THE GREAT IMPORTANCE OF IMPROVING THE MISSISSIPPI RIVER.

THE Mississippi River, taken in connection with the Missouri, is the longest known river on the earth, and, with its tributaries, waters the greatest extent of territory. Yet large as is the number of towns and cities at present upon its banks, whose commercial interests are directly connected with its waters, it is not a hundredth part of what it is one day destined to become; and vast as is the amount of produce from the interior which now descends, and of imports that ascends that river, they are really inconsiderable, when compared with the most moderate estimate of the amount that must, at some future day, find a way to their respective markets, along its channel. Being the outlet of an immense valley, and the traveling and commercial thoroughfare of a population, increasing beyond all ordinary calculation, whatever affects the permanency of its channel, or general character as a navigable stream, must excite an interest in the minds of all who reside sufficiently near its waters to have their property affected by its overflows, or a change in its channel. These overflows have been of such a character for the last few years, as to spread consternation among those whose agricultural interests lie exposed to their ravages; while the changes evidently taking place in the lower channel of the river, have begun to excite alarm in those who see their business and real estates likely to be endangered by their continuance. The agricultural and commercial interests, immediately connected with the lower Mississippi, and liable to be affected by its changes, are too vast and important to the general prosperity of the whole country, to permit the necessity for its improvement to be much longer overlooked, or the improvement itself to be much longer deferred. People must be blind, indeed, to their interests, and to the

consequences which already begin to stare them in the face, much longer to stand with folded arms, indifferent to the condition of a river, the yearly damages from which already amount to millions; and the time cannot be far distant, if want of foresight, or reckless indifference to consequences, continue to characterize the action of the legislature of Louisiana, when the river, breaking through its limits, and entirely changing its channel, will so affect present interests in that state as to bring total ruin to many, and leave others no longer possessing any interests capable of being protected by its improvement. Convinced as I am, that, when threatened dangers are overlooked, and all prevention neglected, these consequences become inevitable, I feel anxious that those, whose interests are so deeply involved in the subject, should be fully aroused to a sense of its importance and its danger, and induced to take it up in such a way as to insure the adoption of effective means to save themselves from ruin, and secure the permanent agricultural and commercial prosperity of Louisiana. With this view I now write. I see great danger before the people of that state, which science and experience tell me, if not met by counteracting remedies, is inevitable; and I cannot but feel astounded at the ignorance of some, the blindness of others, and the apathy of all. If I succeed in impressing upon their minds the necessity for action, and that action follows, I shall have accomplished a great good; if I fail, I shall, at least, have performed a duty, the neglect of which I should hold inexcusable.

The causes of the present condition of the river.-The condition of the lower Mississippi, its tendency to overflow, the frequent changes in its channel, and consequent threatened dangers, are the result of many causes, among which the following may be considered the principal:-the sinuosity of the bed, and the want of uniformity in its breadth. Flowing through an alluvial soil, which, no doubt, was originally formed from the materials brought down by the river itself, it is natural that its bed should be subject to continual change, where change is so easily effected, and where so many causes for change are permitted to exist. The slightest irregularity of the banks, or a deepening or shoaling of the bed on one side or the other, will cause the current to change its previous channel, and, in its efforts to continue the obtained motion in the same direction, and with the same velocity, it will abrade whichever bank interferes with that direction. Thus a curve is commenced, which, by degrees, becomes more extended by the continual abrasion of the concave bank, while the opposite convex side increases, at the same time, by deposits of material brought down-its advance keeping pace with the retreat of the other. The curve continues to progress until the river, in its circuitous sweep, returns towards the point where it commenced, leaving only a narrow isthmus at the neck of the bend, between the channel above and the one below, through which the water, during some high flood, at last finds its way, and opens for itself a new and more direct bed. This may be called a natural cut-off, being one of those efforts which the river, under the direction of Nature's laws, makes to regulate a defect in its channel. No person can look over the map of the

Mississippi River, without perceiving that it has frequently exercised this self-regulating power, and, we may say, always to advantage.

Different degrees of density in the soil composing the banks, presenting more or less resistance at different points, will (all other things being equal) have a tendency to produce a similar result; while the same cause existing in the soil of the bed, will cause such irregularity in the breadth and depth of the channel, as to vary materially the velocity of the current in different parts, and thus destroy everything like permanency and uniformity in the channel. The irregularity in the velocity, thus produced by the sinuosity of the bed, and by the want of uniformity in its breadth, also increases its tendency to overflow. For wherever the velocity is diminished, and the free discharge checked, there must be a greater head of water in time of flood, and, consequently, an increased danger of inundation.

Such are the evils consequent upon the present condition of the river: from the point where it enters the lower valley, to its mouth, it may almost be said to consist of a series of curves. The channel being irregular, the velocity is diminished, and its deposits increased; so that, while it apparently retains its usual depth in some parts, in others the bed is evidently rising, and the tendency to overflow, from want of a regular and free discharge of its waters, is increased. There is also a prospect that the present channel may so fill up, as to force the river to open a new passage for itself, and thereby cause the utter ruin of the great commercial interests which have grown up upon its banks.

There are other causes, also, operating upon the Mississippi, which have more or less contributed to its present condition, and continue to exercise an injurious influence upon its channel. Above NewOrleans there are three outlets: the Atchafalaya, Plaquemine, and La Fourche, through which no inconsiderable portion of the water of the main river finds its way in time of flood. These outlets, reaching the gulf by a shorter course, have a greater fall than the main river; and their channels not being so deep, the velocity of their currents is greater at the bottom, consequently they are experiencing a gradual but steadily progressive deepening of their beds and enlargement of their cross sections. On the other hand, the volume of water in the main river being diminished by the discharge through these outlets, loses velocity in proportion, while its deposits are increased. Thus the bed of the main river, below these outlets, must experience a gradual and progressive elevation, and while these outlets are clearing out, deepening and enlarging their channels, the Mississippi is gradually filling up. Indeed, such is the effect produced upon the channel of the main river by means of outlets, that, in the passes, where they are numerous, the depth of the channel decreases regularly from their upper entrance to their mouths. The reason is obvious:-The volume of water which enters the passes from above is diminished, and the breadth of the bed being extended towards the sea, the velocity is likewise diminished; and the current, no longer able to sweep into the gulf the sedimentary matter which it holds in suspension, or which it carries along at the

bottom of the bed, nearly chokes up the mouths of the passes with it. Thus it is that, while there is a depth of over a hundred feet at New-Orleans, there is only twelve at the mouths of the passes; and thus it is, that the free discharge of the water through the mouths of these passes, being impeded, the surface of the river higher up is made to reach a greater elevation in time of a flood than it would if the mouths of the passes were deep enough to admit of a free discharge of water into the gulf. It requires a certain centralized volume of water to keep open the channel of a river, as it acquires a different cross section after the volume of water is diminished; because the river will fashion the size of its bed to the volume of water that remains.

The rapid increase of settlements along the tributaries of the Mississippi, the clearing of the woods, and the cultivation and draining of the lands, by affording a freer and more rapid passage for the waters of the valley into the streams, and carrying along a greater quantity of sedimentary matter, serve to increase still further the tendency to overflow in the main river. For though the quantity of rain that falls throughout the entire valley may not be greater than before, yet much of the impediments in the way of its discharge being removed, and the absorption and evaporation diminished by the increased rapidity of the discharge, the water, after heavy rains, makes its appearance in the main river more speedily, and more simultaneously, and it consequently rises to a greater height. This evil, however it may be provided against by an improved condition of the bed of the river, cannot be prevented. On the contrary, it may be expected to increase in proportion as the settlement and cultivation of the lands throughout the Great West continue to progress.

Incident to the condition of the river may be considered the swamps, lagoons or dead lakes interspersed along the low grounds that lie on both sides of the river, throughout much of its length in the lower valley. These act as reservoirs or feeders to the main river. In time of floods, much of the surplus water flows into them, and, remaining there until the water in the river begins to fall, returns to the main channel. In this way they tend to equalize the volume of water in the river, preventing it from rising as high, in time of flood, as it otherwise would, and also, from falling too rapidly. The effect which they have upon the condition of the river is beneficial, not only because they check, in some degree, the tendency to overflow, and shorten the time of low water; but, also, because they serve as repositories for much of the sedimentary matter brought down by the water which otherwise would remain in the river channel.

The Remedy. Before proceeding to state the remedy for the present evils and threatened dangers, it may be well to lay down a few simple general principles in Hydrodynamics. The velocity of running water depends upon volume, fall and resistance. When these are uniform, the velocity is always the same; but, in proportion as the volume and fall are lessened, and the resistance increased, so is

the velocity diminished, and vice versa. From this arises the fact, that in a straight reach of equal cross sections, where the volume, fall and resistance are uniform, the velocity remains the same; while in a sinuous course of unequal cross sections, where the fall is diminished, the resistance increased, and both constantly varying, though the volume may remain the same, the velocity is not only lessened, but it becomes varied in different parts of the channel. Velocity also varies where uniformity is wanting in the breadth of the bed; being greater where the bed is narrow and deep, than where it is wide and shallow. Water, in a state of motion, is enabled to take up and carry with it the sediment from the bottom of the bed along which it flows; while still water deposits there whatever body heavier than itself may fall into, or be contained in it. The quantity and character of the sediment thus taken up, depends upon the degree of velocity with which the water runs. It requires less to take up alluvial sediment than sand, sand than gravel, and gravel than stones, or boulders. Thus the velocity of the current regulates the depth of its bed. Where it is great, the channel is deep, for the current is able to take up the sediment, or sand, and carry it along; and where it is languid, the channel is shallow, because the current is not only unable to scour out its bed, and keep it deep, but even to carry the sediment brought from those parts of the channel where the velocity is greater, but deposits it along the bed, thus elevating the bottom, and making the river more shallow. From these few simple principles it is plain, that the course of a river should be straight, and its bed of a uniform breadth, or cross sections, whereby a regular velocity may be secured, the discharge of water be performed in the shortest time, and the abrasion of the banks prevented.

In accordance with these principles, the remedy for the evils in the present condition of the Mississippi is as follows:

1st. If a straight course cannot be given to the river, from its too great expense, or other local difficulty, it can be made to approximate as nearly as practicable to such a direction of its channel: that is, to alter the present curves, so that those of small radii may be replaced by others of much larger radii; and the angles of incidence be considerably enlarged. This alteration in the course of the river, by diminishing resistance, and increasing its fall, would have a tendency to lessen abrasion, and by rendering the velocity more uniform, deepen the channel, remove present shoals, prevent their re-formation, and relieve the river in time of flood, by causing a freer discharge of its water.

2d. Establish a uniform cross section between the principal tributaries and outlets, so as to adapt it to the volume both at high and low water mark. This would aid in accomplishing the result sought for above.

3d. Regulate the width, and centralize the current, by giving the channel such a form, that the greatest depth and velocity may be in the middle of the bed, and its least depth and force near its banks and levees. This would prevent abrasion, and secure permanency to the channel.