Missouri Valley times. [volume] (Missouri Valley, Iowa) 1874-1931, 1903-02-26

10 carry any NJO0 that would more
than It'll the excavated channel.
Ii the material frOm the excavation
Is not sufficient to bulld the bikes. n
should be borrowed from adjacent
lands
The most economical channel ia
build is one with vertical sides and q
depth equal to One-haif the bottom
width.
The best traperoidal form Is one in
which the width of the water surface
is double the bottom width, and equal
to the sum of the side slopes.
Such crOss-SectlOns as this. however.
would call for an unusually lirm. com
pact material.
| In India the large canals have been
given y proportion Of depth to width,
similar to that of the great rivers.
The grade line should be continuous
and unbroken from end to end. except.
perhaps. when there are curves nh the
! line, aud the increased friction or an
curves should ha compensated nv an
increase ut grade or a cnange i'm the
cross-sectiOn
4 Reducing the rate of grads toward
the discharge end of the dl,ch will. of
course, reduc. the cufrent velocity and
tend to deposit silt carried in susper-
sion, while an increase grade would
prouuce the opposite result.
| Slope and CROSS section are nearly re-
lated, and are ln.erdrpendenl one upon
the other Having determined the dis
charge required. tho Carrying capacity
for this quantity can be attained bv
increasing the slope and consequent
velocity and Diminishing the cross.
sectional area, cr by increasing the
crOss-sec flOnal area aid diminishing
the valncitv.
4 A velocity of two to three feet per
second Ia ordinarily sufficient to pre-
vent the growth of vegetation UT the
deposi. of silt. ard this velocity il CON
sid red he mnst desirable i'm channels
in,.nced tor the purpose ut irrigation.
i Much higher grades are required In
! Small than in large channels To produce
4 the same velocity.
Oh the bottom lends in this vicinity
the slope is tixel aud the grade lines
(! C ln rarely be land 80 that the fall viii
exceed the general slope of the land
In large channels ut 60e width of
bottom or more, IN sandy OF light soil,
grades as low Us six inches per mile
produce As high q velocity as the ma
terl4l will stand
In lirmer material this grade may be
Increased from l2 to Is inches per mule
whereas SIN 4ller channels will under
the same conditions stand slopes Of
two to five feet per mile. according to
the material and dlminsions of the
channel.
These facts are abundantly proven
bv experiences OH the Canals in India,
France. and in our far western states.
On the Ganges canal, the bottom nt
when liz l7O feet with q slope of IA
lnches per mile, in y sandy soil, pro-
duced such velocity that the current
last ceased to erode the banks or to de-
post silL-ln another portion of the
same canal the banks were nearly de-
struyed by increasing the slope from
1 Is to II inches per mile.
A velocity of three feet per second
given to Sodne canals is found too great
for the material, ana much damage
was caused by erosion.
In the light. sandy loan aoils Of the
San Louis valley. in Colorado, q slope
of six inches tn the mile has proven
very satisfactory /; so low slope as this
is possible in that locality, because the
water is comparatively free of silt. and
there is little chance for its deposition.
while the temperature of the water IL
so low that there is little likelihood of
the growth of weeds affecting the anal
bed.
In the gravelly clays through which
the Turlack canal runs, a satisfactory
grade has been found to- be 1.5 feet per
mile, although the grade is changed on
portions of the channel, according to
the character of the soil.
Perhaps the highest grade on any
cannal is that on a short portion of the
Del Norte canalin Colorado, where the
fall is IS feet per mile. through rock
cut. On several miles of this canal
the grade is feet per mile, but after
reaching the bottom landsit is reduced
TO about two feet per mile and the
cross-sectiOn increased to compensate
for the diminished velocity.
| There are seasons when the cnlti-
waited areas suffer on account of q lack
of moisture. and while this matter
properly belongs to irrigation. think
that irrigation and drainage should be
considered together.
With the construction of storage
reservoirs in the higher elevations. the
excess rainfall can be imDOunded and
utilized in case of a drought.
These reservoirs will also prevent the
Violent rush of water which comes
down the ravinss and channels. and
will also act as settling Basins and pre-
vent the silt from covering the lower
lands.
do not know of an instance where
this has been put in practice, but 1t
would be an interesting study. and with
all our study there arc conditions and
results in hydraulics that are at vari
ance with the most carefully prepared
tables and formulas.
One of the most eminent hydraulic
engineers says: "The science of n.y.
draulics in many of Its departments, ls
but imperfectly understood, and many
of the rules and formulas given on the
subject are to be regarded merely as
furnishing an approximation to the
truth"
AS to financial aud sanitary results,
will mention single example.
The Indiana Bureau of Statistics
made an Investigation of the Influence
Of tile drainage on health and crops,
selecting single township In the state
where drainage was one of the marked
Improvements, and taking a period OF
five years before drainage began and
five years after the most of the town
ship had been drained. by consulting
farmers who had Ii, ed in the township
during bo:h periods, they found thai
the average crop of wheat in the five
years before drainage was 91a bushels
per acre. The same land after drsin-