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United States Department of Agriculture

Agricultural Research Service

Title: Laboratory Experiments of Rill Initiation and Critical Shear Stress in Loose Soil Material

Authors
item Lei, Tingwu - PURDUE UNIVERSITY
item Nearing, Mark

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 1999
Publication Date: N/A

Interpretive Summary: Scientists work to develop a better understanding of soil erosion processes in order to devise and develop better ways to preserve soil for the future and to reduce water pollution. Soil erosion models are used as tools for conservation planning, so that various land use options may be tested on the computer prior to implementation. Models are used as tools for soil erosion inventory so that policy makers have an understanding of regional and national erosion and conservation problems. Models are also used by engineers and government planners for designing and regulating projects as diverse as the building or evaluation of reservoirs to the development of the rural-urban interface. This study was undertaken to help fill a gap in our knowledge of soil erosion processes. Soil is eroded largely by the forces of flowing runoff waters. This study helps us to better understand the effect of slope steepness and runoff rates on rates of erosion. The results will help us to better design and evaluate the potential for erosion on disturbed lands.

Technical Abstract: Dynamic soil erosion processes involve the spatial and time dependent processes of detachment, rill formation, deposition, re-detachment of deposited sediment and scouring of rills. Rill scouring associated with sediment re-detached from a depositional area can be an important phenomenon in rill narrowing and deepening. In this study, an apparatus with adjustable slope (from 0 to 50 percent) and inflow rate of water (to a maximum 8 l/s m) was designed to measure the parameters for rill cutting in loose material similar to deposited soil. A sandy-loam (Cecil) soil was used to conduct experiments on 11 slopes: 0, 3, 7, 10, 15, 20, 25, 30, 35, 40 and 50 percent with 2 replicates and 4 aggregate size groups: 0 - 2 mm, 2 - 5 mm, 5 - 8 mm and the unsieved mixture of the 3 groups. The simulated deposited soil samples in boxes of 195 by 195 mm were set to the pre-adjusted, desired slope. Flow rate was gradually increased from zero until rill formation began. Then flow rate was decreased until the rill ceased cutting. Experimental results were presented as the flow rates at which rill formation starts and ends for each aggregate group and slope. Critical shear stress as related to bed slope was calculated. The results improve our understanding and quantification of rill cutting in loose material as well as the relationship between critical shear stress and slope. The results may be of particular value in developing process models of rill evolution wherein rills re-cut through deposited material.

Last Modified: 7/22/2014
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