Elmore County Republican. [volume] (Mountain Home, Idaho) 1910-1915, 1912-02-03

amount OF water flowing over 1t
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 a distance equal to
it's length.
Weir Box-In order to main
tain the weir in a proper and con
slant position and to prevent leak
age around and under it and IN
order that all water that is to be
measured should be conducted oy,r
it, it is usually necessary to con
struct some sort of box or frame
to hold the weir in place A
common form or type Of this box
which is recommended for a one
foot Cippoletti wier is 8 feet long,
212 feet deep and 3 feet wide IN
side measurement, and with a one
foot weir will measure with ac-
curacy amounts ranging from 10
to 80 Idaho miners inches.
| Where weir box is built, it
is necessary that it be made Of
sufficient size and depth in com
parison to the size of the weir
notch to eliminate all excess vel
ocity of approach. If the box is
built too narrow or even too shall
low it will add to the velocity Of
the approach to such an extent
that correct measurement can not
be secured. 1t is but a mere mat
ter of convenience, however, to
have box of the exact length
prescribed, for that part OF the
box above the weir may be omit
ted if a settling basin or pool OF
the same size is constructed in the
ditch above the weir. The weir
boxes and pools which should be
constructed for weirs Of larger
sizes should be in the same pro-
portion with respect to the size
of the weir as for the one-foot.
The size of weir box that is re-
qumed in order to eliminate vel
ocity of approach has been found
by experiment, to be approx
mately seven times the cross sec
tion of the weir notch.
Discharge-The discharge OF
weirs has been accurately calcu-
lated by various engineers who
have carried on hundreds of ex-
periments covering years of time.
and it is found that under like
conditions the same depth always
produces the same discharge ovel
the same size Of a Weir. The
conditions given for construction
and installation of weirs must be
rigidly adhered to, however, if
accurate measurement is to be
made. The formula which has
been evolved and which gives the
discharge of accurately construct
ed Cippoletti weirs is y equals
1867 l. H 80
Where Q equals the number OF
cubic feet per second
L equals the length of crest in
feet and H equals the depth of
waters on the crest in feet
provided the same is measured
from a point level with the crest
and up stream from it at a dis
lance equal to the length of the
crest. In order to facilitate the
determination of the discharge
over weirs and to reduce the liza
bility for error to minimum,
tables of discharge for weirs have
been compiled These may be
secured from my office or from
any reliable book on the measure
ment OF water.
Throughout all of the expert
ments upon which the weir for
mula is based certain conditions
have been observed with regard
to the setting and placing Of
the weirs and these conditions
must be reproduced if it is expect
to secure accurate measurements.
Ii these conditions are rlgidly
carried out, water can be meas
ured with an error of less than
| per cent. These conditions APP
ply equally to all weirs whether
triangular, rectangular or Cippo-
lett.
l. The weir box should be
set with it's floor even with the
bottom of the ditch and should
be level in all directions. The
weir itself should be exactly level
.,l