186 ALEX. L. DU TOIT. 



From these figures there follow two conclusions of the 

 highest importance: — 



Firstly, that none of the present rainfall over the intake 

 will become available within the Basin, even along its 

 margin, till after the lapse of centuries, and 



Secondly, that, unless the underground supplies are being 

 augmented by magmatic waters, only the stock at present 

 within the reservoir can be drawn upon. 



Consequently, since renewal of the reservoir througli 

 purely meteoric contributions may not be counted upon in 

 the near future, it behoves us to investigate more fully the 

 alternative factor; this will be done later on. 



That the permeability of the water-horizons must vary 

 greatly from point to point will be inevitable, from the 

 mode of deposition of the Jurassic sediments, but this 

 property can be demonstrated in a more tangible way by 

 an analysis of the frictional losses in bores during their 

 discharge. The resistance to flow through the bore-casing 

 may be very considerable, as shown by Table B, computed 

 for clean wrought-iron or mild-steel pipes of five and six 

 inches internal diameter. The co-efficient of friction has 

 been taken as 0*00575, but, from Osborne Reynold's work 

 on the effects of temperature upon flow, it is clear that the 

 co-efficient should be smaller, except when the casing is 

 rough and encrusted. 



Having worked out a number of cases with the aid of his 

 formula, it seems to me that for the majority of bores with 

 temperatures ranging from 100° F. to 150° F. the values 

 given in the table ought to be multiplied by about 0*9 and 

 0'8 respectively. 



Since the frictional losses vary inversely as the fifth 

 power of the diameter (for 5 and 6 inch casing as 2*49 : l) r 

 it might be worthy of consideration whether some of the 



