Fig. 675.
TABLES AND DATA.
Miner’s Inch Measurement. The term miner’s inch is of California origin, and not known or used in any other locality, it being a method of measurement adopted by the various ditch companies in disposing of water to their customers. The term is more or less indefinite for the reason that the water companies do not all use the same head above the center of the aperture, and the inch varies from 1.36 to 1.73 cubic feet per minute each, but the most common measurement is through an aperture 2 inches high and whatever length is required, and through a plank 11⁄4 inches thick, as shown in the engraving, Fig. [675]. The lower edge of the aperture should be 2 inches above the bottom of the measuring box, and the plank 5 inches high above the aperture, thus making a 6-inch head above the center of the stream. Each square inch of this opening represents a miner’s inch, which is equal to a flow of 11⁄2 cubic feet per minute. Time is not to be considered in any calculation based upon a miner’s inch measurement.
Explanation of Weir Dam Measurement. Place a board or plank edgewise across the stream to be measured as illustrated in Fig. [676].
This plank will be supported by posts sufficiently strong to resist the pressure likely to be brought upon it by the head of water which will form in the pond above this temporary dam, saw out a gap in the top of the dam whose length should be from two to four times its depth for small quantities of water and longer for larger quantities. The edges of this gap should be beveled toward the intake as represented. The over-fall below the bottom of gap should be not less than twice its depth, that is, twelve inches if the gap is six inches deep, etc.
Drive a stake above the dam at a distance of about six feet from the face of the plank and then obstruct the water until it rises precisely to the bottom of the gap and mark the water level on the stake. Complete the dam so that all the water will be compelled to flow through the gap and when the stream has assumed a regular flow mark the stake at this new level.