The Blackfoot optimist. [volume] (Blackfoot, Idaho) 1907-1918, 1911-12-28
Everything Up-to-date

weir with an error of less than per
cent. These conditions apply equally
to all weirs whether triaL gular, rec
tangular, or Cippolettl.
/. Weir box should be set with its
floor even with the bottom of the ditt q
and should be level in all directions.
The weir itself should be exactly level
and perpendicular
@ The chanIel leading to the weir
should be CT uniform cross section, or
what is still better, should gradually
enlarge as the weir is approached. 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 be free from internal cross cur
rents or eddies as these have influence
upon the discharge.
3. The water should be brought as
nearly as possible to the state of rest
before it enters the weir. An excess
ity Of the curreLt advancing will eff
than almost any other one thing This
velocity can be reduced by widening
and deepening the box or pool above
the weir. 1t is calculated that weirs
3 feet lolg with a depth Of water Of
II inches, should not have greater
velocity Of approach than 6 inches per
second, which amount may be allowed
to increase very slightly where great
r,,;I yN.,
BY constructing the box or pool above
the weir with cross section at least
seven times that of the weir notch, a
sufficient low velocity of approach is
! usually secured.
A. The issuing stream of water must
have full contraction; that is, it must
! be sharp and clear cut. This is brot
about by making the upstream, edge
of the weir board as nearly a knife
edge as possible, and by keeping the
sides and bottom of the box below the
weir at a good distance from the fall
ling stream so that the air may pass
freely clear around and in under the
issuiLg stream. The water below the
weir should never be allowed to buck
up to the level Of the crest SO as to
exclude the air from under the issuing
stream else complete contraction will
not be secured and the discharge will
be effected If air can pass freely un
derneath the issuing stream the Level
of the water below the weir has nc
influence on the discharge. An OBJ.
servance of the following rules will us
ually insure complete contraction.
a. a. The opening of the weir or the
weir notch must be made in a plane
surface perpendicularly to the direc
ton of the flow of water.
b. The opening itself must have 9
sharp edge on the upstream side ant
l the walls should be beveled away OF
the downstream side.
c. The distance of the crest of the
weir from the bottom of the box Of
basin should be at least three times
the depth of the water on the crest.
d. The distance Of the sides of thu
weir notch from the sideso the boz
or channel should be at least twice
as great as the depth Of the watel
a flowing over the crest.
e. In order that the lateral cOntrac
ton should not be disturbed the lengt
.: of the weir crest should be approving
4 ely three times that of the depth 0
water flowing over it.
5. The depth of water flowing owe
the weir should not be less than
. inches nor more than one-third of tn
length of the crest, and it should b.
, measured where it will not be affecte
. by waves, wind or eddies, and ia
enough up stream SO that it will no
be influenced by the curvaturd induce
by the falling water. This can no
;. be done by measuring it exactly owe
!, the crest The distance above the ores
which is usually found sufficient,
. up sire N from the crest distanc
] equal to the length Of the crest. 4
!, handy method OF establishing a poin
1, from which to measure the head an
:. method which is to be recommends
: iseto drive a heavy stake up strear
from the weir and at the side wher
> it can easily be reached. This stsk
! should be driven in firmly so as ne
\ to be easily changed and should b
+ sawed off squareely at a point Sigh
h ly below the level of the crest whic
! can be determined by the aid of a ca
4 penters level and straight edge.
heavy spike or nail should then b
= driven vertically into the top of tn
= stake and the top of it's head shoul
be exactly leveled with the crest b
the same method. The head of waite
o flowing over the weir can then be tai
en- by measuring down from the su
n face of the water to the head of tn
i nail with an ordinary carpenters. rul
3 or square. The head must be measure
o within 1900 of the length of the ere!
j. in order to limit the error to Y Of OF
n per cent A very accurate messur
:, mant Of the head can Onlv he mad
m with the hook gauge which consis'
d of long rod terminating in an VI
ward metallic hook. the rod sliding u
S and down on a fixed support bein
d actuated by screw motion, while IL
2 head Of water is read from VERNE
1 attached to the rod. The rod is ru
! down until the point Of the hook is
9 low water and then raised slowly Vi
T.. til the point reaches the surface INN
tt istely over the hook. so