Dynamics of single-barred embayed beaches

Abstract

Keywords:subtidal sand bar nearshore morphodynamics video imagery artificial beach Barcelona MediterraneanThe dynamics of single submerged sandbars of two artificial embayed beaches (La Barceloneta and Bogatell, Barcelona, NW Mediterranean) has been studied with a video-recorded data set of 4.3 years. The alongshoreaveraged cross-shore migration, the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions, alongshore sediment transport and shoreline variability. In general, the submerged bars follow the general cyclic morphological behaviour observed in natural beaches, switching among the four intermediate morphodynamic states, but the studied beaches can be arrested during long periods of low wave conditions. The dominant up-state transition in Barcelona beaches during storms is the transition toward the rhythmic bar and beach state, the complete morphodynamic reset (longshore bar and trough state) only occurring during extreme wave events. The cross-shore migration of bars is dominated by the weekly and interannual components. The interannual component shows an onshore bar migration trend at both beaches, in contrast with the net offshore migration observed in multibarred open beaches. Bar disposition is located progressively seaward in the dominant alongshore transport direction (i.e., oblique with respect to the shoreline). At La Barceloneta beach, shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found, suggesting that alongshore transport can play a significant role in barline orientation. Finally, bar sinuosity increases during eastern storms in both beaches. This indicates that the formation of crescentic bars occurs for approximately shore-normal waves. Some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves (beach indentation).

Morphological response and coastal dynamics associated with major storm events along the Gulf of Lions Coastline, France

“…Such a relationship between beach change and nearshore morphology is widely described in the literature (see for example McNinch, 2004;Castelle et al, 2007;Hequette and Aernouts, 2010), but further analysis of the hydrodynamics/morphology interactions is required to fully understand the longshore variability of morphological responses. In very similar hydrodynamic environments of the Mediterranean Sea, several authors have recently investigated the morphodynamics of nearshore morphology in natural (Ferrer et al, 2009;Armaroli and Ciavola, 2011) or urbanised beaches (Ojeda et al, 2011), with long term and high frequency datasets. Their observations on microtidal sites suggest that even if the morphodynamics of the nearshore bars and their patterns are largely storm driven, the modal alongshore morphology of a particular site (number of bars; large scale patterns) very often remains stable over years, or evolves extremely slowly.…”

Observations on sandbar behaviour along a man‐made curved coast

“…For shoreline datasets, for example, interannual (Ojeda et al. , ; Ranasinghe et al. , ), seasonal Harley et al.…”

“…() and Ojeda et al. () reported on the rotation of a sandbar due to longshore differences in 2D behaviour, similar to beach rotation (e.g. Harley et al.…”

“…, ; Ojeda et al. , ). The spatial variability herein received minor attention, especially bar behaviour at daily to seasonal timescales.…”

Quantifying Nearshore Morphological Recovery Time Scales Using Argus Video Imaging: Palm Beach, Sydney and Duck, North Carolina

“…Over the last three decades, a considerable amount of research effort has gone into understanding the morphodynamic processes governing the upstate/downstate transitions between beach states (as defined by Wright and Short, 1984), using field observations (Wright et al, 1985;Brander 1999), ARGUS video imaging (Lippmann andHolman, 1990;Ranasinghe et al, 2004, Turner et al 2007Ojeda et al, 2011;Price and Ruessink, 2011), and numerical modelling (Damgaard et al, 2002;Reniers et al, 2004;Drønen and Deigaard, 2007;Calvete et al, 2007;Smit et al, 2008;Castelle et al, 2012). However, to date, there has been no concerted research effort focussing specifically on the important issue of nearshore morphological recovery time scales.…”