The Cairo bulletin. [volume] (Cairo, Ill.) 1872-1878, 1877-11-04

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nels must then require q sleeper slope, or
more force than If the whole volume
flowed In one channel. Hence in pro-
portion as the whole volume Is diulh-
ished by an outlet which abstracts any
part OF Its water, the remainder must ac-
quire sleeper slope and need higher
levees than before. Bayou Atchafalaya
Reaches the sea level by route not one'
third as great as that by the main
river. At the point where 1t
leaves the river, the river and bayou
levels are tina same, therefore the slope
of the bayou is more than three times as
steep as the river, yet the rate OF current
in each is not materially different. 1t
must be the normal rate, or the size OF
the channel would enlarge or diminish
under the influence Of either scour or dc.
post. In Bayou Lat0urch5 the river can
not keep up the normal velocity, owing
10 the loss OF slope that has occurred by
the lengthening OF the bayou, and the
bayou is gradually becoming extinct I'M
der the depositing action.
II the river volume be spread out 10
great width the friction OF the bed Is
greatly increased, and q sleeper slope
becomes inevIteble. The deposlting ae-
ton builds up the bottom of the channel,
the increased slope is attained and
higher leyees must be constructed.
;,r else the river pours its Hoods over the
-anks and builds them up also with its
,ediment to correspond with the eleya-
ion OF its bed.
The fact that the river is flowing
over a bed of its own deposits, and that
these deposits can be easily and rapidly
removed by its current, should teach us
that the river controls that current, so
that it shall not unnecessarily destroy
what il has made. Abundant proof en-
lists thar il does regulate it through the
action OF scour and deposit, so as TO dis
charge very nearly just as much sedi-
ment as ii receives, and no more.
The highest mean velocity of flood cur
rent recorded by Hum phreys and Abbott
was e. % feet per second ut Carrollton,
feet at Vicksburg, 400 above, and SAG at
Columbus, 1000 miles above CarrolltOn.
This remarkable uniformity existed at
these localities, Notwithstanding the
slope at the first is less than an inch and
half per mile, three and 4 half
inches at the second. and five
inches at the third Here
we have proof that these various slopes
are adjusted tOprOduce the normal yelOc-
ily, and that they are necessary to oyer
come the different degrees of resistance
to the flow of the streams that exist at
these different localities.
We find that where the volume Is
greatest, and flowing IN one compact
mass and uniform width, as 1t does below
Red river for over 300 miles, it's slope Is
only an inch and tffree-quarters
per mile, while above Red river it rapidly
increases, being three and fifth inches
from there to NatcheZ. Above NatcjeZ
it becomes sleeper and sleeper, until it
attains five inches per mile ut Cairo.
The planter whose lands are over
flowed should study intently this ques-
ton OF flood slope and its causes, espcc-
tally when he reflects that if the slope
from Red river to Columbus
$50 niles were lowered only so much as
the One-flith part of an inch the flood at
Cairo would be reduced twelve and half
feet in height. IL now attains the enorm-
Gus elevation OF almost iiity-two feet at
that point.
The rapidly increased slope above Red
river is due: First, to the diminished
volume as we ascend above each tribut-
airy; second, to the numerous Islands;
third, to the excessive width OF the river
at many localities. Tie last two causes
can he easily removed
When atlood occurs, the water acquires
its greatest velocity in the deep anu mar
row parts Of the stream where the least
fractional resistance occurs. When the
water enters one of the wide places its
current sackens, and it deposits the
| heavier particles OF suspended
matters, and forms shoals. The
water, having lost part OF Its burden here,
is again contracted in with al the next
narrow place. II has then less trictiOnal
resistance, and soon acquires greater
velocity, and with it the power to sus.
| pend Il greater quantity OF sediment.
| ScOur at once commences, as the caylng
banks near by attest The vigOr with
which the enlargement is made. The
material thus removed is carried by the
| current to the next wide place, where ii
| is dropped to elevate the bed there, and
create higher slope. In this way the
worst and most dangerous shoals have
| been created, at each OF which the float
ing snags are arrested and Embedded, and
| become dangerous Obstructlcns.
| The same causes produce the OverflOws
which create the shoals. and this is most
| fortunate for tie planter, Tor
! his Interests and those of navigation and
commerce being identical, increase his
chances Of relief at the cost Of the cOun-
try. Whereas, if the question were sim
ply one OF building levces to protect ms
| land, and not to Improve navigation o!
the river. it would be probably deemed
less national in character.
| | do not propose TO grapple with the
floods, INT with the causes which pro-
duce them. Throughout the entire basin
we see repeated Illustrations OF the fact
that the greater Is the volume the lower
Is the slope. Turn the waters OF Red
river down the Mississippi. by closing At.
chaialayas, and we will increase the yo-
lume and reduce the slope. If 1t were
reduced from the Passes to Red river
only q quarter OF an inch, 1t would lower
the high-water mark nearly seven feet al
Red RIVER, and the same amount all th(
way up. 1t would then be sleeper thar
it Is for 100 miles below New Orleans
Outlets are pernicious, and inevitably
raise the food line. The river should be
brought to uniformity of width, ant
where its volumeis subdivided by islands
it should be confined to u single channel
| do not propose to shorten or straight
en- the river. Mature study has convln'
ced me that no cutoffs will be needed tC
reduce the flood line below the level Of
the land. | once thought that one OF
two might be required. The treatment
propose is simply high water treat.
ment. A uniformity of width of its
banks will insure a uniformity OF depth
and not less than twenty feet from Cairo
to the sea In low water. A uniformity II
width will bring uniformity OF current
which will more rapidly discharge thu
floods, and will stop the caving of banks
In anticipated results these plans arr
immensely different. One contemplate
the flood waters rising from ten TO TWEEN