1911 Encyclopædia Britannica/Mississippi River

​MISSISSIPPI^[1] RIVER,the central artery of the river systemwhich drains the greater part of the United States of Americalying between the Appalachian Mountains on the east and theRocky Mountains on the west. It rises in the basin of ItascaLake, in northern Minnesota, and flows mostly in a southerlydirection to the Gulf of Mexico. In the region of its headwatersare numerous lakes which were formed by glacial action, butthe river itself was old before the glacial period, as is shown bythe crumbling rocks on the edges of the broad and driftlessvalley through which it flows along the S.E. border of Minnesotaand the S.W. border of Wisconsin, in contrast with the precipitousbluffs of hard rock on the edges of a valley that is narrowand steep-sided farther down where the river was turned fromits ancient course by the glacier. So long as the outlet of theGreat Lakes through the St Lawrence Valley was blocked by theicy mass, they were much larger than now and dischargedthrough the Wabash, Illinois and other rivers into the Mississippi.Below the glaciated region, that is from southern Illinois to theGulf, the river had carved before the close of the glacial perioda flood-plain varying in width from 5 to 80 m., but this has beenfilled to a depth of 100 ft. or more with alluvium, and in the post-glacialperiod an inner valley has been formed within the outerone. The total length of the river proper from the source nearLake Itasca to its mouth in the Gulf of Mexico is 2553 m.;but the true source of the river is at the fountain-head of theMissouri, in the Rocky Mountains, on the S.W. border of Montana,8000 ft. above the sea, and from this source there is a continuousstream to the Gulf which is 4221 m. long—the longestin the world. The Mississippi and its tributaries have morethan 15,000 m. of navigable waterways and drain an area ofapproximately 1,250,000 sq. m. The system extends throughthe heart of the continent and affords a direct line of communicationbetween temperate and tropical regions. Certain physicaland hydrographic features, however, make the regulation andcontrol of the Mississippi below the influx of the Missouri anexceedingly difficult problem.

Engineering Works.—Below Cape Girardeau there are atleast 29,790 sq. m. of rich bottom lands which require protectionfrom floods, and this has been accomplished to a great extent bythe erection of levees. The first levee was begun in 1717, whenthe engineer, Le Blond de La Tour (d. about 1725) erected one amile long to protect the infant city of New Orleans from overflow.Progress at first was slow. In 1770 the settlementsextended only 30 m. above and 20 m. below New Orleans; butin 1828 the levees, although quite insufficient in dimensions,had become continuous nearly to the mouth of the Red river.In 1850 a great impulse was given to systematic embankmentby the United States government, which turned over to theseveral states all unsold swamps and overflowed lands within theirlimits, to provide a fund for reclaiming the districts liable toinundation. The action resulting from this caused alarm inLouisiana. The aid of the government was invoked, andCongress immediately ordered the necessary investigations andsurveys. This work was placed in charge of Captain (laterGeneral) Andrew A. Humphreys (1810–1883), and an elaboratereport covering the results of ten years of investigation waspublished, just after the outbreak of the Civil War in 1861. Inthis report it was demonstrated that the great bottom landsabove the Red river, before the construction of their levees did ​not, as had been supposed, in Louisiana, serve as reservoirs todiminish the maximum wave in great flood seasons. Furthermore,the report argued that no diversion of tributaries waspossible; that no reservoirs artificially constructed could keepback the spring freshets which caused the floods; that the makingof cut-offs, which had sometimes been advocated as a measureof relief, was in the highest degree injurious; that outletswere impracticable from the lack of suitable sites; and, finally,that levees properly constructed and judiciously placed wouldafford protection to the entire alluvial region.

During the Civil War (1861–65) the artificial embankmentswere neglected; but after its close large sums were expendedby the states directly interested in repairing them. The workwas done without concert upon defective plans, and a greatflood early in 1874 inundated the country, causing terriblesuffering and loss. Congress, then in session, passed an actcreating a commission of five engineers to determine and reporton the best system for the permanent reclamation of the entirealluvial region. Their report, rendered in 1875, endorsed theconclusions of that of 1861, and advocated a general leveesystem on each bank. This system comprised: (1) a mainembankment raised to specified heights sufficient to restrain thefloods; and (2) where reasonable security against caving requiredconsiderable areas near the river to be thrown out, exteriorlevees of such a height as to exclude ordinary high waters, butto allow free passage to great floods, which as a rule occur onlyat intervals of five or six years. An engineering organizationwas proposed for constructing and maintaining these levees,and a detailed topographical survey was recommended to determinetheir precise location. Congress promptly approved andordered the survey; but strong opposition on constitutionalgrounds was raised to the construction of the levees by thegovernment.

In the meantime complaints began to be heard respecting thelow-water navigation of the river below the mouth of the Ohio.A board of five army engineers, appointed in 1878 to considera plan of relief, reported that a depth of 10 ft. could probably besecured by narrowing the wide places to about 3500 ft. withhurdle work, brush ropes or brush dykes designed to cause adeposit of sediment, and by protecting caving banks by lightand cheap mattresses. Experiments in these methods weresoon begun and they proved to be effective.

The bars at the efflux of the passes at the mouth of theMississippi were also serious impediments to commerce. Theriver naturally discharges through three principal branches, thesouth-west pass, the south pass and the north-east pass, thelatter through two channels, the more northern of which iscalled Pass à l’Outre. In the natural condition the greatestdepth did not exceed 12 or 13 ft. After appropriations byCongress in 1837, 1852 and 1856, a depth of 18 ft. was finallysecured by dredging and scraping. The report of 1861 discussedthe subject of bar formation at length, and the stirring up of thebottom by scrapers during the flood stages of the river (sixmonths annually) was recommended by it. After the war thisrecommendation was carried into effect for several years, butexperience showed that not much more than 18 ft. could besteadily maintained. This depth soon became insufficient, andin 1873 the subject was discussed by a board of army engineers,the majority approving a ship canal. In 1874 Congress constituteda special board which, after visiting Europe and examiningsimilar works of improvement there, reported in favour of constructingjetties at the south pass, substantially upon the planused by Pieter Caland (b. 1826) at the mouth of the Meuse; andin 1875 Captain James B. Eads (1820–1887) and his associateswere authorized by Congress to open by contract a deep channelthrough the south pass upon the general plan proposed by thisboard. As modified in 1878 and 1879 the contract called forthe maintenance for twenty years of a channel through the passand over the bar not less than 26 ft. in depth throughout, awidth of not less than 200 ft. and with a middle depth of 30 ft.The work was begun on the 2nd of June 1875. The requireddepth was obtained in 1879, and with few interruptions has beenmaintained. In 1902 Congress authorized preparations for theconstruction of a deeper (35 ft.) and a wider channel throughthe south-west pass; the work was begun in 1903 and virtuallycompleted in 1909.

In the year in which Captain Eads opened the south pass of deep-waternavigation Congress created a commission of seven membersto mature plans for correcting and deepening the channel of the river,for protecting its banks and for preventing floods, and since then largeexpenditures for improvement between the head of the passes andthe mouth of the Ohio have been under the control of this commission.In protecting the banks, mattresses of brush or small trees,woven like basket-work, were sunk on the portion of the bank atthe time under water, by throwing rubble stone upon them, an excessof stone being used. A common size of mattress was 800 ft. long,counted along the bank, by 250 ft. wide. Sometimes a width of300 ft. was used, and lengths have reached 2000 ft. The depth ofwater was often from 60 to 100 ft. At first these mats were lightstructures, but the loss of large quantities of bank protection by thecaving of the bank behind them, or by scour at their channel edges,forced the commission steadily to increase the thickness and strengthof the mattress, so that the cost of the linear foot of bank protection,measured along the bank, rose from $8 or $10 to $30 in the laterwork. The contraction works adopted were systems of spurs orpile dykes, running out from the shore nearly to the line of the proposedchannel. Each dyke consisted of from one to four parallelrows of piles, the interval between rows being about 20 ft. and betweenpiles in a row 8 or 10 ft. The piles and rows were stronglybraced and tied together, and in many cases brush was woven intothe upper row, forming a hurdle, in order further to diminish thevelocity of the water below the spur. By 1893 it was evident thatthe cost, which had been estimated at $33,000,000 in 1881, wouldreally be several times that amount, and that the works would requireheavy expense for their maintenance and many years for theirexecution. Navigation interests demanded more speedy relief.The commission then began experimenting with hydraulic dredges,and in 1896 it adopted a project for maintaining a channel from themouth of the Ohio to the passes that should be at least 9 ft. deepand 250 ft. wide throughout the year. Centrifugal pumps are used,the suction pipes being at the bow and the discharge at the sternthrough a line of pipes about 1000 ft. long, supported on pontoons.Water jets or cutters stir up the material to be dredged before itenters the suction pipes. The later dredges have a capacity of about1000 cub. yds. of sand per hour, the velocity in the 32- to 34-in. dischargepipes being from 10 to 15 ft. per second. They cost from$86,000 to $120,000, and their working during a low-water seasoncosts about $20,000. These dredges begin work on a bar wheretrouble is feared before the river reaches its lowest stage, and makea cut through it. A common cut is 2000 ft. long by 250 ft. wide,and 3 or 4 ft. deep. Since 1903 a channel of the proposed depthor more has been maintained.

In 1882 occurred one of the greatest floods known on the Mississippi,and extensive measurements of it were made. A maximumflood of 1,900,000 cub. ft. per second crossed the latitude of Cairo.Much of it escaped into the bottom lands, which are below the levelof the great floods, and flowed through them to rejoin the riverbelow. The flow in the river proper at Lake Providence, 542 m.below Cairo, was thus reduced to about 1,000,000 cub. ft. per second,while if the river had been confined by levees the flow between themwould have been double, or about 2,000,000 cub. ft. per second.The volume of the levees in 1882 was about 33,000,000 cub. yds.,and by the 30th of June 1908 had been increased to 219,621,594cub. yds., of which the United States had built about one-half,and has expended on them $22,562,544. The length of the leveesis about 1486 m., and they are continuous save where interruptedby tributaries or by high lands, from New Madrid, or 80 m. belowCairo, to Fort Jackson, 1039 m. below Cairo. The width of theinterval between levees on the opposite banks of the river variesgreatly; in many places the levees are built much nearer the normalmargin of the river than is consistent with keeping the flood heightsas low as possible. This has arisen from two causes: firstly, to giveprotection to lands already cultivated, which lie usually near thebank of the river; secondly, to avoid the lower ground, which,owing to the peculiar formation, is found as one goes back from theriver. Another bad result of this nearness of the levees to the bankof the river is the loss of levees by caving, which was nearly 5,000,000cub. yds. in 1904–1905, and can only be prevented by bank protection,costing $150,000 per mile, to protect a levee perhaps 16 ft. high costingabout $30,000 per mile. The levees have top widths of 8 ft., sideslopes of one-third, and banquettes when their heights exceed about10 ft. The grades of the levees are usually 3 ft. above the highestwater, and have to be raised from year to year as greater confinementof water gives greater flood heights. When this system is completedthere will probably be hundreds of miles of levee with heightsexceeding 14 ft. In 1899, after about $28,000,000 had been spenton levees by the United States and by the local authorities, thecommission submitted an estimate for additional work on levees,amounting to 124,000,000 cub. yds. and costing $22,000,000. Theeffect of the levees has been to increase flood heights. Though the ​Mississippi River Commission was forbidden by Congress to buildlevees to protect lands from overflow, a majority of its membersbelieved them useful for the purpose of navigation improvement.They have, however, effected no sensible improvement in the navigationof the river at low stages, and at other stages no improvementwas needed for the purposes of navigation. Neither did they preventa destructive flood in 1897 and again in 1903. By the 30th of June1908, $57,510,216.81 had been appropriated for the commission’swork below the mouth of the Ohio.

From the mouth of the Ohio to the mouth of the Missouri, adistance of about 210 m., the river is affected by back water fromthe Ohio which increases the deposit of sediment, and although thebanks increase in height above Cape Girardeau the channel was in its.natural state frequently a mile or more in width, divided by islands,and obstructed by bars on which the low-water depth was only 31/2to 4 ft. The improvement was begun in 1872, and in 1881 a projectwas adopted for narrowing the channel to approximately 2500 ft.In 1896 dredging was begun and in 1905 the further execution of theoriginal project of 1881 was discontinued, because of a new planfor a channel 14 ft. deep from the Great Lakes to the Gulf.

The Upper Mississippi carries only a small amount of sedimentand was navigable in its natural state to St Paul, although at lowwater the larger river boats could ascend no farther than La Crosse,Wisconsin. In 1879 Congress adopted a project for obtaining achannel with a minimum depth at low water of 41/2 ft., chiefly by meansof contraction works. In 1907 Congress authorized further contraction,dredging, the construction of a lateral canal at Rock IslandRapids, and the enlargement of that at Des Moines Rapids with aview to obtaining a channel nowhere less than 6 ft. in depth at lowwater. By means of two locks and dams, which were begun in 1894and were about three-fourths complete in 1908, a navigable channelof the same depth will be extended from St Paul to Minneapolis.The United States government has constructed dams at the outletsof lakes Winnibigashish, Cass, Leech, Pine, Sandy and Pokegama,and thereby created reservoirs having a total storage capacity ofabout 95,000,000,000 cub. ft. This reservoir system, which maybe much enlarged, is also beneficial in that it mitigates floods andregulates the flow for manufacturing purposes and for logging.

Although the United States government has expended more than$70,000,000 on the Mississippi river between the mouth of theMissouri and the head of the passes, the improvement of navigationthereon has not been great enough to make it possible for riverfreighters to force down railway rates by competition. But it isno longer merely a question of competition. The productivity ofthis region has become so enormous that railways alone cannotmeet the requirements of its commerce, and a persistent demand hasarisen for a channel 14 ft. deep from the Great Lakes to the Gulf.The first great impetus to this demand was given in 1900, when acanal 24 ft. in depth, and known as the Chicago Drainage Canal,was opened from the Chicago river to Lockport, Illinois, on the DesPlaines river, 34 m. from Lake Michigan. Two years later Congressappropriated $200,000 for the Mississippi River Commission to makea survey and prepare plans, with estimates of cost, for a navigablewaterway 14 ft. in depth from Lockport to St Louis. The commissionreported favourably in 1905, and in 1907 Congress provided foranother commission, which in June 1909 reported against the 14 ft.channel, estimating that it would cost $128,000,000 for constructionand $6,000,000 annually for maintenance, and considered a 9-ft.channel (8 ft. between Ohio and St Louis) sufficient for commercialpurposes.

The Ohio is commercially the most important tributary, and inflood time most of the commerce on the Lower Mississippi consistsof coal and other heavy freight received from the mouth of this river.Its navigation at low water has also been improved by dredging,rock excavation and contraction works. In its upper reaches achannel 9 ft. in depth had been obtained before 1909 by the constructionof a number of locks with collapsible dams which are throwndown by a flood. It is the plan of the government to extend thissystem to the mouth of the river, and it has been estimated that achannel 12 to 14 ft. in depth may ultimately be obtained by a systemof mountain reservoirs. Furthermore, the government has given toa corporation a franchise for the connexion of the Ohio at Pittsburgwith Lake Erie near Ashtabula, Ohio, by means of a canal 12 ft.in depth. The Missouri is navigable from its mouth to Fort Benton,a distance of 2285 m., and it had become a very important highwayof commerce when the first railway, the Hannibal & St Joseph,reached it in 1859. Its commerce then rapidly disappeared, butregular navigation between Kansas City and St Louis was re-establishedin 1907 and a demand has arisen for a 12-ft. channel from themouth of the river to Sioux City, Iowa. The Red, Arkansas, White,Tennessee, and Cumberland rivers, which are parts of the Mississippisystem, have each a navigable mileage exceeding 600 m.