Payette enterprise. (Payette, Canyon Co., Idaho) 1909-1935, 1912-01-25

a sharp edge on the upstream sid
and the walls should be bevele
away on the downstream side.
: c. The distance OF the crest O
the weir from the bottom OF III,
box or basin should be at leas
three times the depth OF the waite
J on the crest.
d. The distance of the sides O
the weir notch from the sides o.
the box or channel should be al
least twice as great as the depth Of
the water flowing over the crest.
e. In order that the lateral con
traction should not be disturbed
the length OF the weir crest should
be approximately three times that
OF the depth Of water flowing over
It.
B. The depth OF wator flowing oy.
er the weir should not be less than
inches nor more than one-third OF
tho leagth Of the crest. and II
should be measured where Il viii not
be affected by waves. wind or ed
dies. and far enough up stream 80
that II VIII not be influenced by
the curvature induced by the fall
Ing water. This can not be done
by measuring 1t exactly over the
crest. The distance above the crest
which is usually found sufficient,
is up stream from the crest a dis
lance equal to the length OF the
crest. A handy method of setab-
fishing a point from which to meas
ure the head and a method which
Is to be recommended, is to drive
heavy stake up stream 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 saw
ed off squarely at point slightly
below the level OF the crest which
can be determined by the aid of
a carpenters level and starlight
edge. A heavy spike or nail should
then be driven vertically into the
top of the stake and the top of it's
head should be exactly leveled with
the crest by the same method. The
head of water flowing over the
weir can then be found by measur-
ing down from the surface Of the
water to the head OF the nail with
an ordinary carpenters rule or
square. The head must be measur-
ed within 1900 OF the length of
crest in order to limit the error
to IL of one per cent. A very ac-
curate measurement OF the head
can only be made with the hook
guage which consists of long rod
terminating in an upturned metallic
hook, the rod sliding up and down
on fixed support being actuated by
a screw motion, while the head o,
water is read from "A vernier at
tached to the rod. The rod is run
down until the point of the hook Is
below water and then raised slow
ly until the point reaches the sur
ace Immediately over the hook.
This method eliminates the eff
foot OF capillary attraction on the
rule, but is not practical for farm
o@S' welrs on account of the ex-
pense of installation. II care is
used, the head can be measured ac-
curately enough for all practical pur-
poses with an ordinary rule In the
manner previously described.
The most frequent cause of err
ror In weir measurements is ex.
coss velocity of approach and this
must be guarded against by pro7id-
ing good sized pool above the
weirs which aust be kept clean and
free front sediment.
"Don'ts" In Regard to Weirs.
1, Do not set a weir immediate
ly below a curve in the ditch, feE
tho curve will cause the water to
flow to the side Of the crest.
2. Do not set It Immediately be-
low or too close to head gate
where the water has high velocity,
rs by so doing. it win cause too
high velocity of approach.
3. Don't allow the water below
the weir 10 back up even with
the crest as il viii not allow com
plete contraction and will cut down
the discharge.
4. DO not set the weir any 9TH
er way than perpendicular and at
right angles to the flow of the I
stream.
5. Do not attempt to use too
small a weir. Put in a larger weir |
where the water TO be measured ex-
reeds depth on the crest Of 1-3 |
the crest length.
6. Do not allow the pool above
the weir to fiji up with sediment.
rs the resulting decrease IN the !
cross section viii increase the vs
.ocity OF approach