Abstract
The coast of French Guiana is characterised by the northwestward migration of large mud banks alongshore and by high concentrations of suspended particulate matter (SPM) resulting from the strong influence of the Amazon River outflow. Surface OLI SPM concentration, linked to the footprint of the subtidal part of mud banks due to resuspension and migration processes, was used to develop a method to estimate the location of this footprint. A comparison of the results from this method with those obtained by locating the limit of the wave damping, which characterises muddy coasts, revealed good performance of the method based on recurring SPM values. The migration rates of the mud banks in French Guiana were calculated according to the delimitation of their subtidal parts, and showed slightly higher values (2.31 km/year) than suggested by earlier studies. In comparison with other methods, the migration rate estimated using the method proposed within the framework of this study takes into account the variability of the shape of the subtidal part for the first time. It was also shown that the mud banks existing on the coastal area of French Guiana present two different shapes. Our results clearly demonstrate the advantage of ocean colour data to describe mud banks according to their subtidal part, delimited using the assessment of SPM temporal variability.
Highlights
As is the case along the 1500 km long coast between the mouths of the Amazon and Orinoco Rivers, the coastal waters of French Guiana are strongly impacted by the mud supply from the Amazon [1]
Even though high-resolution sensors are limited by their temporal resolution when compared to medium-resolution satellite data, this study shows for the first time the potential of the Landsat 8-OLI sensor to locate the subtidal part of the entire mud bank system of French Guiana using the method developed
This study illustrates for the first time the potential of high-resolution sensors, such as Landsat 8-OLI, for characterising the subtidal part of mud banks in the French Guianese coastal waters
Summary
As is the case along the 1500 km long coast between the mouths of the Amazon and Orinoco Rivers, the coastal waters of French Guiana are strongly impacted by the mud supply from the Amazon [1]. There may be 15 or more actively-translating mud banks between the Amazon and the Orinoco They are spaced out 15–25 km apart (interbank areas), migrate at velocities ranging from 1 to 5 km/yr, and are 5 m thick, 10 to 60 km long, and 20 to 30 km wide [6,8]. Transport on the inner shelf of these migrating mud banks has been mainly attributed to wind waves [9]. These waves interact with the subtidal part of the mud bank, composed of soft to fluid mud, at spatial and temporal scales defined by wavelength and period. Several studies have been carried out on wave energy dissipation in the world’s muddy areas; for example, mud banks on the shore of the Surinam and Guyana coasts are estimated to account for 88% to 96% wave energy dissipation [10,11,12]
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