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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #212322
Title: The Role of Preferential Flow Through Soil-Pipes on Ephemeral Gully Erosion

Author
item Wilson, Glenn
item Alonso, Carlos

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. 2007. The Role of Preferential Flow Through Soil-Pipes on Ephemeral 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. 136-137.

Interpretive Summary: Ephemeral gullies are small channels that can be filled in by tillage and reform again in the same location. The USDA estimates that ephemeral gully erosion ranges from 18 to 73% of the total erosion. Surface runoff is generally considered the cause whereas subsurface flow is often overlooked. Pipe-erosion is the movement of water through large pores in the soil that results in the large pore eroding and enlarging into a soil-pipe. Pipe erosion may occur without being seen at the surface until the pipe collapses to form a fully developed ephemeral gully. Tillage operations fill-in the ephemeral gully thereby leaving the soil-pipe, which was previously at the gully head, buried and cut-off from its previous path. The conditions under which such cut-off soil-pipes reestablish ephemeral gullies following tillage to refill the gully is seriously lacking. The objective of this study was to determine these conditions. Experiments were conducted on a cut-off soil-pipe (2 cm i.d.) that extended 50 cm into the soil bed with 30 cm topsoil depth and a 5% slope. Experiments were also conducted on a soil-pipe (1 cm i.d.) that extended the entire 150 cm length of the soil bed with 10 cm topsoil and 15% slope. Soil-pipes did not produce mature ephemeral gullies by tunnel collapse but did re-establish filled in gullies. When pipe flow occurs with rainfall, surface runoff and subsurface flow worked together to produce pop-out failures which may be up to 20 times higher than sheet erosion.

Technical Abstract: Estimates by the USDA for 17 States suggest that ephemeral gully erosion ranges from 18 to 73% of the total erosion with a median of 35%. Concentrated flow is generally considered the controlling process and subsurface flow is often overlooked. Pipe-erosion may occur with no visible evidence until pipe collapse results in a fully developed ephemeral gully. Tillage operations fill-in the ephemeral gully thereby leaving the soil-pipe, which was previously at the gully head, buried and discontinuous. Quantification of the conditions underwhich discontinuous soil-pipes reestablish ephemeral gullies and continuous soil-pipes initiate ephemeral gullies is seriously lacking. The objective of this study was to quantify these hydrologic conditions. Experiments were conducted on a discontinuous soil-pipe (2 cm i.d.) that extended 50 cm into the soil bed with 30 cm topsoil depth and a 5% slope. Experiments were also conducted on a continuous soil-pipe (1 cm i.d.) that extended the entire 150 cm length of the soil bed with 10 cm topsoil and 15% slope. Soil-pipes did not exhibit sudden development of mature ephemeral gullies by tunnel collapse but did exhibit sudden re-establishment of filled in gullies. When pipe flow occurs with rainfall a synergistic effect is produced that results in cataclysmic pop-out failures which may be up to 20 times higher than sheet erosion.