Ohio River, the principal eastern tributary of the Mississippi river, U.S.A. It is formed by the confluence of the Allegheny and Monongahela rivers at Pittsburg, Pennsylvania, and flows N.W. nearly to the W. border of Pennsylvania, S.S.W. between Ohio and West Virginia, W. by N. between Ohio and Kentucky, and W.S.W. between Indiana and Illinois on the N. and Kentucky on the S. It is the largest of all the tributaries of the Mississippi in respect to the amount of water discharged (an average of about 158,000 cub. ft. per sec.), is first in importance as a highway of commerce, and in length (967 m.) as well as in the area of its drainage basin (approximately 2 10,000 sq. m.) it is exceeded only by the Missouri. The slope of the river at low water ranges from 1 ft. or more per mile in the upper section to about o. 75 ft. per mile in the middle section and 0.29 ft. per mile in the lower section, and the total fall is approximately 50o ft. Nearly twothirds of the - bed is occupied by 187 pools, in which the fall is very gentle; and the greater part of the descent is made over intervening bars, which are usually composed of sand or gravel but occasionally of hard pan or rock. The greatest falls are at Louisville, where the river within a distance of 2.25 m. descends 23.9 ft. over an irregular mass of limestone. The rock floor of the valley is usually 30 to 50 ft. below low water level, and when it comes to the surface, as it occasionally does, it extends at this height only part way across the valley. In the upper part of the river the bed contains much coarse gravel and numerous boulders, but lower down a sand bed prevails. The ordinary width of the upper half of the river is quite uniform, from 1200 to 150o ft., but it widens in the pool above Louisville, contracts immediately below the Falls, and then gradually widens again until it reaches a maximum width of more than a mile about 20 m. from its mouth. Islands are numerous and vary in size from an acre or less to 5000 acres; above Louisville there are fifty or more, and below it about thirty. Many of them are cultivated.
Besides its parent streams, the Allegheny and the Monongahela, the Ohio has numerous large branches. On the N. it receives the waters of the Muskingum, Scioto, Miami and Wabash rivers, and on the S. those of the Kanawha, Big Sandy, Licking, Kentucky, Green, Cumberland and Tennessee rivers.
The drainage basin of the Ohio, in which the annual rainfall averages about 43 in., is, especially in the S. part of the river, of the "quick-spilling" kind, and as the swift mountain streams in that section are filled in February or March by the storms from the Gulf of Mexico, while the northern streams are swollen by melting snow and rain, the Ohio rises very suddenly and not infrequently attains a height of 30 to 50 ft. or more above low water level, spreads out ten to fifteen times its usual width, submerges the bottom lands, and often causes great damage to property in the lower part of the cities along its banks.
Robert Cavelier, Sieur de La Salle, asserted that he discovered the Ohio and descended it until his course was obstructed by a fall (thought to be the Falls at Louisville); this was probably in 1670, but until the middle of the next century, when its strategic importance in the struggle of the French and the English for the possession of the interior of the continent became fully recognized, little was generally known of it. By the treaty of 1763 ending the Seven Years' War the English finally gained undisputed control of the territory along its banks. After Virginia had bought, in 1768, the claims of the Six Nations to the territory south of the Ohio, immigrants, mostly Virginians, began to descend the river in considerable numbers,' but the Shawnee Indians, whose title to the land was more plausible than that of the Six Nations ever was, resisted their encroachments until the Shawnees were defeated in October 1774 at the battle of Point Pleasant. By the treaty of 1783 the entire Ohio country became a part of the United States and by the famous Ordinance of 1787 the north side was opened to settlement. Most of the settlers entered the region by the headwaters of the Ohio and carried much of their market produce, lumber, &c., down the Ohio and Mississippi to New Orleans or beyond. Until the successful navigation of the river by steamboats a considerable portion of the imports was carried overland from Philadelphia or Baltimore to Pittsburg. The first steamboat on the Ohio was the "New Orleans," which was built in 1811 by Nicholas J. Roosevelt and sailed from Pittsburg to New Orleans in the same year, but it remained for Captain Henry M. Shreve (1785-1854) to demonstrate with the "Washington," which he built in 1816, the success of this kind of navigation on the river. From 1820 to the Civil War the steamboat on the system of inland waterways of which the Ohio was a part was a dominant factor in the industrial life of the Middle West. Cincinnati, Louisville and Pittsburg on its banks were extensively engaged in building these vessels. The river was dotted with floating shops - drygoods boats fitted with counters, boats containing a tinner's establishment, a blacksmith's shop, a factory, or a lottery office. Until the Erie Canal was opened in 1825 the Ohio river was the chief commercial highway between the East and the West. It was connected with Lake Erie in 1832 by the Ohio & Erie Canal from Portsmouth to Cleveland, and in 1845 by the Miami & Erie Canal from Cincinnati to Toledo.
In the natural state of the river navigation was usually almost wholly suspended during low water from July to November, and it was dangerous at all times on account of the numerous snags. The Federal government in 1827 undertook to remove the snags and to increase the depth of water on the bars by the construction of contraction works, such as dikes and wing dams, and appropriations for these purposes as well as for dredging were continued until 1844 and resumed in 1866; but as the channel obtained was less than 3 ft. in 1870, locks with movable dams - that is, dams that can be thrown down on the approach of a flood - were then advocated, and five years later Congress made an appropriation for constructing such a dam, the Davis Island Dam immediately below Pittsburg, as an experiment. This was opened in 1885 and was a recognized success; and in 1895 the Ohio Valley Improvement Association was organized in an effort to have the system extended. At first the association asked only for a channel 6 ft. in depth; and between 1896 and 1905 Congress authorized the necessary surveys and made appropriations for thirty-six locks and dams from the Davis Island Dam to the mouth of the Great Miami river. As the association then urged that the channel be made 9 ft. in depth Congress authorized the secretary of war to appoint a board of engineers which should make a thorough examination and report on the comparative merits of a channel 9 ft. in depth, and one 6 ft. in depth. The board reported in 1908 in favour of a 9-ft. channel and stated that fifty-four locks and dams would be necessary for such a channel throughout the course of the river, and Congress adopted this project. At the Falls is the Louisville & Portland Canal, originally built by a private corporation, with the United States as one of the stockholders, and opened in 1830, with a width of 50 ft., a length of 200 ft., and three locks, each with a lift of about 83 ft. In1860-1872the width was increased to 90 ft. and the three old locks were replaced by two new ones. The United States gradually increased its holdings of stock until in 1855 it became owner of all but five shares; it assumed the management of the canal in 1874, abolished tolls in 1880, and thereafter improved it in many respects. Sixty-eight locks and dams have been constructed on the principal tributaries, and the Allegheny, Monongahela, Cumberland, Tennessee, Muskingum, Kanawha, Little Kanawha, Big Sandy, Wabash, and Green now afford a total of about 960 m. of slack-water navigation.
See the Board of Engineers' Report of Examination of Ohio River with a view to obtaining Channel Depths of 6 and 9 ft. respectively (Washington, 1908); A. B. Hulbert, Waterways of Westward Expansion (Cleveland, 1903) and The Ohio River, a Course of Empire (New York, 1906); also R. G. Thwaites, Afloat on the Ohio (New York, 1900).
