628 PROCEEDINGS OF SECTION J. 



Trafalgar Tunnel, six hundred and fifty-eight and two-thirds 

 feet in length. The canal then terminates in a basin at a 

 little beyond thirty-nine and three-quarter miles, with an 

 overflow weir, sluice gate, and gauging weir, after which 

 it flows into a concrete channel leading to Prospect 

 Reservoir ; the inclination of this channel is one in 

 38.25, the level of the overflow weir at the end of the canal is 

 243.15 feet above the sea level, that is, 48.15 feet above the pro- 

 posed high water of the reservoir. A thirty-inch main has been 

 laid from the basin above the reservoir to the canal below it, 

 for the purpose of supplying the latter independently of the 

 reservoir, and also to give head for working valves, &c. 



All the tunnels above described are similar to the Sugarloaf and 

 Mount Anna in section and grade, and are lined throughout with 

 three-brick rings. 



The capacity of the works above Prospect is slightly over 

 one hundred and and fifty millions of gallons per day. 



The Prospect Reservoir when full will have a storage capacity 

 of 10,812 million gallons, the area of the water surface will be 

 1,261 acres, the greatest depth will be seventy -five feet, and the 

 depth from which water will be drawn twenty-five feet, giving an 

 effective storage capacity of 7,110 million gallons. The reservoir is 

 formed by the construction of an earthen dam, one hundred and 

 ten chains long and eighty-five feet high in the deepest part, the 

 width at the top will be thirty feet, the slopes are three to one 

 inside and two and a-half to one on the outer side with fifteen feet 

 berms at reduced levels, one seventy-five and one hundred and 

 forty-seven. The reduced level at top of dam is two hundred 

 and three feet, top water level, one hundred and ninety-five 

 feet ; lowest level to which water can be drawn off, one hundred 

 and seventy feet ; the maximum width of the base of the dam 

 at the ground level is five hundred and twenty-five feet. The 

 water slope is pitched with diorite blocks eighteen inches deep. 

 The puddle-wall is carried down from a di.^tance of about six 

 feet below the top of the bank to the solid shale and is eight feet 

 wide at the top, battering one in eight outwards to ground level, 

 and inwards below the ground level to the shale foundation ; it 

 is protected on each side with selected materials, consisting of red 

 and white clay rammed in layers six inches deep sloping one in 

 twelve downwards towards the puddle wall. The remainder of 

 the dam consists of similar materials sloping in a similar manner 

 towards the puddle wall but rammed in layers twelve inches deep. 



The works for drawing water fi'om the i^eservoir consist of a 

 curved tunnel nine hundred and thirty-two feet long driven 

 through the solid ground altogether clear of the embankment ; it 

 is circular in form and twelve feet in diameter and is brick lined 

 throughout. There is a stopping formed by building out the 

 brickwork in stepped concentric rings, and filling up the space 



