Seepage erosion impacts on edge-of-field gully erosion

Abstract

Concentrated flow is generally considered the controlling mechanism for gully erosion whereas subsurface flow is often overlooked. The two mechanisms of subsurface flow attributed to gully erosion are seepage flow and preferential flow through soil-pipes. Seepage erosion typically occurs in duplex soils in which a perched water table develops above a water-restricting horizon. The effect of seepage is usually considered to be limited to the production of surface runoff and the impact of increasing soil water pressures on reducing soil shear strength. However, recent studies by Wilson et al. (2007), Fox et al (2006, 2007), and Chu-Agar et al. (2007) have demonstrated that seepage erosion can be the controlling process of streambank failure and by analogy may be a significant contributor to gully erosion. Seepage erosion is used to describe the process of sediment transport out of the gully face by liquefaction of soil particles entrained in the seepage. The undercutting of the gully face by seepage erosion results in bank failure which may be a contributing factor to headcut migration and gully widening. This paper will review this recent work on seepage erosion.