The Meridian times. (Meridian, Idaho) 1909-1938, 1912-03-15
Duty and Measurement
Xxx Of Water Xxx
By DON "A. BARK, u. s. Engineer,
In Charge Of irrigation Investi-
cations in Idaho.
Oregon Short Line Railroad Dem.
onstration Train Lecture.
(Continued nom Iast week)

+
f. The issuing stream OF water
must have full contraction; that Is. II
must be sharp and clear cut This
II brought about by making the up
stream edge OF the weir board as
nearly knife edge as possible, and
by keeping the sides and bottom Of
the box below the weir at a good dis
lance from the falling stream SO that
the air may pass freely clear around
and IN under the issuing stream The
water below the weir should never be-
allowed to back up To the level Of
the crest 80 as TO exclude the air
from under the issuing stream, else
complete contraction will not be Sc
cured and the discharge will be affect
ed II air can pass freely underneath
the Issuing stream the level OF the
water below the weir has no influence
on the discharge An observance OF
the following rules will usually in.
sure complete contraction.
q. The opening Of the weir or the
weir notch must be made In plane
surface perpendicular To the direction
OF the How OF water
b. The opening itself must have a
sharp edge on the upstream side and
the wallis should be beyeled away on
the downstream side.
d. The distance of the crest or the
weir from the bottom Of the box or
basin should be at least three times
the depth Of the water on the crest.
d. The distance Of the sides Of the
weir notch from the sides OF the box
or channel should be at least twice
al great as the depth OF the water
flowing over the crest.
., In order that the lateral con.
traction should not be disturbed the
length Of the weir Great should be
approximately three times that OF the
depth OF water flowing over IL,
81 The depth OF water flowing over
the weir should not be less than two
inches nor more than onethird OF the
length OF the crest, and II ahould be
measured where Il viii not be affect.
ed by waves. wind or eddies, and far
enough up stream so that Ii viii not
be influenced by the curvature In.
dueed by the falling water This can
not be done by measuring II exactly
over the crest The distance above |
the crest which Is usually found suffi-
cient. Ii UP stream from the crest a
equal to the length Of the
crest
The most frequent cause OF error
In weir measurements ~ excess ys.l
iocity "a approach and this must be
guarded against by providing a good
sized pool above the weirs which
must be kept clean and free from
sediment.
"Don'ts' In Regard 70 Welrs.
1, DO not set weir Immediately
below a curve Ia the ditch. for the
curve will cause the water to flow to.
the side OF the crest
2. DO not set II Immediately below
or too close to head gate where tho
water has high velocity. as by so do.
ing, II will cause too high a velocity
OF approach,
3. Don't allow the water below the
weir 70 back up even with the crest
as II win not allow complete contrac-
TON and will cut down the discharge,
4, DO not set the weir any other
way than perpendicular and at right
angles 70 the flow OF the stream
s. DO not attempt TO use too small
weir. Put In larger weir where
the water 10 be measured exceeds a
depth on the crest OF 10 the crest
length
G. DO not allow the pool above the
weir to ill up with sediment, as the
resulting decrease In the cross sec.
ton will increase the velocity OF APP.
proaeh.
l. The weir box should be set with
Its floor even with the bottom OF the
Duty Of Water.
To know the proper amount of ir,
rigation water that should be applied
to the different soils and crops In or
der to make the greatest possible
yield, has always been a serious prob.
lem 60 all irrigators 1t has always
been known that In order to secure
the biggest possible crop II IL neces
sary to apply different amounts TO
different crops aud 10 different soils
with the same crop but just how
thuCh NttS dHlhuAlh sntulN ub mus HtNeT
been known only In an indefinite way
The Irrigation Investigations de-
partment. which represent In the
state OF Idaho. has. In cooperation
with the state engineers office, been
carrying on series of experiments
for the past two years by means OF
which II Is hoped to determine this
very important factor. and we have
secured a vast amount OF data con.
corning IT, These experiments have
all been carried out on comparatively
large areas and in a practical way.
Il does not give any indication oil
how much water is necessary for
maximum crop production on any
soil 70 merely measure the amount
that some farmer applies for the rea
son that the same or a larger croT
might have been produced with either
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