Knoxville journal. [volume] (Knoxville, Iowa) 1874-1986, 1875-06-03
Wha. Are Jetties!

1 W hss< AAC SSssaSSs
| This and similar questions are so
often propounded OF late that we are
impelled to transfer to our columns
from the Scientific american the fol-
lowing explanation in reference to
the jetty system which is to be ap-
lplied in opening the mouth of the
Missippi river to vessels of heavy
| draft:
! The long discussion relative to the
most practical method of improving
the Mississippi, so as to render the
same passable to vessels of deep draft
and thus to open the river ports to
direct ocean traffic, was virtually ter
minated by the granting OF an appro-
i priation by Congress, for the con-
struction of a system OF jetties, at one
of the passes through which the
stream eaters the Gulf. The plans
INVOLVING canals, which have been
streauously advocated by many emf
nent engineers, are therefore for the
time at least set aside, and to Cap. j.
l.. Esds, an engineer now widely cell
ebrated for his successful construction
of the st. Louis bridge, has been en-
trusted the task ofcausing the mighty
current of the Father of Waters liter
ally to undo its own work and to
break down the barrier which itself
has created.
The Delta of the Mississippi is
formed of narrow strips of land,
mostly low lying banks, through
(which the river winds till 1t makes
its exit TO the Gulf by number OF
narrow passes. In some of these
channels, previous attempts have
been made to deepen them by dredg-
ing, with but partial success, how
ever, as single food has been
known to carry down sufficient sedi-
ment to fill them to their original
depth; and the current, besides,
emptying into the open waters at tho
mouths, speedily left at that point
bars OF blue clay, surmountable only
by light draft ships. The gist OF
lCapt. Eads' plan will now be readily
unprecedented when IL Is regarded as
shifting the point of deposit of these
barriers from the sboal water at tho
entrance of one pass, out into the
deep water where filing up by nat.
ural causes IL impossible. BY this
means the river current Is to DO made
| To cut out ana Bcour its own chaunel
across the present bar. To do this, 1t
IL obvious that the banks OF the pass
must be extended, 30 AZ to lead the
stream far enough out; another Sec
ton of conduit, as 1t were, must be
added, and this Is now to DO formed
of the submarine dykes or jetlies.
The materials Of which these struct-
ures are to be composed are willow
twigs bound i'm bundles, termed by
engineers facines," eight or ten feet
in length, and about as many inches
in diameter. A large number OF
facines will DO lashed together to
form RATS. The RATS will be from
seyenty-iiye to two thousand feet In
width, the largest being suAk In tho
deepest water. The RATS will next
be towed to the proper point, there
loaded with stones and submerged,
and thus the work will continue, ono
raft being sunk above another until
the surface Ii reached. Each line of
the RATS will be narrower than tho
one below 1t until the upper course
will not be more than ten feet wide.
The two which will thus be con-
structed will be proloDgations OF the
banks, and between them VIII form
channel with sloping sides. In the
course of time, the interstices OF twigs
and stones will fill up with sand and
mud, so that eventually two soiid
submarine levees Will be produced.
Very little pile work, 1T Is said, VIII
be required except, perhaps, at inc
head of South Pass, which IL the OUT
let at which the jetties are to'be
lbuilt, In order to provide for the
proper regulation OF the volume Oh
| water In the new channel at various
stages Of the river.
Captain Eads has already begun
his surveys, in which work, toge'her
with the making of necessary con-
tracts for materials, labor, etc. the
summer will be consumed. The fr5t
raft, it is expected, will be sunk py