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Keywords = Authie estuary

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20 pages, 60853 KiB  
Article
Satellite-Derived Topography and Morphological Evolution around Authie Macrotidal Estuary (France)
by Philippe Bagot, Nicolas Huybrechts and Philippe Sergent
J. Mar. Sci. Eng. 2021, 9(12), 1354; https://doi.org/10.3390/jmse9121354 - 30 Nov 2021
Cited by 5 | Viewed by 2764
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Remote Sensing Advancements in Sustaining Coastal Zones)
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14 pages, 7884 KiB  
Article
Sand Net Device to Control the Meanders of a Coastal River: The Case of the Authie Estuary (France)
by Anh T. K. Do, Nicolas Huybrechts and Philippe Sergent
J. Mar. Sci. Eng. 2021, 9(12), 1325; https://doi.org/10.3390/jmse9121325 - 23 Nov 2021
Cited by 2 | Viewed by 2101
Abstract
The Authie estuary is characterized by an important southern sand spit and a northern shoreline subject to strong erosion due to the meandering of the coastal river. In order to reduce this erosion, a new soft coastal defence, namely the sand net device [...] Read more.
The Authie estuary is characterized by an important southern sand spit and a northern shoreline subject to strong erosion due to the meandering of the coastal river. In order to reduce this erosion, a new soft coastal defence, namely the sand net device (SND), has been implemented inside the Authie estuary. It consists of several nets assembled in an inverted V creating a porous structure and thus trapping sand as shoreline protection. However up to now, little proof has been provided on the explicit influence of this SND on the hydrodynamic pattern and associated morphodynamics. In this paper, field surveys of morphological developments combined with numerical modelling (Telemac-2D/3D) analyze the influence of the SND into flow pattern and morphodynamics. In situ monitoring clearly points out sedimentation around the SND and a deepening of the main channel. Modelling results show that, without SND, erosion is observed around its location. With a SND implemented, the velocity has been reduced and created a deviation in its direction by a circulation around the SND location. The impact area of the structure is around 500 m in both directions, upstream and downstream part. Full article
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