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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, T - YANGLING, SHAANXI, CHINA
item Nearing, Mark

Submitted to: Chinese Society of Agricultural Engineers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2001
Publication Date: N/A

Interpretive Summary: Most severe erosion on agricultural land occurs in conjunction with small channels, which we call rills, which form as a result of surface water runoff on sloped lands during rainstorms. This study was undertaken in order to better understand how such rills are initiated. If we can understand under what conditions the rills initially form, we may have a better chance to predict areas that are in danger of severe rill erosion and we may also find methods to control such erosion. In this study, we designed an instrument, which allows us to measure precise conditions of water flow rate and land slope whereby the rills just begin to form. As expected, rills form as either of these two factors is increased beyond a particular threshold, or critical state. What we found that was unexpected was that this state did not appear to follow previously believed patters. The critical rilling threshold was more sensitive to slope than to flow rate, whereas previous assumptions have been put forth that both are equal in effect. These results will ultimately provide the basic information needed to protect our nation's soil resources to produce food for future generations of Americans.

Technical Abstract: Dynamic soil erosion processes involve the spatial and time dependent processes of detachment, rill formation, deposition, re-rilling from 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 was designed to measure the parameters for rill cutting in loose material similar to deposited soil. Experimental results were conducted for determining 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: 8/30/2014
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