Evaluating the Impacts of Riparian Plants on Flood Hazard Within Vegetated Rivers

In the last few years, vegetated rivers have been managed with the main purpose of achieving water drainage and improving conveyance through vegetation removal. However, this leads to peak discharge augmentation and wave travel time reduction. This study assesses vegetation shredding and selective cut impacts on flood risk management. Flow resistance was obtained considering vegetation morphology and hydrodynamic measurements performed during two field campaigns conducted just before the destructive cut and in the growing season after 4 years. Järvelä model was adopted by modeling shrubby vegetation Leaf Area Index (LAI), while Nepf model was selected for herbaceous vegetation, based on flexible plants reconfiguration, strongly dependent on vegetation species and type. Finally, Baptist et al. model was employed for woody rigid plants, modeled as a random or staggered array of rigid cylinders. Results of one-dimensional unsteady hydraulic numerical simulations show higher water levels 4 years after the severe cut, while selective thinning reduces them. This methodology allows the quantification of flood propagation and peak flow delay: wave celerity decreases up to 21% and up to 34% (for undisturbed vegetation and clear cut scenarios, respectively) because of vegetation re-growth, causing a flood delay from 20 to 30 min at the downstream cross-section.