PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 



185 



The flow, it will be observed, is inversely proportional to 

 the viscosity /*, and, since the latter varies from '0080 at 

 86° F. to '0032 at 194° P., full allowance has to be made 

 for this factor, in view of the high temperatures so uni- 

 versally met with. 



From this formula the following table has been computed, 

 to show the effective rate of flow per square foot of rock 

 in feet per annum, under a difference of head of one foot 

 per mile, for sandstones of different mean average diameter 

 of grain, assuming a porosity of 30%. The "effective 

 velocity" is not the actual speed of the water in the capil- 

 lary passages, but the more convenient quotient of q by s, 

 and with a constant hydraulic gradient is independent of 

 the horizontal distance involved. 



Diameter of Grain. 



86° F. 



104° F. 



140° F. 



194° F. 



*3 



CD 

 CD 



0-20 mm. 



1-90 



2-31 



3-03 



4-76 



0-25 mm. 



2-98 



3-61 



5-07 



7-45 



hi 



0-30 mm. 



4-29 



5-20 



7-30 



10-73 



F* 



0*35 mm. 



5-84 



7-07 



9-93 



14-60 



Is 



0-40 mm. 



7-60 



9-24 



12-12 



19-04 



Even allowing values several times these for the aug- 

 menting effect of joints and bedding planes, as shown by 

 King's application of Slichter's formula, and reckoning a 

 fall of potential of four to five feet per mile (such as is just 

 attained along the margin of the Basin, more especially 

 about Hughenden), it will be seen that the rate of flow 

 may rise to 100 or 150 feet per annum at the most. 



This value would probably be maintained in the deeper 

 parts of the reservoir, for the effect of the lower hydraulic 

 gradient would be compensated for by the diminished 

 viscosity; moreover actual boring operations have fre- 

 quently proved the artesian beds to include some rather 

 incoherent "sandrock." 



