CuTHBEETSON. — 0)1 a Water Supply for Invercargitt. 121 



Art, XIII. — On a Source of Water Supply for Invercargill. 



By John E. Cuthbektson. 



[Eead before the Southland Institute, 4:th May, 1881.] 



[absteact.] 

 It seems certain that the whole of the country between Invercargill and the 

 Hokonuis consists of a comparatively level deposit of silts and clays, resting 

 on a bed of sandstone sloping gently to the south. This deposit of gravel, 

 etc., lying on the impervious subjacent rock, has been proved by actual 

 experiment to be absolutely saturated with water ; and that, as soon as we 

 pass the first bed of clay, at a very considerable pressure indeed. Here 

 then is what we want ; an inexhaustible supply of well-filtered water, close 

 at hand. Why go thirty miles for what can be had within less than thkty 

 yards ? Supposing for a moment that artesian springs wiU never be dis- 

 covered strong enough to reach the surface, and that even the supply from 

 a series of tube wells might not prove sufficient, why not sink an ordinary 

 shaft, protected by suitable casing (say a bridge cylinder), as far as such a 

 shaft could be sunk, and kept dry with a good pump and a ten horse-power 

 engine ? When the engine can no longer keep down the water, then you 

 have got all you want, namely, a water supply which will suffice for many 

 a year to come, and that at a very moderate cost. From what I have seen 

 I should be much surprised if such a shaft ever reached the depth of 100 

 feet, the quantity of water is so great. Then as to the permanence of the 

 supply. There seems no reason to suppose that the vast subterranean 

 stream which it is proposed to tap should be less permanent than any river 

 flowing on the sm-face. Of the existence of this immense supply of water, 

 all who witnessed the progress of the borings are firmly convinced ; and it 

 seems reasonable that others should accept their testimony. The water 

 was in fact the one difficulty, and an ever-present difficulty, in the way of 

 the boring. A recent bore put down at Clinton to a depth of 102 feet, i^re- 

 sented precisely the same features, so far as the constant inrush of water 

 was concerned. There is really no question as to the quantity. Then as 

 to quality : the water from aU the lower levels tasted perfectly pure and free 

 from any mineral solution. As to its freedom from organic matter, twenty 

 miles of natural gravel filter, from the base of the Hokonuis to Invercargill, 

 is a sufficient guarantee for that. This is an advantage which no water 

 collected from surface gathering-grounds can possibly possess ; for where 

 the water, or any considerable portion of it, passes over ground covered 

 with herbage and the droppings of animals, organic matter in various 

 stages of decomposition is always present ; and where that is found, living 

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