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UBC Theses and Dissertations

Nature-based flood protection : the contribution of tidal marsh vegetation to wave attenuation at Sturgeon Bank Forysinski, Krista


Coastal communities are at an increasingly elevated risk of coastal flooding from storm waves, storm surge, and sea level rise due to climate change. The risk of coastal flooding means that coastal communities are actively planning and preparing for future flood risk reduction. While some communities are using traditional dike and protect strategies, others are exploring alternative nature-based flood protection solutions that maximize benefits for communities and ecosystems. Tidal marsh ecosystems can act as a buffer to flooding by dissipating wave energy and reducing wave heights, even in storm conditions. Many studies have investigated the potential of foreshore marshes to attenuate wave energy and to reduce wave loads on protective structures like dikes. However, there have been no similar studies focused on Canada and the Fraser River delta, where low-lying coastal communities are exposed to flood hazard and are also bordered by expansive tidal marshes. Using a case study of Sturgeon Bank near Richmond, British Columbia, Canada, this thesis evaluates the wave attenuation capacity from vegetation in a varied brackish foreshore marsh, considering seasonal differences in vegetation conditions as well as changes in vegetation extent from the 1980s to present. Vegetation and wave height data were collected along transects at Sturgeon Bank in summer and winter seasons, and historical vegetation data were gathered from previous field surveys. These data were used in the SWAN (Simulating WAves Nearshore) wave model to evaluate the wave energy dissipation by vegetation at Sturgeon Bank under a variety of conditions. Based on the modeled results, wave attenuation from vegetation makes up nearly one third of the total wave energy dissipated in winter, and two thirds of total wave energy dissipated in summer under normal wave conditions. Most of the wave energy (>80%) is dissipated in the first 100 metres of marsh vegetation. Even during storm conditions, current vegetation dissipates up to 20% of the total wave energy and acts as a buffer for flooding. This research provides evidence to inform future policy and planning for nature-based flood risk reduction, and adds support for the conservation of tidal marshes in the Fraser River delta.

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