Quantifying additional overland flow resistance induced by changes in vegetation distribution patterns

Abstract : While a thorough understanding of overland flow resistance is crucial for the development of numerical simulations and soil erosion models, the influence of the vegetation distribution patterns of combined grass and shrubs on flow resistance remains an area requiring further investigation. Therefore, for five slope gradients (2–10°) and ten unit discharges (7.5–120 L/min), we conducted fixed-bed drainage tests with a single-row alternating pattern (SR), double-row alternating pattern (DR), upstream shrub and downstream grass pattern (UD), combined vegetation uniform pattern (UP), single shrub (SS), single grass (SG), and bare sandpaper (BS). The key findings include the following: (1) A methodology was developed to calculate the equivalent resistance coefficient ( f e ) and its components for vegetated slopes, comprising grain resistance ( f b ), grass resistance ( f g ), shrub resistance ( f s ), additional combined vegetation resistance ( f c ), and additional pattern resistance ( f p ). The calculated f e demonstrated strong agreement with experimental measurements (Nash-Sutcliffe efficiency > 0.95, relative root mean square error < 0.08). (2) Vegetation distribution patterns significantly influenced f e values, following the hierarchical order: UD > SR > DR > UP > SS > SG > BS. The UD configuration yielded the maximum f e , approximately ten times greater than BS conditions, revealing its strong application potential. (3) The f p represented the most variable component across different vegetation patterns. For SR, DR, and UD configurations, f p reached peak contributions to total resistance of 54.84%, 48.76%, and 73.09% at specific discharges of 40, 15, and 30 L/min, respectively. These findings directly inform practical strategies for optimizing vegetation distribution patterns throughout the Chinese Loess Plateau.