On the Botany Watershed. 85 



the cord with extreme tightness, and I think with great unfair- 

 ness to their detriment, in order to show that this source of 

 supply can " barely be made adequate to the existing wants of 

 Sydney." Eirst, as before stated, they say that two-thirds of 

 the rainfall must be absolutely lost. Secondly, they deduct for 

 evaporation at the rate of six (6) feet per annum. And thirdly, 

 they assume that 665 millions of gallons is the utmost possible 

 amoimt of storage room that can be had on the Botany water- 

 shed. In order to be in a position to shew the fairness or other- 

 wise, of these deductions, I have taken the greatest possible 

 pains, during the present year, to keep such a registration of 

 facts as will enable me to show with tolerable accuiacy what is 

 the actual proportion of flow to rainfall on the Botany water- 

 shed. The rainfall at Double Bay, the 31st August, this year, 

 was 53 "56 inches, the fall at No. 1 Dam was 43 '37 inches, 

 96"93 inches, mean 48 "46. The average is 48"46 inches between 

 the two points, and this I take as the average rainfall over the 

 Botany and Lachlan swamps, which cover an area of 4249 acres ; 

 the quantity of water which fell upon this area durmg those 

 eight months was 4,671,307,230 gallons. The quantity pumped 

 into Sydney during the same time was 1,074,508,992 gallons; 

 quantity passed through the tunnel, 266,400,000 gallons ; 

 quantity passed over the weir into the sea, 525,432,794 gallons ; 

 quantity passed through floodgates into the sea, 1,831,820,542 

 gallons ; quantity now in the dams, 174,000,000 gallons ; quantity 

 used and accounted for, 3,872,162,328 gallons. Now, if this 

 quantity be deducted from the entire rainfall, 4,671,307,230 

 less 3,872,162,328, — 799,145,902. Thus the quantity to be 

 accounted for to the end of August is 799,145,902 gallons, or 

 about one-sixth of the entire rainfall. If this quantity be 

 divided by the acreage of the catchment, viz., 4249 acres, the 

 quantity for every .acre equals 187,000 gallons, or for every 

 superficial foot of watershed a little over 4^ gallons. Now the 

 average depth of the sand comprised in the watershed is 

 not less than 35 feet. This gives 35 cubic feet to every 

 superficial foot, then considering the absorbent nature of sand. 

 I think 4i gallons is not a large quantity of water to be diftused 

 throughout 35 cubic feet of it, nor is it. But it must be borne 

 in mind that ^vhen the wet season commenced in Pebruary, 

 although the dams were nearly dry, there was a copious stream 

 running into Botany, which enabled us to pump into Sydney 

 nearly five millions of gallons per day ; this water was that 

 which had been retained in, and was being given off" by the sand, 

 and when, on the 26th of Pebruary, the rain commenced, there 

 was still a very large quantity of water retained in the sand, 

 which was absorbed last year, and would have been at our service 

 for pumping into Sydney some weeks longer at the same rate. 



