THE SYDNEY WATER SUPPLY. 223 



The difficulty they had to contend with was that, owing to 

 the faulty nature of the rock when crossing the Hudson 

 River, they had to go down 1000 feet below the water level ; 

 elsewhere, it was found that sufficiently sound rock was ob- 

 tainable at not less than 150 feet below the surface of the 

 rock. Their "pressure tunnels" were lined with 4-2-1 con- 

 crete, of varying thickness, according to the hydrostatic 

 pressure, up to 17 inches thick below the Hudson River, the 

 tunnels being 14^ feet in internal diameter, to carry five 

 hundred million gallons per day. 



I feel sure that in our Hawkesbury sandstone rock it will 

 be possible at a reasonable depth to take the water safely 

 through a tunnel similarly lined, and, in my estimate, have 

 made provision, when passing under George's River, and 

 also across the Harbour to Ryde, to locate the tunnel at not 

 less than 500 feet below high water level with 17 inches 

 thickness of concrete lining. 



My scheme provides for a tunnel from the Cataract Reser- 

 voir direct to Bankstown, 27.3 miles in length. There it 

 would be bifurcated, one branch going direct to Crown 

 Street Pumping Station, 11.55 miles long, and the other 

 direct to Ryde, 8 . 3 miles in length. The main tunnel would 

 be capable of delivering 150 million gallons per day to 

 Bankstown, and the branch tunnels would each carry 75 mil- 

 lion gallons per day. At the termination of each branch 

 tunnel, the water would be taken up a shaft specially 

 designed at the top to admit of connections being made with 

 the rising mains. The pumping engines could then stop 

 work, and the water would be delivered under the pressure 

 due to the head at the Cataract Reservoir, which would be 

 sufficient to supply the maximum quantity, if required, to 

 Wahroonga, on the north side, or to Waverley, on the south 

 side. 



