River Channel Changes: Adjustments of Equilibrium

Abstract

A method for predicting river channel's adjustments of equilibrium is presented and illustrated by examples. This method is based upon the quantitative relationships among the variables of water discharge, bed‐material discharge, slope, sediment size, channel width and depth for sand‐bed rivers under dynamic equilibrium. In response to changes of certain variables, the directions and magnitudes of adjustments for the others may be determined using this method. The adjustment in equilibrium may sometimes involve a dramatic transformation in channel character, or channel metamorphosis, because of certain thresholds separating channels of distinct characters. Such thresholds are intrinsic to the relationships of this method. For this reason, it is useful to identify potential dramatic changes of a river channel induced by a plan of river regulation or river control. Applications of this method are illustrated by the instability problem for alluvial canal design, adjustment of ephemeral rivers to flood, downstream changes of the Chippewa River, and the response of the lower Mississippi River to cutoffs. The cause and effect of channel adjustment for each case is elucidated.