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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).

Abstract. Thirty-year time series of hindcast wave data were analysed for 10 coastal locations along the eastern Mexican coast to obtain information about storm events occurring in the region, with the goal of examining the possible presence of interannual trends in the number of storm-wave events and their main features (wave height, duration and energy content). The storms were defined according to their significant wave height and duration, and the events were classified as related to either tropical cyclones or Norte events. The occurrence and characteristics of both types of events were analysed independently. There is no statistically significant change in the number of storm-wave events related to Nortes or their characteristics during the study period. However, there is a subtle increase in the number of events related to tropical cyclones in the western Caribbean region and a more evident increase in wave height and energy content of these events.

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Low-crested detached breakwaters (LCDBs) have been widely employed as a mitigation measure against beach erosion. However, only a few studies have assessed their performance in sea-breeze-dominated environments. This work investigates the beach morphodynamics behind LCDBs deployed on a micro-tidal sea-breeze-dominated beach. The study area, located in the northern Yucatán peninsula, is characterized by low-energy, high-angle waves, which drive a persistent (westward) alongshore sediment transport (O(104) m3/year). High-resolution real-time kinematics global positioning system (GPS) beach surveys were conducted over a one-year period (2017–2018) to investigate the performance of LCDBs at three sites. Moreover, unmanned aerial vehicle flights were employed to evaluate far-field shoreline stability. Field observations revealed a distinct behavior in the three study sites, dependent on the breakwaters’ transmission characteristics, geometry, stability, and shoreline orientation. Impermeable LCDBs, made of sand-filled geosystems, induced significant beach accretion (erosion) in up-(down-)drift areas. On the other hand, permeable LCDBs, made of Reef Ball™ modules, induced moderate beach changes and small erosion in down-drift areas owing to higher transmission coefficients. Measurements of LCDBs’ freeboard height show that sand-filled geosystems’ breakwaters presented a significant loss of sand during the study period, which explains the unexpected beach morphodynamic response on the lee side of the structure. Observations suggest that the study area is highly sensitive to the presence of LCDBs with low transmissivity.

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