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United States Department of Agriculture

Agricultural Research Service

Title: Ephemeral Gully Erosion by Preferential Flow Through a Discontinuous Soil-Pipe

Authors
item Wilson, Glenn
item Cullum, Robert
item Romkens, Mathias

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2007
Publication Date: March 15, 2008
Citation: Wilson, G.V., Cullum, R.F., Romkens, M.J. 2008. Ephemeral Gully Erosion by Preferential Flow Through a Discontinuous Soil-Pipe. Catena, 73(1): 98-106.

Interpretive Summary: Lateral flow through large pores, termed soil-pipe, in the soil can cause shallow gullies. These soil pipes are buried when the shallow gullies are filled-in by tillage. The objective was to determine the effect of flow through soil-pipes that are cutoff by tillage on gully erosion. Experiments were conducted on 150 cm long by 100 cm wide soil bed with an artificial soil pipe at the upper end that extended 50 cm into the soil immediately above a compacted soil layer that restricts water movement through it. Treatments included a 15 cm water pressure and a 30 cm water pressure on the soil pipe without rainfall, rainfall alone without water pressure on the soil pipe, and rainfall applied simultaneously with 15 cm and with 30 cm water pressure on the soil pipe. Rainfall alone on bare soil resulted in high (11 Ton acre-1) soil losses by sheet erosion but no large blow-outs of soil that would result in ephemeral gully formation. Establishment of water pressure on the soil pipe resulted in seepage out of the soil bed while tensiometers 1 cm above the restrictive layer indicating unsaturated conditions. Pipe flow alone did not result in large blow-outs of soil in three of the four test. However, the combination of rainfall with pipe flow produced extensive (16-63 kg) soil losses that occurred as sudden, cataclysmic pop-out failures. The total soil losses by sheet erosion were four times higher with rainfall and pipe flow combined (13.6 kg) than by rainfall alone (3.6 kg). The total soil loss by pop-out failures was close to 20 times higher than sheet erosion for rainfall alone as a result of pipe flow combined with rainfall.

Technical Abstract: Lateral flow through soil pipes has been postulated to facilitate the development of ephemeral gullies, yet these soil pipes are buried and thereby made discontinuous when gullies are filled-in. The objective was to determine the effect of flow through discontinuous soil-pipes on ephemeral gully erosion. Soil erosion experiments were conducted on 150 cm long by 100 cm wide soil beds with an artificial soil pipe at the upper end that extended 50 cm into the soil immediately above a water restricting horizon. Treatments included a 15 cm head and a 30 cm head on the soil pipe without rainfall, rainfall alone without a head on the soil pipe, and rainfall applied simultaneously with a 15 cm head and with a 30 cm head on the soil pipe. Rainfall alone on bare soil resulted in high (11 Ton acre-1) soil losses by sheet erosion but no mass wasting that would result in ephemeral gully formation. Establishment of a head on the discontinuous soil pipe resulted in hydraulic nonequilibrium in which seepage occurred while tensiometers 1 cm above the restrictive layer indicated unsaturated conditions. Pipe flow alone did not result in mass wasting in three of the four test. However, the combination of rainfall with pipe flow produced extensive (16-63 kg) soil losses by mass wasting. The mode of mass wasting appeared to be sudden, cataclysmic pop-out failures. The total soil losses by sheet erosion were four times higher with rainfall and pipe flow combined (13.6 kg) than by rainfall alone (3.6 kg). The total soil loss by mass wasting was close to 20 times higher than sheet erosion for rainfall alone as a result of pipe flow combined with rainfall.

Last Modified: 10/25/2014
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