SIMULATED SMALL-CHANNEL BED SCOUR AND HEAD CUT EROSION RATES COMPARED

Concentrated-flow erosion is often a major part of cropland erosion. T he concentrated-Bow processes of bed scour and head cut need improved characterization to better predict and prevent erosion. This study was conducted to compare the erosion rates due to simulated small-scale b ed-scour (Db) and head-cut (Db) processes. A 6.4-m-long by 0.15-m-wide hydraulic flume was used to simulate concentrated-flaw erosion on fiv e Midwestern soils: Barnes (fine-Loamy, mixed Udic Haploboroll), Forma n (fine-loamy, mixed Udic Argiboroll), Mexico (fine, montmorillonitic, mesic Udollic Ochraqualf), Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll), and Sverdrup (sandy, mixed Udic Haploboroll). For sl opes of 1.5, 3.5, and 5.0%, Bow rates of 3.78, 5.67, 7.65, 11.34, and 15.12 L min(-1) were used to provide a range from low (0.5 Pa) to mode rate (2.5 Pa) shear stresses (tau). Soil detachment rates are function s of slope, flow rate, and shear stress. Slope, how, their squares, an d the slope X flow interaction were highly significant predictors of D b. Only flow, its square, and its interaction with slope were signific ant predictors of Dh. Nonlinear power regressions using tau as an inde pendent variable were better predictors of detachment than simple line ar regressions. Erodibility for the soils from this study does not rel ate well with soil erodibility calculated using the Universal Soil Los s Equation. Differences in the slope and intercept of detachment vs. t au exist among soils. The value of D-h was at least four times greater than D-b for all soils at equal slope and flow rate, indicating that head cutting is the main process of detachment for the conditions test ed.