Abstract Accurately determining flexible vegetation resistance remains challenging due to vegetation bending and resistance reconfiguration under water flow. This study conducted laboratory experiments to explore the bending and resistance reconfiguration for single submerged flexible vegetation under water flow, and corresponding factors influencing resistance have been analyzed and quantified. Four diameters and five heights of vegetation were tested to observe the changes in bending posture of vegetation under a wide velocity range (0.05–1.85 m/s), with the resistance including drag force and skin friction measured. Results indicate that resistance changes from quadratic law to linear relationship with velocity as both the Cauchy number and vegetation bending angle increase, attributed to streamlined structure and resistance reconfiguration. The skin friction acted on flexible vegetation became significant under both low and high flow velocities, and thus should be considered in related analysis. Furthermore, the calculated drag coefficient accounting for micro‐element bending angle presents a trend of first decreasing and then increasing with the Reynolds number and Cauchy number. The drag coefficient factor and effective length combined with the Cauchy number were used to compare drag force between flexible and rigid vegetation and explain the resistance reconfiguration effects. Finally, a new empirical formula integrating the Reynolds number, Cauchy number and bending angle was established. The new formula outperforms traditional formulas based solely on the Reynolds number in predicting the drag coefficient for both high and low ranges. This study provides valuable references for flexible vegetation‐flow interaction mechanisms and improves resistance calculations in vegetated open channels.
Liu et al. (2026) studied this question.