HYDRAULIC FLOW AND WATER-QUALITY CHARACTERISTICS IN RILL EROSION

The effects of interaction between water flow characteristics, soil sodicity, and water quality on the detachment of soil particles by flowing water was studied in the laboratory. Specific objectives of this study were to evaluate: (i) the use of flow shear stress and stream power for estimating soil detachment, (ii) the effect of low soil sodicity (exchangeable sodium percentage [ESP] <10) and water quality (deionized water [DW] and 0.005 M CaCl2 solution [TW]) on soil detachment, and (iii) the effect of negatively charged polyacrylamide (PAM) polymer on soil detachment. Detachment rates were measured in a small hydraulic fume. Several bed slopes and flow rates were studied. Detachment rate increased linearly with both shear stress and stream power of the flow. The rill erodibility of the Miami soil (fine-loamy, mixed, mesic Typic Hapludalf) agreed well with field data. Water quality had no effect on rill erodibility for the soil tested when ESP < 3.0. Use of TW reduced the erodibility of soils with ESP 5 and 10 compared with DW. Surface treatment with PAM (0.05 g m-2) prevented soil detachment in flows with high shear stress. The formation of a surface soil layer with high cohesion and aggregate stability prevented soil detachment. Soil surface properties and not bulk soil properties determined soil detachment.