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

Abstract

The Guiana coastline, stretching for 1500 km between the Amazon and Orinoco Rivers in South America, is one of the most dynamic shorelines in the world. The shoreline is characterised by alongshore migratory, shore-attached mudbanks, with shoreline accretion and mangrove colonisation during in-bank periods, followed by significant shoreline erosion during interbank phases. While considerable research has been undertaken along the Guiana coastline, not all analyses have used sufficiently long temporal sequences of imagery to track at least one complete accretion–erosion cycle and analysis has often been limited to a localised region. To address these concerns, this paper provides the first ever analysis of shoreline change across the entire Guiana coastline annually over a 35-year period (1988–2023). Using the seaward extent of mangrove forest extracted from Landsat multispectral satellite imagery as a proxy for shoreline position, annual rates of shoreline change were measured at 200-m intervals along the 1500-km shoreline, providing new insights into the evolution of the entire shoreline system. This analysis identified nine mudbanks migrating alongshore at rates of between 0.26 and 1.38 km year⁻¹, lower than previously cited values of 0.9–5 km year⁻¹. These lower rates challenge the traditionally accepted 30-year oscillatory model for this coastline, instead suggesting a minimum 40-year minimum periodicity. Furthermore, and also contrary to previous research, this analysis identified no evidence of a cycle in shoreline accretion—erosion across two extensive regions of the Guiana coastline: Saramacca in Suriname and the entire coastline of Guyana. In these locations, other landforms affected shoreline position: naturally migrating headlands, emplaced polders and sites of rapid accretion along anthropogenically modified coastlines. Correlation analysis was conducted between shoreline change metrics, wave metrics and climate indices including the North Atlantic Oscillation and the El Niño Southern Oscillation. At the landform scale, significant wave height and direction had the strongest statistical relationship with shoreline change. These findings revise understanding of mudbank-driven shoreline dynamics and highlight the need for long-term observations for coastal monitoring and management.