New-York tribune., 1907-12-23
READY FOR BIG SHIPS.
NEW JETTIES FINISHED.
Loper Mississippi Gets One of
World's Deepest Harbors.


New Orleans Dec Zone of the greatest chan
mel making undertakings in the history of Ameri
river Improvement will be brought nearly TO
completion this week when the iettles at the
mouth of the Southwest Pass of the Mississippi
River finished. These jetties after
dredging between them is completed. will give the
South of the deepest harbors in the world by
opening to the access of the largest steamships
afoat the 100 and 200 foot depths of the lower
Mississippi River
The harbor thus made accessible has navigabe
water connection with at least dozen states bor
dering the Mississippi and its tributariesthe Ohio,
the Missouri. the Arkansas and the Red rivers.
About 100000 is being spent this improvement
by the United States government, which has the
work in charge.
The new jettes were begun four years ago They
are larger scale and substantial than
the famous jetties the Mississippis South Pass.
an outlet which for more than thirty years has
been the rivers commercial entrance. They
nearly parallel walls, about three and the
other about four miles long. lying than half
mile apart and built in the shoal water the
juncture of the Pass with the Gulf of Mexico
Their purpose is TO confne and thus accelerate the
rivers current across mud bar about three miles
broad, so as to produce channel at least 1000
feet wide, with minimum depth of thirty-fve
feet.
The swift current which they have produced,
aided by dredging. before their completion.
made so to s. feet of water in places where
at the beginning of the work the depth only
little over mans head To make the uniform
contract depth there Is still in several spots about
ten feet of mud TO be removed It is expected that
the high water due within few weeks will sweep
the remaining mud deposits out to sea by the be-
ginning of next summer.
Probably few walls ever have been constructed
under greater difficulties than these jetties.
They are made of willow, scantling, stone and con-
crete. Although in places they not six
feet deep, and although their greatest depth is
barely fifteen feet they have s2.1n0000 Every
material entering into their construction has been
brought from distances of hundred to five hun
dred miles.
The jetties have foundation. but rely for sta
bility upon their extremely broad bases being from
100 to 80 feet wide at the bottom contrast
this great width of base. the concrete Gaping
which forms the top of the jetties, and which is
the work receiving its furnishing touches this
week, is only few feet wide. The Gaping is
sea wall AZ feet high and is the only portion OF
the jettfes not submerged. The wall weighs be-
tween two and three tons TO each linear foot.
The submerged structure supporting this mass of
concrete is made almost entirely of willow poles
and brush With the aid of frame works of scant-
ling the willows formed into so-called mat
tresses-broad. fat structures resembling bed mat
tresses In form-cach about two feet thick. 30 feet
long and varying in width from 50 TO $50 feet. The
mattresses were sunk above the other. with the
widest the bottom and those above uniformly
diminishing in width they approached the sur
face The topmost mattresses were uniformly
thirty-fve feet wide. and level with the sur
face of the water. Heavy broken stone was spread
evenly over the mattresses to sink them. that
Iayer of stone rests between each OF these willow
structures The greatest number of superimposed
mattresses is five.
The Mississippi has done some interesting work.
IN addition securing out channel, for 1t has
made the mattresses practically indestructihie to
any normal agency OF nature in this region by
These deposits follow closely the contour of the
ietties I'm conjunction with which they form new
hanks of the river. The only change likely To
occur in jetties is their gradual sinking. until
In time the concrete Gaping entirely disappears
This sinking already has occurred 10 the jctties at
South Pass.
In the course of many years bar may form
Hy silt deposits in the Gulf 10 the deep water
beyond the mouth of the 1etties. and then the rem
edy will be the extension the jetties dis
ance further. The rate OF bar extension during
nearly seventy years preceding the starting of
the ietties was between $50 and go feet annually,
and the deposits responsible for this advance were
made when conditiors, now greatly changed, ia
vored such accretionS-
Of the 100000 allotted to making the chan
mel is being spent IN safeguards several miles
above the jetties prevent any increase flow
of other large outlets from the main river to the
Gulf This is being accomplished by placing stone
covered mattress siils the river bottom across
the entrances to those outlets Several small
bayous leading from Southwest Pass the Gulf
will be entirely closed up.