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United States Department of Agriculture

Agricultural Research Service

Research Project: EROSION PREDICTION TECHNOLOGY TO ENHANCE CONSERVATION PLANNING Title: Critical Conditions for Rill Initiation

Authors
item Yao, Chunmei - WSU
item Lei, Tingwu - CHINA AG UNIV, BEIJING
item Elliot, William - USDA, FOREST SERVICE
item McCool, Donald
item Zhao, Jun - CHINESE ACADEMY OF SCIENC
item Chen, Shulin - WSU

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 31, 2007
Publication Date: February 14, 2008
Repository URL: http://hdl.handle.net/10113/19580
Citation: Yao, C., Lei, T., Elliot, W.J., McCool, D.K., Zhao, J., Chen, S. 2008. Critical Conditions for Rill Initiation. Transactions of the ASABE. Vol. 51(1): 107-114.

Interpretive Summary: Quantifying critical conditions of rill formation can be useful for a better understanding of soil erosion processes. Many studies lack a consensus and related rationale on how to describe these conditions. This study was based on the concepts that: (1) the flow shear stress available for erosion at any given point is a function of the runoff rate, the slope steepness, and hydraulic characteristics of the surface; (2) rill incision begins when overland flow shear stress exceeds soil critical shear stress; and (3) the distance from the top of the slope to the point where rills form can be measured and analyzed as critical slope length and decreases with increase in slope and overland flow discharge. These concepts were tested with a representative silty-clay soil from the Loess Plateau in western China on a large indoor sloping plot (8m×3m) using simulated rainfall with five different slopes and three rainfall intensities. Values of hydraulic parameters at rill initiation were determined from the experimental data. The results showed relationships among slope steepness, overland flow from rainfall, and location of rill initiation. It was found that slope was relatively more important than rainfall intensity in determining the location of rill initiation. Soil critical flow shear stress ranged from 1.33 Pa to 2.63 Pa, with an average of 1.92 Pa. Soil critical flow shear stress decreased with slope; and was not significantly influenced by rainfall intensity. The results of this study were comparable with those of previous investigators.

Technical Abstract: Quantifying critical conditions of rill formation can be useful for a better understanding of soil erosion processes. Current studies lack a consensus and related rationale on how to describe these conditions. This study was based on the concepts that: (1) the flow shear stress available for erosion at any given point is a function of the runoff rate, the slope steepness, and hydraulic characteristics of the surface; (2) rill incision begins when overland flow shear stress exceeds soil critical shear stress; and (3) the distance from the top of the slope to the point where rills form can be measured and analyzed as critical slope length and decreases with increase in slope and overland flow discharge. These concepts were tested with a representative silty-clay soil from the Loess Plateau in western China on a large indoor sloping plot (8m×3m), using simulated rainfall with five different slopes and three rainfall intensities. Values of several hydraulic parameters at rill initiation were determined from the experimental data. The results showed relationships among slope steepness, overland flow from rainfall, and location of rill initiation. It was found that slope was relatively more important than rainfall intensity in determining the location of rill initiation. Soil critical flow shear stress determined in this study ranged from 1.33 Pa to 2.63 Pa, with an average of 1.92 Pa. The soil critical flow shear stress had a decreasing trend with respect to slope and no significant difference with respect to rainfall intensity. The results of this study were comparable with those of previous investigators.

Last Modified: 11/22/2014
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