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United States Department of Agriculture

Agricultural Research Service

Title: Sediment Transport in Rill Flow under Deposition and Detachment Conditions

Authors
item Polyakov, Viktor - PURDUE UNIVERSITY
item NEARING, MARK

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 3, 2002
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 his or her local county conservation office, the conservation officer in that office will use an erosion model to help him/her select the type of management practices for the 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 amount of sediment that can be carried by surface water runoff as might occur during a rain storm. In particular, we were interested in how much soil can be detached by the surface water flow, and after it is detached, how much can be carried. 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. Since we will know where severe erosion is occurring, we can target those areas and spend less money to conserve more soil. Society will benefit from better and more ecoomical conservation of soil resources used in growing food and less water pollution from farmlands.

Technical Abstract: The understanding of soil erosion processes and the development of accurate erosion prediction models require understanding of detachment, deposition, and sediment transport in rills. The objectives of this study were to determine whether sediment transport capacity is a unique value for given soil, flow rate and slope, and to determine if the equilibrium sediment concentration in the flow obtained by detachment was different from that obtained under depositional conditions. Experiments on a Carmi loam (fine, mixed, mesic Typic Hapludalf) simulated rill erosion under net detachment and net deposition conditions. Two discharge rates of 6 and 9 L min-1, and two sediment input regimes of 0 and excess of transport capacity were tested on soil beds with lengths of 2, 4, 6, 7, and 8 m at 7 % slope. Sediment load reached steady state conditions within the 8-meter distance on the rill. At 9 L min-1 discharge, 8 m length, and excess sediment added to the flow, sediment delivery was 71 g L-1 versus 31 g L-1 for the case with no sediment added. Overall for the tested conditions, rill flow transported 2 times more sediment than it could detach. The flow did not reach its maximum potential transported load through detachment of particles, due in part to changes in the sediment size distribution under deposition and possibly to the protective action of bedload particles moving along the rill bottom and/or changes in flow turbulence associated with sediment laden flow.

Last Modified: 8/19/2014
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