Nonequilibriun River Form

In the absence of man-induced changes and climatic changes and in the engineering time scale, the form of many rivers is primarily a result of the flood history of the river. Evidence of the effects of floods on river channel width is found in the scientific literature. The extreme event flood is the erosional agent that widens the river channel; in some cases the entire river valley has been gutted by the extreme event flood. Succeeding floods of lesser magnitude result in channel deposits that narrow the river channel. The problem is to recognize river systems that are changing form or are susceptible to change in form. If the ratio of each individual flood-peak discharge to the average annual peak-flood discharge is small, the river form can be in equilibrium or in regime. If the ratio of some individual peak discharges to the average annual peak discharge is large, the river channel can exhibit nonequilibrium river form, i.e., the form will change with time.