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  • Writer's pictureAaron Salyer

Designing with Nature: How Artificial Reefs Protect and Play

Updated: Mar 27

In the quest for harmonizing coastal protection with recreational and ecological enrichment, Multi-purpose Artificial Reefs (MPARs) emerge as beacons of innovation. Bridging the gap between engineering marvels and natural sanctuaries, these structures represent a significant leap forward in coastal management strategies. This blog post delves into the intricate process of designing MPARs that not only safeguard our shores but also promote biodiversity and recreational activities, showcasing the groundbreaking work led by International Coastal Management (ICM).

Multi purpose artificial reef by International Coastal Management

The Genesis of MPARs

The inception of MPARs was driven by the dual need to combat coastal erosion and to enhance the marine ecosystem. Traditionally, coastal protection involved hard engineering structures that, while effective, often detracted from the natural beauty of the coastline and offered little to no ecological benefits. The innovative concept of MPARs was born from the idea that coastal defense mechanisms can be designed to work with nature, not against it.

The Gold Coast, with its pristine beaches and dynamic coastal environment, has long been a premier destination for both tourists and residents alike. However, this beautiful stretch of coastline has not been without its challenges, particularly in terms of erosion and coastal protection. The need for innovative and sustainable solutions led to the genesis of Multi-Purpose Artificial Reefs (MPARs), marking a significant shift in the approach to coastal management and protection.

Erosion Challenges on the Gold Coast

The history of the Gold Coast is punctuated with episodes of significant erosion, threatening infrastructure, recreational spaces, and natural habitats. Traditional responses, including hard engineering solutions like seawalls and groynes, often provided temporary relief but sometimes at the expense of the natural dynamics of the coastline and visual amenity. As the understanding of coastal processes evolved, so did the realization that a more integrated and sustainable approach was necessary to address the multifaceted challenges of coastal erosion and community needs.

before and after Multi purpose artificial reef by International Coastal Management

The Northern Beaches Protection Strategy

In response to these challenges, the Gold Coast embarked on the ambitious Northern Beaches Protection Strategy in the late 1990s. This comprehensive plan aimed to address erosion while preserving the natural beauty and functionality of the coastline. A key component of the strategy was the recognition that the protection of the coastline could not rely solely on traditional methods. Instead, it required a holistic approach that included nearshore nourishment, dune vegetation enhancement, and innovative solutions like the construction of MPARs.

The Role of Narrowneck Artificial Reef

The Narrowneck Artificial Reef, constructed as part of the Northern Beaches Protection Strategy, emerged as a pioneering project in the application of MPARs for coastal protection and enhancement. The reef was designed not only to stabilize the shoreline by reducing wave energy and encouraging sediment accumulation but also to enhance marine biodiversity and provide recreational opportunities, particularly for surfing.

The construction of the Narrowneck reef was based on a detailed understanding of coastal processes and the need for structures that could work in harmony with the natural dynamics of the coastline. This approach recognized that effective coastal protection requires flexibility and adaptability to changing conditions and that enhancing the ecological and recreational value of the coastline can be complementary goals.

Comprehensive Coastal Management

The implementation of the Narrowneck Artificial Reef was part of a broader set of interventions under the Northern Beaches Protection Strategy, which also included beach nourishment and dune vegetation enhancement. These measures worked in tandem to create a "healthy beach profile" and "living shoreline," addressing both the immediate concerns of erosion and the long-term sustainability of the coastal environment.

Sand nourishment replenished the beaches, providing immediate relief from erosion, while dune vegetation played a crucial role in stabilizing the newly placed sand and enhancing the ecological value of the dunes. Together with the artificial reef, these measures exemplified a new paradigm in coastal management, where the protection of the coastline is achieved through the enhancement of its natural and recreational assets.

healthy beach profile with living shoreline

Balancing Act: Protection Meets Recreation

The design of MPARs is a delicate balance between providing robust coastal defense and creating a habitat for marine life and recreational spaces for humans. One of the key challenges is engineering a structure that can dissipate wave energy to protect the shoreline while also creating surfable waves. The ICM-led Narrowneck Reef project exemplifies this balance by not only reducing erosion along the Gold Coast but also improving surf conditions, attracting surfers and bolstering local tourism.

The reef itself becomes an attraction, drawing surfers to its engineered breaks under the right conditions. More intriguing, however, is the reef's influence on the surrounding seabed morphology. By disturbing and 'trapping' sand on the downdrift side, MPARs inadvertently sculpt the underwater landscape, creating varied and dynamic surf conditions that extend well beyond the reef itself.

surfing on Multi purpose artificial reef by International Coastal Management

Enhancing Marine Biodiversity

Beyond protection and recreation, MPARs play a crucial role in enhancing marine biodiversity. By mimicking natural reef structures, these artificial reefs provide new habitats for a variety of marine species. The design process involves selecting materials and shapes that encourage the colonization of marine flora and fauna, turning these structures into thriving underwater ecosystems. The Narrowneck Reef, for instance, has seen a rapid development of a diverse marine ecosystem, demonstrating the ecological success of MPARs.

Environmental impact assessments use quantitative methods to evaluate changes in habitat area, species diversity indices, and potential for biomass accumulation on the reef structure. Models estimating artificial reef colonization rates consider variables such as surface area, complexity (rugosity indices), and proximity to natural habitats. Eco-hydrodynamic models simulate changes in water quality parameters (e.g., dissolved oxygen levels) due to altered flow patterns around the reef, ensuring that the design promotes a healthy marine ecosystem.

marine life on Multi purpose artificial reef by International Coastal Management

Navigating the Design Complexities

The design and construction of MPARs involve navigating complex hydrodynamic, geological, and environmental variables. It requires a deep understanding of the site-specific wave climate, sediment dynamics, and ecological considerations. Utilizing advanced numerical modeling and physical experiments, designers can predict how these artificial reefs will interact with natural processes, ensuring their stability, effectiveness, and safety for all users.

Purpose and Functionality

The purpose of the artificial reef dictates its design parameters, including orientation, dimensions, and location. For surf enhancement, wave transformation models calculate the refractive effects of the reef on incoming waves, using parameters such as wave height, period, and direction. Coastal protection designs utilize sediment transport models to estimate the reef's impact on longshore and cross-shore sediment movement, requiring inputs like current velocities, wave energy flux, and grain size distribution of the seabed material.

User Safety

Safety assessments involve the calculation of wave breaking intensity, water depth above the reef, and velocity fields around the structure. Models like SWAN (Simulating Waves Nearshore) for wave transformation and MIKE 21 for hydrodynamic simulations help estimate areas of potential rip currents and wave heights at various tidal states. The safety design criteria might include setting maximum velocities (e.g., < 0.5 m/s for swimmer safety) and minimum water depths over the reef crest during low tide to prevent injuries.

Risk Assessment Guidelines

Risk assessments quantify the probability of hazardous events and their potential consequences. This involves statistical analysis of wave climate data to identify extreme conditions and simulations for estimating injury risks based on user density, activity types, and environmental conditions. For example, the use of Poisson distribution to model the occurrence of accidents or dangerous interactions with the reef structure.

Impact of Design Parameters on Safety

Design parameters such as reef crest width, slope, and roughness directly influence wave breaking characteristics and energy dissipation rates. Computational Fluid Dynamics (CFD) models can simulate flow over the reef, providing detailed information on turbulence intensity and shear forces, which are critical for assessing the risk of user impact or entrapment. The design might aim for specific thresholds, like limiting wave height reduction to less than 20% over the reef to maintain surf quality without compromising safety.

Construction Tolerances and Physical Modeling

Construction tolerances are evaluated through sensitivity analysis in physical and numerical models to understand the impact of deviations from the design profile on hydrodynamic and morphological responses. This could involve adjusting the reef height or crest level within a range (e.g., ±0.1 m) in model simulations to assess changes in wave transmission and sediment deposition patterns around the reef.

Risks and Management Strategies

Management strategies are informed by quantitative risk assessments, including the calculation of incident rates (incidents per user-hour) and the effectiveness of mitigation measures (e.g., reduction in rip current velocity by 50% with the installation of signage or barriers). Hydraulic models predict areas of high energy or currents that could pose risks to users, guiding the placement of warning signs or designated safe zones.

physical modelling Multi purpose artificial reef by International Coastal Management

A Vision for the Future

As we face the escalating challenges of climate change and coastal erosion, the role of MPARs in coastal management strategies becomes increasingly vital. These structures offer a promising pathway towards sustainable coastal protection, providing a blueprint for future projects around the world. The continued success of MPARs relies on innovative design, rigorous scientific research, and a commitment to preserving our planet's coastal and marine environments.

Gold Coast beach

International Coastal Management

The journey of designing MPARs is a testament to human ingenuity and our ability to work in harmony with nature. The ICM-led Narrowneck Reef project stands as a shining example of how artificial reefs can protect our coastlines while enriching the marine ecosystem and enhancing recreational opportunities. As we continue to pioneer in the field of coastal resilience, MPARs represent not just a piece of the solution but a vision for a sustainable and harmonious future between humanity and the ocean.

Join us as we explore the depths and crests of creating Multi-purpose Artificial Reefs, where every structure is a step towards a more resilient, biodiverse, and joyful coastline.

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