Water Erosion by Splash and Wash and the Erodibility of Albertan Soils

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Abstract
The theoretical significance of soil erodibility variations in the processes of hillslope erosion has long been recognized by geomorphologists, but few attempts at assessment have been made. A laboratory simulated rainfall test for soil erodibility is briefly described and the results of testing 154 soil samples from a variety of pedogenic environments in Alberta, Canada, are presented. Soil-loss under test conditions varied from 0.11 to 17.77 kg/m2, with a mean value of 3.09 kg/m2. The relative importance of soil properties in determining erodibility was tested. It was demonstrated that by far the most significant property was the quantity of water-stable aggregates, which far outweighs the importance of any textural separate except on extremely poorly aggregated soils. The influence of textural separates is most apparent on sand-rich soils which are generally poorly aggregated. The main mechanism of aggregate breakdown on hydration is shown to be slaking rather than differential swelling. Accordingly clay mineral type is not an important control of erodibility although montmorillonite content can influence infiltration capacity. The test permitted separation of material transported by wash from that transported by splash. For most soils “wash” loss is consistently higher than splash, particularly when antecedent moisture content is high. Data derived from relatively deep channel flow experiments indicate that the flow velocity achieved by the base of the very short slope would not be competent to entrain material. Accordingly the high “wash” losses recorded are interpreted to indicate: 1) that much of this material is entrained by splash though transported by runoff, 2) that critical velocities observed in deep channel flow are much higher than those in very thin layer flows where particles project through the surface.

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