The New Orleans bulletin. [volume] (New Orleans [La.]) 1874-1876, 1875-05-25
CAPT. JAS. B. EADS.
His Address to the Chamber of
Commerce.

The call for meeting Of the Chamber of
Commerce to hear Capt Jas. B. Eads, on the
subject Of his jetties, resulted last night in
one OF the largest meetings that the Chamber
has ever held. At about 1880 o'clock, Presi-
dent Bussey took the chair and called the
meeting to order.
He explained that Capt. Eads had not ex-
pected to meet such large sssemblage. That
the call for a general meeting was made
through error. It was the desire of Capt
Eads to meet few gentlemen to whom he
could explain his plans and elucidate them
by maps which had been carefully prepared.
These maps were too small to be submitted
to such a large meeting, but Capt. Eads had
determined to make use Of blackboard.
He then introduced Capt Eads, who
opened
| HIS REMARKS
with and expressions of regret that he should
be under the necessity of commencing them
with an apology. He had not expected to
meet such a large and respectable audience.
He had come prepared to address few, and
| to use the maps he had brought with him.
| He continued: To properly comprehend the
/
stand the cause of the continual advance of
the river into the sea. Its mouths are now
thrust out about sixty miles into the Gulf and
their progress goes steadily forward in conse-
quence OF some of the simplest laws of which
we have knowledge.
| The opponents of the jetty system main
tain that the chief portion of the sedimentary
matters transported by the river are pushed
along the bottom. II those who believe this
error will only discard it for few moments,
and permit their minds to picture the sand
and earthly matters of the river carried in
suspension, and that the magnitude OF the
burden thus carried is proportional to the
velocity of the stream, I will promise to make
plain to them every phenomenon presented
at the mouth of the riger and throughout the
one thousand leagues of its alluvial bed.
In proof that it carries sand in suspension,
you have only to dip up cupful Of water
from its surface, and you will find it not only
opposite your city, but far beyond the crest of
its bars out in the Gulf. So long as it moves
onward it holds these matters in suspension,
and Just as its current is slacksned will it
drop the heavier particles and sustain the
lighter ones on to the last.
Accidental causes may show that the water
| is sometimes charged with less or greater
amount of sediment than is due to given
depth and velocity, but every apparent excep-
| ton to the law that all alluyial streams carry
their sediment in exact proportion to their
velocity modified by the depth of the stream,
can be easily reconciled with the law. 1t is
this law which gives the stream the power to
regulate the size of its channel to suit its own
wants. Where it is too small for the flood
the current is accelerated, its scours up big
ger burden there, and soon scours out the
requisite room for ITSELF If the channel at
another place is too large the current is there
slackened and the excess of load is dropped
until the channel is diminished and the cur
rent restored. When the channel is big
enough the scour ceases. When it is suffici-
emily reduced in size the depositing action
ceases. The bend caves in because the river
channel above is too big There the slack
! current has been depositing its excess load
and forming sand bars. Ia the bend the
enamel is too contracted and the current is
then made too rapid for it's reduced load, and
it scours up the deficiency out of the bottom
and side of the bend.
Let us apply this law to the advance of the
Southwest bar. On the bar we find the
depth fifteen feet, and throughout the pass
not less than sixty feet. The bottom is,
therefore, forty-fve feet higher on the bar
than it is at the foot of the pass, where nature
has completed her jetties, between which the
river flows in magnificent channel OF almost
uniform width and great depth. This hill
forty-five feet high, begins to rise just where
the banks of the pass begin to widen out to the
sea, and between these two points the river is
building its jetties. Evidently the effect OF the
hill against which the riveris discharging is to
check the velocity of the stream which is
flowing down with the load of sediment due
to its speed. Checking the velocity means
dropping the excess OF load. The current on
the sides is more sluggish than the central
channel, and hence they are gradually built
no to the surface and the continual dropping
of sentiment on their margins gradually mar
rows them in until they become so steep that
no more deposit will rest upon them. When
thus narrowed in they are completed, and are
of the width of the channel above.
Now let us note the effect upon the bar OF
this building up and narrowing in OF these
incipient banks The bar is to-day about
seven and one-third miles from where the
mouth of the pass begins to widen. When
Talcot surveyed it in S-thirty-seven yeara
Iago-the bar was seven and one-third miles
from the narrow part of the pass, but the pass
has by this narrowing-in process been gradu
ally concentrating a more rapid current
against the bar, and this incre ased scour
ling power has cut out the hill on the upper
side and transported the material over it,
crest, and dropped it on the seward side
of it.
In proof of the narrowing in of this un
finished part of the pass, will refer to the
fact that i've miles above the bar of Talcot
the pass is now only about 1900 feet wide,
whereas it was $500 feet wide when Talco
surveyed it. Col Longs map of 1857 shows
the width to have been three-e ighths of q mile
greater at Pilot Town, about six miles above
the bar, than it is to-day. 1t is evident thai
the river is building at the Southwest Pass
parallel jetties about 1900 feet apart, and that
It preserves depth between them Of at least
sixty feet of water Is it not evi
dent that the hill or bar is an
absolute necessity in this natural jetty
work, without which the river could not
throw down its sediment on its two incipien
lietties? At the rate the river is building al
this pass it would take it 17S years to build
its ietties seven and one-third miles, or from
where they are completed out to the crest O
the bar. If man we're to extend two artificial
ietties out suddenly seven and one-third milei