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NOTES ON THE NEWHOBAET STORAGE RESERVOIEv 

 By T. Stephens, M.A., F.G.S. 



As the New Storage Reservoir will probably be completed 

 before the next evening meeting of the Royal Society, 

 I submit some remarks upon the geological conditions of the 

 locality, based upon notes made at various times during the 

 progress of the works. In a paper read before the Society 

 on the 11th of September, 1877, on the causes of the failure 

 of the dam of the old reservoir, I mentioned incidentally that 

 another fault, in addition to those then under consideration, 

 crossed the valley of the Sandy Bay Rivulet close to the 

 upper end of the reservoir. In the following year I visited 

 the place in company with the members of the Waterworks 

 Committee to inspect the site selected by the Corporation 

 Engineer for the dam of the proposed new reservoir, 

 on which a good deal of work had already been done, 

 and which proved to be at that part of the valley 

 which I had described as being traversed by a great 

 fault. A cutting had been made into the mudstone rock 

 on both sides of the rivulet, and a shaft sunk to a depth 

 of about 40 feet in its bed, with the object, I believe, of 

 ascertaining whether the character of the rock was such as to 

 serve for a good foundation ; but all the information thus 

 obtainable might have been readily gathered from an exami- 

 nation of a few of the sections exposed in road cuttings or 

 otherwise, where an opportunity is afforded of studying a far 

 greater thickness of the beds of the mudstone series. 



The two points at which I had noticed signs of a break in 

 the formation were about half-a-mile apart, and the inter- 

 vening rocks were at that time too much obscured by surface 

 soil and low scrub to enable one to trace its direction with 

 accuracy. The evidence, however, was too strong to be set 

 aside, and after another look at the country, I had no hesi- 

 tation in informing the Waterworks Committee that the fault 

 previously described must cross the valley near where the 

 shaft was being sunk, and that it would intersect the line of 

 the dam not far from the S.E. end of the open cutting. 

 Whether a seciu^e dam could be constructed under such 

 conditions would depend on the character of the filling of the 

 fissure produced by the break in the rocks, and to test this 

 point I recommended that the cutting should be extended for 

 a short distance in a S.E. direction, by Avhich means the 

 question of security could be set at rest at a trifling expense. 



