The southern press. [volume] (Washington [D.C.]) 1850-1852, 1850-07-26
For the So,lther, Press

!. q. & 4 E .
For the Souther7, Press.
Which is the best and cheapest method
OF reciaiming the submerged lands Of
Louisiana?
Several plans have been suggested--one is
to straighten the rivers and so increase the velo
city as to enable the current to dig out char
mel sufficient to dischare the waters brought in
by its numerous tributaries.
Another is to open new outlets into lake Pom.
chetrain, and thus discharge the water.
A third is to make embankments of sufficient
height and strength to confine all the water
within the channel, and thus prevent overflow.
Professor Robinson, in his able treatise or
Mechanical Philosophy, has deduced from
numerous experiments made at great labor and
expense, by men of practical sciences Theory
of Rivers" which reduces the whole question to
simple proposition.
| He says: ave learn from observation that q
| velocity of three inches per second at the bot
tom will just begin to work on fine clay, fit fol
pottery and however firm and compact it may
be, it will tear it up Yet no beds are more
stable than clay when the velocities do not ex-
coed this; for the water soon takes away the
mpalpable particles of fine clay, leaving the par
tices of sand sticking by their lower half in the
rest of the clay which they now protect making
very permanent bottom, if the stream does not
bring down gravel or coarse sand, which will
rub off this very thin crust, and allow another
layer to be worn off; a velocity of six will lift
fine sand eight will lift sand as course as lin
seed; twelve inches will roll along fine gravel
twenty-four inches will roll along rounded peb-
bles nm inch in diameter and it requires three
feet per second at the bottom to sweep along
shivery, angular stones the size of an egg See
p. 1885, VOL q"
! We learn from the same authority that the
velocity of a current depends upon certain fixed
| laws which have in like manner been ascer-
tanned by numerous experiments. He tells
us, (page 452,) on the authority Of Mr..
Watt, that canal Is feet wide on the surface,
seven feet at the bottom and four feet deep,
with slope of four inches in mile, has a veo-
city of seventeen inches per second on the sur
face ten at the bottom, and fourteen in the mid
die. On the next page he tells us, that the We
| locity Of the Pc Grande, whose breadth is 759
feet, and depth 81 feet, with declivity of six
inches per mile, is thirty-one inches per second,
and that the current of the Rheno, whose breadth
is lS9 feet, and depth feet, with declivity of
fifteen inches in the mile, is forty-four inches
per second.
He shows that the. velocity of the current is
continued on smaller slope, as the rivers, in
creased by the addition Of their tributary
streams approach the sea- This continued velo-
city he terms the "energy of deep waters" and
on page 476, ATT, says: "We have seen in what
this energy consists 1t is only a greater guam
tity of motion remaining in the middle of a
great stream after quantity has been retarded
BY the sides and bottom, and we clearly see that
since the addition Of a new, and perhaps an
equal stream does not occupy bed Of double
surface the proportion Of the retardations to the
remaining motion must continually diminish as
the river increases by the addition of new
streams IT, therefore, the slope were not di-
minished the regimen would be destroyed and
the river would dig up its channel. We have a
full confirmation OF this in the many works that
have been executed on the Pc, which runs with
rapidity through a rich and yielding SOIL About
the wear 1000, the waters Of the Panaro, very
considerable river, were added to the Pc Grande,
and although it brings along with it, in its
freshes vast quantity of sand and mud, it has
greatly deepened the whole Troneo di Verregia
from its confluence to the sea. This point was
clearly ascertained by Manfred, about the year
1920, when the inhabitants of the vallies ada
cent were alarmed by the project of bringing in
the waters of the Rheno, which then ran through
the Ferrarese. Their fears were overcome, and
the Pc Grande continues to deepen its channel
every day with prodigious advantage to navi-
cations, and there are several extensive marshes
which now drain off by it after having been for
ages under water; and it is to be particularly
remarked that the Rheno is the foulest river in
its freshes of any in that country"
Professor Robinson adds: awe insert this
remark, because it may be of great practical util-
ity as pointing out a method of preserving and
improving the depths of rivers and drains in fiat
countries, which is not obvious and rather APP
pears improper; but it is strictly conformable
to true theory and to the operations Of nature,
which never fails to adjust everything SO as to
bring about an equilibrium"
1t will be seen that hi" theory applies to the
Mississippi river. In its character it is like the
Po and it follows that as the effect of the intro
duction of two additional rivers Of nearly equal
volume has been to deepen the channel of the
Pc, greatly for the advantage of navigation, and
that instead of causingit to overflow its banks
it has drained off large marshes, which had been
for ages under water, so instead of causing it to
overflow, embankments combining its waters
within its channel, would cause the Mississippi to
increase its energy, and thus deepen its bed
From the mouth of the Ohio to the Balize, is
a continuous delta, exhibiting the same phe-
nomena, which is fully explained by Professor
Robinson's theory. 1t requires velocity of
eight to twelve inches per second to lift and take
along coarse sand, whereas a velocity of three
inches will lift and carry forward fine clay. Thus
as the river approaches the sea, and the velocity
of the current is diminished, the coarser particles
held in suspension are deposited, and the lighter
clay is carried forward to the Gulf. As the
whole delta has been reclaimed from the ocean
by the same process, it follows that the lower
part of the formation that is the particles carried
forward to the Gulf and deposited from the bot
tom to the surface Of the WATER are chiefly parti-
cles Of fine cay,-and hence we find that the soil
at and below New Orleans is made of fine impal-
pable particles Of clay, because in obedience to a
fixed law, the river has deposited the sand and
heavier PARTICLES above, carrying forward the
lighter clay to the Gulf.
We can now well see why it is that the chan.
mel is not more than twelve or eighteen feet deep
at the Balize, and not more than ten or twelve,