Its erection occupied eighteen months, and
cost about L18,000. It is curved in plan to a radius of 300 ft., and the
greatest depth or head of water is 52 ft. 4 in. The width at the crest is
only 2 ft. 8 in., although surmounted by a heavy coping of bluestone 3
ft. 3 in. broad and 1 ft. 9 in. deep. There being no facility for making
a by-wash at the side, the center of the dam is dished to form a weir 30
ft. long. There are both outlet and scour pipes, and valves of 2 ft.
diameter, and the capacity of the reservoir is 143,145,834 gallons.
The Paramatta dam, in New South Wales, built of masonry in hydraulic
mortar, is another instance of a dam built on the curve, and which has
resisted a flood of water 4 ft. in depth over the crest; and in the case
of a dam of about 40 ft. high across the river Wyre, in connection with
the Lancaster Water Works, made of cement concrete in proportion of 4 to
1, there has, according to Mr. Mansergh, frequently been a depth of 5 ft.
of flow over it. This dam is built to a radius of 80 ft. only, and as it
measures 100 ft. along the crest, must include about the fifth of a
circle.
There now remain only two other examples of masonry dams, the first being
that in connection with the Liverpool water supply, and known as the
Vyrnwy dam, Fig. 17, this being thrown across a stream of that name in
North Wales.
Pages:
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55