Page:The New International Encyclopædia 1st ed. v. 13.djvu/685

MISSISSIPPI RIVER. there is a broad extent of bottom land on the east side, known as the Yazoo Bottoms, which are intersected by many bayous, the chief of which is the Yazoo. On the west side is also a wide bottom land, which extends almost continuously to the Gulf of Mexico, widening southward. On the east side the river impinges against the bluffs for some distance south of Natchez, but below the boundary between Mississippi and Louisiana bottom land appears again on this side of the river and rapidly widens toward the Gulf. The entire valley of the lower section of the river is margined by bayous or arms, which leave the main stream to rejoin it farther down, and considerable parts of Louisiana, Mississippi, and Arkansas are intersected by them.

Another characteristic feature of the adjacent bottom lands are the countless crescent-shaped lakes, oxbows, as they are called, which line the river on either side, but are partly or wholly separated from it. These are formed by cut-offs. The river flows in great curves, which constantly tend to increase in diameter. Thus they encroach on one another, and finally at flood-time, when the impact of the current becomes strongest, cut through the narrow neck separating adjacent curves, thus shortening the course, and leaving the loop as a crescent-shaped lake.

Below the mouth of Red River, the Mississippi divides into branches, the Atchafalaya, Plaquemine, and Lafourche bayous being examples of such distributaries. In the lowlands near its mouth below New Orleans it divides still further, entering the Gulf by means of several passages known as passes, the principal of which are the Southwest and South Passes and the Pass à l'Outre. At the mouth of each of these passes, except the South Pass, where jetties have been built to prevent it, is a bar formed by the deposit of silt from the river on meeting the quiet waters of the Gulf. The quantity of sediment brought down by the river is enormous, being below the Missouri .0035 of the volume of water, which latter amounts to 145 cubic miles per annum. The area of the delta of the river is estimated at over 12,000 square miles. It is everywhere threaded with interlacing bayous and navigable channels, placing every cultivable acre of its lands near to steamboat navigation, one-tenth of the land being estimated as taken up by such water surfaces or channels. The timber in the delta region is mostly sycamore, cypress, and oak—the sycamore margining the streams, the cypress occupying the swamps, and the oaks the lands not liable to frequent inundation.

The climate of the Mississippi Valley ranges from semi-arctic to semi-tropical. At the Falls of Saint Anthony, and above, spirit thermometers must be employed to register the extreme low temperature in winter, which often touches 40° F. below zero; and yet the extreme of summer heat is but a few degrees less at Saint Paul than at New Orleans, 97° to 104°. The range between the extremes is about 65° more at the source than at the mouth of the river. The annual mean temperature at New Orleans is 69°; at Cairo, 45°.

. The mean annual precipitation over the entire basin is estimated by Humphreys and Abbot at 20.8 inches. The estimated discharge of the river is 610,000 cubic feet of water per second. The precipitation, however, is subject

to great variations at different seasons—which fact, together with the sudden melting of the stored-up snow in the spring, causes considerable variations in the volume of the various tributaries. Fortunately, all are not at their highest at any one time; for if they were, probably nothing artificial could resist the force of the accumulated waters. The regions from which the floods come are so far apart and differ so widely in climate that, as a rule, one flood passes before another comes. As it is, the volume of the floods that come is sufficient to make a variation of over fifty feet between high and low water marks. The greatest difference recorded at Cairo is 53.2 feet, and at Vicksburg there has been known to be a difference of 55 feet. At flood times the water at Cairo is 320 feet above the mean tidewater at the mouth of the river. At low water it is 274 feet above mean tide. This fall in a channel 1097 miles long fully accounts for the great velocity of the current, which varies from three to six feet a second, according to existing conditions. In high floods the river formerly overflowed nearly all the surface between the mouth of the Ohio and the Saint Francis River in southeastern Missouri and eastern Arkansas, filling the lakes and lagoons of that region, and then flowing by numberless channels to the White River and Arkansas, the Bayou Macon, Washita, Red, and Atchafalaya rivers into the Gulf. Even since the levees have been built (see below), the river sometimes breaks through these; its waters then flow down the slope of its ridge, and collect in the lowlands, forming lakes. These rise gradually, extending up the slope of the ridge, and so flooding the farms and plantations. In the spring of 1897 a flood created many crevasses in the levees and swept over a great tract of territory, causing heavy losses in stock, crops, and other property. On March 14th the water reached the highest point ever recorded at Memphis, Tenn. On April 5th, according to an official statement of the Department of Agriculture, the total area under water was 15,800 square miles, the submerged land being for the most part in Missouri, Mississippi, Tennessee, Arkansas, and Louisiana. Further damage was subsequently caused by breaks in the levee at Biggs and La Fourche Crossing, La., which resulted in the flooding of large tracts of land below Vicksburg, Miss. It was estimated toward the close of April that 20,000 square miles, containing 46,930 farms, according to the census of 1890, were under water. According to some estimates, from 50,000 to 60,000 persons suffered serious losses, from the floods. The Citizens' Relief Committee of Memphis cared for large numbers of the refugees. The destitution was so widespread, however, that President McKinley sent a special message to Congress, which appropriated $200,000 for the immediate relief of the sufferers.

. The first attempt to guard the lower part of the valley against the river floods was made early in the eighteenth century, when the French Governor, De la Tour, ordered embankments for the protection of New Orleans. In the old slave days, when labor was cheap, each planter erected barriers on or near the river front of his own ground. These were called levees, and were simply artificial mud banks, sometimes strengthened with ribs or foundations of timber, sometimes not. So long as they were watched carefully and kept in good repair,