Subsurface Drainage for Erosion Reduction on Croplands of Northwestern Oregonby G. E. Formanek, West Natl Technical Cent, Portland, OR, USA,
E. Ross, West Natl Technical Cent, Portland, OR, USA,
J. Istok, West Natl Technical Cent, Portland, OR, USA,
Abstract: Subsurface drains installed as a relief system on sloping cropland reduced surface runoff and soil loss from silty soils with underlying slowly permeable layers in northwestern Oregon. Flows from the subsurface drains during the storms averaged 0. 24 inches per day with a minimum depth to water table averaging 12. 4 inches. The runoff curve number was lowered by 10 as calculated with Soil Conservation Service procedures and measured runoff. The change in curve number was used to estimate changes in runoff for certain storms used to calculate long term average erosivity due to runoff. The calculated change in the long term average annual erosivity resulted in an erosion reduction of 28 percent when compared to similar but undrained soils. Therefore, for similar conditions in northwestern Oregon, a Universal Soil Loss Equation practice factor value of 0. 72 is proposed for subsurface drains installed as part of a resource management system that maintains soil infiltration.
Subject Headings: Subsurface drainage | Agriculture | Runoff | Erosion | Soil loss | Permeability (soil) | Subsurface flow | Drainage systems | Oregon
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