ing,
the outer side of the flume is raised in accordance with the curve. No
rule can be given for the exact amount of rise, but it can be readily
determined by wedging up the flume. This is very essential in cold
climates, as ice forms where any splashing occurs.
Waste-Gates.—Waste-gates
should be placed every half-mile, so that the water can be readily
turned out, as may be required from time to time, and are especially
necessary in case of any accident. They should discharge the water
clear of the line to prevent any undermining. They are useful also for
clearing the canal of snow and ice.
Precautions against Cold.—In
the snow belt the flumes are covered with sheds in the most dangerous
places where they are exposed to snow slides. The most approved form of
snow shed consists of sets of timber 4X6 inches to 7X9 inches in size,
placed at intervals of four feet and covered with boards or lagging.
Where the flume is set in close to the bank the circulation of air
arotlnd it during the winter is partially prevented by snow, and
freezing of the water is not so probable as where the flume is exposed
on all sides.
Great
difficulty is experienced sometimes in keeping flumes and ditches open
during long continued very cold weather, on account of the formation of
anchor ice on the bottom. When this occurs it is necessary immediately
to turn out the water, otherwise they will fill up solidly with ice and
remain closed until spring. Should snow fill the flume when empty, it
can be readily run out if the water is turned on before it is allowed
to pack.
In
Nevada County, at the head of the Bloomfield ditch, the snow falls in
depths of from six to thirteen feet on a level. The temperature ranges
as low as zero, but ordinarily has a winter mean of 300
Fahr. The Bloomfield ditch, carrying 80 cubic feet of water per second,
is seldom troubled by the forming of ice or snow blockades. This ditch
is supplied from a reservoir, the water of
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