The Cairo bulletin. [volume] (Cairo, Ill.) 1872-1878, 1877-11-09

exists in the 100 miles between uie Passes
and New Orleans, where 1t Is less than an
inch and q half per mile; while the steep
eat slope exists in the river from Cairo TO
Memphis, where 1t averages nearly i've
inches, and In Bayou Atchalalaya, where
II Is about six inches. AS the channel OF
the river is continually shifting. especial
| IL from CARO- to Red RIVER, bends caving
Ia, and cut>olls forming, it follows that
| the river must possess some means OF
establishing and altering these various
slopes to regulate the current, so that
through all these changes II shl' malh'
tain the capacity or size OF i.,- channel
| intact, and not run riot This l. done by
scour and deposit. Too much velocity
increases the suspending power OF the
water, and it takes up the material of
which the bed is formed. This Is called
scour, and the result is Il deepening OF the
channel and lowering OF the surface
slope. AS this IL lowered the cur
rent falls to the normal rate and the sc0ur
ceases. II the current be too slack the
water can not uphold its burden, a pOr-
| ton falls and builds up the bottom. This
| Is called deposit. AS the bottom rises
| the flood slope increases, and the current
becomes more rapid, until fnall 1t flows
so fast that the normal speed rs estab'
| lshed aud deposit ceases. Raising the
slope necessitats raising the lcvecs. Just
as the slope can be lowered can leytes be
disnensel' with. Whatever increases the
resistance to the flow OF the water makes
sleeper slopes and higher levees lnevita>
BILE. Friction of the bed of the stream
does this to much greater extent than
all the other retarding influences com
blned. This is least where the stream is
narrowest, and it is lesscned in ratio as
| the volume is increased. For instance,
| from Red river to the Passes, 800 miles,
the slope is about one and three quarter
inches per mile. Ii the river were divl-
ded into two equal streams, this slope
would be much sleeper in each and the
leyees would have to be higher. Bayou
Atchalalaya, at Red river, takes Oft about
one-tenth of the volume to the sea
with slope OF SIX inches per mile
Ii it took OF half of it, the
slope OF the main river would haye to be
stet per than it Is or it would dry up and
Atcllafalaya would become larger and
flatter. Ii the waters of the whole river
were equally divided with Atchaialaya,
1t would soon abandon its channel below
that outlet and would dis barge the en-
tire volume through Atchatalapa. The
greater ratio OF friction to volume in At
ehalalaya now prevents its steep slope
and route to the sea from being taken by
the whole river. 1t is about one third the
distance by it to the Gulf that it is by the
main river. Steep slopes and small vol
umes are always found together in alluvl-
al streams, unless the channel is filing up
or abandoned. hence IL Is suicidal to the
planters to permit Red river to discharge
through Atchatalaya. It's volume, add
ed to that OF the main river, would in>
: crease the volume anu lower the slope
from Red river to the sea at least one
fourth iEch per mile. This would lower
the floods from Cairo to Red river over
six feet.
The islands Increase the slope for the
same reason that they divide the volume
into smaller streams and increase the
friction. The wide eXpanses which are
SO frequent above Red River increase the
/ slope, for they also increased the friction.
By bringing these to uniformity OF
width corresponding to the narrow parts
! of the river, and compelling it to flow in
Q one channel where it IS divided by islands
|, Mr.. Eads is confident the flood slope Cal
4 be lowered Sufficiently to render leveel
= unnecessary.
u BY applying the principles laid dowl
s IN the theory of Capt. Eads at the begin
, ming, it will be seen that the wide, lake
like places in the river are the cause o
nearly all the troubles which beset boil
navigation and agriculture Throughout
] the alluvlal basin. When flood occurs
, the current is very rapid in the narrow
, places, and consequently highly charged
with sediment. In the wide places it is
sluggish, hence deposit takes place ex'
, tensiyely in the latter, and great shoals
result, which are infested with snags
The water, after passing out of these
. wide places, deprived of part OF its bur
e den, increases its speed and loads ur
, again from the bed and banks OF the mex
narrow part, and carries the spolls takel
here to the next wideplace This create
: the Caylng banks, the cut-offs and rapit
G changes in the stream. The shoals ar
simply efforts of tho river to build VI
y, the bed and produce sleeper slope Il
u restore the normal current velocity.
n BY uniform width of the river banks
n a uniform depth would be secured; thi.
3 would produce uniformity OF current
u ane prevent the caving of banks, and il
!, would lower the flood.slope below tn,
|. surface of the lands because it would re
G move the excessive fractional res!stanc
It created by the wide river-bed. 1t Onl.
IS needs the One-titth part of enc inch pc
n mile of reduction Of slope from Cairo {,
t Red river to lower the floods l2t feet a
v Cairo.
r The narrow parts of the river below
4 Cairo seldom haye less depth thar
4 thirty feet IN low water in them, ant
Capt. Eads is confident that reducing thu
: river to n uniformity OF width would give
q uniform depth from Cairo to the sea
G during the lowest water, OF at least TWEEN
# ty feet. No Strengthening OF the river is
e recommended by him.
e The plan of Capt. Eads is thus shown
}. to be widely different from that of thu
C United States Engineers, while it will in
vOlve but little more outlay of money
/ and require no more time for its eXecu
d ton. One plan inclOses between cnOr.
:, nous levees the present bed of thu
n stream, with all OF the wide places which
d are shown to be the cause of its cavins
t banks, and 1t contemplates increasing by
@ several feet the height OF any previou.
G flood levels. 1t leaves the terrors of an
= ticipated crevasses to depress forever the
o value of the lands, and involves constant
r watchfulness and vast annual eXpendi
;, lures to maintain control of the floods
It which will be uncertain at best; while the
Ie plan OF Capt. Eads proposes to remove
r the causes OF the overnows by q correc'
E. ton of the river channel, which will lift
s. as It were, the whole alluvial basin, {
70 territory much larger than the State O
re Indiana. absolutely above overflow for al
In time. Besides doing this. 1t will leat
9. ocean navigation into the very centre o
a. the republic, along coast line of 2,3Ot
40 miles OF the borders Of six OF the larges
e. States In the Union, and will thus Oper