Resumen

CASTILLO-CHINCHILLA, Maikol et al. Spatial and Multitemporal Variation of the Coastline in Sandy Beaches of the South Caribbean Region of Costa Rica. Invest. Geog [online]. 2023, n.111, e60726.  Epub 04-Mar-2024. ISSN 2448-7279.  https://doi.org/10.14350/rig.60726.

Multiple factors interrelate to define the boundary between the sea and the mainland. However, this demarcation has undergone significant variations in the coastline in recent decades due to the various effects of climate change, the deterioration of coral barriers, and the construction of containment infrastructures, among others. The objective of the present research was to analyze the spatial and multitemporal variations of the coastline in sandy beaches of the South Caribbean region of Costa Rica. The study area was delimited between the center of the Limón province (10°00’29” N; 83°15’06 W), and the mouth of the Sixaola River in the Talamanca canton (09°25’40” N; 83°01’20” W). This area was divided into two sections based on beach sand biogenesis and the irregularity features of the coast. The Northwest sector, from CSA1 to CSA3, comprised from the center of the Limón province to the right bank of the Estrella River (9°47'39.26 N; 82°53'37.24 W"). The Southeast, from CSB1 to CSB7, covered from the left bank of this river to the mouth of the Sixaola River (9°34'16.25” N; 82°33'59.51” W). In each of these ten sectors, we determined the variation of the coast using aerial images (1960, 1976, 1998, 2005) and satellite images (RapidEye for 2011, WordView 2 and 3 for 2018, and Sentinel 2A for 2023). Using the Digital Shoreline Analysis System (DSAS 4.3) tool for ArcGIS, we produced 1547 orthogonal transects separated by 50 m, considering as baseline the 200-meter continental protection limit established by the Law on the Land-Maritime Zone of Costa Rica. The spatial and temporal displacement of the coastline was estimated with the End Point Rate (EPR) statistic and the Net Shoreline Movement (NSM) for the past 63 years. The displacement of the coastline was verified using a matrix of 700 georeferenced points obtained from in-situ monitoring over the past decade (2012-2022) in nine beaches of these sectors This information was used to perform a cluster analysis (hot spots) using the Getis-Ord GI* algorithm (QGIS). This study evidenced that, between 1960 and 2023, 70.14 % of the transects maintained erosive rates, which were concentrated in the Cahuita National Park (-1.63 m/year), Puerto Viejo-Cocles (-0.37 m/year), Manzanillo (-2.07 m/year), and Gandoca (-1.74 m/year). Coastline displacements by accretion occurred mainly in areas close to or influenced by rivers such as Banano, Estrella, and Sixaola, at average rates ranging from 8.01 m/year to 76.14 m/year. The NSM net balance between 1960 and 2023 varied from moderate to stable, both due to erosion and accretion, reaching the most critical coastal loss values to the southeast of the SC, in areas including Puerto Vargas, Manzanillo, and Gandoca. On the other hand, the analysis of hot spots revealed the consistency between EPR and NSM in the areas showing the greatest coastal displacement due to erosion. This behavior was also confirmed by analyzing the topographic profiles of these sandy beaches; they maintain semi-reflective and reflective patterns, evident by changes in width and slope angle. It is concluded that the sandy beaches of the South Caribbean have been impacted mainly by erosive processes over the past 63 years, which coincide with the behavior from the cluster analysis and topographic profiles. This trend of spatial and multitemporal displacement of the coastline due to erosion will cause medium-term impacts that will increase the vulnerability and affectation of coastal ecosystems and human communities in this stretch of coastline.

Palabras llave : climate change; erosion; accretion; sediments; infralittoral.

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