The daily crescent. [volume] ([New Orleans, La.]) 1848-1851, 1850-07-25
Memoir on the Phy.Ic. Of the Mississippi River
BY CALEB Q. roRsnET. A. NJ. Q. <.

CALEB FoRsHEY, A. NJ, O. K.
H. Application of Statistics and Principles
Reasoning priori the following inducsions and
conclusions seem unavoidable:
The channel of the river is made by the abrasive
force of its waters. A greater force would produce
greater channel; and less force less channel.
The greater the channel, the less the liability 10
overflow.
Concentration of force increases abrasive power,
1 and diffusion of power reduces lk
Levees confine and concentrate the waters, con-
centrate and increase the force therefore increase
the abrasion, therefore the capacity of the channel
4 Outlets diffuse the waters, reduce the abFasive
| force, and therefore reduce the capacity Of Tie
| channel
If the channel be already greater than necessary
for its servitudes, it would be safe to relieve it ol
| some OF its growing force by outlets
If the channel be too small for its setvitudes, it
| would be wise to increase the ehannel-making
power, by closing outlets.
49, The Mississippi river discharges given
quantity annually, and this is divided into daily
supplies, with maximum here, in April and May.
Ii can produce no more.
If this supply be discharged with great velocity
it must maintain lower level, even if the channel
remain unchanged; for there can be no more than
the supply be discharged, and hence the Uolusie
discharged in month year must remain the
same.
greater force, with the same volume, implies
a greater velocity
Therefore, the evees which confine the waters
and concentrate the force increase the velocity and
depress the LeueL Of discharge.
10. BY reference to the diagram M and table G,
we shall find these inductons, prSoyS, sustained
by the facts.
From the year 1917 to 1927, there were no con
siderable leyees above the mouth Of Red River.
From 1897 to 1897, levees were being extended the
whole length OF Concordia coast say $50 miles
And from 1887 TO 1S47, we may regard the system
of levees in full operation, for a long distance
,bo,ro kaln
During the first ten years 1Sl7 to 1927 the
mean height of the rivers surface was for the year
| inches above the mean height of the following
ten years (1827 to 1887, while evees were being
| constructed and inches higher than the mean
height Of ten years 1S37 to 1Sa7 under the levee
| system. This relates to the mean annual height
| and is reduced to the range of Carrollton.
But the mean high acGtsr mark OF these decen-
NAL periods is in like manner reduced. being a "A
inches lower in the second, than the first period,
and inches lower in the third period.
But we have from the dates Of highest water
very unexpected result-namely, the date of high
est water is later in the second aud third periods
| than in the first
The mean dates of elimination are for Vidalia
| April 26, April 80, and May 49, for the three pc
RODS, in their order, and the mean Of the 80 years
is on May the 7th.
The common impression, that levees produce
earlier high waters, would appear to be unfounded
| and this is the conclusion which, it seems to me,
| would be arrived at, from section lS because the
| supply cannot be increased or hurried before the
rains and thaws Of the spring, and our levees can
have little effect in Fastening the dates of high
water at any point within the influence Of levees
The mean dates of elimination, given here, then
only prove to me, that the periods observed are toe
short to obtain fair mean, when the range is from
March 18th to July 18th.
90 Cut-ofs-By application of the principle.
and reasonings to facts, we shall find
That cutoff shortens the channel, increases tn,
decvity, accelerates the velocity strengthens IN,
channel-making power, abrases the banks and bot
tom with more vigor, and ultimately produces
| lower mean level then before the cutoff
Accordingly, the effect Of Shreeves cutoff at th
mouth OF Red River, presented in 1874 these phe
nomena, namely AT the cutoff, the water was
feet, or more lower than the water-m mark OF 1928
Twenty miles above, it was 80 inches lower, forty
miles up, 1t was IA inches lower at Vidalia sixty
miles above, it was ~ inches lower and at Water
proof ninety miles, it was 8 inches lower, and al
points above Waterproof, it was regarded as equal
to 1928.
AT Morganza, it was IS inches lower and at
NewOrleans and Carrollton full inches lower
than in 1928.
These facts were determined by myself at the
time and since, and carefully noted.
We conclude hence that the effect was percep
tible about 100 miles above, and at least 200 mile
below CUTOFF abridging the distance Of current Il
miles, and 3 54 feet to the fall OF water thence L
a the Gulf; and that it showed reduction Of high
water level both above and below the cutoff
2l. The Raccourci Cutoff has been too recent
! made, for full illustration Of the effects Som
have already been severely felt. Il shortened Ii
distance 2S miles, with fall at high.water OF 4 .
feet. The effect in draining the district above
have been realized as anticipated. Its effect q
Vidala was about 4 5 inches, and expired at
distance OF about 100 miles. Below il has not ha
time to produce the new channel due to its aecele
ration, and has raised the water probably in slgl
degree, but not to the mark of 1928, at Bayou Sag
by 30 inches. BY the best information l can OF
tain, the difference is about 2 inches in the ben
above Carrolton. By changing points Of create,
force, it has committed great ravages upon h
banks, both above and below the cut-off II wi