The Idaho Republican. [volume] (Blackfoot, Idaho) 1904-1932, 1911-12-22

observed in the measurement, practi
cally the only difference existing
being, as has been stated, in tn
shape of the notch and the formul;
used in the computation of the dis
charge The Cippoletti weir motel
is trapezoidal in shape, having ;
straight bottom or crest with side,
that slope outward from the vertica
at the rate of one horizontal to foul
vertical. A one foot Cippoletti wei
has straight horizontal bottom OF
crest one foot in length with a Width
between the sides of Is inches at {
height"of 6 inches above the crest
If the notch is made of wood the
sides and bottom should be beveled
off on the down stream side, leaving
a sharp thin edge on the upstream
side. This is necessary in order to
secure sharp clear-cut issuing
stream which it is necessary to Sc
cure If accurate measurement is to
be obtained. 1t is usually the best
policy to line or face the upper side
of the weir board with a piece OF
galvanized iron from which the prop
er size and shape notch has been
cut. In this case the notch in the
board should be cut slightly larger
than that in the galvanized iron
sloping or beveling the edges in the
same manner as before. The use of
the galvanized iron or other metallic
crest is especially recommended as it
not only insures sharp clear-cut is
suing stream upon which accurate
measurement depends, but in addi-
ton, it also furnishes a permanent
interchangeable crest for the water to
flow through. Provided the neces-
sary requirements are observed in
the construction and installation of
a weir, the amount of water flowing
over it depends upon but two factors
the length of crest and the depth
OF the water on the crest. The
length OF crest being known, the
depth of the water should be meas
ured, not on the crest, but from a
point level with the crest and up
stream from it distance equal to it's
length.
Weir BoX-In order to maintain
the weir in a proper and constant
position and to prevent leakage
around and under it, and in order
that all water that is to be meas
lred should be conducted over it, it
IS usually necessary to construct
some sort of box or frame to hold
he weir in place. A common form
)r type of this box which is rec
for one foot Cippoletti
weir is 8 feet long, 21s feet deep
Ind 3 feet wide inside measurement, |
md with one-foot weir will meas
Ire with accuracy amounts ranging |
rom 10 to so Idaho miners inches.
Where a weir box is built, it is
necessary that it be made of suffic-
ent size and depth in comparison to |
he size of the weir notch to elimin-
tie all excess velocity of approach. II
he box is built too narrow or too
hallow it will add to the velocity of
pproach to such an extent that cor
ect measurement can not be secured.
is but mere matter of convent
nee, however, to have box of the
Xact length prescribed, for that part
f the box above the weir may be
mitted if settling basin or pool of
he same size is constructed in the
itch above the weir. The weir box
S and pools which should be con-
tructed for weirs of larger sizes
hould be i'm the same proportion
18th respect to the size of the weir
S for the one foot. The size of weir
OK that is req ired in order to elm
late velocity of approach has been
ound by experiment, to be approx
lately seven times the cross section
f the weir notch.
Discharge-The discharge of welrs
as been accurately calculated by
arious engineers who have carried
n hundreds of experiments covering
ears of time, and it is found that !
nder like conditions the same depth ,
ways produces the same discharge :
YER the same size of weir. The y
)nditions given for the construction .
nd installation of weirs must be rig !
lily adhered to, however, If accur-
lie measurement is to be made. The -,
,rmula which has been evolved and
hich gives the discharge of accur-
ELY constructed Cippoletti weirs is
equals 1897 l. H 80
here @ equals the number of Gu ;
bic feet per second
equals the length of crest in feet
I'd H equals the depth of water on
the crest in feet,
'ovided the same is measured from
point level with the crest and up !
ream from it at distance equal to
lie length of the crest. In order to :,
cilitate the determination of the !,
scharge over weirs and to reduce
e liability for error to minimum, {
bles of discharge for weirs have
zen compiled. These may be Sc
lred from my office or from any
liable book on the measurement of
ater.
Throughout all of the experiments b
BON which the weir formula is based C
rtain conditions have been observed t.
18th regard to the setting and plac-
g of the weir and these conditions |,
ust be reproduced if it is expected t
secure accurate measurement. ills
ese conditions are rigidly carried /,
It, water can be measured with the
ppoletti weir with an error of less t
an / per cent. These conditions C
,nlv euuaIIy tn all wairS Whethe1 n