Southern sentinel. [volume] (Plaquemine, Parish of Iberville [La.]) 1848-1858, 1852-03-13
Report on the Bayou Manchac.

| OF the water OF the Mississippi river, the under
| signed begs leave to submit the following com
| munication
The Bayou Manchac is the first of the natu
raj outlets of the Mississippi, on its eastern
side, and is situated at the distance of fourteen
miles from the terminus of the high lands be
low Baton Rouge. In periods of high water
it formerly connected the Mississippi with tht
gulf of Mexico by way of the Amite. Lake
Maurepas and Lake Pontchartrain. The dis
tance from the head of the Bayou, by its mean
derngs, to the Amite, is about twenty-five
miles, and the whole distance of the water
communication with Lake Borgne is about one
hundred. During the last war with England
it was greatly obstructed to prevent the British
from reaching the interior by that route, and in
1926 it was closed by a substantial dixie to pre-
vent its water from overhowing the settlements
upon its banks and in its vicinity.
In descending the Bayou, its first tributary
is the Bayou Crocodile, on its southern bank,
which drains Spanish Lake and its inlets into
the Manchac. The junction is nine miles from
its head. Abouta half mile below it receives
the Bayou Fountane on its northern bank, and
a few miles below, Wards Creek on the same
side
At its head it is about ninety feet by depth
of twelve, and its elevation above the lowest
water of the Mississippi, twenty feet, the great
est rise of the river here being thirty-two feet
Consequently, it is necessary for the river to be
twenty feet above low water before its waters
can escape by the Bayou. From its head to
its junction with Bayou Crocodile, it is
usually dry Bayou and very tortuous in its
course. Itdiminishes very rapidly in size as
you descend from the river, and at distance
but little over mile from its source. it has
only width of forty-four feet from the bank
to bank, depth of ten feet and width at
bottom of fifteen feet. 1t is but little larger
than at this point till it reaches the Crocodile.
Below its junction with the Crocodile and
Fountaine, it is 90 feet wide by depth of fif-
teen, at the water surface being seventy feet.
This may be considered sas the highest point
of navigation in its present condition. The
banks of the bayou are very low nearly all the
way on its southern bank from its source to
the Crocodile, and on the north to the Bayou
Fountaine. From these points to the Amte
there is tolerably high land on both Sides The
overflow from some miles, in case OF creyasse
above the Crocodile and Fountaine, is from
eight to fifteen feet.
By taking cross sections at the end of every
mile from the head to the Crocodile, it is found
that the average channel Of discharge is three
hundred feet
A cross section of the Mississippi at its
head, is about two hundred and fifty thousand
feet Its capacity compared therefore with the
Mississippi, is as 800 to 250,000, but if it be
estimated in another method its capacity will be
more fully shown.
IF we take a section of twelve feet of the
Mississippi at flood and multiply it by twenty
five Hundred, its width, and compare this with
the medium cross section of the Bayou, we
will.probably form the best idea ofits capacity.
The proportion will be as 10000 II 800
to the depicting effect that the Bayou would
have on the river, if opened The result we
arrive at, is that the Bayou, supposing its cur
rent equal to that Of the Mississippi at flood,
would lower the river only about one inch and
half The current of the Bayou would not
be greater than that of the river from its being
constantly retarded by short bends.
If, now, we suppose that the current of the
Mississippi would be slightly retarded below
by the depletion, we see that the river would
not be sensibIy lowered by the outlet. Fifty
miles below it would not be felt.
AS depicting outlet, therefore, ofthe river,
the Bayou Manchac is utterly insignificant, and
unreasonable to suppose its Importance would
ever be materially augmented.
Knight here close this report, but I am aware
attached both here and abroad, to the opening
The Manehac, and the subject should be consid-
cred in reference to that point.
If the Bayou were opened, as an inevitable
consequence, a large portion of the parishes of
Ascension and Baton Rouge would be over
flown. Suppose this could be prevented by
levving the banks ofthe Bayou, still the expense
would be very great. Levees would have to
be built of miles in length, from twelve to ff-
teen feet in height, to sustain the back water
from the Amte, as well as that coming down
from the Mississippi. But, even with this, the
country could not be protected.
There is an important popularity of the Man
chac which is not found on our other natural
outlets, that demands our special attention. The
other outlets have no inlets flowing into them,
and if we can by levees carry off the water de-
rived from the Mississippi, all is well. The Man.
ehac, on the contrary,has several large inlets,
and in this respect, if no other, it has some claim
to the name of a river.
If the banks of the Bayou were leveed, the
water would be backed up Crocodile, Foun-
taine and Wards Creek, and overflow the coun-
try almost as effectuay as if it had no levees
at all. IF these were closed with dikes, the
water usually discharged by them would have
no outlet, and would spread over the whole
adjacent country. They are inlets of the Bay
ou and it must bear the servitude of their
drainage 1t is therefore inevitable if the dixie
is removed at the head of the Bayou, that the
adjacent country must be abandoned. This
could only be prevented by an extensive sys-
tenn of locking to which shall refer in the Sc
quel. r
The low water navigation nseould not be effc-
ted, even without regard to safety, except by
enormous expenditures. -
The rise in the Mississippi, as has been seen
is about thirty two feet, and this must come