Assessment of wave attenuation over salt marshes on the East coast of England.
Supervisor: Ivan Haigh (U Southampton)
Nature-based Solutions (NbS) are an effective tool to address contemporary societal challenges such as coastal flooding. They employ ecosystem services derived from natural features to solve relevant issues to communities all over the world. One of the most common ecosystems used in coastal protection projects are salt marshes, which are a valuable resource that has been shown to save millions of pounds in terms of avoided damage. Although there is extensive literature illustrating the effectiveness of salt marshes for wave attenuation, specially under storm surge conditions, there are still knowledge gaps hampering the mainstreaming of NbS. The lack of monitoring data before and after the implementation of NbS projects is often reported in scientific publications. In this context, the overall aim of this study was to assess how salt marshes attenuate wave energy and thus function as a nature-based solution for flood protection. To achieve this, two methods were employed: a GIS toolbox (WATTE) and a numerical model (XBeach). The first one requires little input, and it is less complex than the latter, which requires a more detailed dataset with bathymetry and wave heights information. The results from both methods were compared and a brief evaluation of coastal flood risk management frameworks is presented to assess the applicability of different outputs to such frameworks. This study concluded that both methods are reasonable to estimate wave attenuation, but its application depends on the purpose of the end user and level of detail required. The coastal flood risk management framework selected as the most compatible with the outputs from WATTE and XBeach includes three main phases: visioning, backcasting, and quantifying and selecting. Given its limitations, WATTE is recommended to support the identification of salt marshes that can be used as a protective feature during the backcasting phase. XBeach can be employed in the same stage if data inputs are assumed or estimated, but it can also be used for quantifying and selecting the final alternative in case field data are available. Both methods were shown to be effective; however, the safest recommendation prior to the implementation of a NbS project is to verify in-situ characteristic if the remote methodologies are correct and will meet the desired goals that were initially established.