"The Ohio Basin is second in size of the six great natural divisions of the Mississippi Basin, yet it ranks first in importance in the causation of damaging floods in the larger stream. The topography of the basin in the western and northern portions is generally flat and rolling, but between those portions and the eastern and southern boundaries of the basin almost all conditions of surface contour may be found. It should be remembered that the eastern and southern boundaries, for the most part, lie along the crests of the Alleghenies and related mountain ranges, and that down the ragged western slopes of these mountains flow the streams which form the southern tributaries of such rivers as the Monongahela, the Little Kanawha, The Great Kanawha, the Big Sandy, the Kentucky, the Cumberland, and the Tennessee. On the headwaters of these rivers the slopes are steep, gradually becoming less as the lowlands are reached"--Introduction.