190 Charles Fenner: 



(c) liu/i-off, etc. — It is probably in the steep, wooded ranges of 

 the upper part of the basin that the maximum run-off occurs. The 

 •contributing factors there are (1) steepness of the valley sides, (2) 

 fairly impervious nature of the rock, and (3) the higher average 

 rainfall. Percolation is probably at a maximum where the sand- 

 stones of the permo-carboniferous period outcrop, as these are very 

 porous, and much fractured and faulted. They provide good, but 

 not permanent springs. 



In the figures published by the State Rivers and Water Supply 

 Commission (River Gaugings, 1905, p. 7, et. seq.), it is shown that 

 peculiar anomalies exist with regard to the percentage of run-off of 

 Victorian Rivers, and also that very great variations occur. From 

 the table showing the maximum and minimum annual discharges for 

 the Avhole period, covered by their gaugings, it appears that the 

 average maximum discharge is 31.5% of the total rainfall, while 

 the average minimum is 7.9%. 



We may compare with these the following figures for the Werri- 

 bee and its tributaries : — 



Q. ,. -^ Mean Annual Total Avera<,'e Percentage of 



*'^''^^'"" ^*^^^ Rainfall cischarge Total discharged 



Pyke's Creek "^ - 1909 - 37 in. - 34,170 acre-ft. - 34% 



near Ballan ) - 1912 - 36 in. - 3,490 acre-ft. - 4% 



This great variation in the amount of run-off must be due to the 

 different distribution of the fall throughout the years mentioned. 

 The Werribee River, at the mouth of the Gorge, shows similar 

 variations, with an unusually high percentage discharge in 1909 : — 



station 



Werribee River | 

 near the Grorge ^ 



Year 



Meati Annual 

 Rainfall 



Total Average 

 discharge 



Percentage of 

 Total discharged 



1909 



- 30 in. - 



73,970 acre-ft. 



- 40% 



1912 



- 22 in. - 



14,450 acre-ft. 



- n%- 



The gaugings on the Lerderderg at Darley are incomplete, and 

 do not show any evidence bearing on this matter. Those taken at 

 the town of Werribee, not far from the mouth, should really 

 approximate to the total annual run-off for the whole river basin. 

 They are : — 



<5i.„i.;-_ VoQ.. Mein Annual Total Average Percentage of 



'^ """ ^^^"^ Rainfall discharge Total discharged 



Werribee River "^ - 1911 - 34 in. - ] 79.920 acre-ft. - 19% 

 at Werribee ^ - 1912 - 19 in. - 36,990 acre-ft. - 7% 



