Holistic analysis of shoreline change and mudbank dynamics across the Guiana coastline

The Guiana coastline, stretching for 1500 km along the northeastern coastline of South America between the Amazon and Orinoco Rivers, is one of the most dynamic shorelines in the world. The frontage is characterised by a series of alongshore migratory, shore-attached mudbanks, with shoreline accretion and seaward expansion of mangrove vegetation during in-bank periods, followed by significant shoreline erosion during inter-bank phases. These coastal dynamics are of great concern to the nation states of Guyana and Suriname and the French overseas department of French Guyana where > 90% of the urban population live within the low elevation coastal zone.

Whilst considerable research has been undertaken along the Guiana coastline over the last four decades, the full determination of the dynamics of this long coastline remains challenging. Not all analyses have used sufficiently long temporal sequences of imagery to track at least one complete accretion-erosion cycle. Where high temporal resolution has been achieved, analysis has often been limited to one, and often only part, of the regional administrations.

This presentation provides the first ever analysis of rates of shoreline change across the entire Guiana coastline annually over a 35-year period (1987-2023). The seaward extent of mangrove forest or other coastal vegetation was selected as the shoreline proxy. This was extracted from Landsat multispectral 30 m resolution imagery using machine learning and image thresholding techniques. Annual shoreline change rates were measured at 200 m intervals over the 1500 km frontage, providing unprecedented insight into how the entire shoreline system has evolved.

This analysis discovered differences in the position, size, and speed of alongshore migration of nine mudbanks along the Guiana coastline, with mudbanks exhibiting either a graded or abrupt form of alongshore migration. Contrary to previous research, this analysis identified no evidence of a 30-year cycle in shoreline accretion – erosion across two extensive regions of the Guiana coastline: Saramacca, Suriname and Guyana. In both these locations, three other categories of landform were identified as affecting shoreline position: naturally migrating headlands, the presence of emplaced polders and sites of rapid accretion along anthropogenically modified coastlines. In addition, correlation analysis was conducted between shoreline change metrics, wave metrics derived from ERA5 reanalysis data, and climate indices including the North Atlantic Oscillation (NAO) and the El-Niño Southern Oscillation (ENSO). This analysis identified a statistically significant relationship between pan-Guiana shoreline position and the 18.6-year nodal cycle. However, at the landform scale, significant wave height and direction had the strongest statistical relationship with shoreline change. This analysis is supported with the release of a comprehensive pan-Guiana shoreline change dataset, facilitating future holistic research and management of the Guiana coastline.