VARIATIONS OF THE COASTLINE IN A MEDIUM PERIOD (1985-2017) OF A TROPICAL ISLAND: THE CASE OF SOURE (MARAJÓ - PARÁ/BRAZIL)

Abstract

The margins of Marajó Island, influenced by large estuaries (rivers Amazonas and Pará), are con- ditioned to constant morphological changes. This article shows the multitemporal dynamics of the coastline (1985-2017 - 32 years) and the quantification of the areas in accretion and erosion in the Northern Margin (Sector I), Cabo Maguarí (Sector II) and Eastern Margin (Sector III) of the Soure municipality. The method- ology included the acquisition of medium resolution satellite images LANDSAT 5 TM (bands 5, 4 and 3 - 1985) and LANDSAT 8 OLI (bands 6, 5 and 4 - 2017), orthorectified and georeferenced, with spatial resolu- tion of 30m. They were processed using the ArcToolbox tool. The visual interpretation of the images and the vectorization of the coastline were done in ArcMap, using the ArcGis 10.6 software. The overlapping of the vectors of the years 1985 and 2017 allowed the caCLulation of areas and rates. The results show the predom- inance of the accretion of the coastline. The under accretion totaled 25,382,783.18 m² ± 575.28 m² (4.72 m year-1) and mean linear advance of the coastline of 151.10 m. However, the eroded areas totaled 6,696,780.64 m² ± 575.28 m² (3.03 m year-1) and the mean linear retreat of the coastline was 97 m.