Assessment of erosion and accretion rates along the Pacific coast of Panama

Coastal erosion is a global concern, with nearly a quarter of sandy beaches retreating at rates exceeding 0.5 m/yr and projections suggesting that half may disappear by 2100. Panama, despite its high vulnerability to sea-level rise and coastal flooding, lacks a standardized national assessment of shoreline change. This study quantifies erosion and accretion along 1349 km of the Pacific coast of Panama using Landsat satellite imagery and the Digital Shoreline Analysis System (DSAS) over a study period ranging from 20 to 24 years across seven coastal zones. Results show that 68% of the shoreline (913 km) is eroding, with intense erosion (−3 to −1 m/yr) the dominant category across more than 500 km. Zone-average median erosion rates range from −0.835 m/yr in Zone B (mangrove-fringed Montijo) to −1.840 m/yr in Zone G (Darién), and Zone A in the Gulf of Chiriqui recording the highest mean erosion rate (−4.209 m/yr), driven by extreme localized transects. Critical erosion hotspots include Pedasí, Punta Chame, Playa Farallón, and Playa Grande, while accretion is concentrated in sheltered embayments and in Zone G, where large river systems are inferred to sustain active sediment delivery to the coast, as indicated by the observed accretion pattern. Mean accreting EPR values cluster consistently between 1.511 and 2.861 m/yr regardless of wave exposure, while mean eroding EPR values span a far wider range across the same significant wave height gradient — a pattern consistent with sediment budget, rather than wave energy, being the primary control on shoreline change direction in this macrotidal tropical setting. The contrast between Zone F (low wave energy, extreme localized erosion, lowest accretion in the dataset) and Zone G (highest wave energy, sustained accretion consistent with fluvial sediment supply from the Darien river systems) strongly suggests that fluvial sediment supply governs net coastal behavior in the eastern Pacific sector, though direct river sediment monitoring is required to confirm this mechanism. Zone B, the most mangrove-fringed zone in the dataset, records the lowest erosion rates and narrowest EPR variability, consistent with mangrove-fringing providing morphodynamic buffering relative to adjacent exposed sectors. EPR uncertainty values ranged from ±0.569 to ±0.819 m/yr, and all zone-average EPR values exceed their respective uncertainty thresholds, confirming that the observed signals represent statistically robust shoreline change.