On tJie Water Supply of Sydney. 143 



shown that the average quality of the water from the tributaries 

 and main stream of the George's River, above the dam at Liver- 

 pool, is unobjectionable, I will proceed to show the probable time 

 required to get rid of the sea water impounded between the pre- 

 sent dam at Liverpool and proposed dam at Kangaroo Point. 



4. As near as I have been able to ascertain, the average 

 annual rainfall of 50 inches is at least eighteen times as much as 

 the contents of George's River with its bays, &c, between the 

 two dams, below low water the sluices running over during the 

 purification. Taking only one-third of the annual rainfall as the 

 available rainfall, we should have six times as much fresh water 

 as sea water. Again, allowing the salt retained by the mud and 

 left by the tide between high and low water to be equal to that 

 contained in the sea water impounded, we should then have the 

 proportion of fresh to sea water as three to one at the end of the 

 first year, at the end of the second year it would be nine to one ; 

 at the end of the third year as twenty-seven to one ; at the close 

 of the fourth year as eighty-one to one ; the fifth year would 

 reduce the sea waters and salt to the proportion of one to 243 or 

 less than half per cent. 



I have mixed sea with fresh water in these two last propor- 

 tions that you may judge of the probable quality of the im- 

 pounded water at the end of the fourth and fifth year after the 

 completion of the dam. 



5. As to the pollution of the river by the population I think 

 little is to be feared. The Royal Commission, before alluded to, 

 speak of the Thames basin above Hampton, as being thinly pop- 

 ulated. About 230 persons per square mile, or rather less than 

 three to the acre, is the population, [Builder, 7th August, 1869,] 

 of the watershed supplying one-half of the ninety-eight million 

 gallons daily supplied to London in 1867. I find from the Blue 

 Book giving the population of New South "Wales in 1861, that 

 the parishes forming the watershed of G-eorge's River then 

 contained about 6000 persons ; as the probable increase is not 

 more than 4 per cent, per pnnun, the present population would 

 be about 8200, or less than twenty-three persons per square mile, 

 being one-tenth the population of the upper portion of the 

 Thames River basin. I have not ascertained the relative 

 proportion of cultivated land and manufactories, but believe 

 the disproportion would be greater, since the Builder of 

 the 28th August, 1869, in an article on the Pollution of Rivers, 

 after referring to another Royal Commission appointed in 1865, 

 to inquire into the effect of sewage, &c, upon the rivers of Eng- 

 land says, — ' On the Thames and its tributaries above the intake 



