Author
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McCool, Donald |
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WILLIAMS, JOHN - USDA-ARS |
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Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/30/2005 Publication Date: 9/30/2005 Citation: Mccool, D.K., Williams, J.D. 2005. Freeze/thaw effects on rill and gully erosion in the northwestern wheat and range region. International Journal of Sediment Research Vol. 20, No.3, 2005, pp.202-210. Interpretive Summary: Winter storms and melt events cause much of the runoff and erosion in the non-irrigated cropland of the inland Pacific Northwest. Fifty-five to sixty-five percent of the precipitation occurs from November through March, and formation of impermeable frost, intensified by excessive tillage and tillage pans, has long been a major factor in rill and channel formation in the region. Saturated zones can form above tillage pans, freeze solid, and significantly reduce infiltration. Frozen surface soils thaw and weaken with warming temperatures or rain. Runoff from rain or snowmelt or a combination of the two is almost inevitable, concentrating in rills and larger channels, and carrying the loosened soil. Slopes are frequently quite steep and there may be little deposition above the bottom of the slope. Concentrated flow channels form because of collection of water from impervious areas such as conventionally tilled fall seeded small grain and bare grass seed fields. Larger gullies are created in some soils by seepage from saturated layers above permanent restrictive layers in the soil. Gullies can also result from terrace failures due to rodent burrows or low compaction at the time of construction. Rill measurements on conventionally tilled fields in Oregon, Washington, and Idaho were used to determine coefficients for relationships between slope length and steepness and size of rills. This paper describes these studies and results as well as results of analysis of long-term erosion and weather records from southeastern Washington. Technical Abstract: Hydrology of the Northwestern Wheat and Range Region (NWRR) of the Pacific Northwest USA is dominated by winter events. Fifty-five to sixty-five percent of the precipitation occurs from November through March, and formation of impermeable frost, intensified by excessive tillage and tillage pans, has long been a major factor in rill and gully formation in the region. Saturated zones can form above tillage pans, freeze solid, and significantly reduce infiltration. Frost heaved surface soils thaw and weaken with warming temperatures or rain. Under these conditions, runoff from rain or snowmelt or a combination of the two is inevitable, concentrating in rills and channels, and carrying loosened soil. Slopes are frequently quite steep and there may be little deposition above the toe slope. Classical over-fall head-cut gullies are uncommon. Concentrated flow channels form because of collection of water from impervious areas such as conventionally tilled fall seeded small grains and bare grass seed fields. In some soils, gullies are created by seepage from saturated layers above permanent restrictive layers in the soil. Gullies can also result from terrace failures due to rodent burrows or low compaction at the time of construction. In naturally unconsolidated soil, rodent activity can lead to piping failures that remove large quantities of subsurface soil and can become gullies. Rill measurements on conventionally tilled fields in Oregon, Washington, and Idaho were used to determine coefficients for relationships between slope length and steepness and size of rills. This paper describes these studies and the results as well as results of analysis of long-term erosion and weather records from southeastern Washington. |
