New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1874-06-14

rises on the salt water. Hence the neces-
sity of extending the jetties as fast as the
bar is extended, if we wish to maintain a
uniform depth OF water at the entrance.
This extension of the jetties must be
made in from thirty to forty feet water,
and will cost in the case of the Southwest
Pass about 81 ZOO, 900 annually.
We have, then, for deepening to and
maintaining the depth of twenty-seven feet
at low water capital of S23,0O0,o0O.
Applying the jerty system te the South
west Pass tor the same depth the estimate
600; annual cost of maintenance, including
dredging through shoals in the pass. $780,
0Oas which together represent capital OF
about ST.. 100000.
/ am aware that Mr.. Eads states that it
will not be necessary to extend the jetties
after they have once deepened the bar TO
the desired depth, and presentstthe grounds
OF his conclusion substantially AS follows:
The Mississippi river, he says, carries IN
suspension certain amount of earthly mat
ter, which is fixed and UNMARRIED for each
velocity of current; when the velocity is &C.
creased the sediment is at once reduced in
quantity, some of it being dropped to the
bottom; when the velocity is increased the
quantity Of suspended sediment is at once
increased by the current picking up earthy
matter.
| i1c ucAG etdtcS lUdu inc CuTroul VI tuo
river being suddenly and largely checked
where it meets the Gulf at the outer edge
Of the bar, its suspended matter is dropped
there in large quantities and forms the an
| nual addition to the bar.
His proposition is directly contradic.ed
by the observed conditions existing on the
Mississippi river, and, indeed, everywhere
else. II was found by long series Of meas
urements on the river near New Orleans
and at Columbus, twenty miles below the
mouth of the Ohio, that when the velocity
OF the current was greatest the quantity of
earthly matter was about the same as when
the velocity was least; and that the greatest
quantity OF suspended earthly matter found
near New Orleans was at time when the
velocity Of the current was two feet per.
second less than the greatest velocity.
Similar results were found at Columbus.
one of them being that when the velocity
OF the current was only two and a half feet
per second the quantity of earthly matter
IN suspension was about equal to the maxi
mum quantity. In short, there was no d.
rect relation between the velocity of cur
rent and the quantity of earthly matter sus-
| pended; the latter depending upon the
tributary river which at the time furnished
the chief volume Of the Mississippi, and
being kept in suspension by the stirring up
process, caused by the great irregularities
! in the bed of the Mississippi. Mr.. Eads re-
| fers to the Bonnet Care crevasse as f1rn-
ishing an instance in poin: of the deposit Of
earthly matter when the current decreased
in velocity, but the bottom of the river
where it was said this deposit had occurred
was found by the Mississippi Delta investi-
| gaslon TO be hard blue clay, which had
| been there for centuries. In fine the
tons of the Mississippi Delta survey
| prove this proposition Of Mr.. Eads to be
| utterly unfounded.
His second proposition, that the current
| of the Mississippi river receives a sudden
| check upon meeting the salt water of the
| gulf, is as unfounded as his first. Personal
observation alone. without the use of instru-
| ments, would make this plain to one accus-
toned to the observation OF currents, but
| these currents have been measured. and it
| is found that there is no sudden check to
the current OF the river where it enters the
gulf; on the contrary, ii decreases so slowly
| that repeated nice measurements over long
distances are required to detect any de-
| crease in the velocity of the current, and in
fact it decreases very slowly from the point
where the pass begins to widen until it
finally ceases, in the case of the Southwest
Pass, at the end of twenty or thirty miles.
The oils l have seen proposing to con-
tract with Mr.. Eads to deepen the entrance
to the Mississippi river to twenty-eight feet
at high water are based, l understand,
upon the adoption of his view that there
jetties after they have once deepened the
entrance to the required depth, although it
is explicitly stated in these bills that
100000 is to be paid TO Mr.. Eads
for deepening the entrance to the
required depth, and another;s5. geo, 900 sub
sequently for deepening and maintaining
the depth certain time. After the last
II 70 = L.
the second clause, what security is there
that he will continue to maintain the depth
if he should find that he was mistaken in
his views, and that it will cost him 81 .0O0,-
O00 annually to maintain the depth! None
is proposed IN the bills have seen, and it is
manifest that in reality the United States |
takes all the risk of his views and project.
and if he should be found TO be mistaken
the United States will be in the condition |
of having expended S5,000,000 for Jet |
ties and $3,000,O 600 for their maintenance,
and then be Obliged either to abandon the !
work or go on with perpetual annual ex-
penditure of about million. Now the |
canal once built is permanently useful at |
a small expenditure, and the sums involved |
by the differences OF opinion respecting its |
cost are small compared to the magnitude |
of those resulting from the differences of !
conclusion respecting the permanent effects |
OF the jetty system; the adverse conclusion |
respecting the use OF jetties being based |
upon carefully observed facts and investi- |
cations, and the other upon suppositions in
direct conflict with the conditions known !
from investigation to exist.
There is one feature in these bills which.
if it could be introduced in the appro- |
priations for river and harbor improve
ments, would conGuce to great economy. l |
refer to the provision that is made for a
permanent fund for the construction of the
work. Such provision would save the
cost of outfit from each annual appropra-
ton for work, since under existing laws
every improvement must be carried on by |
contract with the lowest responsible bidder
as each annual appropriation is made.
Very respectfully. your Obedent servant
A. A. HUMPHREYS,
Brgadier General, Chief of Engineers.
Hon. L. A. Sheldon, House of Representatives.
Mr.. Sheldon-Jetties. as plan for Deep
ening rivers, have no history. In few cases
only have they been tried. No river of
magnitude has ever been jettied. They
have never been attempted except in rivers |
comparatively small. And SO unsuccessful
have been the experiments that engineers
of ability and reputation have never resorted
to them except under the most favorable cir.
and so signal have been the fail
ures that single precedent is cited to sus-
tain the theory of their application to the
mouth OF the Mississippi river To say
that because jerties have proved etfica-
cious at the mouth of the Sulina, there
fore they will be successful at the mouth
of the Mississippi, would be like saying
that because suit of clothes will fit a
mere child, therefore it can be put on a full
grown man. The conditions are all unlike,
in magnitude of river, in volume of water,
IN character and quantity of sediment, in
the matter of littoral current, in expos
ure to storms, and in the character of earth