Foreshore Assessment using Space Technology

Abstract

FORESHORE ASSESSMENT USING SPACE TECHNOLOGY. Vegetated foreshores and floodplains provide important ecosystem services. These include benefits for coastal defence: the foreshores attenuate waves, enhance sedimentation and reduce erosion, mitigating flood risk. At present, this function of wetland ecosystems is hardly incorporated in coastal defence schemes. Yet considering foreshores and floodplains in water safety assessments and in levee design can result in considerable cost reductions for flood risk management. In the EU-funded project FAST (Foreshore Assessment using Space Technology, 2014-2018), we aim to develop a GMES/Copernicus downstream service, combining Sentinel satellite data and in situ data to integrate the functioning of wetlands in flood risk management strategies. Sentinel data will be used to retrieve relevant biophysical parameters to characterise the foreshore, such as the morphology/topography of the foreshores, the density/biomass and type of vegetation, and the sediment type. Because of their location at the dynamic interface of land and water, foreshores and floodplains pose particular challenges for satellite observation and analysis, both regarding spatial and spectral resolution (due to the large environmental gradients and heterogeneity) and regarding temporal resolution (due to the large temporal variation as a result of, for example, tidal inundation). Information on some key variables is not readily available, and applicability of some relevant biophysical parameters and indicators developed for the terrestrial realm (such as Leaf Area Index, NDVI) remain to be tested for the characterisation of foreshores. The advent of the superspectral Sentinel-2 MSI opens up the potential to detect such characteristics from a spaceborne platform in a consistent way, based on an appropriate spectral, spatial and temporal resolution, with substantial (regional) coverage. However, a thorough assessment is required to optimize and validate retrieval schemes for the spatial characterisation of foreshores. At eight case-study sites across Europe (Spain, Romania, United Kingdom and the Netherlands), ground referencing will be executed to aid the retrieval of information from Sentinel imagery. Validation includes measurements of sediment type and vegetation density/biomass and hyperspectral reflectance of vegetation types. The in situ and remote sensing data will be combined with measurements on wave attenuation and erosion/deposition regimes. The results will provide insight in forshore stability and in the buffering function of foreshores and floodplains. From the collected data general relationships between foreshore and floodplain characteristics and flood risk mitigation properties will be derived. These will be implemented in a GIS based tool for integrating wetlands into cost efficient and safe flood risk management strategies.