The effect of mudbank morphometrics and coastal morphology on multi-decadal coastline changes in the Guianas

Understanding the factors that drive coastline evolution is complex, yet essential for managing coastal environments. For Guyana, Suriname and French Guiana, coastline changes can shed light on the relative contributions of alongshore migrating subtidal mudbanks compared to human or climate induced changes. This study addresses the impact of mudbank morphometrics on the Guianas' coastline morphology from 1985 to 2023, using Landsat’s optical earth observation data. We found that during mudbank phases, the coastline advanced significantly, averaging 4 to 40 m/yr, while in their absence, retreat averaged 16 to 21 m/yr. Relative low migration rates of 1 - 1.2 km/yr combined with the characteristics of mudbanks, some extending up to 8km offshore, explained part (R2 = 0.2, P <0.05) of the coastline's progradation and retrogradation. This computed frequency of mudbank occurrence, linking the position and shape of a mudbank, thus proves to be a key factor controlling the number of years a coastal section is protected and accretion is facilitated. Understanding these dynamics is crucial for future coastal protection efforts and ecosystem restoration. Our findings also highlight where coastlines do not benefit from mudbank-induced accretion, possibly due to irreversible changes in the system, emphasizing the need for tailored coastal management strategies.