Vegetation-induced hydrodynamic alterations on convex slopes: Mechanisms of flow resistance and erosion control

The hydrodynamic response of overland flow to vegetation coverage on convex slopes remains inadequately quantified despite it is critical for soil erosion control in terrains dominated by such topography. This study systematically investigated the influence of varying vegetation coverage (0%, 1.08%, 3.24%, 4.69% and 9.81%) on the hydrodynamic characteristics of convex slopes through indoor flume experiments under diverse flow discharges (5.5–13.5 m³/h) and slopes (5°–25°). The results revealed three key hydrodynamic mechanisms: (1) Flow retardation and energy dissipation: Increasing vegetation coverage significantly reduced overland flow velocity and promoted higher flow depth, thereby enhancing water retention and energy dissipation. Both stream power (Ω) and unit stream power (ω) declined by 13.9%–30.1% compared to bare slopes. (2) Flow Regime Transition: Froude number (Fr) decreased with increasing vegetation coverage, promoting the transition from supercritical to subcritical flow. The Reynolds number (Re) consistently exceeded 500, indicating the absence of laminar flow. (3) Modification of flow resistance: Vegetation resistance increased nonlinearly with coverage. Maximum bed shear stress was observed at 4.69% coverage (23.5% higher than bare slopes). However, Manning's (n) and Darcy–Weisbach (f) coefficients did not correlate clearly with Re, indicating that vegetation coverage and slope type feedback significantly change flow resistance mechanisms.