New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1876-07-02
THE WEEKLY REPUBLICAN
General Comstock's Report ON the South
Pass Jetties.

General ComstOck's report to the chic
OF engineers was submitted to the Senat
June %, and ordered to bs printed. 1t il
accompanied By maps, to which reference
is made in the text. Owing to the conflict
ing and exaggerated statements concerning
Che works at South Pass, this report will b.
gead with great interest:
OFFICE CNIrRp STATES LAKE SURVEY I
Detroit Mich. June 8, 1876.
GENERAL-I have the honor to report the
Condition of the works for the improvement,
of the South Pass of the Mississippi rive,
con April 80, 1876.
The soundings on the three sheets OF
Tracings transmitted herewith are of dates
from April q to May IL. All soundings re.
ferred to in this report, except those in
Grand bayou, whether made by the coast
survey or under my direction, are reduced
TO the plane of average food tide.
The location of the jetties and the method
OF constructing the mattresses has been
fully described in my previous reports. As
there has been little change in either, it is
unnecessary to repeat the description.
EAST JETTY.
The work done on this jetty since Fsbru-
AIRY Z, 1876 has been confined to raising the
jetty ia low places by additional mattresses,
and to extending its mattress work toward
the point called the end of jetty, which is
ll,94l feet from beginning of jetty, or
1900 feet from station East Point. On
April 80 this extension had been brought
up, or nearly up, to the water surface, to
swithin 400 feet ST the end Of jetty. Along
the line of sheetlpiling, which continues for
about 5000 feet from the beginning of the
jetty, additional mattresses have been
placed in the second tier, go that now there
care two tiers of mattresses for nearly the
whole length of the sheet piling.
In general, it may be said that the east
Jetty now confines the water at low tide
pretty thoroughly to within 400 feet of the
end of the jetty. There are, however,
gut, or where there are holes through the
mattress dixie, which permit small amounts
of water to pass through the east jetty,
thus giving shallow channels through the
the general shOal which exists outside of
ehis lefty. There has been some shOaling
un the outside Of this jetty since the work
Nvas commenced.
Starting from East Point, and going sea-
sword on line parallel to and 100 feet out
eide of east jetty, the following figures give
for each 2000 feet the average depth, as
ashOwn by the coast survey map Of May and
June, 1875, and by the map of eOundings |
forwarded herewith, of May, 1876. both |
being referred to average food tide.
Depths, 1854 feet; 80; 80; 40; 40;
@.5.
. Depths, ls76-lo feet; IL; IA: 80; 40;
IS.
Within few hundred feet of the end of |
fne east jetty, piles have disappeared from
time to time. In some cases they may have
been washed up by heavy seas, or the to
redo may have injured some enough to en-
able the sea to break them of; but the
evidence seems to show that many have
sunk gradually out of sight, although their
tops were at first several feet above water.
At this place the top of the jetty has also
sunk, and, apparently, not from it's top mat
tresses being destroyed by the waves. Both
seem to indicate settling of the strata into
which the piles are driven, or upon which
the mattresses rest, TO distance of from
i've to ten feet. Less marked phenomena
If the same kind have been observed in the
vest jetty; in places where the settling of
he top Of the jetty is small, it might be
attributed to the compression OF the lower
mattresses.
The cross section of the jetties remains
the same as heretofore. The
utter edge of each mattress rests against
he vertical piles. The bottom mattresses
airy from thirty. five to fifty feet in width;
where the water is so deep as to require
rom three to six layers, the top mattresses
re from twenty-five to twenty-five feet in
1idth. An ordinary mattress occupies
bout three feet in height in the jetty;, De- I
ails of the state of the mattress work are
hown on sheet No. =, herewith.
WEST JErrY.
As in the east jetty, the work on the west
,tty since February Z, 1876, has been I
lainly confined to the filing Of gaps in the {
tty where it had not been brought up to q
10 water surface, and to the extension of q
9 mattress work. I
On April 30. 1876, the mattresses were up, f
+ nearly up, to the low water surface from q
lie No. 355, which is opposite the end of il
lst jetty, and has heretofore been called Ii
10 end Of west lefty. The number of layers t
mattresses along this jetty is from three o
seven, varying with the depth of water
ID the amount Of settling The advance
the outer face of the bar, which will be n
ferred to hereafter, give now but eleven 4
ct six inches Of water ct pile No: 355, q
here year ago the coast survey found q
7enty one feet, and the piling for the istty Il
10 accordingly been EXTENDED about 200 p
ct beyond pile No. 355. r.
Extensive shoaling has taken place on p
Q outside of the west jetty, IS appears 81
I'M the following figures, which give. ct
ersge flood tide, the depths. 200 feet out m
le Of west jetty, for each 1000 feet below 81
.st Point station, derived from the coast it
rvey map of June, 1875, and from the re- CT
mt survey: 81
Depths, May and June, ls75-l4.l feet; =,
9.8; z. N
Depths, May, 1866 feet; 2; ls; Is. IL
The shealing can be seen on the sections OF
ross jetties given on sheet No. 2 Of tracings or
rewirh, showing the progress Of mattress RI
.rk and giving details. N
It will be noticed that in 1875 shoals ex. sh
ed little to the east of tho east jetty, to
d west of west jetty for nearly their DC
,ole lengths, and that much of the subse- Fl