THE WATER SUPPLY OF SYDNEY, CIX, 
and, although the record does not allow of the determin- 
ation of a cycle, if such exists, it has undoubtedly shown 
periodicity, in the accumulated loss and gain of rain with 
respect to the averages, which demonstrates a run of dry 
and wet years, however irregular the periods may at 
present appear to be. ‘“‘He thought my figures as to the 
run off were too great. I was too optimistic in expecting 
40% from the catchment area; that percentage was not 
got elsewhere. Mr. McKay in his investigation of the run 
off from the Murrumbidgee adopted 21°67. He (Mr. Cardew) 
found in looking into the Sydney rainfall figures that the 
percentage above the average was 48%, and below the 
average 597 in the 76 years rainfall.’’ 
With reference to Mr. Cardew’s statements about the 
run off, I may say that the last rain over the catchment 
area of the Cataract reservoir, has resulted in over 50% 
being impounded by the dam. Although we have not as 
many rainfall stations there as might be desired, there are 
sufficient to arrive ata fair estimate of the average fall 
over the catchment area, and the contour suryey of the 
reservoir admits of a pretty close approximation of the 
amount of storage as the water rises. The result of the 
rainfall mentioned is as I have stated, which Mr. Cardew 
can verify if he will take the trouble to go into it. The 
result rather surprised me, in view of the fact that the fall 
took place over a ground surface not previously saturated, 
but at the end of a very long dry season. The average 
rainfall over the 50 square miles of catchment area was 
124 inches, and the storage during that time was 4,500 
million gallons. This is by no means an exceptional fall in 
this locality, and if it had occurred during the wet season, 
when the ground had been previously saturated, or even 
partially so, the percentage of run off would have been very 
much greater. Who can doubt therefore, that 40% run off 
