Highly Commended 2023

EMU - Erosion Mitigation Units

Reef Design Lab / Alex Goad / City of Greater Geelong / Ralph Roob (Senior Environmental Engineer at City of Greater Geelong)

The 2m wide EMU's form a permeable barrier designed to reduce wave energy and act as a habitat substrate.

EMU (erosion mitigation units) are a series of artificial reef modules that form a permeable barrier designed to reduce the height and energy of waves. This provides coastal erosion protection during storm surges, supporting sand accretion while also providing intertidal habitat for native oysters, seagrass, fish, and marine invertebrates. When positioned together the modules create an undulating effect allowing snorkelers to safely glide between the system. Manufactured from a reusable moulding system and cast in a low energy concrete mixture with recycled shell and integrated lifters the modules are easily installed in the marine environment using standard low impact techniques.

Design Brief:

The City of Greater Geelong required a series of cost effective reef modules that would attenuate wave energy while creating habitat for native species and a snorkelling attraction for local residents. Standard coastal protection approaches are often seen as unsightly and can alter ecological and physical processes. Therefore the solution needed to be sympathetic to the natural environment and designed to blend in harmoniously over time.

The brief also required that the units be easy to install and made from low energy eco friendly materials that would withstand the harsh marine conditions.

This project was developed by:

Design Process

From the very beginning a guiding principle was to not hide the fact the modules were artificial but rather develop an aesthetic that is sympathetic to the environment it is being placed. By creating curves and crevices the overall geometry replicates the complexity that is found on naturally occurring temperate reefs including caves, overhangs, crevices and textures. This complex habitat range allows for a more biodiverse ecosystem to develop which allows the installation to quickly blend into the environment over time.

Underwater sampling of rocky shoreline was performed by the RDL team using video and 3D scanning techniques to build a database of complex habitat naturally found in Port Phillip Bay. This information was used to develop the early geometry of the modules and informed the undulating nature which would make the system more interactive for swimmers.

During the design process we were able to perform wave modelling analysis on various designs arrays which led us to the final outcome. We also found that greater surface complexity was essential to meeting the wave attenuation goals. As safety standards for this type of interactive wave break don’t exist we needed to take on in house risk assessment. By using playground equipment standards we created geometries that wouldn’t allow swimmers to get stuck.
Stainless steel 316 reinforcing and swift lift system was included meaning the units could be easily lifted into position and shifted in the future which was critical in having permits approved for the first installation. This lifting design also provided significant on site cost savings for the client and the first installation of 46 modules were installed in under 6 hours.

Design Excellence

The project is one of the first to consider the human and environmental response to a coastal protection structure. We used expressive design and eco engineering principles to appeal to both user groups. While traditional structures are solid, the EMU modules undulate allowing people to swim through the system at high tide providing a safe and engaging area for people to experience the marine environment. Swimming in the open ocean can be a daunting activity and people often feel safest in shallow water with structure close by like underneath a pier or along a reef edge. This was a major consideration for the design and provided a perfect opportunity to make a more inclusive coastal structure. The modules have made a significant splash amongst the local community with residents snorkelling and monitoring the colonisation process with underwater cameras.

The project has also contributed to significant change in public opinion on nature based solutions with many councils beginning plans for similar approaches to coastal protection. There have been multiple papers published on nature based solutions leading to changes in UK government legislation encouraging the use of eco engineering and we expect to see similar changes in Australia soon.

Environmental monitoring is currently being conducted on the modules by the University of Melbourne’s Centre for Coasts and Climate and will continue over the next 5 years.

Design Innovation

Traditional concrete breakwaters are generally flat surfaced utilitarian shapes that always seem out of place in the marine environment. To avoid this the design of the modules had to push the level of complexity that can be economically achieved in precast concrete to the extreme. Utilising digital moulding analysis and traditional casting know-how we were able to create a design that looks expensive and complicated but is actually highly economical to produce.

The project is one of the worlds first examples where expressive sculptural design and ecological design principles have been combined to provide coastal protection.
We used an eco cement in the concrete mixture which substitutes part of the Portland cement content with pozzolan by-products from industry such as furnace slag and fly ash. We also substituted part of the aggregate content with locally sourced recycled shell which was incorporated as additional micro texture which is ideal for colonising organisms. The shell was vibrated to the surface of each cast and sandblasted to be reveal on the surface.

The design was optimised from the very beginning to reduce the material required and maximise colonisation of reef building species. By designing the surface to attract species like mussels and oysters we are able to get better wave attenuation outcomes over time as the reef develops creating a true living breakwater.

Design Impact

As climate change drives extreme weather events there is a global movement away from hard coastal engineering towards softer nature based approaches. Through ecologically inclusive design our solution is redefining what these approaches can look like and how they can work to benefit the local community and the environment. The installation for Geelong has already become a safe and accessible location for school tours where students can learn about nature based solutions to coastal erosion and how habitat design can be included in marine structures.

Marine restoration and coastal protection projects are a slow process due to the current permitting requirements, installation of the first EMU’s took almost 10 years to be approved. It is a conservative and complex jurisdictional space that requires many elements to come together. However, since the first installation of EMU modules for the City of Greater Geelong it has inspired multiple councils to investigate similar nature based solutions to coastal protection. The project has clearly demonstrated that ecologically inclusive design principles do not have to come at a high cost nor does it impact the engineering requirements of the solution. Multiple benefits have been identified since the installation of EMU’s including a variety of colonising native species including oysters and mussels, effective wave attenuation, local engagement with swimming and snorkelling groups, school tours and educational activities.

Designing for nature as well as humanity is an important next step in the evolution of the built world and this project is an important catalyst for that change in the coastal protection space.

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