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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #212325
Title: Seepage Erosion Impacts on Edge-of-Field Gully Erosion

Author
item Wilson, Glenn
item FOX, G.
item CHU-AGOR, M.

Submitted to: International Symposium on Gully Erosion Under Global Change Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/12/2007
Publication Date: 9/17/2007
Citation: Wilson, G.V., Fox, G.A., Chu-Agor, M.L. 2007. Seepage Erosion Impacts on Edge-of-Field Gully Erosion. Proceedings of the IV International Symposium on Gully Erosion. September 17-19, 2007, Pamplona, Spain, J. Casali and R. Gimenez (eds.). Public University of Navarra. pp. 134-135.

Interpretive Summary: Studies have found that the main source of sediment in streams can be from erosion of the stream bank. Flow through the soil contributes directly to bank erosion by the seepage out of the bank carrying soil with it. Seepage also increases water pressures in the soil which result in loss of soil strength. Seepage erosion results in undercutting of the gully face which causes bank failure. This paper will review recent work on seepage erosion involving field measurements, laboratory experiments and mathematical modeling of the seepage erosion process. The stability of the banks was modeled together with the saturated and unsaturated flow through the soil. The stability model computed a factor of safety which was related to the degree of undercutting. These results show that failure of gully banks can be the result of seepage erosion undercutting gully walls. This process was shown to be of equal or greater importance than the impact of seepage on soil strength properties. The question remains as to what role this process plays in ephemeral gully erosion. It is common to observe ephemeral gullies formed on soils that have a loose surface layer over a less permeable soil layer. Such conditions are naturally prone to seepage erosion processes.

Technical Abstract: Studies have found that the dominant source of sediment in streams can be from bank erosion. Subsurface flow contributes directly to bank failure by seepage erosion and soil-pipe erosion and indirectly by the impact of increased soil water pressures on loss of soil shear strength. Seepage erosion involves sediment transport out of a 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 recent work on seepage erosion involving field measurements, laboratory experiments and numerical modeling of the seepage erosion process. Stability modeling integrated with variably-saturated flow modeling indicated that the mean factor of safety was exponentially related to the degree of undercutting. These results show that mass wasting of gully banks can be the result of seepage erosion undercutting gully walls. This process was shown to be of equal or greater importance than the impact of seepage on soil strength properties. The question remains as to what role this process plays in ephemeral gully erosion. It is common to observe ephemeral gullies formed on duplex soils, i.e. an erodible surface layer over a water restrictive layer, which are naturally conducive to seepage erosion processes.