ABSTRACT
One important characteristic of a river is the slope of the land over which it flows. Referred to as the gradient, this slope is determined by calculating the vertical drop in elevation of the channel over some horizontal distance. Gradient is commonly given in meters per kilometer or feet per mile. Also used is meter (drop) per meters in channel length or foot (drop) per feet of channel length. If a river falls 2 feet per mile the slope is 2/5280 or 0.0004 (0.04 percent). The gradient of a river is steepest at higher elevations and levels off as the river approaches its base level. The base level of a river is the lowest elevation to which it may erode. Most often, this elevation is at or close to sea level, although a river may have a temporary base level such as a lake. Rivers, thus, flow downhill to their base level, and a graph showing the downstream changes in a river’s elevation is the longitudinal profile (Figure 6.1b).
