Simulation of Water Surface Profiles in Channels with Linear Rigid Emergent Vegetation

Vegetation in watercourses is increasingly recognized as a vital Nature-Based Solution (NBS) for ecosystem preservation. However, from a hydraulic perspective, rigid emergent vegetation also increases flow resistance, which can lead to higher water levels if not properly managed. To calculate the water surface profiles, it is essential to assess the drag coefficient values. Numerous formulas have been proposed in the literature for staggered and random arrangements, while relatively fewer ones have been suggested for linear configurations. Generally, these formulas were derived under uniform flow conditions, and it remains uncertain whether they are relevant for steady-flow conditions, which are more commonly encountered in natural settings. Consequently, the reliability of the estimated drag coefficients is often questionable. In this study, four formulas from the literature, derived for linear arrangements, and one formula for staggered and random arrangements, were employed to simulate thirty-six water surface profiles from two experimental series. These profiles span a broad range of vegetation densities, from 0.008 to 0.42. The profiles belong to accelerated subcritical flow (M2 type), and the standard step method was applied for their simulations. A comparison between the experimental and computed profiles was performed using several statistical parameters, particularly the Taylor diagram. One of the equations analyzed was applied over the aforementioned range of vegetation density, and the computed profiles exhibited a root mean square relative error of approximately 6% compared to the experimental data. The best-performing equation is dependent solely on vegetation density and is likely applicable to higher Reynolds numbers than those encountered in the experimental conditions. Finally, providing a reliable tool for estimating flow resistance is crucial for the successful implementation of vegetative NBSs, allowing engineers to perfectly balance flood discharge capacity with environmental sustainability.