L 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 No. 7. Taken at low water of 1893. ridge pointing upstream. This was known as the "fish-hook." rever As the changes due to this cut-off are quite interesting, they Attention has now been called to some of the most import features of the hydraulics of the river that affect its regulation and the history of the regulation works will now be attempted, ginning with the formation of the Mississippi River Commissi FORMATION OF THE MISSISSIPPI RIVER COMMISSION Prior to the organization of the Mississippi River Commiss the Federal Government did not give to the improvement of i Mississippi River as much attention as the magnitude of the inte 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 Humphreys and Abbot, whose report was published as Profe sional Papers No. 13, Corps of Engineers. This voluminous and 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 of 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 flood 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 levees 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 naviga ion. This report is very interesting, containing as it does a genral description of the hydraulic forces and their action and speial descriptions of particular portions of the river, with maps of hem; thus on page 515 and on sketch No. 7 are described and shown the crossings and a part of Plum Point Reach, the improvenent of which is to be later described in detail. In this report, as in Humphreys' and Abbot's, certain conclusions are, owing to the lack of data, drawn from theory rather than observation, and are consequently somewhat in error. (A supplement to this report will be found in the Report of the Chief of Engineers for 1878, Vol. II, page 845.) In the Report of the Chief of Engineers (1879, Vol. II, page 1007) will be found another report on the subject of the improvement of the Lower Mississippi River, in which the Board recommends a plan for the improvement of the river and selects Plum Point Reach as the point where these improvement works should first be tried. The proposed method of improvement is, in short: "The work to be done here is to narrow the low-water river where it is now wide and nearly straight, to give that channel a regular form without great curvature or sudden changes of curvature and to protect caving banks, where that caving threatens the permanence of the improvement.' No action was taken by Congress on this recommendation, as the Mississippi River Commission was shortly afterwards organized. MISSISSIPPI RIVER COMMISSION By the act of June 28, 1879, the Mississippi River Commission was created. In accordance with the law it consists of seven members, of whom three are officers detailed from the Corps of Engi neers. The duties of the Commission are stated in the act as follows: * * * * 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. 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 ful detailed report of their proceedings and actions, and of such plans, with mates of the cost thereof, for the purposes aforesaid, to be by him trans to Congress; Provided, That the Commission shall report in full upo practicability, feasibility, and probable cost of the various plans known & jetty system, the levee system, and the outlet system, as well as upon s others as they deem necessary. Under this act the Commission was organized and proceeded the consideration of the subjects upon which it was to report, a as must almost always happen in engineering discussions wher large part of the subject-matter is based rather upon theory the upon observation, differences of opinion were developed. Thi differences consisted of a diversity of views, not only as to t) minor points involved, but extending even to the manner in wh some of the fundamental hydraulic principles affected this riv and as to the theory and manner of its improvement. As a result this diversity of views, the first report of the Commission ec tained in some points majority and minority opinions. This va submitted in February, 1880, and was afterwards published in th Report of the Chief of Engineers, 1881, page 2719. This report contains a discussion of the subjects which the Cor mission was ordered to consider, notably the outlet and levee tems, and a preliminary project for future work. In general, th project related to three subjects: Surveys, flood protection, an channel improvement. The protection from flood was to be ob tained mainly by levees, and the improvement of the chann mainly by what we may call regulation works. The subjects of surveys, for reasons previously stated, will not be discussed, but the works which have been constructed in these districts for flood pro tection and channel improvement will be now described. However, as these two classes of work are quite different in character, they will be treated separately and independently. REGULATION WORKS 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 nent, and these can not be given better than by quoting from their original report: 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 therefrom. It has been observed in the Mississippi River, and is indeed true of all siltbearing streams flowing through alluvial deposits, that the more nearly the high river width, or width between the bank approaches to uniformity, the more nearly uniform will be the channel depth, the less will be the variations of 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 secured by contraction will produce increased velocity, and therefore increased erosion of bed at the shoal places, accompanied by a corresponding deposit of 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 be no violent eddies and cross-currents, and no great and sudden fluctuations in the silt transporting power of the current. There will therefore be less erosion from oblique currents and eddies, and no formations of shoals and bars produced 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 it is narrow and deep. It follows, therefore, that after the wide shoal places are suitably narrowed, and the normal sectional area is restored by deepening 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 surface. It would seem, therefore, that the plan of improvement must comprise, as its essential features, the contraction of the waterway 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 |