The Meridian times. (Meridian, Idaho) 1909-1938, 1912-03-08
Duty and Measurement
~& of Water %g
BY DON II. BARK, Y. s. Engineer,
In Charge OF irrigation InvestI-
cations IN Idaho.
Oregon Short Line Railroad Dem
onstration Train Lecture.

onstEhtlOn Tram LecluIe4
The greater part OF the land in the
west would be practically worthless
without water with which to irrigate
II, yet there is far less attention
given to the measurement Of this
water than there Is 70 the measure
rnent OF the land Under the Carey
Act the land is sold to the settler
for so cents per acre and would
hardly be worth that without the
water, while water costs the settler
all the way from s25 to 500 per
acre.
Miners inch.
Water was first used In Idaho and
other western states for mining pur.
poses. the common method OF meas.
urement being called the miners
inch method. The miners inch was
the unit upon which such measure
mant was based, being the amount
OF water that would flow through a
sharp edged orifce one inch square
under given pressure The guam.
thy called for by a miners inch.
however. varied In different states.
due to the fact that the pressure over
the oriiice was not the same
Cubic Foot Per Second.
The cubic foot per second, which
represents definite tangible amount
that Is easily understood, was adopt
ed as the legal standard for the
measurement OF water by the Idaho
legislature In 1899. II Is commonly
known as the second foot" and rep
resents the flow OF water which will
exactly al vessel containing one
cubic foot each second OF time for
as long a period as II Is allowed TO
flow. Hence, flow OF one cubic
foot per second delivers go cubic feet
per minute. or 5000 cubic feet per
hour. or $4,000 cubic feet In day Of
twenty-four hours,
II Is found that one cubic foot per
second equals flow Of almost exactly
so Idaho miners inches. or $50 gallons
per minute A flume one foot wide
and one foot deep, II filed with water
that Is flowing at the rate OF exactly
one foot per second. win carry one
cubic foot per second, and otner
fumes or bitches IN the same proper.
ton The quantity discharged de.
ponds upon the velocity OF the flow
and the area OF cross section of the
advancing stream OF water. These
two factors are taken Into consider,
alton when determining the flow oil
large streams and canals II being
only necessary TO determine the area
OF the cross section and tho average
velocity, which two amounts multi.
piled together gives the discharge.
The cross section Is found by multi.
plying the average depth OF the
stream by the width. The average
velocity is found. by measuring the
rate OF the same either, with floats
or with a current meter especially
constructed for the purpose. A close
approximation OF the velocity can be
secured by noting the time that is
required for surface float to ad.
vance through 100 or more llneal
feet Of the ditch This gives the sur.
face velocity, and 10 find the average
velocity one must multiply the sur.
face velocity by IS. since the aver.
age velocity Is that much slower
than the surface velocity. owing to
the friction on the sides and bottom
Of the channel.
Acre Foot.
Where large volumes Of water are
20 be considered the expression of
the amount In cubic feet would in
yoIys the use OF such large numbers
that the same would be cumbersome.
In order TO simplify these expires.
sions the term "aere.foot" Is used,
which represents enough water to
cover an acre one foot 10 depth. OF
1850 cubic feet The use of this
term has the additional advantage OF
being easily compared with the acre
age: as for example. a reservoir con
tanning $4,000 acre feet OF water
would furnish a depth of two feet
for $4,000 acres of land. A cubic
foot OF water per second flowing con
tinuously for twenty,four hours fur
nishes almost exactly TWO acre fee
of water,
Hydraulic Equivalents Which viii b
Found Useful TO Irrlgators.
l. Idaho miners inch equals mp
pruximately l.60 of II cubic foot pc
second, or nine gallons per minute,
2 The flow Of cubic foot pc
second equals approximately so min
ers inches, or $50 gallons per min
ute
3. One cubic foot per second 70
"a hours equals approximately acr
feet
4. One acre foot equals enoug
water TO cover an acre exactly
foot In depth, or 1850 cubic feet.
5. One miners inch per acre fo
100 days equals 3.97 feet deep on tn
land.