Submitted to: International Symposium on Gully Erosion Under Global Change Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2003
Publication Date: 6/30/2004
Citation: Prasad, S.N., Romkens, M.J. 2004. Mechanical energy and subsurface hydrologic effects in head-cut processes. International Symposium on Gully Erosion Under Global Change Proceedings. 109-120. Interpretive Summary: One of the major modes of soil erosion on upland areas is that by overland flow. The mechanism involved manifests itself on one extreme by the uniform removal of soil material due to the flow¿s sheer forces, and on the other extreme by mass removal of localized places in the flow path of runoff. In most cases, localized erosion prevails which often manifests itself in head cuts or stepwise changes in the flow path topography. The source of differences in these local erosion rates are due to an array of factors, including local variations and differences in soil mechanical properties, hydrodynamic forces, and subsurface flow regimes. This article presents an analysis of head cut growth in relation to some of these factors, specifically the role of surface sealing in head cut growth, the overland flow component, and subsurface flow regime factors. The analysis arrives at useful mathematical expressions, which can be used in prediction models of head cut growth on upland areas.
Technical Abstract: The present study concerns an investigation of the effect of surface seal mechanical properties on head-cut development. It has often been observed that in many cases, head-cut growth rates are quite small (less than one centimeter per minute) and that they occur in increments in which chips break off at points where cracks have developed in surface seals. The substrate soil under the seal collapses and is removed by the flow. This mode of head-cut development is the result of a strong interaction between the surface and the subsurface processes. The surface process is energetically controlled by the mechanical features of the seal whereas the subsurface process is hydrologically controlled. The analysis yields estimates of the temporal scale of head-cut velocities. It is found that the flexural wave velocity (seismic sound velocity) inversely affects head-cut velocity.