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And of all means of keeping information from the public I know of none more effective than that. [Laughter.] Gentlemen, there is one of our reports, clothed in the regulation black of a Government document, I have no doubt it looks dry at a hundred feet range, [laughter] and, in fact, it is not a book which you couldn't lay down without finishing. Four years ago I thought I would contribute to the spread of intelligence by a generous distribution of these documents, and I sent a number around to my friends ; several of those people died within a year. [Laughter.]
There is a part of the work which was by law intrusted to the commission, of which little public notice is taken, but of which I wish to speak a moment. It comprises the surveys, observations and examinations necessary to the complete stndy of the physical facts pertaining to the life and flow of the river. For five years that work has been in progress, aud as-part of the results of it I am gratified to exhibit to you the first complete map of the lower Mississippi, made from actual surveys, which you ever saw. Upon this map, eleven feet long as you see it, is presented upon a scale of five miles to the inch, the entire river from Cairo to the Gulf, with the lands adjacent, and subject to overflow. The surveys from which this map has been made have been most painstaking and thorough. And in these reports have been preserved the recorded data of those surveys with such minuteness and care, that at any time in the future, be it a hundred years hence, an engineer can compare the river of that time with the river here outlined with snch exactness as to disclose every rod of its shifting, and every foot of its deepening, or shoaling. And to this I may add, that in these uninviting reports are preserved all measurements, gaugings, and observations of every kind made by the Commission. If that body shall misinterpret the laws of the river, and err in its plans, here are the facts by which its blunders will be shown, and its errors corrected.
But it is in the practical work of improvement, gentlemen, that yon are most directly and deeply interested, and it is to a brief statement of what has been done and is proposed in that work that I invite your attention. The Mississippi river has three great faults; it tears down its own banks; then with the material taken from them, it builds great bars across its own path; then having blocked up its channel with them, it overflows its banks and spreads over the adjacent country. It is a self-willed and headstrong stream, and must be managed as a woman manages her husband,—never offering to contradict him, and letting him think all the while that he is doing as he pleases. [Laughter.]
A reach of bad navigation presents ordinarily an abnormal width, numerous dividing channels and shifting bars. The first step in the improvement of such a reach is to lay out a track for the regulated channel through it—a task requiring the greatest skill and good jndgment, as upon its wise execution the success of all subsequent work may depend'. The next step is to induce the river to flow in the path thus prepared for it, which is accomplished by the closure of all other channels, and the narrowing of the space on the bar where necessary, by deposits of earth secured by means of permeable dikes, as open as a fence, through which the water flows freely, but which check its velocity below them sufficiently to cause it to make deposits of sediment. These structures are called "contraction works." They are in progress at Plum Point and Lake Providence reaches, and in those places have been entirely successful in execution and result. I do not believe that any greater obstacles can be found anywhere in the execution of this kind of work than those which have been met and overcome in Bullerton and Stack Island chutes, and on Baleshed andJElmot bars. In their effects they have answered every expectation of their construction. Three years ago an experienced river pilot said to a member of the Commission,—speaking of the work laid off at Lake Providence,— "You've staked her out right where she ought to run; the thing is to make her go there." Well, "she" is going there now, and with a channel depth at low water double that which she had be/ore. [Applause.] The like is true at Plum Point. The practicability of narrowing the channel by contraction works, and the certainty of increased depth from the scour thereby induced, have been demonstrated by actual success. And it is a success at which I have never ceased to marvel. The deposits which fill these chutes and build banks on these bars are mere specks of earth. A teaspoon would hold thousands of them. As the water bearing them slackens its speed after passing the permeable dikes, they quietly drop to the bottom like microscopic flakes of snow. And yet the space which has been filled with solid earth by this process in the reaches under improvement measures thousands of acres in area, and from a few indies to fifty feet, and upward, in depth, and well on to three hundred million cubic yards in contents. The works by which these deposits have been secured have been costly,—more so than like workH would be now,—and yet I think it safe to say that the cost of the earth filling has been little, if any, above a cent a cubic yard.
If the river would stay in the improved channel thus prepared for it* the work of improvement would be completed. But this it will not do until some means are employed to check the violent caving of banks in
and about the reaches to be improved. Indeed, it will require but a moment's attention to perceive that the caving of the banks is really the prime cause of all the ills that afflict the river. As it cuts into the earth on one side and deepens the curve of its channel in that bend, it necessarily alters the direction by which its current swings into the bend next below, and so that bend, in its turn, is cut and carved in a new outline to fit the new curve of the channel. By the same process these changes are transmitted to the second bead below, and so on, from bend to bend, as the undulations travel down the back of a snake. And, indeed, you have but to look at the map before you, and mark the crescent-shaped lakes—fragments of old river bed—that line its course on either side, to see how literally true it is that the Mississippi has writhed like a serpent in its broad, black nest through all the centuries that have measured its life.
As the river washes away its bank on one side it commonly adds to the opposite shore by deposit; so that one bank advances as the other recedes. Rut where the caving is violent it is impossible for the river to build the convex side up to full bank height as rapidly as it cuts away the concave side: so that the net result of the process is au increase of width. And finally the coarser parts of the earth taken from the caving bank are carried only a short distance, and go to build up flu? bars below, and as the caving is more active their growth more rapid.
So that we have three distinct consequences — instability of channel location, increase of channel width, and an acceleration, at least, of bar formation, each directly traceable to the caving of the banks. But these are the very things that impair the channel. If we could be rid of them our task would be done. It is necessary, therefore, to employ some means to fix and hold the banks—not everywhere, but wherever the location and rapidity of the caving are such as to endanger the other works of improvement about or below them. The devices used for this purpose—mainly brush mattresses, I cannot take time to describe. They constitute a distinct class of work known as "revetment" or "bank protection."
The third kind of work employed is levees. The place which these structures hold in the general work of improvement has been defined repeatedly in the reports of the Commission and elsewhere. In brief it is this: The ordinary flood is the period of the river's greatest energy; confined within the banks of uniform grade that energy is made useful in scouring and deepening the channel; allowed to escape through Varying and uneven depressions, not only is its energy lost, but there is caused an irregularity of flow in the channel which tends to produce increased deposit of sediment.
Tbese are the measures of improvement which have been recommended and inaugurated by the Commission. Opinions differ as to their relative value, but in my humble jndgment each of the three has its own specific usefulness—the levees for general conservation, the contraction works for local concentration, and the revetment to secure the permanence and augment the results of the other two. As means to the grand end, these three are as inseparable as Liberty and the Union. They are the orthodox trinity, the true Godhead of Mississippi river improvement; and no complete salvation is possible by any plan which leaves out any one of the three. [Applause.]
It is the presence of sediment that makes all the trouble in the Mississippi. It is the original sin of the river, the vice of its constitution. The law wtiich govern its suspension, transportation and deposit have been the subject of mnch stndy. Within a limited degree they may be ascertained by ordinary observation, but in their ultimate and exact uatnre and operation they have so far elnded investigation. It is obvious that at some places the water takes up large quantities of sediment which it throws down at others, and that these alternations are accompanied by changes of velocity. In this way it forms the pools and bars which are the most important characteristics of the river.
These pools are narrow, deep and curved. The outer and concave bank is high and perpendicular; the inner and convex bank low and sloping. The bar is a hill of sand lying like a dam across the channel. Its crest may be fifty or a hundred feet above the bottom of the pool, and two or three times the breadth of the pool between banks. As the high water current emerges from the bend above and swings into one of these pools it comes with a momentuni and power beyond description. It hugs the concave bank as though it woukl fly away at a tangent. It seethes and boils like a cauldron. To the sediment which it brings from above it adds that ground from the bottom and sides of the channel and the masses of the undermined banks, all which it stirs and mixes and churns together, until the whole body of it is so dense and thick that you can't see into it an inch. Then, with all its vast load gathered up, every drop carrying its share, it sweeps out of the narrow pool and up the slanting bar with velocity and power undiminished until at the crest of the hill, where the banks broaden away, it finds room and to spare, and pauses, as if for breath. Iu an instant its fingers relax, and the heavy grains of sand which it could grasp and carry only in the fury of its charge through the narrow defile, rain down on the bar.
A very intelligent gentleman once said to me: "You don't say that the water in the bottom of the pool runs up hill to get over the bar?" "Certainly." "Nonsense," said he, "the water in the pool below the level of the bars lies there dead, while the top flows over it; any one can see that." And he manifestly thought he could see it. But if that were so how would you account for the existence of the pool at all? What dug it out? Here was last year a cotton field forty feet above the water where is now a pool forty feet deep at the same stage. Did the earth leave its bed and climb over the bar of its own volition?
The obvious truth is, that the river at its flood goes through its pools with a burst of energy which nothing could withstand. The quantity of sediment which it will sweep out of its path at such a place depends entirely on what is put m. It is a mere question of supply.
It is impossible to say how much sediment the Mississippi River can carrv. Actual measurements have shown as little as one part to 13453 parts of water, and as much as one part to 610, at the same point in the river at different times. And the heavier of these is nothing to some mixtures that I have noticed, and which von may have noticed if vou have seen a hydraulic grader at work. This machine is a huge force pump mounted on a boat, and is used to grade caving banks to a flat slope before putting on the upper revetment. As the foreman of the hose gang turns the nozzle on a mass of earth before him, and cuts it through and through with the piercing stream it yields, crumbles, dissolves, and at last flows down the bank to the river. It is thick as mush; yet it flows. It is just such a mixture as that in the river, except that it contains more sediment and less water to the cubic inch. It wants only the further dilution which it soon receives, to take its place in the grand sweep seaward of the main river, as orthodox, Mississippi water—that is to say, water which is totally depraved by nature. [Laughter.] And 1 give it to you as my opinion, that the engineer who thinks he hears the voice of the Mississippi singing, in the words of the good old hymn,—
"Feed mo till I want no more." and undertakes, accordingly, to stuff it sick with sediment, will And that he has a larger job on hand than "mortal e'er essayed before." [Great laughter.]
I am led to these observations, gentlemen, by the fact that there is a theory of Mississippi river improvement extant, to which they have legitimate reference, as you will see directly. It is obvious that fu a general way the power of water to transport sediment depends on the velocity of its movement. On this manifest truth has been predicated a doctrine to the effect that every stream flowing through an erosible bed has a tendency to take up sediment to the extent of its carrying power, as limited by its velocity; and that having taken up that quan