Local Erosion Caused by Rapid Forced Infiltration

Examination of the stream bed over a water intake buried beneath it revealed a scoured hole with a dune downstream. Laboratory experiments result in the same kind of feature, providing the bed material is too penetrative to ripple. Theoretical treatment based on momentum changes in the suction zone and limited to two dimensions reproduces, with reasonable success, the behavior of beds of medium sand in a narrow laboratory flume. Grains move faster in the suction zone than elsewhere and their increased reluctance to settle is offset by increased stability of the stationary grains. A stable bed feature is arrived at when these two effects are so balanced that the transport rate of bed load is the same in the suction zone as elsewhere.