Abstract Understanding how surface combined covers influence hydraulic parameters of overland flow is essential for optimizing soil erosion control measures. Surface combined covers significantly alter overland flow hydraulics, yet interactions between upright/non‐upright covers remain poorly quantified. This study systematically investigated the effects of combined cover types (upright stems, non‐upright stems, and their mixtures) and varying coverage percentages on flow hydraulics under controlled laboratory conditions, with a fixed flow discharge of 1 × 10 −3 m 3 s −1 and constant slope gradient of 15°. The results demonstrated that surface combined covers significantly altered key hydraulic parameters. Specifically, increasing total coverage ( Ct ) led to substantial decreases in Froude number ( Fr ), stream power ( ω ), and unit stream power ( P ), accompanied by significant increases in Manning's coefficient ( n ). Regression analyses indicated that Ct reliably predicted shear stress ( τ ), Fr , n , and P ( R 2 > 0.7) in combined‐cover scenarios without upright stems, whereas individual coverage elements provided greater explanatory power when upright stems were present. Among the tested hydraulic parameters, Reynolds number (Re) and ω were poorly described by total coverage alone, suggesting the necessity of considering individual cover elements for accurate predictions. Upright stems exhibited a dominant role in influencing hydraulic behavior by generating localized vortices, enhancing turbulence, and increasing bed friction and flow resistance. The findings contribute to understanding the hydrodynamic mechanisms by which composite covers influence soil erosion.
Zhang et al. (Fri,) studied this question.