Effect of initial step height on headcut development in upland concentrated flows

Experiments were conducted to examine the effect of initial step height on growth, development, and upstream migration of headcuts in concentrated flows typical of rills, crop furrows, and ephemeral gullies. In a laboratory channel, packed soil beds were constructed with preformed headcuts ranging in height from 5 to 50 mm. Each bed was subjected to the same simulated rain, which produced a protective surface seal, followed by an overland flow, which caused soil erosion exclusively at the headcut. After a brief period of bed adjustment, migration rate, scour hole geometry, and sediment yield reached asymptotic values, but the time and length required to reach these asymptotes decreased as the initial step height increased. Steady state headcut dimensions, sediment yield, and the slope of the sediment deposit increased as initial step height increased, but sediment sorting patterns downstream of the migrating headcut remained unchanged.