Modelling Nature III

Previous studies have shown that wave height attenuation positively correlates with the standing biomass of saltmarshes meadows (Maza et al., 2022) highlighting the crucial role played by this variable that can be used to estimate the ecosystem wave damping capacity without using calibration coefficients. In addition, this variable has been already characterized for many ecosystems and it can be estimated by aerial images and remote sensing techniques. However, this new approach has not been extended to conditions where waves and currents act simultaneously. To further explore this new approach based on the ecosystem standing biomass, a new set of experiments using real vegetation with contrasting morphology and biomechanical properties, and subjected to different combinations of waves and currents, is proposed. The obtained standing biomass-attenuation relationship will help to quantify the expected coastal protection provided by different vegetated ecosystems under the combined effect of waves and currents.

The first worldwide attempted large-scale test on coastal salt marsh under the action of extreme design hydrodynamic conditions will be carried out in January 2023. At the conference, the preliminary results in terms of wave attenuation, erosion and removed biomass will be presented as well as the procedures to harvest and maintain the vegetated soil boxes collected in the field and used to realise the marsh in the wave flume.

Living shorelines are a form of Nature-based Solutions, which incorporate natural elements that provide flood and erosion risk management benefits. Climate change impacts are increasingly motivating communities in Canada to consider incorporating living shorelines in coastal protection schemes. Few studies have quantified wave attenuation by real saltmarsh vegetation in large-scale laboratory facilities, particularly for species native to the east coast of Canada. There is a knowledge gap on how seasonality affects wave attenuation by saltmarsh vegetation and how attenuation varies from the lower marsh to the higher marsh depending on species-specific plant traits. To bridge this gap, experiments were performed in a 5-m wide, 5-m deep and 120-m long wave flume facility. Preliminary results show that different saltmarsh species resulted in different degrees of wave attenuation. The experiments are still ongoing with the final test series expected to be run in late October 2023. 

Riparian forests in front of dikes can dampen incoming waves and thereby contribute to flood safety. In real-scale flume experiments with live pollard willow trees (forming a 40-m-long forest), it was observed that during storm conditions, a maximum reduction of 20 % in incoming wave height could be achieved. Notably, this amount of wave damping occurred at a water depth of 3 meters, aligning with the section of the trees with the maximum frontal-surface area. For a larger water depth, measured wave damping however declined. This is potentially partly caused by the frontal-surface area and branch rigidity decrease along the height of the willow trees, potentially leading to less wave damping by the forest when subject to large waves at higher water levels. With this perspective, 1:10 scale flume tests were conducted with simplified branch mimics in the form of conical shapes.