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

due to the velocity OF the add
yancing current will affect (in-
crease the discharge more than
almost any other thing. This
velocity can be reduced by wild
ening and deepening the box or
pool above the Weir. 1t is cal
culated that weirs 3 feet long
with a depth of water of Il in
ches, should not have a greater
approach than 6 inches per sec
ond, which amount may be allow
ed to increase very slightly where
greater depths over wider welrs
are used. BY constructing the
box or pool above the weir with
cross section at least seven
times that of the weir notch, a
sufficiently flow velocity of APP
proach is usually secured.
The issuing stream of water
must have full contraction; that
is, it must be sharp and clear cut.
This is brought about by making
the up stream edge Of the weir
board as nearly knife edge as
possible, and by keeping the sides
and bottom of the box below the
weir at good distance from the
falling stream so that the air may
pass freely clear around and UNI
der the issuing stream. The water
below the weir should never be
allowed to back 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 affected. If air can pass free
ly underneath the issuing stream
the level of the water below the
weir has no Influence on the dis
charge. An observance of the
followinw rules will usually lnsre
complete contraction.
a. The opening of the weir or
the weir notch must be made in
a plane surface perpendicular to
the direction of the flow of water.
b. The opening itself must have
a sharp edge on the upstream
side and the walls should be bev-
eled away on the downstream
side.
c. The distance Of the crest
OF the Weir from the bottom OF
the box or basin should be at
least three times the depth Of the
water on the crest.
d. The distance of the sides
of the weir notch from the sides
of the box or channel should be
at least twice as great as the
the depth of water flowing over
the crest.
e. In order that the lateral
contraction should not be dis
turbed the length of the weir
crest should be approximately B
times that of the depth Of water
flowing over it.
5. The depth of water flowing
over the weir should not be less
than 2 inches nor more than one
third of the length of the crest,
and it should be measured where
it will not be affected by waves,
wind or eddies, and far enough
upstream so that it will not be
influenced by the curvature in
duced by the falling water
This can not be done by measur-
ing it exactly over the crest. The
distance above the crest which is
usually found sufficient, is up
stream from the crest a distance
equal to the length of the crest.
A handy method of establishing
point from which to measure
the head and method which is
recommended, is to drive heavy
stake upstream from the weir
and at the side where it can be
easily reached. This stake should
be driven in firmly so as not to
be easily changed and should be
sawed off squarely at a point
slightly below the level of the
crest which can be determined by
the aid OF carpenters level and
straight edge. A heavy spike or
nail should then be driven verti-
calIy into the top of the stake
and the top of its head should be
exactly level with the crest by
the same method. The head of
water flowing over the weir
can then be found by measuring
down from the surface Of the
water to the head of the nail
with an ordinary carpenters rule
or square. The head must be
measured within 1900 of the