Understanding the coastal variability at Norte beach, Portugal

Silva AN, Taborda R, Antunes C, Catalão J, Duarte J
Journal of Coastal Research, Special Issue No. 65, pp. 2173-2178, DOI: 10.2112/SI65-367.1

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Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazaré submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results suggest that Norte beach variability depends mainly on longshore drift gradients rather than with cross-shore sedimentary transfers. The intense wave refraction over the canyon head, associated with the westerly swell waves, generates a sedimentary convergence at the centre of the beach promoting the increase of the beach curvature, while, northern and/or short waves (more frequent in summer) tend to linearize the beach. This work contributed with valuable information about the sedimentary dynamics of the Norte beach and showed that this site is a suitable candidate to evaluate longshore drift from shoreline changes.