HISTORY OF CIVIL ENGINEERING IN NEW SOUTH WALES. 629 



between tliem with concrete so as to prevent the water creeping 

 along the outside of the tunnel. Two lines of cast-iron flanged 

 pipes forty-eight inches in diameter are laid in the tunnel above 

 referred to, which are continued through the inlet tower to the 

 reservoir and into a basin at the outlet end, terminating in each 

 case with a bell-shaped mouth, and having concentric rings cast 

 on the lengths which pass through the brickwork of the tower. 

 These pipes are also continued below the outlet tower to the scour- 

 ing channel. The four feet pipes also extend to the bottom of 

 the reservoir and can be used as syphons to empty the reservoir 

 should it be necessary at any time to do so. In both the inlet 

 and outlet towers are arranged the various stop valves and the 

 machinery for raising and lowering them, which consists of screws 

 driven by spur and bevel gearing. The valves in the inlet tower 

 are arranged to draw the water from the reservoir at different 

 levels. A lattice girder foot bridge of three spans on brick piers 

 gives access to the inlet tower. 



The canal below the Prospect Reservoir is four and three- 

 quarter miles long, and the cross section is partly with vertical 

 sides, and partly V shaped. The basin and part of the canal are 

 lined with diorite ashlar masonry. The high water level of the 

 reservoir end of the canal is 175.50 above sea level, the level of 

 the top of the canal is the same throughout the entire length of 

 this section, viz., 177.5 feet, this arrangement allows an increased 

 head to be obtained for the works nearer Sydney. Owing to the 

 nature of the ground nine hundred feet of this section had to be 

 covered in and is virtually a culvert under pressure. The fall in 

 the canal is at the rate of six inches per mile. The water is con- 

 veyed over a valley at forty-four miles by means of a brick 

 aqueduct of twenty -two arches each thirty feet span. At the end 

 of the canal there is a straining basin and pipe head reservoir 

 from which the water is conveyed through wrought iron pipes six 

 feet in diameter three-eighths and seven-sixteenths of an inch in 

 thickness for a distance of four and seven-eighths of a mile, termi- 

 nating in a screening chamber at Pott's Hill. The capacity of 

 the canal and six feet pipe from Prospect to Pott's Hill a distance 

 of about nine and five-eighths of a mile is fifty millions of gallons 

 per day. Near this point a large Balance or Service Reservoir is 

 now being constructed. It will be one thousand three hundred 

 feet in length and nine hundred feet in width having a capacity 

 of one hundred millioi;! gallons. This reservoir will be constructed 

 so as to admit of the water rising freely if necessary to the same 

 height as the water at tlie commencement of the canal below 

 Prospect, viz., 175.5 feet. 



A branch pipe, fifteen inches in diameter, leads ofi" the six feet 

 pipe at the Dog-trap Road to supply Granville, Auburn, and 

 South Parramatta. 



