202 



represents the curve drawn by the above method, showing the 

 cumulative effects of variation from the rainfall of 19 in., con- 

 sidering the County of Lowan (Vict.) only. The line C, 

 which has been arbitrarily placed above that of A and B, repre- 

 sents a similar curve to that of B, and is based on the rainfall 

 of the south-eastern counties of South Australia, but with 

 20 J in. as the basis of calculation instead of 19 in. 



1895 



1900 



1905 



1910 



1915 



1920 



Fig. 11. 



Graphs showing the relationship between the variation 

 curve of the lake levels and the curve of the cumulative 

 effects of the annual rainfall above or below certain 

 selected bases. The vertical units represent 2 inches for 

 curves B, C, and D, and 1 foot for curve A. 



It will be noted that the nature of the curves coincides in 

 a remarkable way and demonstrates the correctness of the 

 assumptions upon which the curves are based. Various other 

 curves have been drawn taking other annual rainfalls as 

 providing the equivalent to "x," and these curves are, in ali 

 cases, similar to those shown in fig. 11, but bearing a less 

 close coincidence with the curve A than the ones selected. 



Mention has been previously made of the fact that the 

 lake levels, on the whole, show a distinct rise in December 

 as compared with June. Since this is an area of winter rains 

 it seems clear that a proportion, at any rate, of the water 

 of the Mount Gambier district comes from a distance, and 

 takes about six months to make its influence felt. Further 

 consideration of the curves in fig. 11 show that in some cases 

 the whole effect of a high or low rainfall is not shown even 

 within six months, but may continue to make itself felt for 

 a year or so afterwards. 



It is interesting to note that with variations from an 

 annual rainfall measured in inches, of which only a portion 

 soaks into the ground, we have consequent variations in the 

 level of the underground water amounting almost to an 



