Computation of drag coefficient for real vegetation in wetlands

The flow characteristics in wetlands and vegetated channels are depend on the physical structure, density, and pattern of vegetation. Estimating average velocity in vegetated wetlands requires an accurate determination of the drag coefficient. The innovation of this research lies in calculating the drag coefficient while considering the pattern shape, plant flexural rigidity, and vegetation structure. Laboratory experiments were conducted in a rectangular flume using a parallel pattern of Eleocharis plants at three densities: low, medium, and high, with discharge rates of 18.2, 23.7, and 28.8 L/s, respectively. Comparative analysis revealed that the equation proposed by Kothyari et al. (2009) [23] is just suitable for determining the drag coefficient on rigid cylinders with a staggered pattern and it should be improved for real vegetation with different pattern. A comprehensive equation was developed for real wetland vegetation, incorporating a new pattern coefficient for pattern shape (ζpp) and correction factor (η) to consider plant flexural rigidity and vegetation structure. The results demonstrate that this equation accurately predicts the drag coefficient (RMSE = 0.127, MAE = 0.107, and R2 = 0.9059) in channels with real vegetation with parallel and staggered patterns. •In the wetlands, the vegetation reduces the velocity and increases the turbulences.•A comprehensive equation was recommended to calculate the drag coefficient (CD) in wetlands.•A correction factor was proposed for shape pattern.•Another correction factor was suggested for flexibility of real vegetation.•The recommended equation has high accuracy to estimate CD for herbaceous plant.