The Idaho Republican. [volume] (Blackfoot, Idaho) 1904-1932, 1912-01-26

, always produces the same dischare
over the same size of a weir. TIL
conditions given for the constructio
and installation of weirs must be ril
idly adhered to, however, if accul
ate measurement is to be made. Th
A.. formula which has been evolved an
which gives the discharge of accul
ately constructed Cippoletti Weirs
@ equals 1897 L H 80
Where @ equals the number of Gu
} bic feet per second
L equals the length of crest in fec
and equals the depth of water O
the crest in feet,
provided the ame is measured fror
a point level with the crest and u.
stream from it at a distance equal t.
the length of the crest. In order t,
facilitate the determination of tn,
discharge over weirs and to reduc,
the liability for error to a minimum
tables of discharge for weirs hav,
been compiled. These may be Sc
cured from my office or from an,
reliable book on the measurement Of
water.
Throughout all of the experiments
upon which the weir formula is based
certain conditions have been observed
with regard to the setting and plac-
ing OF the weir and these conditions
must be reproduced if it is expected
to secure accurate measurement. If
these conditions are rigidly carried
out, water a be measured with the
Cippoletti weir with an error of less
than l per cent. These conditions
apply equally to all weirs whether
triangular, rectangular or Cippoletti
T l. The weir box should be set with
its floor even with the bottom of the
ditch and should be level in all direc-
tons. The weir itself should be x
actly level and perpendicular.
2. The channel leading to the weir
should be of uniform Section.
or what is still better, should grad
ually enlarge as the weir is an
preached. The axis of the stream
should pass through the weir and
perpendicular to it.; or, in other
words, the weir should be located at
right angles to the middle of the
stream. The advancing stream should
free from internal cross currents
or eddies, as these have an Influence
upon the discharge.
3. The water should be brought as
nearly as possible to a state of rest
before it enters the weir. An excess
velocity of approach due to the We
ocity of the advancing current will
Effect (fncrease) the discharge more
almost any other one thing.
velocity a be reduced by wild
ming and deepening the box or pool
the weir. 1t is calculated that
veirs 3 feet long with a depth of
water of IL inches, should not have
greater velocity of approach than
inches per second, which amount
nay be allowed to increase very
where greater depths over
'lder Weirs are used. BY construct
1g the box or pool above the weir
18th a o section at least seven
mes that of the weir notch, a suf
GENTLY low velocity of approach is !
sually secured. :
n Issuing stream of water must
ave full contraction. that is, it must T
e sharp and clear cut. This is :
rought about by making the up- i,
ream edge of the weir board as g
early a knife edge as possible. and =
Y Keeping the sides and bottom of q
le o below the weir at a good I
stance from the falling stream so "
at the air may pass freely clear v
'ound and in under the issuing h
The water below the weir ~
ould never be allowed to back I'D g,
the level of the crest so as to ex- =,
lde the air from under the issu- g,
g stream else complete contraction N
II not be secured and the discharge NJ
ii De affected. If air can pass ",
eely underneath the issuing stream +,
level of the water below the weir &c
s no influence on the discharge. n,
observance of the following rules II
II usually insure complete con- to
y:
a. The opening of the weir or the NJ
If notch must be made in a plane 10
perpendicular to the direct fa
n of the flow of water. m
D. The opening itself must have a or
Irp edge on the upstream side and w.
walls should be beveled away on nh
downstream side. ~
;. The distance of the crest of the do
If from the bottom of the box or th'
in should be at least three times of
depth of the water on the crest. N,
|. The distance of the sides of the TO,
r notch from the sides of the box an
channel should be at least twice col
great as the depth of the water an
wing over the crest. VIII
!. In order that the lateral con- ac,
,tion should not be disturbed the an,
9Th of the weir crest should be We,
roximately three times that of the III
of water flowing over it. iah
The depth of water flowing over The
weir should not be less than 2 voI
les nor more than one-third of 1f
length of the crest, and it should i'm,
where it will not be af- wa,
by waves, wind or eddies, and doy
enough up stream so that it will t,1n
be influenced by the curvature tam
ICED by the falling water. This the
not be done by measuring it ex- has
7 over the crest. The distance a h
e the crest which is usually =
d sufficient, is up stream from :
crest a distance equal to the a;.a
tn of thn croct A hondv no.s ulSt