ARS | Publication request: EFFECT OF SEDIMENT LOAD ON SOIL DETACHMENT AND DEPOSITION IN RILLS

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 2000
Publication Date: N/A

Interpretive Summary: Environmentalists and conservationists use computer models to evaluate ecosystems. Soil erosion, for example, is normally evaluated using an erosion model. For example, when a farmer goes to her local county conservation office, the conservation officer in that office will use an erosion model to help her select the type of management practices for her farm which best conserve the soil resource. In order to develop better models of erosion, which give the user more information, we need to understand more about the erosion process. In this study we were looking at the distribution of erosional patterns down a slope, and in particular where erosion occurs, where deposition of sediment occurs, and why they occur in the observed locations. Ultimately, this research will provide erosion models that tell us not only how much erosion occurs on a field, but where the erosion is most severe. The impact of this research is that since the land will know where severe erosion is occurring, he can target those areas and spend less money to conserve more soil. Society will benefit from the better and cheaper conservation of the soil resource needed to grow food and because of less water pollution from farmlands.

Technical Abstract: According to theory, the rate of detachment of soil particles in rills is reduced as a first-order function of the amount of sediment load in the flow. The first objective of this study was to determine if experimental results confirmed current detachment-transport coupling theory. The second objective was to investigate two hypothesized mechanisms responsible for the observed effect. The first was that since turbulence is known to be a critical factor in detachment by flow, and since it is also known that sediment in water reduces turbulent intensity, it was suggested that sediment in flow reduces detachment via a correspondent reduction in turbulent intensities. This hypothesis was tested indirectly by adding a sediment load which was carried entirely in the suspended state. The second mechanism was that sediment covering the soil bed during the erosion process shields the soil from the forces of flow, thus reducing detachment. This hypothesis was tested by introducing bedload sediment. Sediment loads exiting the rill and detachment and deposition along the rill were measured. Detachment was reduced and deposition was increased as a linear function of the amount of sediment introduced into the flow. Results indicated that, in general, detachment did decrease according to current theory, but discrepancies in the erosional patterns were observed which none of the current models explain. Both hypothesized mechanisms of reduction in detachment rates were apparently active in reducing detachment rates, though the shielding mechanism appeared to have a greater impact than did the mechanism associated with a reduction in turbulent intensity.