ARS | Publication request: Modeling Headcut Development and Migration in Upland Concentrated Flows

Submitted to: Electronic Publication
Publication Acceptance Date: April 15, 2004
Publication Date: August 26, 2004
Citation: Bennett, S.J., Alonso, C.V. 2004. Modeling Headcut Development And Migration In Upland Concentrated Flows. In: Proceedings 3rd International Symposium On Gully Erosion, April 28-May 1, 2004, Oxford, Mississippi. 2004 Cd-Rom (Pp. 47-58).

Interpretive Summary: The formation and upstream migration of headcuts in rills, row-crop furrows, and ephemeral gullies is an important factor in soil losses and sediment yield from agricultural lands. Improvements in soil erosion predictions are predicated upon better characterizations of these processes. Recent experimental research has added new insights on erosion due to migrating headcuts. It was observed that once steady state is reached, headcut migration rate, scour-hole geometry, and sediment yield remain constant. Within individual experiments, the morphology of the headcut did not vary significantly during its migration once steady-state conditions were achieved; a behavior that is interpreted as the headcut exhibiting self-similarity properties. The present analysis takes advantage of the observed self-similarity properties to develop a mathematical model of headcut erosion and migration. Computed results yield acceptable comparisons with measured values. This work is relevant to ARS, other federal and state agencies, and to the US farming community because it allows us to make improved predictions of how much soil erosion will occur on agricultural lands.

Technical Abstract: On hillslopes and agricultural fields, discrete areas of intense, localized soil erosion commonly take place in the form of migrating headcuts. Here a unique experimental facility was constructed to examine actively migrating headcuts typical of upland concentrated flows. Results from these experiments show that (1) headcut migration can attain a steady-state condition, where the rate of migration, scour hole geometry, and sediment discharge remain constant with time, (2) higher overland flow rates, steeper bed slopes, and larger initial headcut heights produced larger scour holes with higher rates of soil erosion, (3) during migration, the turbulent flow structure within the scour hole remained unchanged, consisting of an overfall nappe transitioning into an impinging jet with two wall jets within the plunge pool, and (4) the morphology of the scour holes near the headcut face displayed morphologic similarity. The systematic behavior of headcut development and migration enabaled the application of modified jet impingement theory used to predict with good success the characteristics of the impinging jet, the depth and maximum scour, the rate of headcut migration, and the rate of sediment erosion.