The watershed, or reservoir, of the Excelsior
Company embraces the valley of the South Yuba and its affluents, and the
entire cost of its eight amalgamated canals was 750,000 dollars.
The rainfall during three years in the mountains averaged 49 inches
annually, while the medium in the same period did not exceed 20 inches in
the plains beneath. The height of the reservoir above the tailing, or Yuba
River, is 393 feet: and the height of the head above the floor, or outlet
sluice-tunnel, of the Blue Gravel Mining Company was 197 feet.
The exact quantity of water required to wash every class of gravel is
difficult to estimate, but no quantity or pressure would be excessive if
properly arranged. The measurement of water is effected by miner's
inches, by allowing it to flow from the reservoir of the seller to the
purchaser through a box 10 or 12 feet square, with divisions to obtain a
quiet head, with a slide or opening capable of adjustment to any required
measure; thus an opening of 25 inches by 2 inches, with a quiet head of 6
inches above the middle of the orifice, would give 50 inches, or about
89,259 cubic feet of water, flowing during ten hours per day, being an
amount necessary for a first-class operation. The capability of the
Excelsior Canal in rainy seasons reached to a delivery in twenty-four
hours, to the various mining companies, of 21,120,000 cubic feet of water,
or 8,000 miner's inches, and the value of the water paid for by the Blue
Gravel Company in forty-three months ending November 9, 1867, was 157,261
dollars, being at the rate of 15 cents of a dollar per miner's inch; and
the proportion of water used to wash down 989,165 cubic yards of gravel
was 17,074,758 cubic yards, or 171/4 cubic yards of water to 1 cubic yard of
gravel; and when at work the quantity of gravel daily moved was 1,298
cubic yards, and the estimated cost to move one cubic yard of gravel was 5
and 7/10 cents of a dollar.
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