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

Alec Torres-Freyermuth,Paulo Salles,Ernesto Mendoza,Elena Ojeda,Gabriela Medellín

doi:10.3390/w11040635

Alec Torres-Freyermuth, Paulo Salles + Show 3 more

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https://doi.org/10.3390/w11040635

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Journal: Water	Publication Date: Mar 27, 2019
Citations: 13	License type: CC BY 4.0

Affiliation: Universidad Nacional Autónoma de México

Abstract

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.

Highlights

Sandy beaches and their associated front dunes provide both natural coastal protection against storm events and a habitat for different marine and terrestrial species
Horizontal coordinates were referenced to the World Geodetic System of 1984 (WGS 1984) using the Universal Transverse Mercator coordinate system (UTM)Zone 16 N, and the vertical values were referenced to mean sea level using Gravimetric Mexican Geoid version 2010 (GGM10)
Environmental conditions, structure variability, and anthropogenic actions play an important role in beach morphodynamics

Summary

Introduction

Sandy beaches and their associated front dunes provide both natural coastal protection against storm events and a habitat for different marine and terrestrial species. Beach erosion due to either natural or anthropogenic processes may cause environmental and economic impacts in the coast. This is relevant in low-lying coastal areas, which are prone to climate change impacts, such as sea level rise and increasing storm activity [1]. Despite the increasing popularity of soft engineering [2,3], mixed soft–hard systems [4], and eco-engineering [5] solutions, so-called low-crested detached breakwaters (LCDBs), such as submerged rubble mounds, are popular in many locations around the world (e.g., [6]). Previous works have extensively investigated the stability, performance, and ecological impact of rubber-mound (conventional) LCDBs [8,9,10,11], but less

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