New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1876-01-20

Captain Eads' Report ON tho Jetties.
Captain James B. Eads has furnished the
press with the following copy of a letter on
the work at the jetties at South Pass:


Captain James B. Eads has furnished the
press with the following copy of a letter on
the work at the jetties at South Pass:
OFFICE SorrH PASS JErrY WORKS,
New Orleans, January ii. 1876.
Mr.. J. s. Walsh, President South Pass Jetty Com
pany, st. Louis, Mlssou1l
DEAR SIR have the honor to inform
YOU that the ietties being constructed under
my grant from the United States have been
so far extended into the sea, that the al
most complete control of the river discharge
has been accomplished through distance
OF aboat one and halt miles from the
lands end, and within $500 feet OF the crest
of the bar.
Up to the twenty-tifth of December, the
date OF the last complete sOundingS, Mr.
Corthell chief assistan. engineer, estimated
that ,263, 2222 cubic yards had been exca-
waited from the bar between the jetties.
. This has been nearly all accomplished by
the current since the first Of October, and
the larger portion OF it during the month OF
December. AS near as l can estimate the
current seems to be removing from 2O,000
to 30 900 cubic yards per day. large
amount of work has been done at the Jetties
beyond this one and half miles referred
to.
Your stockholders will understand more
clearly the amount of work accomplished
and the amount yet to be done, when state
that to complete the mattress work OF the
etties Up TO the low tide level, and out to
point $500 feet from the lands end, will
require only 100 additional mattresses.
Messrs. James Andrews & Co laid in posi-
tion during the last thirty days ito the tenth
OF january i21 mattresses.
The weather is, however, so unstable at
this period of the year that 1t may require
sixty days to lay this remaining number.
Tie bar crest is now 10000 teet from the
| lands end and when the ietties are extend
ed to this point, We shall have very COM
plete control OF the river, and the disappear
ance of the crest of the bar will then be
only a question OF time, the duration of
which we can more accurately estimate
from tie results thus far developed.
To secure twenty feet depth OF water
about 1000. 600 cubic yards will yet have to
| be excava,ed by the current.
The jet:y works will extend about 100
feet beyond the crest OF the bar when COM
pleteh. A large part OF this work is already
completed, but l am confident that to St
cure from twenty to twenty-five feet OF
water it will not be necessary to raise the
| iet,,es above low tide nor extend them be
| youd the point named, 500 feet.
The material CT the crest OF the bar is
| identicaily the same as that which is belD g
! 80 rapidly secured out by the current from
| anxiety need be INDUCED in on account OF
! the water not being yet deepened on the
| crest OF the bar.
| This is because no acceleratian of the
| current is created On the crest beyond that
! which the water receives by the effect OF
| the iatties about a mile above. The first
| acceleration of current will cause the waite r
to be charged with larger amount OF sedi-
ment. When thus charged it can sustain
no more and unless it receives an additional
| acceleration it must pass over the crest OF
| the bar without aft citing it. But as the
| channel is enlarged by this securing mile
| or so above the crest of the bar, the curreLt
! there gradually falls to the normal condi-
! ton OF the river above, and receives the
| acce.eration farther down and nearer to the
| crest. and this latter result is increased by
| the continual extension and building up o;
| the iettits toward the crest of the bar. Over
| these unfinished parts Ut the jetties soma
1900 or 1000 feet long above the crest Of the
bar it is now flowing out laterally with an
average depth of five feet, and an average
| depth over the crest of the bar OF eight feet
II will thus he seen that the enlargement
! of the iettied channe! first manifested itself
at the upper end of the works, and that il
| is steadily moving Gown toward the cres'
! OF the bar.
The summit of the bar being originally 6
| plateau over half mile in length, is now
| reduced TO a mere ridge, while the base o
the bar, estimating it at twenty feet be
meath tue water surface, was originally
nearly 0C00 feet long, now 1t Is only abou
GOO feet lorg.
These results clearly establish the fact
that the sedimentary matters are carried II
Suspension by the river, and that the Quan
tity carried has direct relation to the
velocity Of the current, and that these
matters are not pushed along the bed o
the river as has been repeatedly and EN-
phatically asserted by the opponents Of The
jetty system.
II this VI ere the casa the current, which
to-day is certainly flowing one and hal
miles sn hour faster over the crest OF the ba
than it ever did before the construction o
these works, would have the effect CT push
ing ths material Oft the crest or highes
part of the bar first, and, of depositing it il
the still. ealt waters of the Gulf, which il
was asserted formed dead angle" on tht
outer slope of the bar below the river dis
charge.
If this pushing theory were correct, tbs
crest of the bar would have been pushe,
off by the efec. OF the jetties, and would b.
found forming another bar in advance o
them, and thus the necessity OF continually
pro,onging the jstties, so confidently pre-
dicted, would be undeniably proven.
But the fact is that the outer slope of tht
bar has been very materially deepened bJ
the tidal action, although it is only par
TALLY controlled by the uncompeted work,
which extend beyond. the crest, and WI
have 10 evidence Of any deposit whatever
Immediately in advance of the jetties.
The concentrated and accelerated outflow
of the river maintains its suspended load
to greater distances in the Gulf than evel
before, and the prevailing westerly sea cur
rent, which is induced by the prevalent cas-
vr;~ honr Wv ofnrc fI,o lodi
westwardly, and into deeper water ard en
tirely away from in front of the jetties.
The works at the head of the Pass ar
being pushed rapidly, aud in the last month
1900 feet OF foundation mattress have bee!
laid along the length of the dyke. This
dyke extends 5000 feet up the river betwaer
the entrances to South Pass and Paas-a
rOu:re. Very respectfully,
JAMES 3. EADS. .