The wide spatial and temporal coverage of remotely sensing images is an essential asset to analyze the morphological behaviour of fast-changing coastal environments such as estuarine systems. This paper investigates the reliability of intertidal topography mapping around the Authie Bay, a macrotidal estuarine system located on the northern coast of France. A Satellite-Derived Topography technique is developed by relating the green band reflectance of Sentinel-2 images to rapid variations in topography. This method is well suited to small sedimentary structures of the coastal zone with a 0.30 to 0.35 m height accuracy of the constructed Digital Elevation Model (DEM). For the more complex estuarine configuration, the waterline method was applied and resulted in the construction of DEMs with a height accuracy of 0.35 to 0.38 m. Video animations and records of Authie meander positions along transects are created from Sentinel-2 and Landsat satellite archives (1984–2020). These materials allow to highlight a sedimentation phase at the east side of the spit since 2015. It constrains the main channel towards the eastern bank, thus promoting coastal erosion. The monitoring of a severe erosion phase throughout 2019 shows a 130 m retreat of the coastline. Topographic map differentiation led to the detection of a sedimentation anomaly upstream of the bay, probably linked to this erosion event.

Preprint v3 submitted to a peer-review journal