Effects of Roughness Loss on Reef Hydrodynamics and Coastal Protection: Approaches in Latin America (original) (raw)
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1 MORPHODYNAMICS OF A CARIBBEAN BEACH FRINGED BY A CORAL REEF Amaia Ruiz de Alegria-Arzaburu 1
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The morphological response of two adjacent beaches, on the Mexican Caribbean coast, exposed to the same offshore wave climate is compared, where one of the beaches is fringed by a coral reef and the other is not. Detailed topographic and bathymetric measurements were collected from 2007 to 2011using a differential GPS and double-frequency echo-sounder. Offshore waves were continuously measured by the NOAA 42056 directional buoy, and nearshore waves were measured from May to September 2007 using an acoustic wave and current profiler to validate the use of offshore waves in the analysis of beach morphodynamics. Investigations showed that the beach with the fringing coral reef was the more stable under the same offshore energetic wave conditions of different directions. The implications of the fringing reef on the local hydrodynamics and energy dissipation were evaluated with the SWAN third-generation spectral wave model. The model was first validated with wave measurements collected a...
Influence of reef geometry on wave attenuation on a Brazilian coral reef
Geomorphology, 2016
This study presents data from field experiments that focus on the influence of coral reef geometry on wave transformation in the Metropolitan Area of Recife (MAR) on the northeast coast of Brazil. First, a detailed bathymetric survey was conducted, revealing a submerged reef bank, measuring 18 km long by 1 km wide, parallel to the coastline with a quasi-horizontal top that varies from 0.5 m to 4 m in depth at low tide. Cluster similarity between 180 reef profiles indicates that in 75% of the area, the reef geometry has a configuration similar to a platform reef, whereas in 25% of the area it resembles a fringing reef. Measurements of wave pressure fluctuations were made at two stations (experiments E1 and E2) across the reef profile. The results indicate that wave height was tidally modulated at both experimental sites. Up to 67% (E1) and 99.9% (E2) of the incident wave height is attenuated by the reef top at low tide. This tidal modulation is most apparent at E2 due to reef geometry. At this location, the reef top is only approximately 0.5 m deep during mean low spring water, and almost all incident waves break on the outer reef edge. At E1, the reef top depth is 4 m, and waves with height ratios smaller than the critical breaking limit are free to pass onto the reef and are primarily attenuated by bottom friction. These results highlight the importance of reef geometry in controlling wave characteristics of the MAR beaches and demonstrate its effect on the morphology of the adjacent coast. Implications of differences in wave attenuation and the level of protection provided by the reefs to the adjacent shoreline are discussed.
Coral Reef Geometry and Hydrodynamics in Beach Erosion Control in North Quintana Roo, Mexico
Frontiers in Marine Science, 2021
Coral reefs are increasingly recognized for their shoreline protection services. The hydrodynamic performance of this ecosystem is comparable to artificial low-crested structures often used in coastal protection, whose objective is to emulate the former. Coral reefs also provide other important environmental services (e.g., food production, habitat provision, maintenance of biodiversity and social and cultural services) and leave almost no ecological footprint when conservation and restoration actions are conducted to maintain their coastal protection service. However, studies have focused on their flood protection service, but few have evaluated the morphological effects of coral reefs through their ability to avoid or mitigate coastal erosion. In this paper, we investigate the relation between shoreline change, reefs’ geometry and hydrodynamic parameters to elucidate the physics related to how the Mesoamerican Reef in Mexico protects sandy coastlines from erosion. Using numerical ...
MORPHODYNAMICS OF A CARIBBEAN BEACH FRINGED BY A CORAL REEF
Coastal Engineering Proceedings, 2012
The morphological response of two adjacent beaches, on the Mexican Caribbean coast, exposed to the same offshore wave climate is compared, where one of the beaches is fringed by a coral reef and the other is not. Detailed topographic and bathymetric measurements were collected from 2007 to 2011using a differential GPS and doublefrequency echo-sounder. Offshore waves were continuously measured by the NOAA 42056 directional buoy, and nearshore waves were measured from May to September 2007 using an acoustic wave and current profiler to validate the use of offshore waves in the analysis of beach morphodynamics. Investigations showed that the beach with the fringing coral reef was the more stable under the same offshore energetic wave conditions of different directions. The implications of the fringing reef on the local hydrodynamics and energy dissipation were evaluated with the SWAN third-generation spectral wave model. The model was first validated with wave measurements collected at intermediate (forereef) and shallow waters (reef lagoon) with Aquadop profilers. Numerical results indicate that during shore-normal energetic conditions, the fringing reef is capable of reducing the incoming wave energy by up to 65%.
Sustainability
The Alburquerque Cay Islands belong to a group of western Caribbean atolls, with a barrier reef of coral that is more than 8 km in diameter. An understanding of the reef ocean dynamics and its direct relationship to the functioning of the ecosystem is important since the significant energies that are involved should play a fundamental role in the coral and fish distributions in the coral reef, which are fundamental for its sustainability. The microtidal regime and the predominance of the trade winds produces coastal circulation, which is induced by waves breaking against the barrier. The study of the water dynamics that are described in this paper was carried out by using a stationary model that is based on the shallow-water equations theory, with consideration to the radiation stress gradients in the waves, whose patterns were evaluated with the pseudo-data of a reanalysis of a virtual buoy in front of the atoll and were propagated in the domain of interest by using the simulating ...
The role of fringing coral reefs on beach morphodynamics
Geomorphology, 2013
This paper examines the degree of energy dissipation provided by a fringing coral reef, and its role on the morphodynamics of adjacent beaches in terms of volumetric sediment transport. Morphological data were collected from the microtidal Mexican Caribbean beaches of Puerto Morelos, fringed by a reef, and Cancun, without a reef, from September 2007 to May 2011. Being exposed to the same offshore wave conditions, the morphodynamics of the coral reef-fronted beach were compared with those of the adjacent beach without a coral reef. Spatio-temporal changes in beach morphology were determined applying empirical orthogonal functions (EOF) to the shorelines extracted from the topographic data, and it was concluded that Puerto Morelos was considerably less dynamic than Cancun. The longshore energy fluxes were larger in Cancun, and the subaerial morphological differences in both beaches and under the same offshore conditions demonstrated that Puerto Morelos was particularly stable under shore-normal easterly waves. A calibrated phaseaveraged wave model was implemented to determine the amount of wave energy dissipation across the coral reef. For energetic shore-normal waves the model determined that the semi-emerged coral reef was capable of reducing up to 85% of the incident wave height. The reef-crest height controlled the amount of wave energy dissipation, and the distance between the reef-crest and the shore determined the vulnerability of the beach to morphological changes. Reef-crest degradation by 1 m resulted in a 10% increase in incoming wave energy, which resulted in 0.9 m 3 /h/m of sand being mobilised along the beaches closer to the reef.
The role of the reef-dune system in coastal protection in Puerto Morelos (Mexico)
Natural Hazards and Earth System Sciences Discussions
Reefs and sand dunes are critical morphological features providing natural coastal protection. Reefs dissipate around 90 % of the incident wave energy through wave breaking, whereas sand dunes provide the final natural barrier against coastal flooding. The storm impact on coastal areas with these features depends on the relative elevation of the extreme water levels with respect to the sand dune morphology. However, despite the importance of the barrier reefs and dunes in coastal protection, poor management practices have degraded these ecosystems, increasing their vulnerability to coastal flooding. The present study aims to investigate the role of the reef-dune system in coastal protection under current climatic conditions at Puerto Morelos, located in the Mexican Caribbean Sea. Firstly, a nonlinear non-hydrostatic numerical model (SWASH) is validated with experimental data from a physical model of a fringing reef. The numerical model predicts both energy transformation and ...
Shoreline erosion in a reef-beach system
Environmental Management, 1978
Beach erosion on Cinnamon Bay in the U.S. Virgin Islands results from storm waves in the North Atlantic. The net trend of erosion, however, is due to local environmental degradation. Reef die-back, initiated during the period of high sedimentation associated with 18th and 19th century sugar cane cropping, has reduced the rate of generation of new coral sands. Sand losses to deep water during periods of storm waves are not replenished. Engineering measures designed to check erosion at Cinnamon Bay have had little effect in this environment of low wave energies, but sand deficiency. The appropriate environmental focus for managerhent of reef-beach systems is reef health and thus, water quality.
Wave Transformation Over Reefs: Evaluation of One-Dimensional Numerical Models
2009
Three one-dimensional (1D) numerical wave models are evaluated for wave transformation over reefs and estimates of wave setup, runup, and ponding levels in an island setting where the beach is fronted by fringing reef and lagoons. The numerical models are based on different governing equations. BOUSS-1D and RBREAK2 are phase-resolving models that respectively solve the time-dependent Boussinesq and shallow water equations. WAV1D solves the 1D wave-averaged energy conservation equation.
Beach Morphodynamic Response to a Submerged Reef
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To develop beach engineering, the submerged structure’s primary physical functions have to be understood. This study focuses on submerged structures in order to understand the strategy of reduced wave energy, stabilizing the shoreline and not generating erosion or adversely modifying coastal processes. Important developments have been made since the 1990s, taking into account the functions of recreational amenity. However, non-dimensional models cannot explain the physical mechanisms that generate accretion or erosion morphological features in the lee of the submerged structure. The present study aims to collaborate with the understanding of the mechanism of beach response to a submerged structure. For this, 26 surveys were made using topographic, Lagrangian, and Eulerian hydrodynamic measures during one seasonal cycle of a beach system from Rio de Janeiro (Brazil) with a natural submerged reef or rocky bank V-shape in the plan. This beach system is energetic and intermediate when r...