The New Orleans bulletin. [volume] (New Orleans [La.]) 1874-1876, 1876-02-06
SUPPLE Nh nj.
NEW ORLEANS BULLETIN
NEW ORLEANS, FEBRUARY 6, 1876.
PROGRESS OF THE GREAT JETI Y
WORKS AT TIE MOUTH OF THE
MISSISSIPPI.

MISSISSIPPI
On January Is, 1876, the jetty works con
Structed under the United States grant, made
TO Mr.. James B. Esds on March last. hao
been so far extended into the sea that the al
most complete control Of the river discharge
had been accomplished through q distance Of
II miles from the lands end, and within $500
1eet of the crest of the bar
Through tho extent of this mile and half
The river current has swept out /, 1868, 22l
cubic yards on the bar on December 25 1875,
and the removal by the river is progressing q,
the rate of about 80, 900 cubic yards per day;
100000 yards more will have to be secured
away before 20 feet depth Of water Is secured
across the bar.
The works on each line Of jetty are partially
constructed out beyond the crest of the bar
70 the full distance they are intended to be-
built, and the work on this portion of the jet
ties is being pushed with the utmost vigor,
ever Is, 600 cubic yards Of willow mattress
work having been constructed and securely
placed in position. and ballssted with stone,
within the last 80 days-the total amount laid
thus far being about 125 600 cubic yards
The construction Of 10000 additional yards
Is all that is now required to build the jetties
up above mean low tide. and out to the crest
Of the bar, 10, 500 feet from the lands end at
The mouth OF tbs Mississippi.
It is confidently believed that sufficient
amount of material is now in place, if no
more work were done, to insure . depth of
twenty feet of water across the bar, within
three or four months. One remarkable fea-
tnre, thus far developed, is the deepening Of
the water between the incomplete jetties on
the outer slope of the bar, which is doubtless
caused by the tidal action that is now partial
ly controlled by the jetty works beyond the
crest. This deepening clearly shows how
groundless are the fears that the effect of the
jetties would simply be to pile out the excs-
waited material on the outer slope of the bar.
The fact that the crest of tho bar has not
deepened, Notwithstanding the immense
amount Of material excavated from above it,
between the lines of the jetties, is in exact
accordance with tho theory upon which Mr.
Eads has based his application of the jetts
system to the improvement of the mOath of
ahe Mississippi.
Those predicting the failure Of the system
have constantly asserted that the chief part of
the sedimentary matter of the river was
pushed out to sea on the bottom by the action
Of the current while Mr.. Eads mas persist
emily declared that this was grave error, and
that these matters were almost wholly borne
30 the sea suspended in tbs water of the river.
and that, the more rapid the current, tLe
BY it in suspension; and hence an increase Of
current above the normal in any part of the
river, flowing over strictly alluvial bed,
would cause the water to take up an additional
load of this matter, which il would re.
tain in suspension SO long as the We
locity of current was maintained; and when
thus charged, it would be simply impossi-
bic for it TO take up any load or produce
any additional securing The current receives
its first acceleration at the upper end of the
lefty works, and here it first becomes charged
with the surplus load 1t receives no further
acceleration in its passage over the crest of
the bar lowing to the incompleteness of the
work there), over which it escapes laterally.
The enlargement produced by the excavation
gradually reduces the current, where it occurs,
by the enlargement of the channel, and the
acceleration and extra loading of the water
then takes place lower down and nearer the
crest Of the bar. The effect of this is to
shorten up the base of the bar, and to deepen
the channel above it. before the crest of the
bar is reduced.
The original crest Of the bar was plateau
$500 feet wide, over which an average depth
Of only "a feet Of water could be found. be-
tween the parallel lines Of the jetties, which
are placed 1000 feet asunder. This plateau is
now reduced to q width of less than 600 feet
and will gradually be reduced to nothing, be- |
fore the deepening of the bar crest will begin |
to take place. IS the current is quite as
rapid now across the crest of the bar as it is |
between the completed parts of the JET |
ties, it is evident that. if the sediment |
ary matters Of the river were pushed |
along the bottom, by tho current, the |
deposits which are most elevated. like the |
summit of the bar. would be the first to be |
pushed of, and piled up beyond the bar
crest, in the sea water beneath the river dis /
charge, or in what has been termed the |
"dead angle" The base ON the bar on the
20 feet line of depth was nearly 10 600 feet
hong when the jetties we're commenced This
base has been shortened still more than tn. |
plai eau forming the bar summit and is now
onlx ahont 6lll feet long measured in the L