In a recent article upon "The Great Lakes,"[A] we remarked, that,
from the conformation of their shores, natural harbors are of rare
occurrence. Consequently, for the protection and convenience of
commerce, a system of artificial harbors has been adopted by the Federal
Government, and appropriations have been made from time to time by
Congress for this purpose; and officers of the United States Engineer
Corps have been appointed to carry on the work. It is to some extent a
new and peculiar kind of engineering, caused by the peculiar conditions
of the case.
[Footnote A: See _Atlantic Monthly_ for February.]
Most of the lake-towns are built upon rivers which empty into the lakes,
and these rivers are usually obstructed at their mouths by bars of sand
and clay. The formation of these bars is due to several causes. The
principal one is this:--The shores of the lakes being usually composed
of sand, this is carried along by the shore-currents of the lake and
deposited at the river-mouths. Another cause of these obstructions may
be found in the fact, that the currents of the rivers are constantly
bringing down with them an amount of soil, which is deposited at the
point where the current meets the still waters of the lake. A third
cause, as we are told by Col. Graham, in his Report for 1855, is the
following:--
"Although the great depth of Lake Michigan prevents the surface from
freezing, yet the ice accumulates in large bodies in the shallow water
near the shores, and is driven by the wind into the mouths of the
rivers. A barrier being thus formed to the force of the lake-waves, the
sudden check of velocity causes them to deposit a portion of the silt
they hold in suspension upon the upper surface of this stratum of ice.
By repeated accumulations in this way, the weight becomes sufficient to
sink the whole mass to the bottom. There it rests, together with other
strata, which are sunk in the same way, until the channel is obstructed
by the combined masses of ice and silt. In the spring, when the ice
melts, the silt is dropped to the bottom, which, combined with that
constantly deposited by the lakeshore currents, causes a greater
accumulation in winter than at any other season."
These bars at the natural river-mouths have frequently not more than two
or three feet of water; and some of them have entirely closed up the
entrance, although at a short distance inside there may be a depth of
from twelve to fifteen or even twenty feet of water.
The channels of these rivers have also a tendency to be deflected from
their courses, on entering the lake, by the shore-currents, which,
driven before the prevailing winds, bend the channel off at right
angles, and, carrying it parallel with the lake-shore, form a long spit
of sand between the river and the lake.
Thus, in constructing an artificial harbor at one of these river-mouths,
the first object to be aimed at is to prevent the further formation of a
bar; and the second, to deepen and improve the river-channel. The former
is attained by running out piers into the lake from the mouth of the
river; and the latter, by the use of a dredge-boat, to cut through the
obstructions.
These piers are formed of a line of cribs, built of timber, and loaded
with stone to keep them in place, and enable them to resist the action
of the waves. They are usually built about twenty or twenty-five feet
wide, and from thirty to forty feet long. They are strengthened by
cross-ties of timber, uniting together the outward walls of the crib.
Piles are usually driven down into the clay, inside of these cribs, and
they are covered with a deck or flooring of plank. As the action of the
currents is constantly tending to remove the bed on which the cribs
rest, and thus cause them to tilt over, their bottoms are constructed
in a sort of open lattice-work, with openings large enough to allow the
stones with which they are loaded to drop through and supply the place
of the earth which is washed away.
The effect of these piers is to concentrate and deepen the
river-channel, and to retard the formation of bars, though they do not
wholly prevent it. In the spring it is often necessary to employ the
services of a steam-dredge-boat to cut through the bar, before vessels
can pass out.
The portion of these cribs above water is found not to last more than
ten or fifteen years; so that it is now recommended to replace them with
piers of stone masonry, wherever the material is easy of access.
As to the cause of the shore-currents which produce this mischief, Col.
Graham says, in one of his Reports,--
"The great power which operates to produce the littoral or shore
currents of the lake is the prevailing winds; just as the great ocean
current called the Gulf Stream is produced by the trade-winds. The
first-mentioned phenomenon is but a miniature demonstration of the same
principle which is more boldly shown in the other. The wind, acting
in its most prevalent lakeward direction, combined with this littoral
current, produces the great power which is constantly forming sand-bars
and shoals at all the harbor-entrances on our extensive lake-coasts. To
counteract the effect of this great power, upon a given point, is what
we have chiefly to contend for in planning the harbor-piers for all the
lake-ports intended to be improved. The point which an engineer first
aims at, in undertaking to plan any of these harbor-works, is to
ascertain as nearly as possible the direction and force of the
prevailing winds."
The length of the Chicago piers is as follows:--North pier, 3900 feet
long, 24 feet wide; south pier, 1800 feet long, 24 feet wide; and they
are placed 200 feet apart.
Harbors of this kind have been constructed at Chicago, Waukegan,
Kenosha, Racine, Milwaukee, Sheboygan, Manitoowoc, Michigan City, and
St. Joseph, on Lake Michigan; at Clinton River, on Lake St. Clair; at
Monroe, Sandusky, Huron, Vermilion, Black River, Cleveland, Grand River,
Ashtabula, Conneaut, Erie, Dunkirk, and Buffalo, on Lake Erie; at Oak
Orchard, Genesee River, Sodus Bay, Oswego, and Ogdensburg, on Lake
Ontario.
For Lakes Huron and Superior it is believed that no appropriations have
been made, the scanty population of their shores not seeming as yet
to demand it, and those two lakes having in their numerous groups of
islands more natural shelter for vessels than Michigan or Erie.
Besides these river-harbors, Col. Graham recommends to Government the
construction at certain points on the lakes of sheltered roadsteads, or
harbors of refuge, to which vessels may run for shelter in bad weather,
when it may be difficult or dangerous to enter the river-mouths. These
are proposed to be made by building breakwaters of crib-work, loaded
with stone, and extending along the shore in a sufficient depth of water
to admit vessels riding easily at anchor under their lee. Many lives
and much property would undoubtedly be saved every year by such
constructions; for it is a difficult matter for a vessel to enter these
narrow rivers in a heavy gale of wind, and if she misses the entrance,
she is very likely to go ashore.
Another very important work to the navigation of the lakes is the
deepening of the channel in Lake St. Clair.
Between Lakes Huron and Erie lies Lake St. Clair, a shallow sheet of
water, some twenty miles in length, through which all the trade of the
Upper Lakes is obliged to pass. At the mouth of the river which connects
this lake with Huron, there is a delta of mud flats, with numerous
channels, which in their deepest parts have not more than ten feet of
water, and would be utterly impassable, were not the bottom of a soft
and yielding mud, which permits the passage of vessels through it, under
the impulse of steam or a strong wind.
Mr. James L. Barton, a gentleman long connected with the lake-commerce,
thus wrote some years ago upon this subject to the Hon. Robert
McClelland, then chairman of the House Committee on Commerce:--
"These difficulties are vastly increased from the almost impassable
condition of the flats in Lake St. Clair. Here steamboats and vessels
are daily compelled in all weather to lie fast aground, and shift their
cargoes, passengers, and luggage into lighters, exposing life, health,
and property to great hazard, and then by extraordinary heaving and
hauling are enabled to get over. Indeed, so bad has this passage become,
that one of the largest steamboats, after lying two or three days on
these flats, everything taken from her into lighters, was unable, with
the powerful aid of steam and everything else she could bring into
service, to pass over; she was obliged to give her freight and
passengers to a smaller boat, abandon the trip, and return to Buffalo.
Other vessels have been compelled not only to take out all their
cargoes, but even their chains and anchors have been stripped from them,
before they could get over. To meet this difficulty as far as possible,
the commercial men around these lakes have imposed a tax upon their
shipping, to dredge out and deepen the channel through these flats."
Col. Graham, in one of his Reports to the Department, writes as follows
upon the importance of this improvement in a military point of view:--
"Since the opening of the Sault Ste. Marie Canal, the only obstacle to
the co-operation of armed fleets, which in time of war would be placed
upon Lakes Superior, Michigan, and Huron, with that which would be on
Lake Erie, is at St. Clair flats. That obstacle removed, and a depth
of channel of twelve feet obtained there, which might be increased to
sixteen or eighteen feet by dredging, war-steamers of the largest
class which would probably be placed on these lakes would have a free
navigation from Buffalo at the foot of Lake Erie to Fond du Lac of Lake
Superior.
"It would be very important that these fleets should have the power of
concentration, either wholly or in part, at certain important points now
rendered impracticable by these intervening flats. It would no doubt
often be important as a measure of naval tactics alone. It would as
often, again, be equally necessary in coöperating with our land-forces.
It might even become necessary to depend on the navy to transport our
land-forces rapidly from one point to another on different sides of the
flats.
"When a work like this subserves the double purpose of military defence
in times of war, and of promoting the interests of commerce between
several of the States of the Union in time of peace, it would seem to
have an increased claim to the attention of the General Government. If
any work of improvement can be considered national in its character,
the improvement of St. Clair flats, in the manner proposed, may, it is
submitted, justly claim to be placed in that category."
The plan proposed by the United States Engineers for this improvement is
to construct two parallel piers of about four thousand feet long, as a
permanent protection to the channel-way, and to dredge out a channel
between these piers, six hundred feet wide and twelve feet deep. The
cost of this work is estimated at about $533,000. This may seem a large
sum of money; but when it is considered that the value of the commerce
which passed over these flats in the year 1855 was ascertained by
Col. Graham to be over two hundred and fifty millions of dollars, or
considerably more than the whole exports of the Southern States for the
year 1860, more than a million of dollars per day during the period of
navigation, and that the increased charge on freights by reason of this
obstruction is more than two millions of dollars per annum, which of
course has to be paid by the producer, the investment of one quarter of
that annual charge in a work which would do away with the tax might seem
to be a measure of economy.
To show the importance of these lake-harbors, and the vast amount of
commerce which depends upon them, and which has grown up within the last
twenty years, we will give an extract from another of Col. Graham's very
interesting Reports, upon the Chicago harbor.
"The present vast extent and rapidly increasing growth of the commerce
of Chicago render it a matter of absolute necessity, in which not
only Illinois, but also a number of her neighboring States are deeply
interested, that her harbor should be kept in the best and most secure
state of improvement, so as always to afford, during the season of
navigation, a safe and easy entrance and departure for vessels drawing
at least twelve feet water.
"The States which are thus directly interested in the port of Chicago
are New York, Pennsylvania, Ohio, Michigan, Indiana, Illinois,
Wisconsin, and Minnesota. The shores of all these are washed either by
Lake Michigan or the other Great Lakes, with which Chicago has a direct
and very extensive commerce through the St. Clair flats. The other
States and Territories, which do not reach to the Great Lakes, but which
are nevertheless greatly interested in the preservation of Chicago
harbor, are Iowa and Missouri, and Nebraska and Kansas. A very large
portion of the wheat and other grain produced in those last-mentioned
States and Territories will be brought by railroads to the port of
Chicago, to be shipped thence to the Eastern Atlantic markets.
"The average amount of duties received annually at the Chicago
custom-house for three years, 1853, '54, and '55, was $377,797.86. The
imports at Chicago for 1855 were,--
By lake shipment, $100,752,304.41
" Illinois and Michigan Canal, 7,426,262.35
" Railroads, 68,481,497.90