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United States Department of Agriculture

Agricultural Research Service

Title: Energy Formulations of Head Cut Dynamics

item Prasad, S. N. - UNIV. OF MISSISSIPPI
item Romkens, Mathias

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 2002
Publication Date: January 1, 2003

Interpretive Summary: Soil erosion on upland areas is a multifaceted phenomenon involving many modes and processes. One of the most important processes of soil removal from these areas is by overland flow. In this process, soil is commonly removed in large quantities at flow-induced topographic sudden elevation changes called head cuts. These head cuts migrate upslope and are a major source of the sediment that is transported downslope. The mechanics of head cut formation and growth is one of the least understood forms of soil erosion, and it is complicated by a host of other factors such as seals/crust, subsurface flow, topography, etc. In this article a fundamental approach is taken to quantify head cut growth using principles of energy conservation for the case where concentrated flow develops on a sealed soil surface. The analysis, based on continuing mechanical concepts, shows that the seal mechanical properties (yield stress, modules of elasticity) in addition to the customary assumed hydrodynamic flow properties of flow depth and velocity play a role in head cut development and growth. This finding represents a significant step forward in understanding the soil erosion mode by head cuts and will be helpful in dynamic soil loss prediction models for upland areas.

Technical Abstract: This study employs the principles of energy conservation to establish the framework for the development of the dynamical equations of head cut as a part of a continuum mechanical analysis of soil erosion induced by surface flow. The dynamics of head cut are controlled by several physically distinct processes, notable among which are surface seal formation, its failure, and the redistribution of flow energy into kinetic and dissipation energies of water and soil. Thus, an erosive energy release rate function is introduced in the global energy equation which is shown to depend on physical parameters governing the dynamics of the process region. The energy release rates are decomposed into line integrals representing motions associated with the translation, rotation, self-similar expansion and the distortion of the head cut cavity. From these considerations, approximate analytical expressions are derived which establish criteria for the initiation and the steady state head cut velocity. The results at this stage of development are preliminary and need testing and validation with data under controlled experimental conditions.

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