Variation in the vertical zonality of erodibility and critical shear stress of rill erosion in China's Hengduan Mountains

Abstract

Soil erodibility is an essential parameter used in soil erosion prediction. This study selected the Liangshan town watershed to quantify variation in the vertical zonality of rill erodibility (k r ) in China's ecologically fragile Hengduan Mountains. Soil types comprised of yellow–brown (soil A), purple (soil B), and dry-red (soil C) in a descending order of occurrence from the summit to the valley, which roughly corresponds to the vertical climate zone (i.e. cool-high mountain, warm-low mountain, and dry-hot valley sections) of the study area. With elevation, vertical soil zonality varied in both soil organic matter (SOM) content and soil particle-size fractions. A series of rill erosion-based scour experiments were conducted, using water discharge rates of 100, 200, 300, 400, 500, and 600 mL min -1 . Additionally, detachment rates (Dr) were measured under three hydrological conditions (the drainage, saturation, and seepage treatments). Results show that both Dr and flow shear stress (Ʈ) values increased as discharge increased. As elevation increased, the k r values decreased, while the vertical zonality of critical shear stress (Ʈ c ) values showed no obvious variation. The highest k r values were observed during the seepage treatment, followed by the saturation treatment then drainage treatment, indicating that variation in vertical hydraulic gradients could significantly alter k r values. This study also found that land-use types could also alter k r and Ʈ c values. Further research, however, is necessary to better quantify the effects of subsurface hydrological conditions and land-use types on k r under different soil zonalities in China's Hengduan Mountains. © 2018 John Wiley & Sons, Ltd.