Through the larger part of the river
works of contraction will not be required, but nearly all the banks on
the concave side of the beds must be held against the wear of the
stream, and much of the opposite banks defended at critical points. The
works having in view this conservative object may be generally
designated works of revetment; and these also will be largely of
brushwood, woven in continuous carpets, or twined into wire-netting.
This veneering process has been successfully employed on the Missouri
River; and in some cases they have so covered themselves with sediments,
and have become so overgrown with willows, that they may be regarded as
permanent. In securing these mats rubble-stone is to be used in small
quantities, and in some instances the dressed slope between high and low
river will have to be more or less paved with stone.
Any one who has been on the Rhine will have observed operations not
unlike those to which we have just referred; and, indeed, most of the
rivers of Europe flowing among their own alluvia have required similar
treatment in the interest of navigation and agriculture.
The levee is the crowning work of bank revetment, although not
necessarily in immediate connection. It may be set back a short
distance from the revetted bank; but it is, in effect, the requisite
parapet. The flood river and the low river cannot be brought into
register, and compelled to unite in the excavation of a single permanent
channel, without a complete control of all the stages; and even the
abnormal rise must be provided against, because this would endanger the
levee, and once in force behind the works of revetment would tear them
also away.
Under the general principle that the local slope of a river is the
result and measure of the resistance of its bed, it is evident that a
narrow and deep stream should have less slope, because it has less
frictional surface in proportion to capacity; i.e., less perimeter in
proportion to area of cross section. The ultimate effect of levees and
revetments confining the floods and bringing all the stages of the river
into register is to deepen the channel and let down the slope. The first
effect of the levees is to raise the surface; but this, by inducing
greater velocity of flow, inevitably causes an enlargement of section,
and if this enlargement is prevented from being made at the expense of
the banks, the bottom must give way and the form of the waterway be so
improved as to admit this flow with less rise. The actual experience
with levees upon the Mississippi River, with no attempt to hold the
banks, has been favorable, and no one can doubt, upon the evidence
furnished in the reports of the commission, that if the earliest levees
had been accompanied by revetment of banks, and made complete, we should
have to-day a river navigable at low water, and an adjacent country safe
from inundation.
Of course it would be illogical to conclude that the constrained river
can ever lower its flood slope so as to make levees unnecessary, but it
is believed that, by this lateral constraint, the river as a conduit may
be so improved in form that even those rare floods which result from the
coincident rising of many tributaries will find vent without destroying
levees of ordinary height. That the actual capacity of a channel through
alluvium depends upon its service during floods has been often shown,
but this capacity does not include anomalous, but recurrent, floods.
It is hardly worth while to consider the projects for relieving the
Mississippi River floods by creating new outlets, since these
sensational propositions have commended themselves only to unthinking
minds, and have no support among engineers. Were the river bed cast-
iron, a resort to openings for surplus waters might be a necessity; but
as the bottom is yielding, and the best form of outlet is a single deep
channel, as realizing the least ratio of perimeter to area of cross
section, there could not well be a more unphilosophical method of
treatment than the multiplication of avenues of escape.
In the foregoing statement the attempt has been made to condense in as
limited a space as the importance of the subject would permit, the
general elements of the problem, and the general features of the
proposed method of improvement which has been adopted by the Mississippi
River Commission.
The writer cannot help feeling that it is somewhat presumptuous on his
part to attempt to present the facts relating to an enterprise which
calls for the highest scientific skill; but it is a matter which
interests every citizen of the United States, and is one of the methods
of reconstruction which ought to be approved. It is a war claim which
implies no private gain, and no compensation except for one of the cases
of destruction incident to war, which may well be repaired by the people
of the whole country.
EDWARD ATKINSON.
Boston: April 14, 1882.
APPENDIX C
RECEPTION OF CAPTAIN BASIL HALL'S BOOK IN THE UNITED STATES
HAVING now arrived nearly at the end of our travels, I am induced, ere I
conclude, again to mention what I consider as one of the most remarkable
traits in the national character of the Americans; namely, their
exquisite sensitiveness and soreness respecting everything said or
written concerning them. Of this, perhaps, the most remarkable example I
can give is the effect produced on nearly every class of readers by the
appearance of Captain Basil Hall's 'Travels in North America.' In fact,
it was a sort of moral earthquake, and the vibration it occasioned
through the nerves of the republic, from one corner of the Union to the
other, was by no means over when I left the country in July 1831, a
couple of years after the shock.
