- OF THE -
An Address Delivered at St, Louis, Mo.
January 26, 1884
- ON THE INVITATION OF THE -
JUDGE ROBERT S. TAYLOR, OF INDIANA,
MEMBER OF THE MISSISSIPPI RIVER COMMISSION
R.P. STUDLEY & CO., PRINTERS, 291 NORTH MAIN STREET
IMPROVEMENT OF THE MISSISSIPPI.
I have accepted with pleasure your invitation to speak on the subject of the work, proposed and accomplished. of the Mississippi River Commission. It is to be regretted, but is nevertheless true, as your committee have remarked, that information on this subject is not within easy reach of the general public. The commission itself speaks only through its official reports, which are accessible to but few, and which, from their necessarily formal and technical character, are not very inviting reading when obtained. And the nature and situation of the works in progress are such that they are practically beyond the reach, even of the indefatigable newspaper reporter. The undertaking is one of great importance, great difficulty, and great cost. Its successful completion will be impossible without the intelligent sod cordial support of the people. And I am glad, therefore, of an opportunity like this, to lay before the public in an informal and familiar way some account of the plans adopted and progress made. I may say, too, that it gives me peculiar gratification to do this here, in the central metropolis of the empire valley, whose citizens have distinguished themselves in many noble works, and pre-eminently as early and steadfast friends of Mississippi River Improvement.
The first duty imposed on the Mississippi River Commission by the law creating it was, in the language of the act, "to direct and complete such surveys of said river between the head of the Passes near its mouth to its head waters as may now be in progress, and to make such additional surveys, examinations, and investigations, topographical, hydrographical, and hydrometrical of said river and its tributaries as may be deemed necessary by said commission to carry out the objects of this act."
It is to this part of the work of the commission that I will invite your attention first. It was surprising information to me and I think will be to most persons, that prior to the present undertaking, no complete survey of the Mississippi river had been made. The Coast Survey had carried its work to a distance of about one hundred and sixty-eight miles from the mouth of the river upward. A stretch Of about forty miles in the vicinity of Memphis, and another of about ten miles in the vicinity of Cairo had been surveyed under the direction of Gen. C. B. Comstock, now President of the Commission. These surveys have been adopted by the commission as part of its general system. Portions of the upper river had been surveyed by Col. Farquhar and Maj. Mackenzie, of the Engineer corps, but the work, though excellent in its execution, was not adapted to the plan fixed upon for the whole, and will not be used. So that excepting about two hundred and eighteen miles of the lower river, the survey undertaken and in progress is a new and complete one, reaching from one end of the river to the other.
The work of surveying proper comprises three successive operations conducted by distinct parties, viz. :
2. Precise Leveling;
3. Topography and Hydrography.
The process of triangulation consists in laying out on the river banks a series of triangles, with sides crossing the river at intervals of a mile or two, in a zigzag line, like the panels of a rail fence. Each of these triangles has a side in common with one preceding and another with one following it. The angles being determined by instrumental observation, and one side of one of the triangles measured as a base, the others are ascertained by computation. These observations and measurements are made with the greatest care and skill, the computation is pure mathematics, and the results are practically exact. The system of lines and stations thus established constitutes the frame upon which all following work is built, and is now complete from the gulf to Keokuk, Iowa.
The system of levelling adopted is equally thorough and exam Beginning at the Gulf of Mexico, a continuous line is carried up the river, every portion of which is covered by at least two independent observations. No work in accepted which shows a disagreement, between two observations, exceeding five millimeters into the square root of the distance in kilometers, or about two-fifths of an inch in seven miles and, as a rule, the observations agree much more nearly than that. At intervals of three miles transverse lines are located across the river, and in each of these line are placed four bench marks--two on each side of the river These bench-marks are the permanent monuments of the Whole survey. The triangulation stations, being necessarily near the river bank, are difficult to preserve. The bench-marks may be placed whatever the most secure location can be found. They are connected by exact measurements of distance and bearing with the triangulation stations, and thus become at once monuments of distance and elevation. There being four of them in each transverse line, three of each set might be lost without serious inconvenience Every possible precaution is taken how ever, to insure the permanence of every one of them. Wherever bed-rock, stone abutments, or stone foundations under public buildings can be found, they an used. In such cases a deep hole is drilled in the rock, in which a copper plug is securely fastened. Upon its surface two lines are engraved, the intersection of which is the point Of reference. Such facilities as these for the location of monuments are, however, comparatively rare, and in most cases artificial monuments are used. A brief description of these will not be without interest. The transverse lines before mentioned are extended from one to two miles from the bank on each side, and a bench-mark station is located at each end of the line, and one at an intermediate point on each side of the river. At each of these stations a thick stone slab, some eighteen inches square, is buried about five feet deep, having a cross cut on its upper surface. The intersection of the lines of that cross is the reference point for distances; and the surface of the slab, at the same point, the reference plane for elevations. Directly over this point is set an iron tube, six inches in diameter and six feet long, securely covered by an iron cap. which terminates in a knob, the exact elevation of whose upper surface above the surface of the slab below is known. The visible monument is, therefore, an iron knob surmounting a little mound of earth about a foot high, and for ordinary purposes reference is made to this; but, when greater exactness is required, the cap is removed and reference is made to the stone below. This part of the work is now complete from the gulf to Savannah, Illinois. a point about fifty miles north of Rock Island. From the latter place a line has been run to Chicago, where it connects with a system of levels brought by other government surveys from the Atlantic ocean by way of the Hudson river and the great lakes It in impossible to make an exact comparison of results at this doe, because the mean tide level of the Gulf of Mexico, wpm which the Mississippi levels rest, has not yet been finally fixed by the Coast Survey or other authority. But, taking it as it has been assumed to be in the work done by the commission, the disagreement between the two lines thus meeting in Chicago is less than twelve inches.
The topographical and hydrographical work is last in order, and comprises, under the head of topography, the determination of the outlines of the river's banks, bars, and islands, and the contour of the adjacent lands for a distance of from one to three miles on each side; and, under the head of hydrography, the determination of the width, depth, boundaries, and shape of the water channel,-all which are referred, both in respect to distance and elevation, to the beach-marks already described. This part of the work is now substantially complete from Cairo, to the gulf.
From these surveys are drawn maps upon a scale of about six inches to the mile, upon which are shown all the triangulation stations, beach marks, soundings, water lines, bars, islands, and other physical features of the surface surveyed. This work is done upon sheets 28 inches wide, and from 40 to 48 inches in length, and is substantially similar to that done by the Coast Survey. These maps exist only in the original manuscript. For practical use they are reproduced and printed in two, reduced sizes. The larger of these is upon a scale of about three inches to the mile, and is upon sheets 23 x 36 inches, and is adapted to use of engineers, public libraries, and offices, and other purposes requiring a high degree of minute exactness. Of these maps two sheets, out of a total series of eighty-five, have been published. The smaller reproduction is upon a scale of one inch to the mile, and is intended to meet the wants of pilots, shippers, and the public generally. From these many of the details embraced in the larger maps are necessarily omitted. The number now published is twenty-two, and with ten more the series will be complete from Cairo down. It is also in contemplation to publish a large wall map exhibiting the river from Cairo to the gulf on one sheet.
From this brief account of it, it will be seen that the survey in progress is designed, not only to furnish fall and exact information for present use, but to perpetuate that information through all time. A very Hide care will preserve all the monuments of it intact. But even with the grossest inattention they cannot be wholly lost. The caving of a bank may occasionally expose a bench mark to untimely resurrection, but enough of them will remain until Gabriel blows his trump to enable an engineer to reconstruct the river channel exactly as it lay when the survey was made. If it shall wander away from under the worm fence of triangles which the engineers have built upon it, we shall have the proof and the measure of its shifting. We shall know whether it fills up its bed, or scours it out, and how much.
Besides these operations of surveying and map-making, there are conducted numerous observations comprised under the general term "hydrometrical," which are scarcely less important. At selected stations on the river parties are placed whose duty it is to measure and record daily the depth, width, vertical area, velocity, and discharge of the water the fill, scour, and other changes of the bottom; and the amount and character of sediment carried in suspension. From the data thus obtained sheets are prepared on which those functions of the river which it is desirable to compare with others are represented by lines. Thus, one line represents the stage, and curves this way or that, as the river rose or fell. Another line represents the velocity, and curves in this direction or that, as the velocity of the current increased or diminished. Another line represents the vertical water area or crosssection; another the discharge per second, and so on. These lines being placed side by side on the same sheet, the whole can be seen at once, and there is thus exhibited a chart, or pictorial history of the river at the locality observed, by means of which its various functions can be compared, one with another, with an accuracy otherwise impossible. There is also maintained in connection with the Engineer Office at Washington, a system of guages at intervals of about fifty miles over the river, at each of which a daily record of the stage is kept. Measurements have been made also of the discharge of the Ohio, and of the overflow discharge of the main river during the great floods of 1882 and 1883.
In order to throw light on the history and character of the alluvial basin, an extensive series of deep borings has been made, the results of which have been submitted to the study of distinguished geologists. And in order to determine the elevations and other features of the great sub-basins, transalluvial lines of levels have been carried across the entire valley at several places.
The object of all this miscellaneous work is not the Mom gratification of scientific curiosity, but to provide indispensable material for practical investigation. As will be more fully explained hereafter there is no possibility of improving the Mississippi river except through the wise direction of its own forces. This requires an intimate and accurate knowledge of its history, life. laws. and methods. which can be obtained only by Minute. patient and intelligent observation. Them- has been much discussion of subjects pertaining to the Mississippi river which has been comparatively profitless, for want of authenticated facts. Such observations as I have mentioned, continued svstematically and long enough, will furnish those facts. and put at rest questions which might otherwise be discussed forever. Of the truth of this remark. I can give you at this moment a recent and interesting illustration.
The effect of outlets upon the flood levels and upon the river channel has been the theme of great controversy for a generation past. There is a class of aquatic doctors who regard the Mississippi in every time of flood as sick. whose diagnosis of the case is dropsy, and whose remedy is tapping. Bills have been introduced in Congress, and vigorously pushed, to provide for the making of vast outlets by artificial means. The opponents of such measures have claimed that the effect of such diminution of volume in the river is, to lessen its energy and transporting power, and so cause deposits of sediment, which choke up the channel, increase the flood hights, and thus make the last state of the river worse than its first. These views have been supported by many observed facts, and by what seemed to be unanswerable reasoning. Nevertheless, there has been felt by intelligent students of the question a strong desire for more facts, and for facts based on observations so made as to afford the highest possible guarantees of their accuracy. Some such facts we we now able to give.
During the great flood of 1832, a number of crevasses occurred below Memphis. Less than three months prior to that time, a survey of that part of the river had been completed, so that we know its exact depth, width and cross section at those points as they were bet-ore the flood. After the Good a resurvey was ordered to be made in the locality of four of those crevasses, for the express purpose of ascertaining what change, it' any, they had produced in the river channel. The results were as follows: at Malone's Landing, where the upper and least crevasse of the four occurred, there was a shoaling of the channel below the crevasse amounting to four per cent. of its cross section ; at Riverton there was a shoaling of fourteen per cent. ; at Bolivar, eleven per cent. ; and at Mound Place, twenty four per cent.
At Bonnet Carre. a few miles above New Orleans, a crevasse occurred a number of' years ago, through which a large volume. of water escaped into Lake Pontchartrain. It remained open until the autumn of 1882, when it was closed. We had a survey of the river adjacent to this crevasse, made before its closure, and have just completed another made since. A comparison of the two shows that since the closure of the crevasse the channel space in the river below it has increased about twelve per cent. We have, therefore, in four cases, a filling up of the river. bed following an outflow through a crevasse, and in one. a scouring out of the bed following the closure of a crevasse and the stoppage of its discharge. I am not now arguing the outlet question, and will not take tune to comment on the significance of these facts; but that they weigh man Asia a foolscap quire of conjecture will be readily admitted.
I have dwelt at some length on this pan of the work off the commision, partly because of its own interest and importance, and partly because it has attracted less attention, and is, as I believe less well understood, than those parts of the work involving larger expenditures. It is, in truth, a work of great and enduring value, not only as a necessary preliminary to any intelligent attempt toward improvement of the river, but as an independent undertaking national in its scope, and of such usefulness to science, commerce, and public interests, as to justify all the expense necessary to carry on and complete it. It has been, and is. the purpose of the members of the commission to observe and perpetuate for the information of others, so far. as the means at their disposal will allow. every fact in the life of the Mississippi river that will help to an accurate understanding of those immutable laws to which, beyond doubt, it is as submissive and obedient as is the rivulet that trickles down the roadside to the laws of its existence and flow. They may tali to interpret their own observations aright, and all their plans for the improvement of the river way go awry, like other plans of mice and men; but, if so, the record of their failure will serve to point out the road to success for those who shall follow.
The other and harder duty imposed upon the commission was, in the words of the Act, "to take into consideration and mature such plan or plans and estimates as will correct, permanently locate, and deepen the channel and protect the banks of the Mississippi river; improve and give safety and ease to the navigation thereof; prevent destructive floods; and promote and facilitate commerce, trade, and the postal service." In pursuance of this requirement a plan for the improvement of the river as a highway of navigation has been prepared, reported, approved, and is now in course of execution. The work is done by the Secretary of War through officers of the Engineer corps of the army, who proceed according to the plans, and under the general supervision of the commission, as to the things to be done, and methods to be employed, but whose contracts, disbursements, and accounts are subject to the supervision and approval of the Chief of Engineers. And to some account of those plans. and the work so far done under them. I now invite your attention : and in that connection will speak, first, of the nature of the obstacles to be overcome; then of the methods employed: and finally, of the progress made.
If the Mississippi river could be emptied of its contents. so as to expose its bottom dry and bare, the appearance presented would be surprising to most of us. Instead of a comparatively level channel floor, corresponding in its general features with lands adjacent to the river, there would be found a succession of great sand hills and intervening depressions. Passing through one of these depressions, the observer would find himself, it might be, a hundred and fifty feet below the surface of the banks on either side. Within a few thousand feet he would encounter a sand hill. stretching across the channel, so steep that you could scarcely drive a horse up its declivity, and perhaps a hundred feet high. Having crossed the top of this, he would descend into another basin. then climb another hill, and so on. When the channel is filled with water the crests of these elevations approach the surface, and so constitute the bars so often mentioned in this connection. In low water the greatest depth above them is sometimes as little as five feet and often only six or seven. This is insufficient for profitable navigation upon a scale adequate to the growing demands of commerce To increase that depth is the improvement desired.
There is an elevation of the bottom, and in that sense a bar, below every bend in the river. But most of them are so deeply submerged that they are far below a steamboat keel, even at low water. The number of those that obstruct navigation below Cairo is not far from forty. Nearly all of these are located in groups, each group being comprised in a stretch of river somewhere from twenty to forty miles in length. Such a portion of the river is known in engineering vernacular as a "reach." Of such divisions there are in the lower river six, known as the New Madrid, Plum Point, Memphis, Helena, Choctaw, Lake Providence reaches. A ten-feet low water channel from Cairo down is the least depth that will answer the need of commerce; the actual demand is fifteen; the ultimate hope twenty. To get ten feet we must scalp from three to five feet off the top of each of the forty sand hills which I have described, to get fifteen, from eight to ten. To do this so that it shall stay done is the whole problem of Mississippi river improvement. Is such a thing possible?
The feature which I have mentioned. of alternate pool and bar, is as invariably characteristic of every alluvial stream as its lateral crookedness. There is thus indicated a law which is universal, by which every such stream tends to make for itself a pathway combining both lateral and vertical curves. Every attempt, therefore, to straighten such a channel, in either respect, is, to some extent. a contradiction of the laws that govern the flow of the stream. In regard to such interferences the Father of Waters has a will of his own, which is not to be violently antagonized. And if it were necessary in order to get a ten or fifteen feet channel to bring the river bottom to a straight line, or anything like it, I should regard the task as impossible. But that is not necessary, and herein lies the hopefulness of the undertaking. To take ten feet off the top of a sand pile a hundred feet high, is not in itself a problem to discourage an engineer, and it does not very greatly alter the shape or proportions of the river bed. It still leaves the crest of the bar from eighty to ninety feet above the bottom of the pool, which, one would think, ought to satisfy any reasonable river. In fact that depth of bottom curvature does satisfy the Mississippi river throughout most of its course. It is only where disturbing conditions exist. that a greater curvature is found. Hence it seems probable, that, upon the removal or amelioration of those disturbing conditions, the river may submit quietly to the comparatively slight alteration of its present pathway which is necessary for its improvement.
With respect to the means by which the improvement proposed is to he attempted, it may be said in the first place, that the forces to be employed must be found in the river itself. None can be found elsewhere adequate to the occasion. The power of the river to pile sand on its bars is beyond all power of man to remove it. It would be as impossible to make and maintain a fifteen feet channel through the bars by digging or dredging, as to lower a flood by carting away the water. At the same time, there are forces in the river powerful enough to do the work needed, if they can be put at it. The present channel is the river's own handiwork. Over three-fourths of its course it is good enough. In those places where the channel is bad, the energy of the river is no less than in the places where it is good, but is not well directed. And if the river can be induced to make as economical and effective use of its powers throughout its course as it now makes over the greater part of it, there will be a good channel from Cairo to New Orleans.
It follows that the engineer who would qualify himself for this great work must take the river as his teacher, and sit at its feet, as a patient, observant, receptive, reflecting pupil. in these diligent studies every bend, every bar, every willow on the shore will have for him its lesson and its suggestion. And when he shall have learned the secret of the river's success where it succeeds, and of its failure by introducing, so far as may be done, the conditions of the success.
The plan which has been adopted proposes. first. to deepen the channel over the crests of the bars by reducing its low water width at those places. This is a simple imitation of the river's own engineering. Its narrow reaches are always deep : its shallow bars are always wide. The reason for the difference is obvious. A concentration of the current increases its velocity, momentum, and scouring power, and so results in increased depth. As a rule, the shallow reaches also contain islands and bars which subdivide the channel. To choose from the existing subdivisions the one most suitable in its location and dimensions to serve as the main channel, regulate it to a width of from three thousand to thirty-five hundred feet, and close all others, is the substance of the project at such a place.
For the closure of chutes and subsidiary channels, and the building of new banks where needed in order to contract the channel. the sediment carried in the water is the sole reliance. The conditions of sedimentary deposit are, first, that water loaded with sediment shall flow upon and cover the area to be filled; that it should there experience such diminution of velocity as to cause the heavier particles to fall to the bottom ; and third, that it shall then flow away, and give place to a fresh supply of silt-loaded water. These conditions exist naturally on the wood and vine covered banks of the river, and are produced artificially by driving piles in rows across the chute or channel, or around and across the space to be filled, and interweaving a wattling of poles and brush among the piles, or placing against them mattresses made of poles and brush and thus forming a permeable darn or screen, by which the flow of the water is obstructed and delayed, but not prevented. It is desirable that the obstruction presented by these dikes shall be sufficient to diminish the velocity of the water passing through them to such degree as to cause rapid deposit, and yet admit the passage of the largest amount of water consistent with such diminution. These piles and their wattling or mattresses are not intended to serve any permanent use. When the deposit which they were designed to produce is complete, their functions are ended, like those of the scaffolding about a house, when the house is finished. This should not require more than two or three seasons at the utmost. When the deposit caused by them has been carried somewhat above the ordinary low water line, there shortly springs upon it a spontaneous growth of willows, which take the place of pike and mattresses as checks to the flow of the water, and so carry the deposit higher and higher, until it reaches the normal bank height of the locality.
It is occasionally necessary to narrow the channel selected as the permanent one, by the creation of a new bank alongside it. But such cases are comparatively rare. Where the whole river flows in a single channel, there is rarely any serious bar obstruction. Hence, the work of contraction consists chiefly in closing chutes. The river being by these means deflected from its erratic and wasteful courses and led along one symmetrical channel, speedily scours out and deepens its bed to the extent necessary to convey its concentrated volume. This gives the additional depth which is the improvement sought. If this depth could be obtained and maintained by contraction alone, the works which I have described would be all that was needed. It is impossible, however, to give complete and permanent effect to this part of the work. without protecting the caving banks in the reaches to be improved, and for some distance above them. The Mississippi river. as every one knows. is a succession of bends. In these the current always tends to hug the concave bank . In order to do this it is compelled to cross the channel every time it passes from one bend to another. The points at which these transitions of the current from one side of the river to the other occur. are called "crossings." The current swings round the bend with greater velocity than it passes over the crossings. The caving banks are on the concave sides of the bends. As the swift high water current sweeps past them, it gathers up a load of sand, a large part of which it drops on the next crossing below, where its velocity is first slackened. Hence it is. that the bad bars are usually at the crossings below caving bends. And one object, therefore, of protecting such banks is. to prevent the filling up of the deepened channels below them. But the great object of bank protection is to secure a permanent location of the channel. The caving back of a concave bank not only shifts the line of the current where the caving occurs, but changes its location and direction at the crossing below, and so the point and direction of its impingement on the opposite bank. This introduces changes in the bend below, and then others in the next one, and so on down the river. In this way a change in one bend may produce changes in half a dozen bends below it.
One of the resources of the skillful engineer is to avail himself, in certain cases, of this ricochet or rebounding of the current from one bank to the other, by placing his works some distance above the point where their results are to be developed, somewhat after the fashion of a stroke in billiards. An instance of this may be found at Cape Girardeau, Mo., where Maj. O. H. Ernst, has removed a bar in front of the town by works placed several miles above, and on the opposite side of the river.
Amid the unstable conditions thus produced by caving banks it would he impossible to maintain the improved channel obtained by means of the contraction works which I have described, however successful they might be at the start. Hence it is indispensable to hold the banks whose caving would he likely to result in changes in the improved reaches.
This part of the work is, beyond doubt. the most difficult, and to the casual observer, witnessing the rate at which fields and forests are devoured by the river, may well seem impossible. But the measure of the possibility of such an undertaking is not its aggregate vastness. It is on end to be reached by steps, and the practicability of each step severally is the true test of the possibility of the whole. It will he seen on close observation that the Mississippi river tears town its banks as it builds them up-little by little. A caving bank rises straight up from the water edge, anywhere from ten to forty feet. At its base there is as incessant lapping and chafing by which it is slowly worn away and undermined. As a consequence it breaks down, piece by piece, and falls into the river, and is them dissolved and carried away. All this is without any violence of attack. The swell of a steamboat breaks against the bank with some force, and occasionally the river puts on a few diminutive white caps under a gale; but for the most part the undulations that play along its margin are ripples rather than waves. There is never anything like the shock of an ocean breaker on the shore. The mischief is dose by wavelets, whose action is more like the work of an infinite army of mist, sapping and mining at the foot of the bank, each excavating its teaspoonful per minute. To check this disintegration over a square yard of surface is slight matter. A woolen blanket laid smoothly against the bank would do it at once. Indeed. the device used for this purpose is next thing to a blanket, being a mattress--made however, of brush and poles., many instead of hair or husk.
This fabric, which holds an important place in many modern engineering works, is woven for use in the Mississippi in webs about one hundred and forty to fifty feet wide, and anywhere from one or two hundred to several thousand feet in length, with slim, flexible willows, twenty to thirty feet long, worked in, top, stem, and branches, for woof, and larger poles, iron rods, or steel wire, for warp. It is made on a boat having a length equal to the width of the mattress, and as it is completed it slides down inclined ways into the water. It can be carried continuously to any length, and in practice is made in such lengths as are beat adapted to the bank surface where it is to be used. It is intended that its inner edge shall extend to the foot of the under water slope of the bank, and its outer edge to a point a little below the low water surface. It is sunk and held in place by stone. From the low water margin to the top of the bank tin earth is graded In a Bat slope. In some places this completes the work. The sunken mattress prevents undermining below the low water line, and the grading down of the overhanging bank stops the undermining above that line. In other, and most cases, the space between the upper edge of the mattress and the line of willow growth is protected by a covering of loose stow. Above that line willows are the most perfect protection possible, and one which nature speedily provides. All this-- mattress, grading, and stone covering --is embraced in the general term - "revetment."
The works which I have thus described comprise all that is done in the channel of the river, and are commonly referred to for distinction as the channel works.* They are in the nature of local regulations of the river's flow. In addition to these, there is contemplated in the plan adopted, another regulation, on a larger scale, and more general in its effect, viz. : the concentration of all the ordinary discharge of the river, including its ordinary floods, within its channel. The considerations upon which this principle rests are very simple. The river makes the channel; the greatness of the channel depends upon the greatness of the river; the strength of the river is in its water ; a waste of its volume is a waste of strength; concentration of its volume is a conservation of strength and increase of energy. These observations apply to all ordinary stages of water-high as well as low-but not to extraordinary or phenomenal floods, which occur at long and irregular intervals. It is doubtful whether it would be advantageous to confine the latter clan of floods within the channel, even if no question of cost were involved; it is certain that it would not be wise economy to undertake it for the sake of channel improvement merely. While there is a clear distinction between the ordinary and the extraordinary floods, in their relations to the channel, it is not easy to locate exactly the line which divides them. Upon this subject studies and investigations are in progress, on which, it is hoped, more definite conclusions can be based than any yet reached. For the present, all that can be said is, that the ordinary flood is that which occurs with regularity from year to year, and which reaches an elevation not greatly above the normal bank. Within this limit, the high stage and the low stage are the summer and the winter of the river's year ; and to this extent the control of the high stage as well as the low, is a necessary part of any plan of improvement having for its fundamental principle the complete utilization of the natural forces of the river.
The proper order of conducting this part of the work is from the lower reaches upward, and it is desirable that it shall be so executed, if possible, as to close at once an entire alluvial front. At the inception of the work undertaken by the commission, there were found comparatively complete systems of levees along the fronts of the Yazoo and Tensas basins. They were not in all respects such levees as would have been constructed for the purpose of channel improvement, but it was so much cheaper and more expeditious to repair the gaps in them and use them, than to build new ones, that that course was taken. The Yazoo front is now substantially closed, as is also the greater part of the Tensas. The good effects of the concentration of water thus produced, are already apparent. It sent the flood Of 11883 from Vicksburg to Red river in undivided volume, and with such velocity and power as to scour out the channel with marked effect. The least depth reported between those two points during the past season was ten and a half feet. The closure of the Tensas front will complete all work of this kind in immediate contemplation.' It will be desirable to allow that pad of the river directly affected by the work there done, time to adjust itself to the new demands made upon it, before increasing them. The St. Francis front is all that will remain to be closed.
Time is not at hand there any such system of levees as existed in front of the Yazoo and the Tensas. The work will be to a great extent new, and will have to be constructed either upon such plan as may be adopted with a view to the improvement of the channel alone (which will not suffice for secure. protection against overflow), or else at an expense which the commission do not feel warranted in recommending.
From the six reaches which I have named, the Plum Point reach and the Lake Providence reach were selected as the first in which the work of improvement should be. undertaken . The former is some sixty miles above Memphis, and the latter about the same distance above Vicksburg. This choice was made partly because these two reaches were. all things considered, the worst on the river, and partly because, being nearly four hundred miles apart, and one of them well toward the foot of bad navigation, they were, in some respects, typical localities, and furnished opportunities for thorough tests and comparisons of means to be employed. It was considered that any device or method which should be found successful at both those places. could be safely employed on any part of the river.
As must necessarily be the case in any work of such novelty, difficulty, and magnitude, the first year was spent in getting ready to begin. An extensive plant was required, much of which had to be designed, and all of which had to be contracted and built. Although a large *am was spent for that purpose before the work began, the supply was inadequate, and has been largely increased since. Newly all the channel work is done from boats, and a great part of it with machinery. There are floating pile-drivers that drive piles in water twenty feet deep and into the ground twenty feet, without a stroke of a hammer, by means of a hydraulic jet. There are snag-boats that will jerk a snag out of a bank in less time than a dentist will extract one from a jaw. There are hydraulic graders that grade caving banks to a flat slope with water-jets, at cost of three and a half cents per cubic yard-a work which would cost from twelve to twenty cents if done with shovel and spade. There is a mattress-boat carrying a steam loom, which, being fed wire and brush, turns out a continuous woven mattress I one hundred and thirty feet wide, and of unlimited length. There are floating machine and repair shops; floating boarding-houses, with appliances for feeding and lodging, all told, nearly two thousand men; and stone, brush, and coal barges in great number. The entire plant, as Dow organized, not including snag-boats belonging to the United States, or chartered tow-boats, embraces 189 barges, 62 pile-drivers, 25 mattress bouts- 39 quarterboats, 5 tow-boats, 4 screen-boats, 3 machine-shop boats, 4 graders, it pumping-boat, and 1 steam-tug, making 333 in all, and representing a cost of over a million dollars.
Large as is this outfit, it is none too large, and could be increased in some particulars with advantage. Experience has shown that each integral portion of the work, once undertaken, must be carried by a single assault. To revet part of a caving bank. or half close a chute, and then mop, hazards the safety of all that has been done. It is therefore necessary that there shall be such ample equipment in every department, that prompt advantage can be taken of favorable season, stage, and other conditions to begin, carry forward and finish extensive works with the utmost dispatch.
Plum Point reach is twenty miles long, and in some parts nearly two miles wide. It embraces eleven bars, some of them, heretofore, among the worst on the river. It contains five chutes which are to be closed, varying from six hundred to thirty-four hundred feet in width. Its complete improvement will require the top of six caving books, Of the shortest is half a mile, and the 'longest four miles in length. Permeable dikes have been constructed screw four of the chutes to be closed. No work has been done in the fifth, known as Yankee bar chute, because it is hoped that the influence of the works above it will suffice to close it. The effect produced by these structures exceeded all anticipations. The quantity of earth which bee basis deposited by means of them is enormous. The deepest fill in any one place is thirty-five vertical feet. In Elmot chute there has been an average fill of six and a half fee, distributed over an area of five hundred acres; in upper Osceola chute an average of five and a half feet, distributed over two hundred and forty acres; in lower Osceola three feet, distributed ova seventy acres; and in Bullerton seven feet, distributed over two hundred and fifty acres. While the closure of those chutes is, as yet, only partially complete, it has produced a large concentration of water in the main channel, which has been followed by marked and gratifying results. The bars which formerly obstructed navigation have been cut down from six to ten feet throughout the reach. The last season was one of unusually low water--the lowest within ten years. In other parts of the river five and six feet depths were so uncommon But here there was a twelve feet channel throughout the season. If every part of the river had been as good as the Plum Point reach, the "J.M. White" and the "Natchez" could have raced from New Orleans ro Cairo in dead low water.
This partial victory over Jupiter Fluvius (if I may be allowed to create a deity for the occasion), has not been won without loss. It was a campaign against an adversary whose resources, strategem and methods had to be learned by actual encounter. When the first picket lines of piles were put out to " feel the enemy." it sometimes happened that the enemy felt them and they disappeared. A few strategic points had to be taken and re-taken at heavy cost before they could be finally held. At the head of Elmot chute-the Sevastopol of Plum Point reach nearly a hundred and fifty thousand dollars worth of work was lost before the river consented to give tip its old by-path. This is the heaviest loss that has occurred so far. and is not likely to be repeated elsewhere, although losses, from various inevitable causes. will necessarily ) occur with greater or less frequency. These permeable dikes while very easy to describe, nevertheless present many nice questions in their construction which can be settled only by experiment and experience. Thus, as they are to serve only a temporary purpose, it is desirable to put no more money in them than is absolutely necessary ; and yet they must he made strong enough to stand unmoved while they are in set-vice. Where they are exposed to active bottom scour, it is necessary to protect them with foot mats, which are brush mattresses, made substantially like those used on the banks, only lighter and narrower, and laid on the river bottom, alongside and among the piles. But where these can be omitted safely it is desirable to avoid the expense of them, as they represent a considerable item of cost. If the dikes are made too open the water flows through them so rapidly that it deposits but little sediment below them ; if they are made too close, they dam up the water, and provoke the river to dig them so. If they are made too low, the floods go over them without sufficient diminution of velocity to cause rapid deposit if they are made too high, drift lodges against them, and accumulates in rafts which finally break them down. To hit the golden mean between all these extremes is the desideratum, and it is only by the carpenter's rule of I I cut and try " that this can be done. In the interest of economy it is obvious wisdom to begin with the cheapest forms of construction which it is believed will answer the purpose, and advance from those to stronger and costlier devices if it shall prove necessary. The dikes at Elmot chute that were swept away were the first that were put in. They were, as results have shown, too high and too weak, and lower And stronger forms are now used. Although I have spoken of them as lost, they did not exist in vain. Besides the valuable experience which they afforded, they, resisted attack long enough to cause large deposits in Elmot chute, and so perished like a soldier on the field, who, before he falls, helps to win the victory which he does not live to see.
When the work was begun, it was regarded as somewhat uncertain whether or not the water in the lower reaches of the river would prove as rich as it is in the upper portions say at St. Louis and thereabout-and capable of yielding as large deposits of sediment. And for that reason the effect of the contraction works at the Lake Providence reach, was looked for with a good deal of anxiety. But all apprehensions on that score have been completely removed by the results, which I will state.
The Lake Providence reach is thirty-five miles long, and in some pieces nearly two miles wide. It contains eleven bars and nine chutes, in seven of which permeable dikes have been built. Its improvement, as now projected, comprises the revetment of seven caving banks, varying from one and a half to eight miles in length. and making a total of twenty-two and one-half miles. Some of this bank protection may prove to be unnecessary if the work already done, and some yet to do, shall produce the full effect hoped for. In Skipwith chute a fill of thirty-two vertical feet has occurred, and the total fill in that chute measures ten million, three hundred thousand cubic yards. In Stack Island' chute a fill of forty-seven vertical feet has been secured since last September. In Baleshed chute five miles and a half of passable dike have been built, and the deposit produced measures thirty-three million cubic yards. The aggregate deposits in the Lake Providence chutes cover over three thousand acres. The building up of such areas of solid land from particles as minute as a pin point, carried by flowing water and laid down a speck at a time, is a phenomenon which fairly staggers the imagination. Obviously, the Mississippi river is in no danger of sedimentary bankruptcy.
By means of these works a channel depth of fifteen feet is maintained in Lake Providence reach during the low water of the last season. I saw it stated in one of the river papers not long since that last year, for the first time in her history, the "J. M. White," the largest steamer on the river, made regular trips throughout the season to points above Lake Providence.
I have thus stated, briefly in one sense, but tediously to you, I fear, what is proposed, and what has been done, toward the improvement of of the lower Mississippi. The question that inevitably follows is, "WiII it last?" To this I can only say "1 don't know." No one knows. Time alone will tell. Work of this kind is not new. It has been employed with successful results in other parts of the world, but not upon such a scale, and under such circumstances as to furnish reliable precedents. So far as it has gone, the work has fulfilled every expectation of its success. In most respects there is absolute assurance of its continued success. It is certain that permeable dikes can be constructed that will stand, and that they will produce deposits of sediment sufficient to close a chute It is certain that the concentration of water produced by closing the chutes, and narrowing the channel where it is excessively wide, will scow out the bars to ample depth for navigation The only thing that remains in any sort of doubt is the practicability of permanently holding the bank,; A devising you in advance that my opinion on such a subject is not of any value whatever, I will nevertheless state what I think about it. l believe that the preservation of the banks depends on the maintenance of certain favoring natural conditions in the river, which I will endeavor to describe.
Between Cairo and the gulf there is a fill of three hundred and twenty-two feet. To a river as great as the Mississippi the journey down such a declivity is like the descent of a very fat man down a very steep hill. To go straight down is impossible without going headlong. Now the river lays out its path in curves, and thus diminishes its slope by increasing its length, exactly as an engineer. in laying out a wagon road, or a railway track. down a mountain side, reduces his grades by adopting a circuitous route. By this means the river seeks to reduce its own velocity to a raft which its banks can bear without destruction. It follows that the crooked" of its channel is no accident. or but a piece of Nature's own wise engineering; and that the hope once expressed by a high official, that the first work of the commission would be to take some of the "kinks" out of the river, was wide the mark. The most perfect condition of the river possible is that in which there is the most perfect equilibrium possible between the velocity of its current and the strength of its banks. It is in search of this equilibrium that it increases its length and flattens its slope by enlarging its bends. But the enlargement of the bends tends to narrow the necks of land between them, and so, in course of time, to cut them off. And the result of such a cut-off is to undo all the equalizing work of years before, and introduce chaos and change through a series of years following Take, for example, a bend twenty miles in length as the current flows. and with a fall of three inches per mile. When the neck of land between the extremities of the bend gives way. there is introduced at that point a sudden fall equal to the entire former fall around the bend, which would be, in the case supposed, five feet. The increased velocity produced by such a change is irresistible, and the banks for miles above and below the cut-off melt away like ash-heaps. If there happens to be another narrow neck not far below, it is certain to give way shortly and thus the river runs riot, until its violence works its own cure, by re-creating the bends, and so restoring its normal length and velocity. We have thus produced alternate periods of stability and of change, each lasting through a number of years and each tending to produce the other. During a long period of stability the river makes for itself hundreds of miles of perfect channel, down which it flows through curves of ample sweep, and between sloping banks that show little change from year to year.
The present is a period of comparative stability. No great cut off has occurred since that at Vicksburg in 1876. And you will find in the river to-day many long reaches of model channel. The gist of the present plan in to copy the models which nature thus offers. That this can be done with approximate fidelity is certain, and I we no reason why the improved channel, once secured, may not be permanently preserved, without extravagant cost, as long as the cronditions of general stability continue. But if the river be allowed to break through these, even to the extent of a single cutoff, it will be like a runaway horse-there is no telling where it will stop. I do not mean by this that such a catastrophe would necessarily destrov improvements then completed, or render other improvements impossible; but it would introduce such grave and additional difficulties into the problem that its solution would become a matter of renewed doubt and experiment. And in order to prevent any such lapse into evil ways on the part of the river, there will be required careful watchfulness, and prompt measures of prevention when danger threatens. With these favoring conditions maintained, I believe that the work of bank protection, which is the key of the whole scheme, can be successfully accomplished and permanently held.
I have taxed your patience to such a degree in description of the work in progress on the lower river, that I am compelled to omit any extended reference to those above Cairo. I can only say that a few miles below your own city, on Horsetail bar, are channel works precisely similar to those at Plum Point and Lake Providence, which have been in progress for several years, under the charge of Major 0. H. Ernst, of the Engineers. and which have proven quite as successful as those below.
Above the mouth of the Illinois river are other works designed also to deepen and improve the channel, but entirely different in character from those which I have described, which are being successfully carried on under the able direction of Major Mackenzie, of the Engineers. But of either of these I cannot speak now at length.
I desire to add, before closing, a word of deserved tribute to the accomplished officers of the Engineer Corps who are in charge of the works on the lower river. If those works succeed, it is to them that the country will owe most thanks for it. It is upon their invention, resources, courage, prudence, and executive ability that everything depends. To the difficulties and responsibilities of the work, are added the deadly dangers of fatigue and exposure in a malarial climate. When a man has to take a hundred grains of quinine to hold the breath in his body, he is in hazardous surroundings. An active military campaign is a less perilous undertaking than a summer on the improvement works of the lower Mississippi to an unacclimated white man. Brave men who thus take their lives in hand at the call of duty, deserve not only the thanks of their countrymen, but substantial recognition by Congress and the government.