Browsing by Author "Senechal, Nadia"

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    SWASH-BASED WAVE ENERGY REFLECTION ON NATURAL BEACHES
    (2015) Almar, Rafael; Ibaceta, Raimundo; Blenkinsopp, Christopher; Catalán, Patricio; Cienfuegos Carrasco, Rodrigo Alberto; Trung Viet, Nguyen; Hai Thuan, Duong; Van Uu, Din; Lefebvre, Jean Pierre; Sowah Laryea, Wahab; Laibi, Raoul; Castelle, Bruno; Senechal, Nadia; Anthony, Edward J.
    Can wave reflection be remotely described from swash dynamics and the shoreface slope inversely from reflected waves? In this paper, we revisit the link between swash dynamics and reflection using contrasting field datasets: swell waves on steep and flat beaches and wind waves on an intermediate beach. Reflection ranges from less than 1% to up to 25%. Analyses are conducted from ~10-m depth directional wave spectra measurements, daily beach surveys and video swash measurements. Our results show that swash saturation can be linked to the offshore reflection cut-off frequency (shortest reflected waves) with a strong dependence on swash zone slope, underlining the importance played by swash processes in nearshore dynamics. Moving towards a more process-based approach, an ensemble-average analysis indicates that swash flow asymmetry and skewness are strongly linked to reflection.
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    Video-Based Detection of Shorelines at Complex Meso-Macro Tidal Beaches
    (2012) Almar, Rafael; Ranasinghe, Roshanka; Senechal, Nadia; Bonneton, Philippe; Roelvink, Dano; Bryan, Karin R.; Marieu, Vincent; Parisot, Jean-Paul
    Remote video imagery is widely used to acquire measurements of intertidal topography by means of shoreline detection, but, up to now, problems of accuracy were still encountered in the challenging case of energetic waves in nonuniform, meso macro tidal environments. Unique, simultaneous, video-based and global positioning system (GPS)-based measurements of shoreline were undertaken at Truc Vert (France), a beach with such characteristics. An innovative video method, referred to herein as the Minimum Shoreline Variability (MSV) method, was developed to cope with highly variable spatiotemporal shoreline properties. The comparison of video-based and GPS-derived shoreline data sets showed that using images averaged over short periods (30 s), rather than the traditionally used 10-min averaged images, significantly improved the accuracy of shoreline determination. A local video-derived, swash-based shoreline correction was also developed to correct for the MSV error, which was found to be linearly correlated to local swash length. By combining shorter time-averaged images and video derived local swash correction factors, the horizontal root mean square error associated with MSV shorelines was reduced to 1.2 m, which is equivalent to errors reported at more uniform, microtidal, and less-energetic beaches.