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Show CLCJ LC1 . . ..... . - - -.?.N, - - -.rv. r';.. n. -; - - " V " $ v - -! i fcri td Flood Waters Raging Through a Break In a Mississippi Levee. (Prepared by the National Geographic Society. Washlnston. D. C.) NATURE played favorites In apportioning ap-portioning the great rivers of the world. Of the dozen largest, larg-est, six are in Asia and three In Africa, leaving only three for the two continents of the New world. And among the twelve leaders, Europe and Australia are wholly unrepresented. The longest single river is the Nile, measuring some 4,000 miles from head to mouth. The Nile is further distinguished distin-guished in that It has no tributaries for the last 1,500 miles of its course to the sea. During this stretch its waters are considerably reduced in volume by evaporation and Irrigation, so that it grows smaller instead of larger toward Its mouth. Other African rivers among the length-scoring twelve are the Niger and the Congo, both fed by the tropical trop-ical rains of hot regions near the Equator. In a general way they more nearly resemble South America's representative, rep-resentative, the Amazon, than the great streams of the colder northern continents. Of Asia's six longest rivers, four are in Siberia, the Ob, Yenisei and Lena, flowing north Into the Arctic ocean, and the Amur emptying into an arm of the Pacific. The other two are the Yangtze and Hwang, or Yellow, river of China. These twelve river basins represent the greatest variety of climate and civilization. The Amazon and the CVmgo flow through lush equatorial jungles inhabited by birds of brilliant plumage, wild animals and savage tribes, while the mouths of the Ye-ulsel Ye-ulsel and the Lena are above the northern timber line and their valleys support the sparsest population. The Mississippi and the Yangtze flow through established, If divergent, civilizations, civ-ilizations, with rich cities along their hanks like jewels on a string. The Nile is one of the cradles of world history; the Mackenzie is still a frontier stream. Five of the dozen rivers flow to the north. These are the Nile, Mackenzie, Ob, Yenisei, and Lena. The Mississippi Missis-sippi and Niger flow south. The' Amur, Yangtze, Hwang and Amazon run eastward. Only the Congo points townril the west. Difference In Floods. All these streams overflow their banks at intervals but the results are strangely different. In the case of the Mississippi and the Yangtze, floods are national disasters bringing untold suffering suf-fering to millions. The annual overflow over-flow of the Nile with resulting fertilization ferti-lization of the valley by the deposit of silt Is the source of the wealth of Egypt. The Hwang, or Yellow river, from its hnbif of overflowing its banks aid changing Its entire course at Intervals In-tervals is known as the "scourge of China." The Amazon and the Congo lie almost al-most under the Equator, and the other oth-er ten longest rivers are in the northern north-ern hemisphere. Four (low Into the Arctic ocean. A reason is not far to seek. The greatest land masses are in the northern half of the world, and without large land areas long rivers are impossible. The smaller continents conti-nents of Australia and Europe are not represented in the dozen. Similarly, the reason for the longest rivers flowing flow-ing to the north and east is that the longest continental slopes extend in those directions. The Y'angtze and tiie Mississippi are lined with wealthy cities largely because be-cause of their location in the temperate temper-ate zone. The tropic Amazon. Niger, and Congo are too hot; the Mackenzie and the Siberian rivers are too cold for the favorable growth of towns. The Nile valley beyond Cairo is n mere strip of green from f to 30 miles wide between two burning des-I des-I erts. The Hwang Is too variable In I its habits to encourage navigation or river ports. From the earliest times these long rivers have furnished high roads for the exploration of continental Interiors. Interi-ors. Nero sent nn expedition to discover dis-cover the headwaters of the Nile, which failed to reach Its objective. Russian penetration of Siberia fob lowed the great river beds. The Amazon and the Congo are still high-ways high-ways of discovery. Head reaches of the Y'angtze nre veiled In Asiatic obscurity. ob-scurity. The Niger was the river of romance In the great days of Timbuktu. Tim-buktu. The histories of the world's river basins have been the history of the world's empires. A great river Is both a roadway and a source of life. Menace of the Mississippi. Although North Anic-rir-a ran claim only "ru of the wo.id's dozen longest rivers, it possesses in the Mississippi-Missouri Mississippi-Missouri the longest of them all. This magnitude of the Mississippi is becoming more and more of a menace because each flood seems greater than the preceding one. Why this should be true has been a problem to some laymen ; but one of the chief factors Is plain enough: it Is the usually laudable laud-able effort of Americans to develop and build up their country. Aside from the fact that several decades de-cades ago there were fewer people living liv-ing and fewer dollars Invested In the regions subject to overflow in the lower low-er Mississippi valley, the flood stages were actually lower In those days. They were lower, to consider one important im-portant fact, for the very good reason that then less water was fed into the Mississippi's 100,000 tributaries In a given space of time. Forests and woodlands that do not now exist held a large part of the rainfall and fed it slowly Into brooks and creeks and rivers. Irregularities in the lie of the land formed puddles that later evaporated, evap-orated, or sent rills in tortuous paths that slowed up the runoiT. In late years a constantly Increasing population has been busy changing these conditions. Every tree cut, every ev-ery roof built, every street paved, every ev-ery drainage ditch dug, and every culvert cul-vert constructed in the vast area drained by the Mississippi river system sys-tem has done Its hit toward pouring rainfall more quickly into the great river. Not only has man helped to put more water into the Mississippi; Ills works have helped to confine it there. When De Soto and his followers first knew the Mississippi It spread out at each flood season over a wide area. Sometimes in Its lower reaches It was 20, 30, and even 40 miles wide. The fact that the flood waters spilled away at numerous places Into swamps and lowlands kept the flood crest down in the lower river. In 1717 three-foot levees protected New Orleans. Now they rise 25 feet or more above the city. Even as late as 1SS2 the highest Hood stage at New Orleans was 16 feet. In 1922 it was above 22 feet. One reason, at least, for this, Is that more efficient levee maintenance for many hundreds of miles along the river has herded the flood waters past New Orleans as well as other lower river points In the regular reg-ular channel. Levees Protect Vast Areas. More intensive development of the lowlands has made tills levee system necessary. Now some 29,000 square miles are dependent on' the levees for protection. Breaks still occur, and when they do they drain off some of the flood waters and so relieve In some measure the strain on the banks farther far-ther down stream. But It Is not the Innocuous nffalr that It was In the days of De Soto. Now towns and plantations, plan-tations, railways and Industrial plants lie In the lowlands, and any "relief" that a levee break may occasion to down-river points Is nt a cost of many lives and much valuable property. On the whole a considerable quantity quan-tity of water finds Its wny from the lower Mississippi through levee breaks and bayous. The most Important natural nat-ural safety valve Is the Atchafalaya river or bayou whlcli flows away from I he Mississippi at the mouth of the Red river, and finds its way dlreclly to the Gulf of Mexico some GO miles west of New Orleans. In Hood times this out-flowing slream takes from the swollen Mississippi as much as .'.10,000 cubic feet of water each second an amount equal to more than half the average flow of the Mississippi. It Is because of such losses ns this, coupled with the much greater depth of the channel In the lower river, that the flood stage can be between .10 and 00 feet at Memphis and Vh-ksburg, nnd only a little more than 20 at New Or-lea Or-lea ns. The Mississippi river system Is truly a continental feature, draining a million mil-lion and a quarter of the three milllou odd square miles of the United Stutes. Thirty of the 48 states send a greater or less contribution of water to this great stream. The main Mississippi river Is more, than 2. .100 miles long, while the Mississippi-Missouri Is 4.200 miles In length the longest river system In t he world. The great scnle on which the Mississippi Is built becomes evident evi-dent when one considers the time required re-quired for floods to pass down Its course. About thirty days are required re-quired for the surging flood crest to pass from the mouth of the Ohio to New Orleans, and from ten days to two weeks from Greenville, Miss., to N'tw Orleans. |