New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1876-07-02
in the deeper water between the Greats of
these shoals and the lines Of the jetties.

in the deeper water between the creets o
these shoals and the lines Of the jetties.
sCOUR.
At 500 feet below East Point station q
line of piles $50 feet long has been driven
starting from east jetty and running n
right angles to it toward the middle Of the
| pass. similar opposite line projects from
the west jetty. 1t SCENE to have been the
intention to put aprons against these spurs
Of pilinR, in order to obtain greater scoul
between them, but the plan has not YET
been carried out.
Similar spurs Of piling were driven 9i5O
feet below East Point, but the spur work
was not completed.
Some attempts have been made at stir.
ring up the bottom, and thus aiding scour,
both at the head and at the mouth 0t South
Pass.
long chain, with heavy pulley at its
end, was dragged over portions OF the bot.
! tom, but this process was soon abandoned.
A kind of rake with iron teeth, which had
two arms running from the ends of it's head
past the sides OF q scow, to transverse
axis on the scOw, about which the rake re-
volved, was also tried; but this was broken
while the scOw was being towed, drs gging
the rake. At my recent visit stronger
| one had inst been constructed and was in
OPT alton, but do not yet know with what
results.
Upon comparing the coast survey map of
| June, 1873, with sheet No. ], herewith, both
being referred to the plane of average flood
tide, it will be seen that at the first date the
lowest point of the thirty foot curve was
! 300 feet below Ea.t Point. where there was
hole Of that depth, which has now in
creased q little in size, but that there has
been no marked change in the pass from
| the head OF the east letty to near the head
| of the west jetty, about 1000 feet below. In
| June, 1875 lSs. feet could be carried down
| to the head of the west jetty, now 2CA feet
can be so carried. II will be seen that
| the twenty foot curve then had it's lowest
point 1900 feet below East Point, and that
now the lowest point Of the main twenty
foo. curve is 5000 feet below East Point,
This twenty foot channel has an average
width Of about 200 feet from its lower end.
where it is very narrow. to the head Of the
west jetty, distance of 1900 feet. The
dis ance from it's lower end to twenty feet
of water outside Of the bar is now 5000 feet.
Perhaps clearer statement would be the
following figures, showing the draft of water
that could be taken through each 1000 feet
of the channel below East Point station in
June, 1875. and in May, 1876
Draft. ls75-2O00 feet, 22,5; 1000 to 1000
fact, Is 7; 1000 to 5000 feet, l6 z; 5000 to
5000 feet, 10 2; 5000 to 10000 feet, 81; 10 O0O
Draft. lS76-2oOo feet, 90 8; 1000 TO 1000
feet. 20 3; 1000 to 5000 feet, go; 5000 TO
5000 feet, 2l0; 5000 TO 10 600 feet, III;
10000 to IL, 100 feet, l5.7.
At the ends of the jstties the bar seems
subject to considerable changes in short
periods. In the sOundiDgs CT May 3 Cap
tain Brown found q least depth in channel
of fifteen feet. On May 10 and II ran
numerous lines of soundings across the bar,
but failed to find more than thirteen feet
six inches on any line. was informed that
between Captain Browns sounding. aud
mine strong southeast wind had blown for |
several days, which may have caused the |
shOaling. A few additional soundings on
May %, by Mr. Parmely, indicated that |
from scOur and raking, the depth on the |
bar had again increased to sixteen feet SIX !
inches.
In considering the advance of the outer
face of the bar at the ends OF the ,jetties. the
movement Of the twenty foot curve will be
q good guide. In June, 1875, this curve,
gently convex toward the sea, crossed the |
present line Of the east jetty about 300 feet
above its end (pile ll0ll, and the present
line of the west ietty, about twenty feet
above pile No. 3j5, hitherto called the emit
of west jetty. On sheet No. it will be seen |
that now the twenty foot curve has ad-
vanced on the line OF the east lefty bout
$50 feet, and on tbs west jetty about 100
l
two jetties it has advanced about 40 feet.
Its average advance in front of the jetties
may be taken at $50 feet: IT the thirty foos
curve be examined the same movement is
observed, but to smaller amount say
about 2OO feet on an average. This curve
has moved very irregularly. some points
feeding instead of advancing.
In 1873 the coast survey map shows that
N passing the outer crest Of the bar where |
%hav l
leepened abruptly to thirty five to forty .
i've feet, and then shoaled. Ga this shoal, |
which ran obliquely in front of the ettes,
nd at distance Of about 500 feet from
heir ends. there was, except in q narrow
hannel drought it, less than thirty feet of
Vater, the minimum depth being thirteen
nd three-quarters feet. At present the
arrow channel has disappeared; and limit
1g the word ''shOal' to the area which has
sss than thirty feet of water on it, it NAV !!
o said that the sboal appears to have
loved from 200 to 300 feet seward, retain
1g about the same area and the deeper
'ater between it and the ends of the jetties .
nd that it has now q minimum depth on it !
fourteen and a half feet. Going outside
MS shoal, the forty foot curve, while irreg.
larly changed during the year, yet shows !
tile or no general advance. G
The shoaling which has occurred is shown
sheet No 3, herewith, which gives three | !
araIlel sections of the gulf bottom, running !
award from the ends of the jet,ies-the \
rst IN the prolcngation of the east lefty, I
le second parallel to the first and half way
stween the jetties. and the third parallel
the others, and from pile 355, or end of =
70 west jetty. e
The sections are constructed from Mr..
arindin's survey of May and June, 1875. :.
I'd from Captains Browns survey of May, II
~, both reduced to average food tide.
These sections show in detail for these |
rec lines, out to the fifty foot curve, what "
II already been stated in q general way -
r the whole area in front Of the ends of ~
e jetties. q
The eastern section indicates very irregu- p
: changes in the first 1900 feet, showing III
opening. in some places and ehoaling in
hers, without decided preponderance of p
her, except near the end of the east ~ ~
,ty. III
The central section shows the shoaling at IL
3 end Of the ietties and the apparent ad- OF
nee OF the shoal 1000 feet in front, already Ut
Tered to. ne
The western section shows shoaling near az
3 end Of the west jetty. IL
All these sections indicate considerable |
opening at distances in front of. the Jet pc
9 between 2400 and 1000 feet. a.
In material sOsCtt as the mud demos q.
d in deep water it is difficult to say what tn
ocular changes may arise, either from its 81
Ting or from wave action on it in storms. /.
t deepening here of eight or ten feet Vi
es not, in advance, seem probable, and w
, work will at once be repeated, to detect IN
error or verify the results of recent sur co
7 of this area. oil
GRAND BAYOU. ne
The work at the head Of Grand Bayou, ar
its closure, has been suspended, appar- 90
ly from the difficulty in building dam pr
oss it there, and it's closure has been un. I'M
taken at point about a mile down the De
u. Three tiers of mattresses aaoh +hrao wa
six inches in thickness, have been sunk WI
oss the bayou; the mattresses of the gu