The relationship between flow depth and hydraulic parameters for high surface roughness of vegetation stem cover under laboratory simulation

Grass, shrubs and tree stems can increase flow depth and resistance and prevent soil erosion, and it is necessary to quantify the relationship between flow depth and hydraulic parameters for high surface roughness of vegetation stem. Therefore, the experimental design included flow depth, velocity and transport capacity, which were measured for different stem covers (bare flume to cover 30%), diameters (2, 10 and 36 mm), and arrangements (bead, tessellation, stagger, random, and stripe) to clarify the relationship between flow depth and the hydraulic radius, Reynolds number Re , Manning coefficient n m , Darcy-Weisbach resistance f and transport capacity Tc . The result shows that flow depth could be effectively predicted by stem cover and stem diameter; the greater the surface roughness was, the more the difference between flow depth and hydraulic radius; and flow depth could not be used as the hydraulic radius to calculate hydraulic parameters for high surface roughness. Re , n m and f were significantly impacted by flow depth. The linear relationship between flow depth and Re , n m , and f became stronger as stem cover decreased and stem diameter increased, and they were more affected by stem cover than by diameter. The relationship between flow depth and f was less impacted by high surface roughness of vegetation stem. Tc was not significantly impacted by flow depth; the Manning coefficient and Darcy-Weisbach resistance were not appropriate for predicting transport capacity; and the Reynolds number could illustrate the mechanism of sediment transport capacity affected by vegetation stem cover from the perspective of flow resistance. • The greater surface roughness, the more difference between H and hydraulic radius. • The relationship between H and Re, n m and f were more affected by stem cover than by diameter. • The relationship between H and Re, n m and f became stronger as stem cover decreased and diameter increased. • Re could illustrate the mechanism of Tc affected by vegetation stem cover.