It is built of rubble masonry, with ashlar facework, laid in hydraulic
mortar. The total amount of masonry is 325,000 cubic yards. There are two
weirs, at a level of 6 ft. below the crest, each 82 ft. wide. The total
height, including the foundations, which are carried down from 3 ft. to 5
ft. into the rock, is 154 ft., and the breadth of the crest, which
carries a road, is 49 ft. 3 in., and at the base 216 ft. The outlet pipes
are carried through tunnels, which are driven on the curve into the hill
side a considerable distance clear of each end of the dam.

Another very important structure is the Villar dam, Fig. 15, in
connection with the water supply of Madrid, and situated on the river
Lozoya. The storage capacity of this reservoir is very considerable,
viz., 4,400,000,000, or nearly thirteen times as great as that of Furens.
The height of the dam is 162 ft., with a breadth of 14 ft. 9 in. at the
crest. It is built on the curve to a radius of 440 ft., and the length of
the dam measured along the crest is 546 ft., of which 197 ft. is by-wash,
thus describing nearly one-fifth of a circle, and consequently well
designed to resist pressure. The dam is built of rubble masonry in
hydraulic mortar, and cost £80,556.

The Stony Creek lower reservoir dam of the Geelong water supply, Fig. 16,
colony of Victoria, is interesting as being constructed of concrete, in
the proportion of 1 to 8½. Its erection occupied eighteen months, and
cost about £18,000. 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.