Wave Damping by Vegetation at Bunkeflo Salt Meadows - Applying an empirical model based on plant biomass

Abstract: Future sea level rise due to climate change increases the risk of coastal flooding and thus necessitates the building of dikes and other protective structures. Coastal vegetation can reduce the impact of waves on such structures by dissipating wave energy and hence reduce incoming wave heights. This thesis attempts to quantify the wave damping by vegetation at Bunkeflostrand (southern Sweden), by using an empirical method based on plant biomass. An analysis is made of how the damping is influenced by the type of vegetation and by the hydrodynamic conditions. Through field surveys in combination with geographical information system (GIS) software, the area was classified into several vegetation types whose biomass and vegetation height were measured and used as an input to the model. The influence of vegetation characteristics and hydrodynamic conditions were studied in hypothetical cases using MATLAB. As a case study, wave damping over four transects at Bunkeflostrand was estimated by applying the biomass method to the classified maps using a script in Python. The results showed that reed reduced wave heights the most when the water depth exceeded 0.5 m. In shallower water, high grass dampened the most. The relationship between water depth and vegetation height was especially important, where emergent vegetation dampened waves better. Over the salt meadows, the calculations showed wave height reductions between 65.6 % and 94.6 %, depending on transect and scenario. Compared to other studies, the biomass method tends to overestimate wave damping. For this reason, it is not recommended for use in design calculations. However, it is recommended to maintain a buffer zone of vegetation in front of dikes, both for the wave damping effect and for other ecosystem services that such zones provide.