Payette enterprise. (Payette, Canyon Co., Idaho) 1909-1935, 1912-01-25
DUTY AND MEASURE
MEnT or WATER
(ContInued DON page I'D

zoo hudliOW IL Nll uld 70 inc FeiOc
ity OF approach to such an exten
that correct measurement can no
DO secured. II is but mere mattel
OF convenience, however, 10 have
box OF the exact length prescribed
for that part OF the box above the
weir may be omitted II a settling
basin or pool Of the same size "a
constructed In the ditch above the
weir. The weir boxes and pools
which should be constructed for weir
OF larger sizes should be In the same
proportion with respect to the size
Of the weir % for the one foot. The
size OF weir box that is required
In order 10 eliminate velocity OF
approach has been found by exper.
imCnt. 70 be approximately seven
times the crcsg section OF the weir
notch.
Discharge The discharge OF weirs
has been accurately calculated by
various engineers who have carried
on hundreds OF experiments cover
ing years OF time. and IL is found
that under like conditions the same
depth always produces the same
discharge over the same sic OF a
weir, The conditions given for the
construction and installation OF weirs
must be rigldly adhered TO. however.
! II accurate measurement is to be
made Tho formula which has been
evolved and which gives the dis
charge Of accurately constructed Clip
Doletti weirs is
Q equals 1857 l. II 80
Where q equals the number OF cub
lc feet per second.
l. equals the length OF crest In
feet
and II equals the depth OF water
on the crest In feet.
provided the same Is measured from
point level with the crest and up
stream from Il at distance equal
10 the length Of the crest. In order
10 facilitate the determination Of
the discharge over welrs and to re-
duce the liability for error to
minimum. tables OF discharge for
wirse have been compiled These
may be secured from my office or
from any reliable book on the meas.
urement OF water,
Throughout all OF the experiments
upon which the weir formula Is
based, certain conditions have been
observed with regard to the setting
AMI placing OF the weir and these
conditions must be reproduced IL Il
r. expected to secure accurate meas
urement. II these conditions are
rigldly carried out. water can be
measured with the Cippoletti weir
with an error OF less than l per
cent These conditions apply equal.
~ to all welrs wheth0r triangular
FoctanSulan or eippoletti.
L. The weir box should be Sc
with It's floor even with the bottom
G. the ditch and should be level in
al directions The weir itslef should
be exactly level and perpendicular
2. The channel leading to the
weir should be OF uniform cross sec
tion. or what Is stlll better. should
gradually enlarge as the we.r is
The axis OF the stream
should pass through the weir and
perpendicular TO It; or, In o,her /
words. the weir should be located |
az r,ght angles 10 the middle of /
the stream. The advancing stream
should be 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 state OF
rlst before II enters the weir An
excess velocity OF approach due to
tho velocity of the advancing cur
rcnt will affect tinereasel the dis.
charge more than almost any ether
ono thing. This velocity can be
reduced by widening and deepening
the box or pool above hte weir. Il .
Is calculated that weirs 3 feet long
with a depth of water OF l2 inches.
should not have a greater ve'o ,ity
Of approach than inches per soc.
ond. which amount may be allowed
10 increase very slightly where
greater depths over wider weirs are
used by constructing the box or
pool above the weir with cross
section at least seven times that
81 the weir notch. sufficiently low
velocity OF approach is usua " Sc
cured
T. Tho issuing stream OF water
must have full contraction; that is
L must be sharp and clear cut.
This is brought about by making the
upstream edge OF the weir board
IS nearly a knife edge as possible,
md by keeping che sides and bot
om OF the box below the weir at
FOOD distance from the falling sire m
10 that the air may pass freely
,lear around and IN ulder the issu.