east of the Slaughter yard amongst the Sandhills passed through the following strata:—

100	feet of clean sand mixed with sea shells
9	feet of clay
2	feet of very small shingle
1	feet of large boulders
112	feet, when water was reached.

Another artesian well, not far from the Green bottle Lake (about 1 mile from the sea shore) gave the following section:—

ft.	in.
18	0	blown sands
0	3	white clay
36	0	(blown?) sands
1	0	clay
37	0	sands
0	6	shingle, scattered
21	0	sands
5	0	yellowish clay full of vegetable remains
0	9	very coarse shingle
119	6

I may here mention that, although I am speaking of the boring of artesian wells, the method now universally adopted is merely to drive down a pipe with a conical plug, and that this is done to a depth of about 80 feet in a single day. Total cost per well £6 to £7.

The rise of the artesian water above high tide mark is about 20 feet in the average, consequently whilst in the highest western portion of the town the water does not reach to the surface, it is rising at New Brighton, opposite the bridge (depth of well 134 feet), to 13 feet, and on the mudflats, near the Heathcote bridge (depth of well 124 feet) to 17 feet. In many parts of the town the water still rises to such a height that by means of rams the water can be brought into the upper portions of the houses, whilst in others it has fallen so low that it can only be obtained by means of pumps. Considering the number of artesian wells scattered over such a comparatively limited area as that of Christchurch and its neighbourhood, and of which about one-half is allowed to run waste night and day, it is evident that the supply of water required must be enormous, and that its gradual page 472diminution could be anticipated with some degree of certainty. However, experience has shown that the height to which the water rises has scarcely been affected in those localities where the wells are more scattered, to about 3 to 4 inches only—except in particularly dry seasons, whilst in those parts of the City where the wells are very numerous and a great deal of water is required, the decrease in height has been about four feet. Thus the artesian wells near the Museum and in the Domain have lost only a few inches, whilst near the intersection of Cashel Street with High Street, the loss in height has been estimated at four feet. The size of the pipes is usually 1¼ to 1½ inches in diameter, those sunk by the City Authorities and some private establishments are of larger size (2 inches). I do not know how many artesian wells are in existence in Christchurch, but I believe there are close upon a thousand, aud a similar number may exist in the suburbs and adjoining districts. The result of several analyses have shown that the water is remarkably pure. It is beautifully clear, and having the mean temperature of Christchurch (about 53 deg.) all the year round, it is delightfully cool and refreshing in summer. The analyses of Professor Bickerton, F.C.S., have shown that its constituents vary in different localities, the total solids, however, never exceeding 4 grains per gallon.

There are two sources from which the water is derived, first from leakage of the rivers, and secondly from rainfall on the plains. Whilst, however, the heaviest freshets in the Waimakariri have never had the least influence upon the water supply, the wells have been known to rise four to five inches after heavy south-west rains, a continuance of dry weather for several months lowering them just as much. It appears, therefore, that the amount of water derived from leakage of the rivers, is constant and not in any way influenced by their volume at the time. In confirmation, the following observations made by Dr. Ll. Powell, F.L.S., will be of interest. Dr. Powell placed a gauge upon his artesian well in Worcester Street west in the early part of 1875. During that year the water stood at an average of 25 inches in the glass tube. On November 28, after four days of heavy south west rain, it reached 29 inches, its greatest height during that year. The strongest North-westers with heavy floods in the Waimakariri did not however make the least alteration in the position of the column of water. On October 27th, 1877, the level had fallen to 20¾ inches, whilst at the beginning of Nov. 1878 it only reached to 13 inches, during a time when fierce Nor-westers had been raging page 473for some days. Dr Powell made also the observation that invariably when the artesian well on the nest section (the Wesleyan parsonage) about 30 feet distant from his own is running, the level of the latter sinks at once half an inch. I need here scarcely point out that it would be very important to have all the obtainable information as to the underground water supply of the district carefully collected, and mapped, and sections prepared. Such documents would be of the greatest usefulness, their study leading us to conclusions the value of which cannot be overestimated.

The sinking of wells on the Canterbury plains in many directions (many of them reaching to a considerable depth), has proved that these plains consist invariably of river shingle and sand, cemented more or less by a ferruginous matrix. In a well between the Ashburton and Rakaia, sunk about 15 years ago, near the main road, where a supply of water was reached at a depth of 220 feet, the shingle at the bottom became much cleaner and incoherent, resembling the small shingle in the Rakaia river-bed. For a number of years past I have urged on several occasions upon the late Provincial Government to undertake trial borings of artesian wells over the most waterless portions of the Canterbury plains, but without success. The obtaining of an ample supply of water by such means would have been of immense value to the country, and would have promoted the settlement of many thousands of acres of land which are now comparatively useless. I still believe that it is well worth the expense upon those portions of the plains where artificial irrigation has otherwise to be resorted to. The copious natural springs in many parts of the lower plains, giving birth to a number of small creeks, such as the Avon, Heathcote, Little Rakaia &c., sufficiently prove that also higher up water-bearing beds are existing, which run out on the plains at no inconsiderable altitude above the sea level.

I am sorry that similar wells have not been sunk at Timaru, where there is all probability that good water by means of artesian borings might also be got without too great a cost.