Imágenes de páginas


Shows cave behind the upper end of the revetment of 1889 at Daniels Point. The recession of the bank above left the upstream end of the revetinent exposed and, the bank being cut away behind this exposed end, has left it on a

This was known as the “fish-hook.”
Taken at low water of 1893.
No. 7.


lower stages deposits and remains for years in eben S. after having been als itions scoured out and he river.

islands are open belon em as the main river file hrough the main river er to cut a proper low

during the food. In chutes be closed by art this is, in the case of Les It connected with the

river bottom as shown a noe-shaped lakes in

ne river cave away and pens that these points i e conditions are such tu a neck, it will get mar

it will be cut in two draulic pressure of 1

cut-off is to shorten i he immediate vicinity ed slope means increasi truction and rapid die

usually be along the o the gradual lengthai he length lost by the ld bed of the river be lly next to the new elu and there is thus fan

zimen due to cut

places considerable
ent them from happel
outside the limits ofte
be made.
ove Memphis 205
river by about 150

As the changes due to this cut-off are quite interesting, the shown on Plate III. It will be seen that the river cut through neck at the time about five-eighths of a mile wide. It then rein, its direction of flow for a few miles and reopened an old che These changes happened at once. A few years later, and as a sult of these changes, the chute of Island 40, some miles de stream, was opened and became the main river, and in it chan: due to caving have been very rapid.

Attention has now been called to some of the most importer features of the hydraulics of the river that affect its regulati and the history of the regulation works will now be attempted, ginning with the formation of the Mississippi River Commis


Prior to the organization of the Mississippi River Commiss:: the Federal Government did not give to the improvement of st Mississippi River as much attention as the magnitude of the int ests involved might have justified. Investigation of various su jects connected with the river were indeed authorized from time ? time, but appropriations were restricted to special localities, su as Memphis, Vicksburg, and the Passes.

Of these investigations the most important would seem to be the of Ilumphreys and Abbot, whose report was published as Profesional Papers No. 13, ('orps of Engineers. This voluminous an valuable report has in it about all the data with reference to the river available at the time and served for many years as the basis oi all projects and plans for the improvement of the river. But, as must necessarily be the case in all original investigations, the authors of this report were compelled, in some matters, to draw their conclusions from insufficient data, and such conclusions were from this cause liable to error. In the Report of the Chief of Engineers (1875, Vol. I, page

536 there is a report of a board to investigate the subject of food protection, and in the Report of the Chief of Engineers for 1879, Vol. II, page 1015, another report of a board upon the effects of levers on the navigability of the river. However, as both these reports relate to the subject of levees, they will be considered later under that head.

In the Report of the Chief of Engineers (1875, Vol. II, page 496) there is a report of a survey of the Lower Mississippi River and an investigation as to its improvement for purposes of navigas cut-off are quite intex


on works will now bwa

37 righths of a mile wide ral description of the hydraulic forces and their action and speill be seen that the meion. This report is very interesting, containing as it does a genew miles and receial descriptions of particular portions of the river, with maps of once. A few years los, hem; thus on page 515 and on sketch No. 7 are described and ute of Island #hown the crossings and a part of Plum Point Reach, the improveme the main river, an nent of which is to be later described in detail. In this report, as

in Humphreys' and Abbot's, certain conclusions are, owing to the illed to some of the lack of data, drawn from theory rather than observation, and are the river that affet, consequently somewhat in error. (A supplement to this report will

be found in the Report of the Chief of Engineers for 1878, Vol. II, the Mississippi Rito page 845.)

In the Report of the Chief of Engineers (1879, Vol. II, page SISSIPPI RIVER COMUM 1007) will be found another report on the subject of the improve

ment of the Lower Mississippi River, in which the Board recomt give to the imporPoint Reach as the point where these improvement works should

mends a plan for the improvement of the river and selects Plum ion as the magnitud first be tried. The proposed method of improvement is, in short: re indeed authorizat it is now wide and nearly straight, to give that channel a regular tricted to special de form without great curvature or sudden changes of curvature and

to protect caving banks, where that caving threatens the perma

nence of the improvement. No action was taken by Congress on report was published = this recommendation, as the Mississippi River Commission was gineers. This rolu shortly afterwards organized.

the Mississippi River

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i indavestigation et e is


important would se


the data with refere

for many years as : vement of the river.

original investigat:

By the act of June 28, 1879, the Mississippi River Commission

was created. In accordance with the law it consists of seven mem1, in some matter

. : bers, of whom three are officers detailed from the Corps of Engi

, and such conclusio


The duties of the Commission are stated in the act as follows:


t's (1875, Vol

. I, pe e the subject of a * Engineers for N

upon the effects er, as both these e considered later

Sec. 3. It shall be the duty of said Commission 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.

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s (1875, Vol

. II. wer Mississippi or purposes of me

Sec. 4. It shall be the duty of said Commission 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; promote and facilitate commerce, trade, and the postal service when so prepared and matured, to submit to the Secretary of War a tu: detailed report of their proceedings and actions, and of such plans, wis mates of the cost thereof, for the purposes aforesaid, to be by him tasto Congress; Provided, That the Commission shall report in full upwa practicability, feasibility, and probable cost of the various plans knowi jetty system, the levee system, and the outlet system, as well as upos others as they deem necessary.

Under this act the Commission was organized and proceedn

' the consideration of the subjects upon which it was to report, a as must almost always happen in engineering discussions who large part of the subject matter is based rather upon theory the upon observation, differences of opinion were developed. TLdifferences consisted of a diversity of views, not only as to : minor points involved, but extending even to the manner in si some of the fundamental hydraulic principles affected this ri and as to the theory and manner of its improvement. As a resul: this diversity of views, the first report of the Commissione tained in some points majority and minority opinions. This w. submitted in February, 1880, and was afterwards published in t Report of the Chief of Engineers, 1881, page 2719.

This report contains a discussion of the subjects which the cu mission was ordered to consider, notably the outlet and levee tu tems, and a preliminary project for future work. In general

, th: project related to three subjects: Surveys, Hood protection, at channel improvement. The protection from flood was to be o:tained mainly by levees, and the improvement of the channmainly by what we may call regulation works. The subjects surveys, for reasons previously stated, will not be discussed, but th works which have been constructed in these districts for food pri tection and channel improvement will be now described. However, as these two classes of work are quite different in character, thes will be treated separately and independently.


General plan.-Though, as stated before, the members of the Commission differed in their views upon many subjects, and though they were not fully agreed as to the relative importance of the various factors in channel improvement, yet they were substantially unanimous as to the methods to be adopted in that improve

litate commerce, trade, and 2

39 tured, to submit to the Beteg nent, and these can not be given better than by quoting from their oceedings and actions, and 4 r- riginal report:

for the purposes aforesaid, to ut the Commission shall reper: id probable cost of the vanta m, and the outlet system, a to

ppen in engineering diers

The bad navigation of the river is produced by the caving and erosion of its banks, and the excessive widths and the bars and shoals resulting directly there. from.

It has been observed in the Mississippi River, and is indeed true of all silt

bearing streams flowing through alluvial deposits, that the more nearly the imission was organized at nearly uniform will be the channel depth, the less will be the variations of

high river width, or width between the bank approaches to uniformity, the more bjects upon which it ma velocity, and the less the rate of caving to be expected in concave bends. This

would seem to be so in the very nature of things, because uniformity of width latter is based rather up! erosion of bed at the shoal places, accompanied by a corresponding deposit of

secured by contraction will produce increased velocity, and therefore increased es of opinion were dei silt at the deep places, and consequently greater uniformity of depth.

Uniform depth joined to uniform width, that is to say, uniformity of

effective cross-section, implies uniform velocity, and this means that there will ner of its improvement. d. from oblique currents and eddies, and no formations of shoals and bars provdraulic principles affet's the silt transporting power of the current. There will therefore be less erosion

be no violent eddies and cross-currents, and no great and sudden fluctuations in rst report of the Comes duced by silt taken up from one part of the channel and dropped in another.

As the friction of the bed retards the flow of the water, any diminution of the friction will promote the discharge of floods. The frictional surface is greater in proportion to volume of discharge where the river is wide and shoal than

where is . , therefore, after the wide - notably the outlet and ening the channel, the friction will be less than it was before. This will result

in a more easy and rapid discharge of the flowing water, and consequently in a lowering of the flood

iversity of views, Dot xtending even to the

y and minority opinions and was afterwards pubik ers, 1881, page 2719.

ion of the subjects white places are suitably narrowed, and the normal sectional area is restored by deep


for future work. Inga

Surveys, Hood proc
. proerimente muise comprise, as its essential features

, the contraction of the water

ection from flood was a

improvement of the -lation works. The sa: , will not be discussed. in these districts for fur I be now described. B e different in characte dently.

way of the river to a comparatively uniform width and the protection of caving banks, and this is presumed to be the plan referred to in the act as the “jetty system.” It is known, from observation of the river below Cairo, not only that shoals and bars, producing insufficient depth and bad navigation, are always accompanied by a low-water width exceeding 3,000 feet, but that wherever the river does not exceed that width there is a good channel. In other words, bad navigation invariably accompanies a wide low-water water-way, and good navigation a narrow one.

The work to be done, therefore, is to scour out and maintain a channel through the shoals and bars existing in those portions of the river where the width is excessive, and to build up new banks and develop new shore-lines, so as to establish as far as practicable the requisite conditions of uniform velocity for all stages of the river.

It is believed that this improvement can be accomplished below Cairo by contracting the low-water channel way to an approximately uniform width of about 3,000 feet, for the purpose of scouring out a channel through the shoals and bars, and by causing, through the action of appropriate works constructed at suitable localities, the deposition of sand and other earthy materials trans


Core, the members many subjects

, and to ative importance of

yet they were suls dopted in that imp

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