132 MEASUREMENT OF FLOWING WATER.
The
La Grange main ditch, 17 miles long, has a sectional area of 22.5
square feet, and a grade of 7 feet per mile. From the delivery, 56.5
cubic feet per second, at its Patricksville junction the coefficient c is
determined to be 52, but it is based upon the assumption that the depth
of the canal is 3 feet, whereas in the original construction ' it was
supposed to have been made 4 feet deep ; the discharge therefore due
to such a sectional area would necessarily diminish the ascribed value
of c*
In
all these canals, after the artificial banks are well consolidated, the
water area is increased beyond the original excavation in the natural
ground.
Accuracy cannot be expected in calculating the values of Q for
proposed ditches of such character. Important losses must vary in every
ditch, depending on the nature of the ground, and the character of the
construction of the work, and the season of the year. The feeders along
the lines largely compensate for these losses. In order to be safe in
estimating the capacity of a ditch, the value of the coefficient c for the dry season should be taken.
The following facts show the magnitude of the losses due to absorption, leakage, evaporation, etc.
Three
thousand miner's inches of water (a flow of 75 cubic feet per second)
turned in during the dry season at the head of the Bloomfield ditch
will deliver 2,700 inches (67.5 cubic feet per second) at the gauge 40
miles distant. 2,400 inches of water (60 cubic feet per second) turned
in at the head of the Milton ditch formerly delivered at the gauge, 29$
miles distant, 1,450 to 1,600 inches (36.25 to 40 cubic feet per
second); but at present 2,500 inches (62.5 cubic feet per second)
turned into the head of the ditch delivers 2,000 inches (50 cubic feet
per second) at the gauge. The exact loss of water between the head of
this ditch and the measuring box is shown in the following
* The grades given in all the above cases, from which the different values of c were calculated, are otherwise independent of the drops, chutes, flumes, etc. Sectional areas represent minimum cross sections.
