River, lake and ocean shorelines are dynamic environments that change over varying time scales driven by a large number factors including lithological composition, wave action, currents, slope angles and tidal influences to name a few. In addition, anthropogenic factors increasingly impact the morphology of coasts as well as lake and river banks either directly, through constructions and sediment deposition/removal, or indirectly, through actions driving climate change. Mapping the dynamics of riverbeds, lakes and coasts is key to understanding current erosion rates and future erosion potential. Risk mitigation strategies require the information for informed mitigation actions.
EO can provide essential historical maps of coastlines during the past 20-30 years as well as quantitative maps of coastal accretion and erosion processes. Changes to shorelines due to urban development and other processes can be detected. For best results, historical and current imagery with a spatial resolution of better than 10m is preferred. This can very well be addressed using historical SPOT and current Sentinel-2 data. Moreover, information on water level height and currents (altimeter data) can be integrated from available sources including the ESA Rivers and Lakes initiative.
SPOT 1-4 images are needed for meaningful mapping results predating the Landsat era. Erosion rates typically vary significantly across longer time scales and due to the complex interplay of erosion driving factors, future scenarios are not readily derived from past trends.
The Sentinel program offers a new image foundation readily available for the mapping of riverbank and coastal dynamics. With time, monitoring activities can increasingly profit from the growing archive of Sentinel 2 data with high revisit frequencies.