The Caldwell tribune. [volume] (Caldwell, Idaho Territory [Idaho]) 1883-1928, 1912-01-05

economical method of water measure
,n1ent that has. been devised for the
measurement of comparatively small
heads of water is the weir measure
ment The weir consists essentially
of thin notch of a suecific shape,
which the water is caused to flow
over. The amount of flow depends
upon the depth of the water flowing
over the crest, as the bottom of the
notch is called. The weir has been
used for the measurement of water
for hundreds of wears and the method
of its installation and the discharge
of water over it have both been work
ed out so carefully that water can be
measured over it with an error of less
than one per cent. if care is used.
There are several forms Of weirs,
the name of each designating; the
shape of the notch. Cippoletti, an
Italian engineer, evolved and perfect
ed the weir which bears his name,
many years ago, this being the weir
that is now most generally used in
the west. Other weirs, namely, the
rectangular and the triangular weirs,
are constructed and operated in much
the same way, the same rules being
observed in the measurement, practi-!
cally the only difference existing be-;
ing, as has been stated, in the shape
of the notch and the formula used in
the computation of the discharge The.
Cippoletti weir notch is trapezoidal in
shape, having, a straight bottom or.
crest with sides that slope outward
from the vertical at the rate of one
horizontal to four vertical. A one;
foot Cippoletti weir has a straight.
horizontal bottom or crest one foot
in length with a width between the.
sides of IS inches at height of 6:
inches above the crest. If the notchl
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 neces-i
sary in order to secure sharp clear.
cut issuing stream which it is neces-t
sary to secure 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 pro-,
per size and shape notch has been cut.
In this case the notch in the board,
should be cut slightly larger than in,
the galvanized iron. sloping or bevel-.
ing the edges in the same manner as;
before. The use of the galvanized:
iron or other metallic crest is espec-,
tally recommended as it not only in.
sures~ sharp clear-cut issuing streamt
upon which accurate measurement de-,
Ponds, but in addition, it also. fur
nlshes permanent Interchangeable;
crest for the water to flow through
Provided the necessary requirements
are observed in the construction and
installation of 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 measured, not on the crest, but.
from point level with the crest and,
up stream from it distance equal toi
its length.
= Weir Box.-In order to maintain the;
weir in proper and constant position;
and to prevent leakage around and!
under it, and in order that all water
that is to be measured should be m.
Quoted over it, it is usually necessary
to construct 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 weir is 9 feet long, 21l feet
deep and 3 feet wide inside measure;
ment, and with a one foot weir. will;
measure with accuracy amounts rang;
ing from 10 to SO Idaho miners inches. ;,
Where weir Dox is built, it is,
necessary that it be made of sufficient,
size and depth in comparison to the,
size of the weir notch to eliminate all!
excess velocity of approach. If the,
box is built too narrow or too shallow,
it will add to the velocity of approach.
to SUCH an extent that erect measure,
ment can not be secured. 1t is but al
mere matter of convenience, however
to have box of the exact length.
prescribed, for that part of the box,
above the weir may be omitted 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 weirJ
OF larger sizes should be in the same
proportion with respect to the size of
the weir as for one foot. The size Of
weir box that is required in order toi
eliminate velocity of approach has
been found by experiment, to be apj
proXlmately seven times the cross sec5
ton OF the weir notch. j
Discharge.-The discharge of weirs
has been accurately calculated by
various engineers who have carried
on hundreds of experiments covering
years OF time, and it is found that un;
der like conditions the same depth
always produces the same discharge
over the same size of a weir. The
conditions given for the construction
and installation Of weirs must be ripi
idly adhered to, however, if accurate
measurement is to be made. This
formula which has been evolved and
which gives the discharge of accul
rately constructed Cippoletti weirs is
Q-3.367 L H 80 !:
Where Q-the number of cubic feet
per second,
1.-The length OF crest in feet
and 1.-THE depth of water on tho
crest N feet,
provided the same is measured from a
point level with the crest and up