ABSTRACT

Local depressions in a sediment bed, caused by local nonuniformity of the flow, are often found in the vicinity of obstacles lying on or embedded in the sediment. It is concluded that current crescent scour marks can be explained as effects of the stretching and accumulation of the vorticity in the flow approaching an obstacle, the fluid-mechanical aspects of vorticity transport being described in some detail. The observed differences between scour-remnant ridges and scour-deposit ridges may be explained in terms of differences in the flow configuration geometry.

Sediment transport is a functional with respect to some of the hydraulic variables--that is to say, the transport depends not only on the range of values of fluid velocity, for example, but also upon the sequence in which the values in the range are attained. This aspect of transport phenomena is emphasized and it is suggested that experiments should be performed to determine the sensitivity of the functionals to the flow functions.