New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1874-06-14

Jettles were once attempted mere; and Whll'
/ consider this experiment LO test as II
their general efficiency. yet the fact tina
structures OF light character cal
not be maintained was illustrated by
their early demolition. The Spanish
once built fort near the mouth
but it was out OF sight so long agt
that the Oldest in habitant is unable 70 polD
out the spot where it Stood and it wal
built not upon earth SO newly formed a.
the bar, nor where srorms and waves could
disturb. If jetties were constructed Will
such deep foundations as TO resist all dis.
turbing forces they might stand for time
at least 1t seems .preopsterous to ne tt
attempt to acquire depth of twenty sever
feet By building jetties on the bar where
the water is but fifteen Ieet deep; TOR i
erosion takes place 20 the extent desired
there would be great danger tina
they would slide into the center and form
more difficult obstruction to remove thai
the bar itself.
The bar is composed OF such material il
part at least as 10 require decided in
crease OF velocity to remove IL within s
reasonable time. Whether such increased
force can be obtained, 10 cut away to deptl
of twentyseven feet is not entirely free
from doubt. 1t is well known law thai
the narrowing OF channel obstructed al
its mouth will cause the water to set bach
and seek escape where there is less resist
ance., The Mississippi river has seventeen
mouths, of all sizes, through which the
water would pass, and Tor many miles
above the banks are low and narrow, an(
no great elevation would be required be
fore the water would pass out over the
banks, cutting away new avenues OF es
cape. The recent overflow causes appre
tensions of danger arising from further OBJ
siructing any one of the many mouths now
existing.
Whether ie.ties can be made to stand oy
not, or whether the velocity of the current
will speedily or leisurely erode channel
through the bar. is Lot the great question
upon which the case is to be decided. The
bar does extend constantly, and .jetties to
be permanently effectual must keep pace
with it. The bar extends now 1873 feet an
nuaIly, and il the channel is narrowed
and the same quantity Of water continues
TO debouch into the sea, fact not
denied. the same amount of sediment must
be precipitated to the bottom as before
and so soon as the same cause is applied.
To narrow the channel will reduce the
width OF surface over which the water will
spread, and the fsr must advance more
rapidly than at present. An enhanced
velocity may prolong at first TIE distance
over which the deposit may take place, but
in brief time the advance of the bar will
assume its logical and natural extension.
General Humphreys estimates the annual
advance under the jetty plan proposed to
be thousand to twelve hundred feet per
annum. This will compel an extension of
jetties at the same rate az cost which the
government has no right TO endure, if a
better and cheaper plan can be devised.
Jetties can not be extended indefinitely. In
time they must be abandoned after baviEg
incurred vast expense, and the obstruction
Will rear its head again, and become at
once as hldeous as We now see it. 1t was a
wise thought in Captain Eads 20 limit his
responsibility TO ten years.
1t has been said that the extension of the
bar will not take place at all, or but slight
II at the worst. ioE the reason that there
are currents which will bear the sediment
away to some remote place. 1t would not
be good logic to say that the Gulf currents
would Go for arsitcial jetties what has
never been done Tor those formed by ma
ture. The mouths Of the river have ad-
vanced ITO the Gulf far beyond all the
surrounding lard. For fifty miles beyond
everything e-se nave they gone seward,
the bar holding the same relative position
az everv step in advance. This is unanswer-
able proof that there is 10 httoral current
there, or Il existing at all, it is so slight as
not 10 produce any appreciate fact. But
beyond this the study of this subject by
engineers and scientists has continued for
more 1han forty years, and repeated exam
nations have been made and tests applied.
and no evidence OF a iictoral current has
been discovered. nor has its existence ever
been claimed until the ietty project was
invented.
The fact that bar does not form in front
OF the jettits az the Sulina mouth of the
Danube is made TIE basis of the theory that
j. Will not form at the mouth of the Nissis.
sipp! river. When conditions are Identical
the application OF principle will be follow
ed by the same results. Sir Charles Hartley
was careful TO find out the existence of a
Httoral current before he attempted the
construction of .jettIes at the SuIina. It's
existence was apparent. because the banks
were already eroded and the shore at the
point in lis general outline was concave.
At the mouth of the Mississippi there is no
evidence OF erosion: on the contrary the
shore or bank is sharply convex The bar
has not formed at the mouth OF the Sulina
after test Of two years or thereabouts. and
whether ultimately it will is not entirely
certain; but as a different condition exists
At the mouth of the Mississippi it is as GER
tain that the bar will extend there as il is
certain that the bar has not formed at the
mouth OF the SulIna. l send to the clerks
desk a letter from the Chief of Engineers.
addressed to Ice on this SUBJECT, which I
1esire to have read.
The clerk read as follows:
WASHINGTON. April Is. 1874.
SIR have received your letter of the
enth instant. asking for ny reasons in full
or considering the plan of obtaining deep
channel between the Mississippi river and
he sea by canal preferable to the plan Of
obtaining that deep channel By construct
ng jetties at the mouth of the river.
A discussion of the engineering questions
involved in the use of .jetties to deepen the
mouth would be out of place in this letter,
md is rendered unnecessary BIZ my having
his Cay submitted a report on the subject
o the Secretary of War. which viii, pre-
ume, be transmitted to Congress as form
ng sequence to the report of the Board
# Engineers upon deepening the entrance
o the Mississippi river By canal and by
cities.
There is 10 question as to the praetica bill
Y Of constructing the canal; and when
INSTRUCTED its maintenance will cost
comparatively small sum, probably not ex-
eeding one per cent of the first cost. That
rst cost, along the route surveyed. is esti-
mated by the majority of the board of en-
ineers 70 be $40 ,273, 000-an estimate which |
entitled to confidence, the officers COM
losing that majority being among the abIest |
nd most experienced in the corps of en-
ineers.
The canal, as proposed to be constructed,
VII afford ample facilities for all the COM
lerce of New Orleans for many years.
In my report to the Secretary Of War of |
o-day's date have submitted an estimate |
f the cost of constructing jetties at the |
louth of the Southwest Pass to deepen the |
hannel to twenty seven feet at low water, |
he structures to be carried down to the |
Ill depth of the channel throughout their
,ngth; the whole to be of a permanent |
naracter. This estimate amounts to
7 100000 II the jetties were simply built |
pom the surface of the bar and not ex-
snded downward, their cost would be