The Delta independent., 1888-06-05
Irrigation Notes.
BY j. \. CURTIS.

STATUTORY IScH. When water flows
through an opening in the side or bottom of
n partition under Aead or pressure repre-
sented by the height Of a column of water,
1t iG common practice TO measurcthe dis
charge in statutory inches. Could she hedd
be kept conStart it would not be a difficult
matter to effect satisfactory measurements,
although there is n slight error arising from
the allowance for contraction and friction
depending upon the size of the aperture.
As defined by the Colorado statutes, the
inch is the amount of water that viii How
through an aperture one inch square in a
vertical partition and under pressure repre-
sented hv Il column of water five inches high,
measured tgm the upper edge of the oriiice.
Head as understood in hydraulics, is the
distance from the water surface to the center
of gravity of the oriiice of discharge, or if
the orifice be of regular shape-circular or
rectangular-the center of such orifice 3: there
fore. ,he head for measuring the statutory
inch is five and one.half inches.
In measuring or distributing water by the
statutory inch, the orifce ofdischarge should
measure, whatever may be its shape, as
many square inches as the required number
oG statutory inches, and the water surface
must be 6ye md one.half inches above the
centre OF the orifce, if Of regular shape.
To change the rate of discharge the orifice
mus, be changed and the head kept constant.
Changing the head to any proportional part
of Eve and one.half inches does not
change the discharge proportionnlly, but
in the ratio of ;he square roots Of the heads.
There are occasions when it is desirable to
measure the discharge when the orifce Is
fixed and the head varying. As the method
is of SO general an application in the measure
ing Of water, it is given in full. The first re-
quirement is to ascertain the velocity Of the
disoharge, which is represented by the tormu-
la " 50. TT ? gh x.e2, in which " velocity
G. force of gravity ~, 1922, and i is the
head in feet 81 is the co.eficient, which
makes the allowance for friction and con-
traction, and for apertures not over about
four by six feet will give results correct
within three per cent.
For most practical purposes shorter
method, derived from the above, however,
may be used viz: Find the square root of
the head in feet and multiply by five for
velocity.
BY both methods V is in feet per second,
therefore multiply 1t by twelve and that pro-
duct by the area of the orihce in square inches
for the discharge in eubicAinches per second.
As statutory inch is equal to a flow of
forty cubic inches in one second, tnlay be
computed by the above method) divide the
discharge in cubic inches by forty, and the
cuotient is the discharge in statutory inches.
The above methods apply when the dis
charss is free aud unobsiructed and the
thickness of the walls of the aperture or the
length Of the conduit is not more than twice
it, least transverse dimension.
Lu Ell EGrsEu renents the utmost accuracy
mas. be secured for at the best the results
aftaiueI are only approximations. The water
sur'1as uHs. be above the or!fce Of discharge
and II the discharge be under wafer. the
head is the difference between the water sur
face OF the supply aud Of the receptacle.