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Annual report of the Secretary of War, Volume 3 online

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fears of battures forming subsequently.

5th. It must be on the shortest line between the river and the sea, on condition, how-
ever, that this advantage shidl not be compensated by a considerable increase in the
expenses.

6th. It must present, at its opening on the sea, natural shelters to protect the approach
of vessels.

7th. It must, besides, offer a direction little inclined with that of the wind prevailing
during the greater part of the year.

8th. It must open on the sea at a point where no accretion and no decrease in the
present depth of water are to be feared.

9th. It must offer to vessels secure anchorage, so they may lie in safety outside the
canal.



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814 REPORT OF THE CHIEF OF ENGINEERS.

"^lOth. It must free veesels from all necessity of pilotage, and, consequeDtly, SToid
their circulation among the islands, keys, and reefs, which in the passes reqniie the
services of a pilot.

11th. It must also do away with the necessity of towing, at least as far as the riTer,
where the wind often permits vessels to ascend directly from the English Towa as Su
as New Orleans.

12th. It must have a constant depth of 22 to 24 feet of water, in order to permit the
access to the river of ships of the greatest tonnage.

1.3th. It mnst be forever secure, by its conditions of existence, from those pertoiba-
tions which render the passes impracticable to the navigation of large vessels ; that Lb
to say, from the action of the sea, from accretions from the river, from sand-banks
formed by any agency.

It will be seen from the description we are about giving of the proposed canal, and
from its topographical conditions, that it will satisfy, strictly and precisely, all these
exigencies.

Section 2. — Topographical and hydrographioal deacripHon.

When, going down the Mississippi, we arrive at Fort St. Philip, we see ti)e
majestic course of the river developing itself on a length of eighteen miles, asfiiras
the head of the passes, without sinuosities or turns. The mass of water moves alwa^
in the same direction, without any sensible inflection in its banks. But as the current
came from the southwest, and has inflected to the southeast from the bend of the forts,
the result is that its greatest swiftness and depth are near the left bank, while the
water is smoother and deposits its accretions near the right bank. From three to
eight miles below the fort repeated soundings have given us depths of 24, 25, '26, and
28 feet, at a distance of 20 and 25 feet from the bank; 20 feet farther the head sinks to
62, 71, and 87 feet.

If we stop seven miles below Fort St. Philip, that is to say, precisely on the 9(P 31'
longitude west, we are at a mean distance of twenty-seven miles from the passes, which,
from the declivity assigned to the river, to wit, 3^ inches per mile, would represent a
diflerence of 7^ feet in the level from that point to the surface of the Gulf. Levelings
made by us between this point and the Gulf show that it is only 3 feet higher than the
Gulf at mean tide. It is ther«^fore possible to shorten the navigation of the river twenty-
seven miles at this point, having to make up for a difference of only 3| feet declivitjat
mean water, and 7 root at the highest water-mark.

This point being chosen at the hei^d of the canal fulfills completely the first three eoa-
ditions mentioned above. Let us see if It can satisfy, equally, the others.

If from the top of one of the few huts to be found on that bank, upon which, from
Fort St. Philip to the sea, there exists no important establishment except the salt-works
opposite the Jump — if from this observatory we turn our back upon the river and we
look around us, we will see, extending indefinitely to the horizon, a scene of extreme
monotony. The left bank of the river from the fort to the head oi the passes is » mere
neck of land hemmed in between the waters of the Mississippi and those of the sea^ Its
width, except at few points, does not exceed a mile, and at other points it is narrowed
down to a few arpents. An additional mile may be considered as a dependency of the
main-land, although cnt up in every direction by canals, lagoons, and bayous of an
average depth of 2 or 3 feet during tide-time, and which are transformed into mndor
sand-banks during low tides. Beyond this is a series of small bays from 3 to 3 feet
deep, and studded with a quantity of islets, between which the sea opens deeper passes
or deposits accretions upon which numerous oyster-bauks are formed.

On the right, on the east line, one of these islets. Bird's Islaud, of more ini[M)rtaDC6
than the others from its length, runs from north to south a distance of four miles; on
its eastern point a watch-tower has been built, which commands a view of the sea.
Going up from east to north, a long sandy beach, kno>#n as Sand Island, forms the limit
of these low lands.

In the direction of the northeast, the last of these islands, called the Pavilion Island,
fronts an island situated six miles off at sea, and to which we will have occasion to
refer ; it is Breton Island.

To the left of this islet another neck of land, called the Hard Battnre, rnns ont to
meet an island, two and one-half miles long, Grandes Coquilles Island, which is in the
due north point, and is only separated by a channel from the smaller Coqaille Islands
connected in low water with the main-land of Fort St. Philip.

It is, therefore, in this semicircle, the center of which we have placed on the rirtf
seven miles below Fort St. Philip, and the circumference of which runs from the south-
east to tiie northwest, that a real archipelago of islands and of lands cut up by htgo^
and bays, but uniform in their aspect and tneir nature, is comprised, evidently created
by sea-deposits, but with materials furnished by the Mississippi ; they reveal to »g*^
logical study the character of the marly accretions to be found in all the deposits of the
river. The bott4>m of the bays and lagoons, covered at certain points by a soft mire
which has not yet hardened, is everywhere else perfectly hard, and the purest clay



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REPORT OP THE CHIEF OF ENGINEERS. 815

fltickB to the lead. All these lands, scarcely ont of the sea, and which it covers in its
usaal tides and destroys or tears up in its ansry moods, only offer to the eye the monot-
onons vefi^etation of sea- weeds, CTamineous plants, and mangroves.

The radins of this semicircle, &om its center on the river to Pavilion Island, is of six
miles. It is on this radins that the projected canal runs. It outs first the two miles
of solid land, crosses the large bay in that part of it where the water is lowest, crosses
a prairie one mile wide, and, pursuing its course through lagoons and mud-banks, it
reaches Pavilion Island, having its ontlet in the pass of Breton Island.

It may appear singular that we should have chosen this point of the coast when we have
already stated that three miles below the salt-works the neck of land has only a width
of a few arpents between the river and the sea ; but a simple reflection will justify this
apparent contradiction. The object in view is not simply to out the canal to the sea,
which may be done by cutting through a leugth of 1,00() feet, but it is to open it on
the deep sea, that is, at a point where large ships drawing 22 to 24 feet can have easy
access. Outside of the main-land there is a border of batture, which in some places
projects twelve or fifteen miles, and beyond this batture, whose conventional line is at
a depth of 12 feet, the declivity is sometimes so small that a long distance must be
made before the necessary depth of water can be met.

The distance of six miles which we have found for the line of the canal is the short-
est between the river and the deep sea that can be formed from the forts to the passes,
and it is even necessary, in front of Pavilion Island, to dig and continue the canal
through a batture for a distauce of 3,000 feet to arrive at the required depth.

Another circumstance, altogether exceptional, militates in favor of this side. Hy-
draulic works or works of embankments made in 2 or 3 feet of water may be cousidered
as made on land ; while those made in 8 or 12 feet of water are extremely difficult and
expensive. Now, on the line indicated, about three-fourths of the passage are made ou
the land, and for the other fonrth, the average depth of the sea does not exceed 2 feet.
This plan conlbines, then, the advantages of the minimum of distance and the mini-
mum of cost.

Let us examine the access to the canal from the seaside :

We have alreiidy said that by followiug the northeast line, which is that of the
canal, there would be found on the main sea, and at a distance of about six miles from
Pavilion Island, an island known as Breton Island. This island, which had formerly
a length of six miles, and was then occupied by a colonist living with his family in the
midst of the vtist Gulf, was out up by a sea-storm that took off from it an islet of half
a mile in length, on which a watch-tower has been raised, which would be replaced
by a light-honse. As cut up as it is, this island, with the batture that extends on its
right and left, has a length of ten miles, running almost straightly from east to west,
and forming consequently an excellent shelter for vessels against north and northeast
winds.

The coast of the river above the tort, and the large peninsula of Lake Borgne, afford
protection against the northwest winds.

The coast of the river below the fort shields the canal from southeast winds.

Finally, the south winds are intercepted by the large eastern opening of the delta.

The head of the canal is therefore exposed to the east wind f^one, and it is
precisely this wind which will bring the vessels from the main sea; it can only facili-
tate their arrival and bring them in a direct line to the port.

The direction of the canal being northeast, it will be seen that the ships with an
east wind will sail directly for the canal with the wind over the quarter, a very favor-
able direction indeed, both for facility of maneuver and speed. The pier that termi-
nates the canal opens in a semicircle, to afford ample and convenient room.

The existence of natural shelters being thus established, can we depend equally
upon the depth of water in the channel formed between Pavilion and Breton Islands?
It is principally that point which we have investigated.

Besides numerous soundings in all that region, represented graphically, we have
inserted in the plans the series of soundings from the head of the canal to the watch-
tower on Breton Island. This line consists of the following points : 26 feet, 36, 35, 36,
39, 34, 19, 14, and 12. These last three soundings are in the vicinity of the batture of
Breton Island, the former occupying a breadth of four miles. We have also (although
it was one mile north of the canal, and consequently of no great importance) deter-
mined a second line from the most advanced point of the reef of Breton Island and of
the island of the Hard Batture, where that pass is narrowest, and we have fonnd the
following figures : 21, 36. 32, 28, 32, 32, 36, 10. It will be seen that ships will have certain
access to the canal with fully sufficient water.

But, with the continual changes made. by the Gulf in that region, is there no fear of
the future creation of olistacles, snoh as those that obstruct the passes of the river t
We will reply to this query first by arguments, then by facts. It is very true that the
tendency of the sea is evidently to fill up all its eastern portion along the river, and to
fill up gradually all the lagoons so as to form them into main-land. If it destroys
accidentally, it creates constantly, and for this very reason certain passes must neceesa-



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816 BEPOBT OF THE CHIEF OF ENGINEERS.

tily remain where the swiftness, and eonseqnently the idepth, will iiioretae insteid oi
diminishing. Sach is the case with the two passes that exist west and east of Breton
Island, that is, on one side between that island and the promontory cauaed by the
canal, and on the other between that same island and the great battnre which Mdns
at Grand Gosier Island and serves without intermption as a basis to the arehipAgo
of the Chandeleur Islands. It is by these two passes alone that commanioation cm
be obtained between the Gnlf and the Mississippi Sonnd within one d^j^rae at longi-
tnde.

So mnch for arguments. As to the facts, the comparison of the sonndiogs made in
1827, and consigned on the fine map of the Gulf of Mexico, by Mr. Edmand Blont,
with the sonndings made by us, prove that the depth of water has increased in the
west pass of Breton Island since that time. These first sonndings give 36 feet only on
one point of the coast ; everywhere else they give 18 and 24 feet.
. Among all the advantages we have pointed ont in this predestined locality, there is one
that we nave mentioned too concisely, and which plays too importaat a part that we
should not dwell npon it now. It is the nature of the sea-bottom and of the eoil of
the island which the canal will have to cross. Reiterated geological sonndings that
have uniformly given us 14 feet of sand-clay enabled us to verify that it is impossible
to find a species of clay more firm, more homogeneous, and more resisting. The anchor
bites freely, and once imbedded in it, runs no risk of dragging. The vessels are, there-
fore, certain of being able to lie at anchor outside of the canal as long as may be de-
sired, under shelter of either Breton Island or Bird Island.

The precious quality of this soil will be again evident when we take up the question
of construction.

These general conditions once determined, their consequences may be drawn natll^
ally. The vessels arrive from the high sea Into a sort of golf, opening due easi,aud
circumscribed to the south by the northern bank of Pass k Loutre, to tne west by the
river and Bird Island, and to the north by Breton and Grand Gosier Islands. Int^pV
oannoi he found a rock, a reef or an islet. Its depths vary in the mean line 90 to 26JeeL Tkt
light-house on Breton Island and that on the pier of the canal will point out the entroMee to
the latter. There will be, therefore, no necessity for pilots ; no port wUl ever htne « euitr
and more direct access.

It is nseless to add that, nntil their entrance in the canal, the ships will have no need
of tows. Once in the canal, the towing will be performed by means of locomotives ran-
ning on a railway built on the top of one of the levees. It is, therefore, only after their
arrival in the river that the ships will, if the wind is not favorable, employ tow-boats to
ascend the river.

Of all the conditions we have set forth as necessary to an artificial opening of the
Mississippi, two yet remain to be fulfille<l, the creating of a depth of 22 to :M feet, and
the assurance that this depth cannot be altered or reduced by either the sea or the
river.

These two conditions do not depend on topographical or hydrographical data, but
on the construction of the canal itself.

Section 3,— Draught and construction.

It may be asserted with confidence that no work more important in its consequences
has ever presented fewer difficulties of execution, and involved less cost, than the canal
of which we have demonstrated the necessity. Consequently, its descriptioo need
not be long nor complicated.

First, the diflerence in declivity between its two extremes isof 4^ feet ; thediflerenco
of level between the waters of the river and those of the sea is only of 3 feet, in ordin-
ary conditions. When the river rises, the sea may be below the level of the river as
much as six feet.

The slope of 4^ feet on the horizontal line is almost entirely level from a distance of
3.000 feet from the river ; it is therefore reclaimed by a single lock, and outside of this
the canal may be considered as being perfectly level. But for the necessity of protect-
ting the talus against the surf of the sea, there would be no necessity for another slaioe
at the other end.

It is an entirely level conn try, with no obstacles to overcome, no trenches to be mao^
no rivers to be crossed, no excaVations to be made. Ir-s alimentation presents no difli-
cnlties ; no fears need be entertained of filtrations or leaks occurring, save those that
might affect the solidity of the work. It is in truth a gigantic dit^h, unsheltered, pex^
fectly rectilinear, and of complete uniformity on a length of six miles. It wiH be a
great undertaking only by its dimensions and its results.

To determine these dimensions we must remember the object of the canal, which »
to open a large road to sea-navigation, to ships and steamers of the greatest nie ; to
continue in some way the draught of the deep sea and of the river without senaihleui-
terrnption. ^ .

But few examples of analogous works can be consulted by way of comparison, ana



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REPORT OF THE CHIEF OF ENGINEERS.



817



among them only one has been executed) another is now in course of execution ; the
two others are as yet but projects.



Cacals.


f




il


1


^1
II




a


Caledonian Guial


MxUt.
21
90


Feet
110
300 to 195
134
147
100


FuL
50
208 to 103


Feet.
80
93
81


Feet
84

a


Feet
40
63


Feet
179


Canul o' tho T^ithninii of Snoz .^^^^.r^wrr r


300


Canal of If ioankgn*, (Garella's project)




Canal of ^icara^aai (Napoleon's project)


1




33
3


47
80


910


Canai from Mf«ifi<wippi Kir^r to the Gnlf


30


400







We owe tome explanations on the remarkable differences presented by the dimensions
proposed by us compared with the others in the above table.

The prevailing thought in oar mind has been to leave free scope to the creations of
the fature, and, while remaining within the limits of what is possible and reasonable,
to give a wide margin to the cuready manifest tendency to constructing very large
ships. Therefore, for all the dimensions claimed for their admission, we have gone
beyond the eiven corresponding figures for the other canals ; 24 feet draught at low
water ; 400-ieet locks ; 80 feet of openings to the sluices. We have taken as a basis for
these speculations on the future the dimensions of the largest steamer ever constructed
except the Great Eastern. The Adriatic has a length of ^6 feet and a width of 75 fdet
outside the wheels. She draws 23 feet of water, and measures 4,144 tons.

The Great Republic, the largest sailing* vessel existing, draws 23 feet and has a length
of 302 feet and a breadth of 48 feet.

Some time will elapse before New Orleans can see vessels requiring such outlets arrive
at her wharves ; but, at all events, if such should come, she will be able to admit them.
However, there is a figure for which we have remained far below the larse sea-canals ;
it is that of the width of the canaL It is only 100 feet ; that is ten feet less than the
narrowest of these canals, the Caledonian CanaL

It must be known, first, that the Caledonian Canal, however small its section, gives
access to the largest merchant-ships and to steamships and prox>ellers of a large ton-
nage. Moreover, in its length, which is of fifty-nine miles, comprising thirty-eight
miles in Lakes Lochy, Oich, and Ness, there is much circulation in opposite directions.
It is, then, necessary that two large ships should be able to pass each other. The
same condition exists in all other canals mentioned.

Such is not the case with our Mississippi CanA. Circulation there can only take
place in one direction, according to whether the towing locomotives are going from the
river to the sea or fit)m the sea to the river. By this combination there is a gain of
one sluice, and for a long time to come circulation will not be rapid enough to require
other means. Thus a convoy of ships arrives fh>m sea and enters the neck formed by
the two piers. The locomotive takes hold of it and tows it to the nearest or seaward
sluice, which opens, and the convoy enters the locks. The gates of the seaward sluice
dose ; those of the head sluice open ; the level is formed and the convoy enters the
river. Then the vessels, awaiting at the wharf on the river, avail themselves of this
leveling to enter in their turn into the canal, and they are towed to sea.

The result from this system of working is that the width of 100 feet in our canal is
equivalent to a width of 200 feet in canals where ships meet and cross each other.
Let ns add here, moreover, that toward the center of the canal will be found a basin
600 feet long and 200 feet wide, to be nsed as a wet-dock.

It will be easily understood that this system would have been impossible had the
canal had a greater length. The time necessary for the towage would have occasioned
too much delay to ships awaiting ingress or egress.

According to the tahle already quoted the movements of import and export nearly
halance ; there were, in 1858-^59, 2,062 arrivals and 2,185 departures, and in 1859-'60,
2,052 arrivals and 2,235 departures.

In the month of November, when this movement was most animated^ 267 vessels ar-
rived, to wit, 152 ships, 40 barks, 18 brigs, 29 schooners, and 28 steamships. This gives
an average of 9 per day, and as many departures. By doubling these figures the result
would only be 18 ships in each direction, or a daily circulation of 36 snips, which, by
taking the average of 574 tons per ship, would g^ve 20,664 tons.

The time necessary to cross the two sluices being about fifty minutes, it will take the
locomotive one hour and ten minutes to take the vessels and run the six miles. This
moderate speed has for object not to injure the embankment ; each trip will then oc-
capy two hours.

At the rate of twelve trips per day it is three ships, or little over 1,700 tons per trip.



52 E



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818 REPORT OF THE CHIEF OF ENGINEERS.

Nothing can be more practicable than these calcalations, although they correspoDd to
a ciiculation double of that Trhich takes place at the time of the year when the com-
mercial movement attains its maximnm.

If we follow the plan of the canal in its short a6d simple line from the river to the
sea, we will find at its head, on the Mississippi, a llfi^ht-house placed on the apper em-
bankment ; the object of this light-hoase is to point out to ships coming down the point
where they must stop. There is to be formed from this embankment, mnDine to a
length of half a mile, a wharf, along which the ships and tows they may need wiUUne
themselves. Behind the wharf, and at the head sluice, is placed the house of the keeper
of the canal and the custom-house office ; opposite, on the other side of the lock, is the
building used as the locomotive-depot, and containing a machine-shop and a store-
house for the urgent repairs and supplying of the vessels.

The head sluice, of a width of 80 feet, gives entrance into a lock 400 feet in leDfi;th,
closed by the middle sluioe; the latter gives passage into a channel formed by levees
in embankments. From this point the shape of the canal is uniform as £ar as the daioe
at the sea-head.

This profile presents a section 100 feet wide at the low- water mark, 24 feet deep, and
30 feet wide at the bottom. The slope of the banks or talus is, therefore, on each side,
of 35 feet base for 24 feet height ; that is, about 1^ to 1, corresponding to an angle of
32^. This easy slope is more tb^n sufficient, with the compact nature of the soil, forthe
preservation of the bank.

On the right and left of the water-line a berme 15 feet wide is formed ; it serves to
receive the falling-in that might occur in the upper levee, and also to increase the
strength of this levee and consolidate its base.

On each side of this base rises the levee formed with the earth from the canal. It is
10 feet high^ and consequently meets the upper level of the lateral walls, the brick-
work of which is 34 feet above the bottom of the canal. The width of the levee at its
top is 15 feet, and for its greater solidity it will have sixty feet at its base ; it is a
«lope of 49, corresponding to an angle of 20'^.

On the lower levee (in relation to the river) the railroad for the towage of the ships
is built. Two turning-tables, situated at the two extremities of the line, permit the
•direction of the locomotive to be changed. .

From the middle sluice the canal runs a distance of 13,880 feet in main-land on a
level. It is a prairie, cut in the last mile by a few unimportant lagoons. It crosses
then the large bay on a width of 5,600 feet. It is during this passage that it spreads



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