The origin of this book was a project involving the geomorphic character of the lower Mississippi River and water-rights litigation between the Forest Service and the State of Colorado. The Mississippi River project revealed to me that large alluvial rivers can vary greatly in morphology downstream, although hydrologic conditions are not greatly different. This suggests that river-control works and activities such as dredging will influence a river differently depending upon channel variability and the diverse character of reaches. The water rights litigation confirmed that generalizations about rivers, such as hydraulic-geometry relations have limits depending upon scale.

It must be recognized that rivers differ among themselves, and through time, and one river can vary significantly in a downstream direction. If the morphology and behavior of large alluvial rivers are determined primarily by hydrology and hydraulics, long reaches of alluvial rivers should maintain a characteristic and relatively uniform morphology. In fact, this is not the case, and the variability of large alluvial rivers is an indication that hydraulics and hydrology are not always the dominant controls. Therefore, the purpose of this book is to present to the fluvial community examples of river variability and the reasons for them. The recognition that marked changes from one type of river or river pattern to another can occur is important for geomorphologists, river engineers, and stratigraphers.