190 



ALEX. L. DU TOIT. 



Hence, if the bores be this distance apart, they will 

 capture the whole of the underflow. If there be n rows of 

 holes uniformly spaced and geometrically arranged to the 

 best advantage, then they will have to be -— miles apart 



o 



in order that each one's yield of a million gallons daily 

 might be maintained; if they cover a belt b miles in width, 

 their distance apart R' will have to be = V'&b miles. 



Hence, if b = 75 miles, R' — 15 miles, and if b = 300 

 miles, B' = 30 miles. 



Of course, owing to the time taken for water to travel 

 from one bore to the next, some years would have to elapse 

 before interference would first become apparent. 



In order to obtain some idea as to the actual rates of 

 abstraction of water from the Basin, two areas A and B, 

 each of 3,250 square miles in extent, were selected N.W. 

 and S. W. respectively, of Moree, and such that, as far as 

 possible (as indicated by the isopotentials), all the water 

 reaching B should first have to pass through A. The 

 results are displayed below: — 



Area. 



Number of 



bores in 



area. 



Mean dis- 

 tance apart 

 in miles. 



Mean depth 

 in feet. 



Average 

 thickness of 

 water-beds 



in feet. 



Mean differ- 

 ence of 



potential in 



feet per 



mile. 



Total output in 



millions of gallons 



per day. 



1912 



1914 



A 

 B 



25 



36 



11-5 



9-5 



3470 

 2435 



450 

 300 



2-7 



2-0 



18-5 



8-5 



16-6 

 6-9 



Assuming, as we have done before, a nearly constant 

 permeability, the flows across equivalent breadths of 

 country would be proportional both to the thickness of the 

 water horizon and the hydraulic gradient, and the relative 

 total yields might be expected to be roughly in the pro- 

 450 • 2*7 



portion of 



or 2 : 1. 



300 2-0 



Actually in 1912 the ratio of A to B was 2*23 to 1, though 

 two years later it was 2*4 : 1; nevertheless, since it can be 



