The work must begin far up the river; at least as far as Cairo,
if not beyond; and must be conducted upon a consistent general plan
throughout the course of the river.
It does not need technical or scientific knowledge to comprehend the elements
of the case if one will give a little time and attention to the subject,
and when a Mississippi River commission has been constituted, as the existing
commission is, of thoroughly able men of different walks in life,
may it not be suggested that their verdict in the case should be accepted
as conclusive, so far as any a priori theory of construction or control
can be considered conclusive?
It should be remembered that upon this board are General Gilmore,
General Comstock, and General Suter, of the United States Engineers;
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;