Ria Formosa barrier island shorelines and long-term cross-shore rates between 1952 and 2014

Published: 04-11-2020| Version 1 | DOI: 10.17632/96sfy77s3z.1
Contributors:
Katerina Kombiadou,
Ana Matias,
Susana Costas,
A. Rita Carrasco,
Theocharis Plomaritis,
Óscar Ferreira

Description

These are results of the EVREST (Evolution and Resilience of Barrier Island Systems) project. http://evrest.cvtavira.pt/ Details on the analysis can be found in https://doi.org/10.1016/j.geomorph.2019.07.006 The morphological evolution analysis was based on aerial photographs that cover the period from 1952 to 2014. Distinct geomorphological units were digitised and analysed, using four boundaries: a) The ocean-side coastline (ca. Mean High Water Level: MHWL). The proxies used were the upper debris line or the beach scarp, in cases of debris absence. b) The dune line (ca. Mean Higher High Water Level: MHHWL), using the ocean-side limit of dune vegetation, as proxy for the position of the foredune foot. c) The backbarrier coastline in the lagoon-side (ca. MHWL). In backbarrier stretches with perched marshes, the limit between the upper-marsh vegetation and the barrier/dune was used, identified by the transition to bushy (more rugose, darker) vegetation. In backbarrier beaches, the debris line or beach scarp/dune limit (if no debris was present) were used. d) The marsh-edge line (transition from marsh to tidal flat; ca. MWL). In cases of vegetated tidal flats (e.g. seagrasses), the boundary between emergent and submerged vegetation was used, identified by differences in colour and texture. Otherwise, the edge of the marsh vegetation was mapped. The boundary lines of these 4 geomorphological units (1952-2014) are given in EVREST_Coastlines.kmz Weighted Linear Regression (WLR) cross-shore rates of these boundary lines (going from from seaward to landward a) ocean-side coastline, b) dune line, c) backbarier coastline and d) marsh-edge line) for 1952-2014 are given in EVREST_WLR_rates.kmz Weighted Least Squares Regression was performed on the entire dataset, using the Digital Shoreline Analysis Tool that defines the shoreline changes along transects, cast perpendicular to a reference baseline. Weighted Linear Regression (WLR) rates were preferred over simple linear ones, as they are weighted towards more accurate coastline positions. Coastline uncertainty (total position error) was assessed as the sum of squares of all measurement errors.

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Results of the EVREST (Evolution and Resilience of Barrier Island Systems) project. http://evrest.cvtavira.pt/ Details on the analysis can be found in https://doi.org/10.1016/j.geomorph.2019.07.006