Morphodynamic Response to Low-Crested Detached Breakwaters on a Sea Breeze-Dominated Coast

• Main Authors: Alec Torres-Freyermuth, Gabriela Medellín, Ernesto Tonatiuh Mendoza, Elena Ojeda, Paulo Salles
• Format: Article
• Language: English
• Published: MDPI AG 2019-03-01
• Series: Water
• Subjects: beach morphodynamics; UAV flights; beach surveys; Reef Balls™; sand-filled geosystems
• Online Access: https://www.mdpi.com/2073-4441/11/4/635

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 Yucat&#225;n peninsula, is characterized by low-energy, high-angle waves, which drive a persistent (westward) alongshore sediment transport (<i>O</i>(10⁴) m³/year). High-resolution real-time kinematics global positioning system (GPS) beach surveys were conducted over a one-year period (2017&#8211;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&#8217; 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&#8482; modules, induced moderate beach changes and small erosion in down-drift areas owing to higher transmission coefficients. Measurements of LCDBs&#8217; freeboard height show that sand-filled geosystems&#8217; 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.