Indeterminate Hydraulics of Alluvial Channels

Field and laboratory data indicate that the relations among width, depth, velocity, and slope are indeterminate unless the constraints on the development of the bed forms are known. A knowledge of the rate of sediment transport will satisfy this deficiency most of the time but not always. Only a full knowledge of the response of one variable to changes in other variables will permit an evaluation and description of the relation of all the variables to each other. It is possible to predict general patterns of stream behavior. Actual stream behavior deviates about these general patterns in two ways. One is a statistical deviation expected when dealing in probabilities. The second results from a change in the general or usual relation between discharges of water and sediment and size of transported sediment. Because it is impossible to have an alluvial channel that will remain in equilibrium under a wide range of discharges of water and sediment, problems associated with alluvial channels can and must be resolved only by recognizing and accepting the lesser of a good many evils.