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United States Department of Agriculture

Agricultural Research Service

Title: Modification of the Wind Erosion Roughness Index by Rainfall

item Zobeck, Teddy
item Popham, Thomas

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 1996
Publication Date: N/A

Interpretive Summary: Accurate estimates of soil surface geometry or roughness are needed in wind and water erosion prediction and other areas of science. This study was conducted to determine how different amounts and intensity of rainfall change the soil surface roughness. Soil surface roughness was measured after different amounts of rainfall that fell at four different intensities. The surface roughness was calculated in several ways. We measured how fast the roughness changed for each rainfall intensity and calculation procedure. We found that the rainfall affected some roughness calculations but not all of them. Roughness generally decreased with additional rainfall and the rate of roughness change was related to the intensity of the rainfall. As expected, the soil surface roughness was reduced at a faster rate at higher intensity rainfall. We also tested a new, easier method of measuring soil surface roughness and related the new method to the roughness calculation procedures.

Technical Abstract: The cumulative shelter angle distribution (CSAD) is a soil surface roughness index used in the Wind Erosion Prediction System to estimate the fraction of the soil surface susceptible to abrasion by saltating particles (FSA). This study was conducted to determine if simulated rainfall amount and intensity has an effect on CSAD parameters used to describe a field with relatively low (92 mm) ridges. Simulated rainfall was applied in cumulative amounts of 0, 6, 19, 32, 44, 57, and 83 mm at intensities of 13, 25, 51, and 76 mm h(-1) on duplicate plots of an Acuff sandy clay loam (fine-loamy, mixed, thermic Aridic Paleustoll). The CSAD parameters were estimated from elevations measured by a laser roughness meter after each cumulative rainfall amount in directions parallel and perpendicular to tillage. The CSAD parameters were used to estimate FSA. We found the parameters were sensitive to tillage direction for this field with relatively low ridges. The tillage ridges were only about 92 mm high yet the mean FSA was 19% greater and the rate of change of FSA over rainfall amount was twice (0.002 vs. 0.004 mm(-1) that when evaluated parallel to tillage compared with measurements made perpendicular to tillage. Analyses of variance of CSAD B and C values and FSA revealed significant differences (P<0.05) due to rainfall amount and intensity for most parameters. The 13 mm h(-1) rainfall intensity had no effect on the roughness parameters. Regressions of B, C, and FSA over rainfall amount for each rainfall intensity showed that for B parallel and B FSA perpendicular to tillage, the data for the 51 and 76 mm h(-1) rainfall intensities could be combined.

Last Modified: 4/19/2014
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