Author(s): Su Kalloe; Bas Hofland; Bregje Van Wesenbeeck

Linked Author(s): Su Kalloe, Bregje Van Wesenbeeck

Keywords: Woody vegetation; Wave attenuation; Scale effects; Flexibility

Abstract: Vegetation such as salt marshes and mangroves can dampen incoming waves. Therefore, using vegetation in front of hard structures is currently seen as an attractive addition to conventional flood defense structures (i.e., dikes and levees). However, more research is needed for reliable wave damping predictions, especially for woody vegetation. We therefore investigate wave damping through forests by conducting small-scale experiments on detailed mimics of pollard willow trees. The small-scale set-up is based on previous large-scale experiments, which were conducted on live trees. The tree mimics in this work were 3D-printed and contained a detailed representation of a real flexible canopy structure. Based on test results with various conditions bulk drag coefficients were determined. To this end the number and size of the branches needs to be known. Often the estimate of these tree parameters is not known or crudely schematized. As we now have a very precise (3D printed) representation of complex trees, we can evaluate bulk drag coefficients for different tree structure schematizations. We illustrate the importance of tree geometry, as the calculated wave damping for cylinder models (simple tree model) deviates significantly from the measured wave damping by the detailed tree mimics. This outcome suggests that a more detailed tree representation is relevant for wave damping as the results differ significantly between the two tree models. Furthermore, the 3D-tree model, which included branch tapering and angles, has the advantage of providing a more realistic representation of the forest during small-scale experiments. More importantly, the frontal-surface area distribution of these mimics can be determined easily from the simulations. This can improve the results obtained from small-scale experiments, which use mimics to represent actual vegetation.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221137

Year: 2022