Experimental Investigation on Effect of Vegetation Distribution Pattern on Hydraulic Characteristics of Overland Flow

The vegetation distribution pattern is crucial for controlling soil erosion on slopes. However, the effects of varying vegetation column ( b ) and row ( d ) spacings on the hydraulic characteristics remain underexplored. To address this, 216 indoor scour experiments were conducted under controlled variations in b and d (0.01–0.09 m), flow discharge ( Q , 0.3–1.0 L/s) and slope gradient ( θ , 15°–45°). Results showed that overland flow consistently remained in the supercritical transition regime. The flow regime was influenced collectively by b , d , θ and Q . Form resistance dominated the total flow resistance, accounting for more than 80%, and its proportion ( P ) decreased with increasing b or d , but increased with higher θ . Variations in d exerted a greater influence on P than those in b . The flow resistance coefficient ( f ) decreased with increasing b or d , but this effect weakened at higher θ or Q . On gentle slopes, increasing b or d amplified the effect of Re on f , whereas this influence diminished on steeper slopes. The relationships of f with b , d and Re were effectively described by power functions. A predictive model for f , incorporating b , d , Re , θ and grass stem diameter, was developed and showed consistent accuracy across all datasets ( R 2 > 0.820). These results support optimised vegetation designs for effective erosion control.