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Title: Influence of Soil Structure, Pore-Water Pressure, and Tailwater Height on Headcut Migration in Upland Concentrated Flows

item Wells, Robert - Rob
item Alonso, Carlos

Submitted to: International Symposium on Gully Erosion
Publication Type: Proceedings
Publication Acceptance Date: 6/21/2007
Publication Date: 9/19/2007
Citation: Wells, R.R., Alonso, C.V., Bennett, S.J. 2007. Influence of Soil Structure, Pore-Water Pressure, and Tailwater Height on Headcut Migration in Upland Concentrated Flows. Proceedings of the IV International Symposium on Gully Erosion. September 17-19, 2007, Pamplona, Spain, J. Casali and R. Gimenez (eds.). Public University of Navarre. pp. 132-133.

Interpretive Summary: Soil erosion and sedimentation by water are major problems that reduce cropland productivity, degrade water quality, and clog water conveyance structures. Laboratory experiments were performed to understand the role of soil texture (sand, silt, and clat content), changes in soil pore-water pressure, and increases in the height of the tailwater (depth of flow downstream of the headcut) on the development and migration of headcut scour holes typical of agricultural fields. For the four soils tested, increasing clay content caused the migration of the scour hole and the depth of the scour hole to decrease. Pore-water pressure was manipulated through water table height changes and, as the water table moved closer to the surface, the scour hole became deeper and the migration rate decreased. An increase in the tailwater height dramatically lowered the sediment yield and migration rate.

Technical Abstract: Soil loss from arable fields caused by surface runoff erosion is composed of several components due to different erosion processes. Bennett et al. (2000) reported experimental data showing that actively migrating ephemeral-gully headcuts display steady-state migration and self-similar organization in the absence of hardpans and upstream sediment supply. Alonso et al. (2002) combined free and impinging jet theory with mass and energy conservation laws to predict soil losses due to headcut erosion and migration in uniform flows. Headcut erosion and migration rates were shown to depend on upstream flow depth and discharge, tailwater depth, and soil and water properties. The hydrodynamic basis for this model was verified experimentally by Bennett and Alonso (2005a, 2005b).The preceding studies have improved considerably our understanding of headcut erosion and migration mechanisms. Obviously, there is a critical need for research aimed at characterizing the influence of varying soil structures, tailwater height, pore-water pressure, dirty water inflow, and channel widening on head cut erosion. The primary objective of this study was to determine the impact of soil texture, soil pore-water pressure, and tailwater height on scour hole dimensions, migration rate and sediment yield in headcuts migrating under steady surface runoff conditions.