Multifunctional Artificial Reefs Research Articles

Numerical analysis of the flow field and cross section design implications in a multifunctional artificial reef

Nowadays, multifunctional artificial reefs are integrated in coastal areas all around the world. The design of such structures is currently complex and subjective. In this context, it is essential to improve overall design approaches to more effectively relate artificial reef geometry, function and optimal performance to specific deployment sites. Part of the solution to this challenge may lie in the use of in situ data to study the hydrodynamic performance of prospective artificial reefs. This research addresses this issue by performing a numerical investigation of the flow transformation of two similar artificial reef geometries, and the analysis of performance indicators based on (i) artificial reef assembly cross section, (ii) upwelling and (iii) wake regions evaluation, (iv) efficiency indices and (v) streamlines particles. Based on typical data related to wave action, a velocity inlet boundary condition was defined adopting the non-uniform velocity distribution, aimed at simulating the most realistic boundary condition at the chosen deployment location. The results showed that the multifunctional artificial reef assembly with the droplet shape cross section exhibited enhanced function performance when compared to a circular shape cross section by providing significantly higher values of the upwelling velocity, wake region and associated efficiency indices. In addition, the procedure presented in this study, which considers oceanographic data at the deployment site, the geometry of the artificial reef, in situ flow characteristics and boundary conditions, as well as the devised fluid flow performance indicators, can be used for the design of artificial reefs during the concept stage in an objective manner to consider the local design requirements.

Hydrodynamics and Morphodynamics Performance Assessment of Three Coastal Protection Structures

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.

The multifunctional artificial reef and its role in the defence of the Mediterranean coast

Multifunctional artificial reefs (MFAR) are being implemented around the world, due to their ability to provide an environment where a sports–economic–recreational use and environmental improvement is implemented, and are also elements of coastal defence. However, a lot of failures have been recorded, possibly due to disregarded local factors in the formulations used, and there is no method that has encompassed all these factors, in order to take them into account in its design. The aim of this paper was to provide the coastal engineer with a method that would be used for the design of such reefs. To do this, the Babilonia beach of Guardamar del Segura, Alicante (Spain), was chosen because it is a fully anthropised area (with houses in the Maritime-Terrestrial Public Domain, marina, channelling and river mouth) with continuous regression, in which all the elements considered in this study, were treated. Based on the performance obtained in studies and projects worldwide, the climatic characteristics, biocenosis, sediment transport, settlements and liquefaction and the evolution of the coastline, were analysed. The multidisciplinary study carried out showed that with the implementation of a MFAR, the problem was reversed. Furthermore, the area was provided with a playful-economic use, and could be used 60% of the time, by surfers whose skill level were low to intermediate, without forgetting that the diversity of the marine ecosystem in the area was increased.

Multifunctional artificial reefs for small islands

Multifunctional artificial reefs (MFARs) have been growing in popularity over the last decade. They are offshore submerged structures which provide coastal protection while also enhancing marine and recreational amenities such as surfing and beach widening. A feasibility study was undertaken for São Miguel Island (Azores) where island-wide general site-selection criteria and local site-specific parameters identified São Roque reef as a potential MFAR location. Expert knowledge addressed multidisciplinary aspects through semi-guided interviews, which provided evaluation criteria for the São Roque reef development. Wave changes before and after reef reprofiling were determined using the Regional Coastal Process WAVE propagation model (CEDAS/RCPWAVE). Results demonstrated additional coastal protection to the historic church and existing seawalls, and no adverse effects on the updrift São Roque and downdrift Pópulo Milicias beaches. Further simulation for an extended reef (30 m seaward) showed model sensitivity together with a greater reduction in approaching wave heights. This analysis suggested that the further seaward the reef is extended, the greater the coastal protection afforded. It also denoted longer, rideable surfing waves and greater substrate surface area for marine colonization, while conversely having an increasing effect on downdrift Pópulo Milicias beach, construction costs and footprint impact. An optimal solution will provide a balance to these advantages and disadvantages. A SWOT analysis showed the potential of capitalizing internal strengths and external opportunities to offset internal weaknesses and external threats. With global growing emphasis on the importance of incorporating amenity values into coastal protection works, this research informs alternative solutions for other small islands, especially similar small volcanic islands.

Maintaining a way of life for São Miguel Island (the Azores archipelago, Portugal): An assessment of coastal processes and protection

Traditional hard engineering structures and recently emerging soft engineering alternatives have been employed to protect vulnerable coastlines. Despite negative publicity, they have ensured community survival where socio-economic benefits outweigh adverse impacts. This is especially true for Small Islands (SI) where increasing sea levels and storm intensities threaten already limited land availability. This paper presents coastal vulnerability in São Miguel Island (the Azores SI archipelago) and considers SI issues with regard to coastal land loss. Regional wave statistics using 1998 to 2011 wind record showed: periods ranging from 7 to 13s (circa 83%); wave heights between 1 and 3m (circa 60%); and increasing trends in westerly (p=0.473), easterly (p=0.632) and southeasterly (p=0.932) waves. Sea level analyses between 1978 and 2007 indicated a statistically significant rising trend (2.5±0.4mmyr−1; p=0.000), while between 1996 and 2007 it was 3.3±1.5mmyr−1 (p=0.025), agreeing with other global sea level studies. Based on 2001 and 2008 population data and using zonal statistics, circa 60% of the Island's population was found to reside within 1km of the sea and the percentage of total population was linearly correlated with distance from the shoreline (r2=99%). Three case studies show hard coastal engineering solutions preserved Azorean coastal lifestyle and had little or no observed negative impacts on their environs. Although hard engineering is likely to remain a valuable and feasible coastal protection option, an inventory of São Miguel's population distribution, surf breaks, bathymetry and coastal erosion rates showed the potential of using multifunctional artificial reefs as a soft engineering solution. These offshore submerged breakwaters offer coastal protection while providing additional benefits such as surfing amenity and beach widening. Consequently, findings of this work can inform other SI communities.

Seeking harmony in coastal development for small islands: Exploring multifunctional artificial reefs for São Miguel Island, the Azores

The Azores is a remote archipelago rich in biodiversity, geodiversity and cultural heritage located in the middle of the North Atlantic Ocean. It comprises nine volcanic Small Islands (SIs) scattered over 600km and are vulnerable to coastal hazards due to limited land availability and ocean exposure. To mitigate and adapt to hazards and human occupation, traditional hard-engineering structures have been used. However, these structures have negative impacts on natural coastal character and amenity value and with growing environmental awareness, soft-engineering solutions designed to work with natural processes, such as multifunctional artificial reefs (MFARs), are globally becoming more appealing. MFARs are offshore submerged structures which provide coastal protection while enhancing marine and recreational amenities such as surfing, diving and beach widening. This paper determines “optimal” MFAR multifunctional design criteria based on current progress and assessment of nine international MFARs installed to-date. It subsequently explores MFAR feasibility in São Miguel Island, the biggest and most populated Azorean Island with the largest surfing population. An assessment of surf breaks was undertaken, including coastal processes and retreat rates, and MFAR site selection, criteria and rationale are discussed. By considering site-specific parameters such as local bathymetry, wave climate, tides, coastal processes and marine environment alongside tourism potential and surf culture, São Roque reef was selected as a potential MFAR to provide both coastal protection and surfing amenity.

Hydrodynamics around an Artificial Surfing Reef at Leirosa, Portugal

As a new alternative countermeasure to protect the coastal zone and to increase the surfing possibilities in the Leirosa area of Portugal, multifunctional artificial reefs were investigated numerically in this paper. The primary surfing parameters used in the design (i.e., breaker type, peel angle, wave height at breaking, and currents around the artificial reef) were analyzed. The reef functionality was also analyzed for coastal protection. Two reef geometries with different reef angles of 45 and 66° were tested, considering two design wave conditions (storm and common) and two tide levels (medium and low). Simulations show that both reef geometries are adequate for surfing, although the reef angle of 66° is more suitable for standard surfers, and the 45° angle is more adequate for advanced/professional surfers. A morphodynamic study should be carried out to analyze the efficiency of the artificial surf reef for coastal protection. DOI: 10.1061/ (ASCE)WW.1943-5460.0000128. © 2012 American Society of Civil Engineers. CE Database subject headings: Coastal environment; Reefs; Hydrodynamics; Parameters; Numerical models; Portugal; Case studies. Author keywords: Surfing; Coastal protection; Multifunctional artificial reefs; Reef parameters; Numerical modeling.

Enhancing submerged coastal constructions by incorporating multifunctional purposes

Surfing has becoming more and more attractive in the past few decades, constituting nowadays an important source of revenue for many countries with extensive coastlines. For this purpose and also for environmental reasons, the conventional ways of protecting a coastline appear to entail some disadvantages. An innovative and interesting way of improving surfing capacities and contributing to protect a local coastal zone is by means of multifunctional artificial reefs. A multifunctional artificial reef (MFAR) is a submerged structure that serves several purposes; in particular, it may enhance the surfing possibilities and the environmental value of the local area. This structure has some promising new aspects, too: first, it provides an unimpaired visual amenity; second, it offers tourist and economic benefits by improving the surfing conditions; third, it can enhance the environmental value of the area where it is built, and fourth, if designed properly, the down drift erosion can be minimal. An appropriate reef design in terms of ‘surfability’, i.e. the possibility to surf a wave, for the Leirosa beach, located to the south of Figueira da Foz, midway along Portugal’s West Atlantic coast, has been investigated. In order to achieve the best design several steps were conducted. First, the performance of the Boussinesq-type COULWAVE model is tested with experimental data. Next, this numerical model is used to define the best values for three design parameters: reef angle; geometry of the reef (without or with a platform), and horizontal dimensions for the appropriate geometry. A preliminary design was achieved step by step, making use of the theory and of the state of the art of multifunctional reefs. This reef geometry is used in the numerical study. In terms of ‘surfability’ and for the conditions of the local coastline of Leirosa, the following values were found for the main parameters: a reef angle of 66°; a structure height of 3.20 m; a reef geometry composed of a delta without a platform; a reef submergence of 1.50 m, and a structure seaward slope of 1:10.

Designing a multifunctional artificial reef: studies on the influence of parameters with most influence in the vertical plane

Multifunctional artificial reefs are submerged breakwaters that serve several purposes. As well as protecting the local coastline, they enhance surfing possibilities and/or increase the environmental value of the area where they are situated. Multifunctional artificial reefs (MFARs) have some promising new aspects, too: first, they provide an unimpaired visual amenity, and second, they can offer tourist and economic benefits by improving the surfing conditions. Regarding the functionality of an MFAR, much research has been carried out on surfability, i.e. whether a wave is good for surfers. However, no research has yet been done on the influence of the submergence and the length of the reef slope on the breaker type, even though this is important for the design of the reef in terms of surfability. A preliminary design was achieved step by step, making use of the theory and state of the art of multifunctional artificial reefs (Voorde et al. 2009a, 2009b). This reef geometry was then used as an initial design in physical and numerical tests. These were performed to ascertain the capacity of a multifunctional reef to serve as a submerged breakwater and so protect the local coastline of Leirosa, Portugal, and improve the local surfing possibilities. This paper describes the numerical study conducted to analyze the influences of the main relevant parameters in the vertical plane, namely: the height, the submergence, and the length and slope of the reef. The investigation was conducted using the COBRAS-UC numerical model in the vertical plane and the main results and conclusions are described and presented; a brief discussion and some recommendations for future work are also included.

Designing a Preliminary Multifunctional Artificial Reef to Protect the Portuguese Coast

Abstract Portugal is one of many countries in the world that suffers from coastal erosion. Conventional ways of protecting a coastline appear to entail some disadvantages. An innovative and interesting way of protecting a local coastal zone by means of multifunctional artificial reefs avoids some of them. A multifunctional artificial reef is a submerged breakwater which, besides helping to protect the local coastline, can have other purposes; in particular it may enhance the surfing possibilities and the environmental value of the local area. The structure has several positive side effects: first, it provides an unimpaired visual amenity; second, it offers tourist and economic benefits by improving the surfing conditions. A preliminary design, achieved step-by-step, is proposed for a multifunctional artificial reef making use of the theory and state of the art multifunctional artificial reef design, a preliminary design, achieved step-by-step, a priliminary design is proposed. The proposed reef geometry, ...

Shoreline response to multi-functional artificial surfing reefs: A numerical and physical modelling study

The results of a series of 2DH numerical and 3D scaled physical modelling tests indicate that processes governing shoreline response to submerged structures, such as artificial surfing reefs, are different from those associated with emergent offshore breakwaters. Unlike the case of emergent offshore breakwaters, where shoreline accretion (salient development) is expected under all structural/environmental conditions, the principal mode of shoreline response to submerged structures can vary between erosive and accretive, depending on the offshore distance to the structure. The predominant wave incidence angle and structure crest level also have important implications on the magnitude of shoreline response, but not on the mode of shoreline response (i.e. erosion vs. accretion). Based on the results obtained here, a predictive empirical relationship is proposed as a preliminary engineering tool to assess shoreline response to submerged structures.