Knickpoint Migration due to Baselevel Lowering

The migration of knickpoints in alluvial channels was studied in 15-m and 20-m long flumes, sloping at 0.01 cm/cm. The channels were formed in response to baselevel lowering with two modes of migration: (1)Migration of a constant vertical knickpoint; and (2)migration of an initially vertical knickpoint which flattens and is finally eliminated. Each mode of migration is described by a different equation of motion, which results in a different migration curve. The rate of knickpoint migration hinges upon the channel ability to transport downstream the sediments supplied to it by the receding knickpoint. In this context the mechanism of transport is very important, because wash load is essentially independent of channel attributes. This study shows that in response to baselevel lowering, a knickpoint migrates upstream at a decreasing rate even when water discharge remains constant, and the rate is also affected by the shape of the knickpoints in plan view.