The Delta independent., 1888-06-12
Irrigation Notes.
BY J. A. CURTIS.

FLUMEs-Any open channel of constant
cross-sectional area, regular grade, made of
lumber, brick, stone, concrete or other ma
terial of a similar degree OF roughness, may
be classed under the category of fumes, and
and its capacity calculated by simple arith
meticaI operation. The velocity of the water
may be ascertained by calculation or expert
ment. In experimenting for velocity the
channel should be divided into equal sections,
both vertical and horizontal, and the velecI-
ty of each section ascertained by floats; the
average of the several velocities is the mean
velocity. This is tedious method, and un-
less done with great care has no advantage
over taking a certain per cent OF the greatest
surface velocity for the mean ueiocity.
If the greatest surface velocity is #. per
second use 81 ger cent; if IT,, So per cent;
if7 f., IS per cent Of it for mean velocity.
To compute the velocity, find area of cross
- width depth; the we; perimeter 81 that
par. Of the bounding line of the cross-sec-
tional area of the water that touches the
hume, and the slope - fall for any distance
divided by that distance. Multiply area by
slope and product divide by the wet perime-
ter, extract the square root of qootieni and
multiply by 92 for velocity. Area multiplied
by velocity gives carrying capacity. ln
straight channels the most rapid current is in
the center and somewhat below the surface,
decreasing toward the bottom and sides.
A common method of dividing water in
fumes is bp parting of a space FROM one side
that shall have width bearing the same
ratio To the width of the iume, as the water
required is to the whole amount of water.
This is truly correct only when the division
is into two equal parts. the partition being In
the center Of the Hume.
As the rate of current charges with the
depth, il follows that division made in one
stage of water would not suffice TOR another
differing in any great degree. Practically
the changes in depth are not so great as to
warrsn: the adjustment Of the division PAR
tition of;en. In fumes not over three feet
deep a division on the basis OF the average
depths is enough. To set the partition, de-
termine the discharge through the entire
flumc per second; by experiment the velsci-
ty Of the water in the space to be parted oil
-this Is KNOWN approximate. pl Nat VI
dinary method-and divide the amounts in
cubic feet to be set OF, by the velocity, and
this auotient by the depth, for the width of
the dividing fume. For example: The width
Of fiume is f.. mean of depths f., mean
velocity 4! f., per second, discharge - cubic
f., per second; amount totbe set off is or .
cubic #. The approximate width is f.,
the mean velocity OF this section is4 f. per
second. divided by 4 .as 2t, the area Of
cross-section. which divided by the depth 2 it.
gives width Of II Il. for the division flame,
When water is divided, not in any speci-
fed amount, but is quantities proportional
TO the whole, the hume method is, all things
considered, the simplest, cheapest and be,t.
Correctness in the measurement of fumes de-
pends largely upon the degree of roughness
of the sides and bottom. Stats or blocks of
wood in the channel yitiste the result very
appreciably. For the class Of canals and
bitches in general use for irrisSting purposes
the above methods do not apply. Irregular.
ties of grade. bushes, weeds and stone, bends
and the nature OF the soil are elements that
very seusibly effect the flow OF water. The
methods employed are too Intricate and ex-
tensive for a newspaper article.