Special Issue "Reefs"

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312). This special issue belongs to the section "Ocean Engineering".

Deadline for manuscript submissions: closed (25 February 2020) | Viewed by 6442

Special Issue Editor

Prof. Dr. José Simão Antunes Do Carmo
E-Mail Website
Guest Editor
Department of Civil Engineering, FCTUC, University of Coimbra, P-3030788 Coimbra, Portugal
Interests: hydrodynamics; morphodynamics; coastal processes; coastal management; marine pollution; waves and currents; storms; natural hazards; climate change; numerical modeling
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Special Issue Information

Dear Colleagues,

There are several conventional methods to protect a coast from erosion, such as groins, detached breakwaters, seawalls/revetments, artificial dunes, and sand supply. Even though these methods adequately solve the local erosion problem in some cases, they have disadvantages. Sand supply and artificial dunes are in most cases an additional measure and not a primary solution for coastal erosion. The drawback of emerged breakwaters, groins, and seawalls/revetments is their large visual impact. In addition, groins cause a large amount of downdrift erosion due to the action of waves and currents along the coastline.

A kind of submerged structures that allow us to overcome these limitations and are able to perform multifunctional objectives are the reefs. These are the result of natural processes, or man-made underwater structures. Natural reefs are developed by the secretions of tiny aquatic organisms (coral reefs), or result from sand deposition or wave erosion of outcropping rocks, eventually enriched by human action. Artificial reefs are man-made or natural objects placed in selected areas of the marine environment (generally deep waters), or structures made from geotextile sand containers, or geotubes, in intermediate and shallow waters.

According to <http://www.coral.org/Threats.html>, coral reefs are home to over 25 percent of all marine life and are among the world’s most fragile and endangered ecosystems. In the last few decades, mankind has destroyed over 35 million acres of coral reefs. Valuable reefs in several countries have been damaged by human activity. If the present rate of destruction continues, 70% of the world’s coral reefs will be killed within our lifetimes.

Artificial reefs are built with the specific aim of promoting the marine life of an area, which is often the case in deep waters, or are built with multifunctional purposes. In addition to increasing the environmental value of the area where they are built, artificial reefs built in intermediate and shallow water conditions can provide shoreline protection by intercepting incoming waves and improving surfing possibilities.

However, comprehensive planning is essential to a successful reef-building effort. Reef location, materials, equipment, assembly area, labor, financing, transportation and possible conflicts of interest must be carefully considered at the beginning of each project. Solutions of these considerations are best worked out by considering not only physical processes and economic interests but also the opinions and participation of citizens, stakeholders, tourism board and local communities in the planning work, decision-making and monitoring processes.

This Special Issue of the Journal of Marine Science & Engineering aims to disseminate case studies and discuss concepts, methods and technologies to assess, preserve and enhance the performance of a wide variety of natural and man-made multifunctional reefs. Original field data and properly validated numerical modelling results are generally well accepted for high quality papers subject to a peer review process.

Prof. Dr. José Simão Antunes Do Carmo
Guest Editor

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Keywords

  • Coral reef 
  • Man-made reef 
  • Multifunctional artificial reef 
  • Coastal dynamics 
  • Coastal protection 
  • Submerged breakwater 
  • Marine ecosystem 
  • Marine life 
  • Geotextile 
  • Surfing 
  • Groyne 
  • Dune

Published Papers (4 papers)

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Research

Article
Performance Assessment of a Semi-Circular Breakwater through CFD Modelling
J. Mar. Sci. Eng. 2020, 8(3), 226; https://doi.org/10.3390/jmse8030226 - 23 Mar 2020
Cited by 9 | Viewed by 1791
Abstract
Coastal defence works, such as breakwaters, are structures that aim to support the action of waves and dissipate their energy. Therefore, they provide conditions for stabilizing the coast, protecting ports, beaches and other coastal infrastructures and ecosystems. Semicircular breakwaters have been applied in [...] Read more.
Coastal defence works, such as breakwaters, are structures that aim to support the action of waves and dissipate their energy. Therefore, they provide conditions for stabilizing the coast, protecting ports, beaches and other coastal infrastructures and ecosystems. Semicircular breakwaters have been applied in different locations around the world due to their aesthetic advantages and high structural performance. Marine structures are subject to hydrodynamic actions normally estimated through physical models. However, these models are complex to implement, involving high costs and long experimental procedures. Thus, alternative methodologies for studying the hydrodynamic performance of these structures are of great use. This work presents the results of the application of a computational fluid dynamics (CFD) tool to study the stability of a perforated semicircular breakwater, based on a rubble mound foundation. The model was validated against experimental results of the critical weight necessary to resist sliding, taking into account the effects of water depth and different characteristics of the waves. A comparison is made between the perforated and the non-perforated solution in terms of the breakwater’s performance to dissipate wave energy. Dissipation conditions of this energy, in the exposed face, are also evaluated in detail, in order to assess the potential of this structure as a biological refuge for marine species. Both solutions show similar performance in terms of results obtained for the wave reflectivity coefficient. The turbulence dissipation on the exposed face of the perforated breakwater is limited to a region of restricted extension around it, which is advantageous in terms of the passage of species into the breakwater. Full article
(This article belongs to the Special Issue Reefs)
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Article
Hydrodynamics and Morphodynamics Performance Assessment of Three Coastal Protection Structures
J. Mar. Sci. Eng. 2020, 8(3), 175; https://doi.org/10.3390/jmse8030175 - 05 Mar 2020
Cited by 8 | Viewed by 1424
Abstract
Coastal areas accommodate a great part of large metropolises as they support a great amount of economic and leisure activities. The attraction of people to coastal zones is contributing to an intense and continuous urbanization of these areas, while the ecosystems are threatened [...] Read more.
Coastal areas accommodate a great part of large metropolises as they support a great amount of economic and leisure activities. The attraction of people to coastal zones is contributing to an intense and continuous urbanization of these areas, while the ecosystems are threatened by the increase of natural extreme weather events (e.g., intensity and duration of storms, floods), which interfere with local wave climate and changes in morphological beach characteristics. Protection of coastal zones predisposed to coastline recession, due to the action of high tides, high sediment transport deficit, and high wave energy, may involve various coastal structures to reduce or at least to mitigate coastal erosion problems. Many of the current coastal protections (notably groins, seawalls, and emerged breakwaters) were built with a single purpose, which was to protect at all costs without environmental or economic concerns, especially maintenance costs, or the negative consequences that such structures could cause up to considerable distances along the coast. The current concept of integrated coastal zone management presupposes studies involving other types of concerns and more actors in the decision-making process for the implementation of coastal works. In this context, multifunctional structures emerge and are increasingly frequent, such as the so-called multifunctional artificial reefs (MFARs), with the aim of improving leisure, fishing, diving, and other sporting activities, in addition to coastal protection. MFARs are in fact one of the latest concepts for coastal protection. Behind the search for more efficient and sustainable strategies to deal with coastal retreat, this study focused on a comparison between the performance of two traditional coastal protection solutions (submerged detached breakwater and emerged detached breakwater) and an MFAR on a particular coastal stretch. In order to analyse the hydro- (wave height and wave energy dissipation) and morphodynamics (sediment accumulation and erosion areas, and bed level) of the structures and beach interactions, two numerical models were used: SWAN (Simulation WAves Nearshore) for hydrodynamics and XBeach for hydrodynamics and morphodynamics. In addition, a comparison between SWAN and XBeach hydrodynamic results was also performed. From the simulations conducted by SWAN and XBeach, it can be concluded that amongst all structures, the emerged detached breakwater was the most efficient in reducing significant wave heights at a larger scale due to the fact that it constituted a higher obstacle to the incoming waves, and that, regarding both submerged structures (detached breakwater and the MFAR), the MFAR presented a more substantial shadow zone. Regarding morphodynamics, the obtained results presented favourable tendencies to sediment accretion near the shoreline, as well as at the inward areas for the three structures, especially for the emerged detached breakwater and for the MFAR in both wave directions. However, for the west wave direction, along the shoreline, substantial erosion was observed for both structures with more noticeable values for the emerged detached breakwater. For all the northwest wave direction scenarios, no noticeable erosion areas were visible along the shoreline. Overall, considering the balance of erosion and accretion rates, it can be concluded that for both wave predominance, the submerged detached breakwater and the MFAR presented better solutions regarding morphodynamics. The MFAR storm wave condition performed in XBeach indicated substantial erosion areas located around the structure, which added substantial changes in the bed level. Full article
(This article belongs to the Special Issue Reefs)
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Article
A Numerical Assessment of Artificial Reef Pass Wave-Induced Currents as a Renewable Energy Source
J. Mar. Sci. Eng. 2019, 7(9), 284; https://doi.org/10.3390/jmse7090284 - 22 Aug 2019
Cited by 1 | Viewed by 1283
Abstract
The present study aims to estimate the potential of artificial reef pass as a renewable source of energy. The overall idea is to mimic the functioning of natural reef–lagoon systems in which the cross-reef pressure gradient induced by wave breaking is able to [...] Read more.
The present study aims to estimate the potential of artificial reef pass as a renewable source of energy. The overall idea is to mimic the functioning of natural reef–lagoon systems in which the cross-reef pressure gradient induced by wave breaking is able to drive an outward flow through the pass. The objective is to estimate the feasibility of a positive energy breakwater, combining the usual wave-sheltering function of immersed breakwater together with the production of renewable energy by turbines. A series of numerical simulations is performed using a depth-averaged model to understand the effects of each geometrical reef parameter on the reef–lagoon hydrodynamics. A synthetic wave and tide climate is then imposed to estimate the potential power production. An annual production between 50 and 70 MWh is estimated. Full article
(This article belongs to the Special Issue Reefs)
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Article
Modeling the Impact of the Implementation of a Submerged Structure on Surf Zone Sandbar Dynamics
J. Mar. Sci. Eng. 2019, 7(4), 117; https://doi.org/10.3390/jmse7040117 - 25 Apr 2019
Cited by 9 | Viewed by 1595
Abstract
Coastal defense strategies based on structures are increasingly unpopular as they are costly, leave lasting scars on the landscape, and sometimes have limited effectiveness or even adverse impacts. While a clear improvement concerning aesthetic considerations using soft submerged breakwater is undeniable, their design [...] Read more.
Coastal defense strategies based on structures are increasingly unpopular as they are costly, leave lasting scars on the landscape, and sometimes have limited effectiveness or even adverse impacts. While a clear improvement concerning aesthetic considerations using soft submerged breakwater is undeniable, their design has often focused on wave transmission processes across the crest of the structure, overlooking short- to medium-term morphodynamic responses. In this study, we used a time- and depth-averaged morphodynamic model to investigate the impact of the implementation of a submerged breakwater on surf zone sandbar dynamics at the beach of Sète, SE France. The hydrodynamic module was calibrated with data collected during a field experiment using three current profilers deployed to capture rip-cell circulation at the edge of the structure. The model showed good agreement with measurements, particularly for the longshore component of the flow (RMSE = 0.07 m/s). Results showed that alongshore differential wave breaking at the edge of the submerged breakwater drove an intense (0.4 m/s) two-dimensional circulation for low- to moderate-energy waves. Simulations indicated that inner-bar rip channel development, which was observed prior to the submerged reef implementation, was inhibited in the lee of the structure as rip-cell circulation across the inner bar disappeared owing to persistently low-energy breaking waves. The cross-shore sandbar dynamics in the lee of the structure were also impacted due to the drastic decrease of the offshore-directed flow over the inner-bar during energetic events. This paper highlights that implementation of a submerged breakwater results in larges changes in nearshore hydrodynamics that, in turn, can affect overall surf zone sandbar behavior. Full article
(This article belongs to the Special Issue Reefs)
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