Characteristics and dynamics of surfzone transverse finger bars

Patches of transverse finger bars have been identified in the surf zone of Noordwijk beach (Netherlands). They consisted of three to nine elongated accumulations of sand attached to the low-tide shoreline. The bars extended up to 50 m into the inner surf zone, had an oblique orientation with respect to the shore-normal, and were quasiregularly spaced in the alongshore direction.Postprint (published version

Nearshore oblique sand bars

The coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence. It is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars. The bars can be down-current oriented or up-current oriented, which means that the offshore end of the bar is shifted down-current or up-current with respect to the shore attachment. In the limit of strong current compared to wave orbital motion, very oblique down-current oriented bars are obtained with a spacing of several times the surf zone width. When wave orbital motions are dominant, systems of up-current oriented bars and crescentic/down-current oriented bars appear with spacings of the order of the surf zone width. The latter feature consists of alternating shoals and troughs at both sides of the break line with the inner shoals being bar-shaped and oblique to the coast. The growth (e-folding) time of the bars ranges from a few hours to a few days and it is favored by constant wave conditions. The range of model parameters leading to growth corresponds to intermediate beach states in between the fully dissipative and the fully reflective situations. Preliminary comparison with field observations shows qualitative agreement.Peer ReviewedPostprint (published version

¿Cómo afectará el cambio climático a las playas de arena?

Aunque ya sabemos que la subida del nivel del mar hará retroceder la línea de costa de las playas de arena, necesitamos modelos matemáticos para cuantificarlo y poder validar potenciales medidas de mitigación. Los avances de los últimos años demuestran que se puede alcanzar suficiente capacidad de predicción, controlando las incertidumbres. Además, se está trabajando en conseguir fórmulas más precisas del transporte de sedimentos, obtener buenos datos observacionales y seguir mejorando los modelos. Todo esto nos permitirá actuar con más conocimiento para proteger estos entornos tan valiosos y vulnerables.Postprint (published version

Characteristics and dynamics of crescentic bar events at Castelldefels beach

Crescentic sand bars have been studied intensively in the last decades, resulting in good knowledge of some of their characteristics, but the processes behind their formation and destruction are not yet clear. This study aims to increase our understanding of the dynamics of crescentic bars at an open, dissipative Mediterranean beach (Castelldefels, 20 km southwest of Barcelona). Their dynamics have been analysed using a 4.25-year dataset of video images. The crescentic bar events have been identified using visual analysis, including the formation and destruction moments. The results show that crescentic bars hardly occurred when the sandbar was located close to the beach, whilst they developed often when the sandbar was further offshore. Wave conditions during crescentic bar formation were low- to intermediate-energy waves with both oblique and shore-normal angles of incidence. Sandbar straightening was preferably observed for oblique waves (of both intermediate and high energy). The alongshore wavelength and cross- shore amplitude of the crescentic bars have been also quantified, giving some 245 m and 10 m on average, respectively.Peer ReviewedPostprint (published version

Climate change impact on beaches

En aquest Research Café es presenten projectes on la tecnologia es posa al servei dels mars i els oceans, i que estan lligats amb els objectius ODS Vida Submarina i Acció pel clima.Objectius de Desenvolupament Sostenible::13 - Acció per al ClimaObjectius de Desenvolupament Sostenible::14 - Vida Submarin

UBathy: a new approach for bathymetric inversion from video imagery

A new approach to infer the bathymetry from coastal video monitoring systems is presented. The methodology uses principal component analysis of the Hilbert transform of video images to obtain the components of the wave propagation field and their corresponding frequency and wavenumber. Incident and reflected constituents and subharmonics components are also found. Local water depth is then successfully estimated through wave dispersion relationship. The method is first applied to monochromatic and polychromatic synthetic wave trains propagated using linear wave theory over an alongshore uniform bathymetry in order to analyze the influence of different parameters on the results. To assess the ability of the approach to infer the bathymetry under more realistic conditions and to explore the influence of other parameters, nonlinear wave propagation is also performed using a fully nonlinear Boussinesq-type model over a complex bathymetry. In the synthetic cases, the relative root mean square error obtained in bathymetry recovery (for water depths 0.75m¿h¿8.0m) ranges from ~1% to ~3% for infinitesimal-amplitude wave cases (monochromatic or polychromatic) to ~15% in the most complex case (nonlinear polychromatic waves). Finally, the new methodology is satisfactorily validated through a real field site video.Postprint (published version

Modelling long-term morphodynamic evolution of mega-nourishments

Peer ReviewedPostprint (published version

Cambios morfológicos en barras sumergidas de playas artificiales

Se analizan los cambios morfológicos que experimentan las barras sumergidas de dos playas artificiales de la ciudad de Barcelona durante un período de tres años. Los desplazamientos transversales de las barras alcanzaron más de 50 m, con tasas máximas de migración hacia mar de 5 m/día y hacia tierra de 3 m/día que ocurren asociadas a determinados temporales. La configuración en planta de la barra puede estar estrechamente relacionada con la línea de costa, especialmente cuando se desarrollan dos cúspides en una de las playas que favorecen la generación de una configuración «crescéntica» (oscilante! de la barra durante más de un año. Aunque se trata de playas artificiales, el comportamiento de las barras es equivalente al descrito en playas naturales

The responses of artificial embayed beaches to storm events

Peer ReviewedPostprint (published version

Nearshore sand bars

This research has been funded by the Spanish government through the research projects CTM2012-35398 (cofunded by FEDER, U.E.) and CTM2015-66225-C2-1-P (MINECO/FEDER).This review summarizes the morphological characteristics and dynamics of nearshore sand bars observed in the surf zone of sandy beaches worldwide, with length scales ranging from tens to hundreds of meters and time scales ranging from hours to weeks. They include shore-parallel bars (straight and crescentic) and transverse bars of different types. Furthermore, the present knowledge on the physical processes behind their formation and development is discussed.Peer ReviewedPostprint (published version