ABSTRACT OF PROCEEDINGS. XV. 



But even so, it by no means follows that there will be any short- 

 age of rain during its second half. The years 1846-86-1902-3-8, 

 all with less than 20 inches of rain in their first half — each had 

 abundant rains during their second half. It is interesting to note 

 the Sydney rainfall in connection with Cataract Dam and other 

 sources of our Water Supply. From the official figures courteously 

 supplied to Mr. Barling, it is evident that the rainfall over the 

 Catchment Area is greater than the Sydney rainfall. So that it 

 is safe to compare the Water Supply with the Sydney records. 



It is found that Cataract Dam was full early in September, 

 1915. Since that time there has been no material addition to its 

 storage. From the end of August, 1915 to 28th July, 1916, say 

 eleven months, the rainfall in Sydney has amounted to 24 inches, 

 and this quantity has been insufficient to maintain a full dam, in 

 fact the stored water is seriously low down. 



It is found from the chart that the last six months of 1875 and 

 the first three months of 1876 — nine months in all — had the low 

 rainfall of but 10 J inches. This is the lowest record for any 

 similar period. At that time abundant rains had fallen immedi- 

 ately before and also immediately following the dry spell. Again, 

 the last five months of 1884, and the first five months of 1885, 

 gave but 16f inches of rain, almost useless for water supply, and 

 this dry spell was followed by great rain in June and July, and 

 also the previous four months to August had abundant rain. If 

 similar dry periods occur again, there may be no shortage in our 

 water supply. 



But there seems to be no reason to anticipate such favourable 

 conditions as occurred then before and after the dry time. With- 

 out such rains the Sydney water supply would be in "parlous 

 case." This shows the urgent need of increased storage. If 

 eleven months of only moderately dry weather has so diminished 

 the water in Cataract Dam, what would be its condition in a 

 prolonged drought? 



It seems safe to assume that all those years (26 out of 61) in 

 which not less than 30 inches of rain had fallen in any six months, 

 would have given a super-abundant water supply with our present 

 storage. And that with increased storage, the present Catchment 

 Area would provide an ample supply for a much larger city than 

 Sydney is now, or is likely to be for many years to come. 



