in thickness. Through this tunnel are laid a 33 in. and 48 in.
main; the former for the water supply, and the latter for scouring or for
emptying the reservoir on an emergency. There is a plugging of brickwork
in cement under the center of the dam in the line of the puddle wall, and
then stop walls built at the end of the plugging, projecting 25 ft.
beyond the sides of the culvert and 8 ft. above, the space between them
being filled up with cement concrete tied into the rock, and on this the
puddle wall rests. This bank, like almost all others pierced by outlet
pipes or culverts, was not destined to be perfect. In 1867, four years
after the completion, spurts of water showed themselves in the culvert
in front of the puddle wall, which began to settle, and the water had to
be drawn off to admit of repairs. Diagram No. 10 shows a structure of a
different character to any of these already described. This character of
work is adopted on the North Poudre Irrigation Canal, in N.E. Colorado.
Timber is there plentiful, and a dam of this character can be rapidly
constructed, although probably not very durable, owing to liability to
decay of timber. That represented is about 25 ft. high.
The author has now concluded the consideration of earthwork dams, and
proposes making a few remarks upon those of masonry or concrete, with
reference to some of the most important, as shown on the diagrams.
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