Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 2/8/2001
Publication Date: N/A
Interpretive Summary: Headcuts are small, vertical steps that occur on farms and hillsides. Soil erosion due to headcut migration plays a critical role in initiation of drainage systems, rill and gully formation, and landscape evolution. In the agricultural areas of northern Mississippi, soil erosion due to headcut formation can be devastating because of the low cohesive strength of the soil. Such erosion processes lead to significant soil losses that may impact both ecology and water quality, reduce crop production, and cause ephemeral gully formation. Experiments were conducted to examine the effect of headcut height on soil erosion in concentrated flows typical of rills, crop furrows, and ephemeral gullies. It was observed that headcut migration rate, scour hole shape, and sediment yield reached constant values, but the time and length required reaching these steady values decreased as the headcut height increased. The size of the scour hole increased as the initial headcut height increased. The systematic variation in headcut erosion described here is enabling the construction of a database to be used in the formulation of new soil erosion prediction technology that specifically addresses headcut erosion in agricultural areas.
Technical Abstract: 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 pre-formed 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.