Марк Твен - Life on the Mississippi

Professor Henry Mitchell (the most competent authority on the question of hydrography), of the United States Coast Survey; B. B. Harrod, the State Engineer of Louisiana; Jas. B. Eads, whose success with the jetties at New Orleans is a warrant of his competency, and Judge Taylor, of Indiana.

It would be presumption on the part of any single man, however skilled, to contest the judgment of such a board as this.

The method of improvement proposed by the commission is at once in accord with the results of engineering experience and with observations of nature where meeting our wants. As in nature the growth of trees and their proneness where undermined to fall across the slope and support the bank secures at some points a fair depth of channel and some degree of permanence, so in the project of the engineer the use of timber and brush and the encouragement of forest growth are the main features. It is proposed to reduce the width where excessive by brushwood dykes, at first low, but raised higher and higher as the mud of the river settles under their shelter, and finally slope them back at the angle upon which willows will grow freely. In this work there are many details connected with the forms of these shelter dykes, their arrangements so as to present a series of settling basins, etc., a description of which would only complicate the conception. 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.

I was in Cincinnati when these volumes came out, but it was not till

July 1830, that I procured a copy of them. One bookseller to whom I applied told me that he had had a few copies before he understood the nature of the work, but that, after becoming acquainted with it, nothing should induce him to sell another. Other persons of his profession must, however, have been less scrupulous; for the book was read in city, town, village, and hamlet, steamboat, and stage-coach, and a sort of war-whoop was sent forth perfectly unprecedented in my recollection upon any occasion whatever.

An ardent desire for approbation, and a delicate sensitiveness under censure, have always, I believe, been considered as amiable traits of character; but the condition into which the appearance of Captain Hall's work threw the republic shows plainly that these feelings, if carried to excess, produce a weakness which amounts to imbecility.