Housing Under the Sea

One of the eight reef structures being lowered into the waters off Sisters’ Island Marine Park PHOTO: NATIONAL PARKS BOARD

Over the last five decades, Singapore has successfully built quality high-rise public housing that now houses over 80 percent of its resident population. But increasingly, it is not just people but also animals in the city-state that can proudly claim to live in a home designed for them.

From intelligent nests for hornbills to hotels for bees, the government has been creating structures to help different species thrive in an effort to strengthen Singapore’s biodiversity. One of its newest initiatives is the nation’s largest purpose-built reef within the waters of Sisters’ Islands Marine Park, located just south of the mainland. Five 11-metre and three 6-metre tall structures have been installed on what was previously relatively flat and bare seabed. Akin to three-storey terrace houses, they hope to eventually be home to some 1,000 square metres of reef substrate and other marine life. If successful, this pilot will pave the way for future restoration efforts in Singapore. Over the years, the city-state has lost some 60 percent of its reefs because of extensive development and reclamation over the years.

The government agency JTC first conceptualised this project in 2010 to support efforts in enhancing the city-state’s marine biodiversity, particularly in the face of climate change and increasing coastal developments. While it is better known for the planning and development of Singapore’s industrial infrastructure such as the petrochemical complex, Jurong Island, this was an opportunity for JTC to lend its engineering and design expertise to scale up previous efforts to restore the city-state’s coral reefs.

Over the years, various researchers had installed small purpose- built reef structures in local waters with mixed results. Thus, when JTC approached the National Parks Board (NParks) to work on this project, the agencies knew they had to be prudent. “It’s not as easy as taking someone else’s example and plonking it into Singapore. Understanding local context is really important,” explains Dr Karenne Tun, the director of the coastal and marine environment branch at the NParks’ National Biodiversity Centre.

This meant first finding a suitable location to house the reefs. Not only are the waters off Small Sister’s Island feasible because of the terrain and current flow, it is also away from Singapore’s busy sea traffic since it is part of the country’s first marine park for research and conservation activities. Having determined the site, JTC’s engineers and project consultants from HSL Constructor then strove to design a structure that would retain these ideal conditions.

Taking a cue from nature, the engineers proposed a sloping structure to mimic the shape of many Singapore reefs, including one near Sisters’ Islands. An early idea was to build a mini mountain by piling rocks, but this required too large an area to achieve the necessary heights to span over the entire water depth. Instead, the eventual concrete structure comes in a series of unobtrusive units to ensure current flows are not affected.

Nooks of different shapes and rocks encrusted on the surface help ensure the structure attracts a diverse marine life. PHOTO BY NATIONAL PARKS BOARD

Another important consideration was to install the structure with as little impact as possible on the seabed. After all, water clarity is vital to ensure sunlight can get through for coral growth. “The bigger the structure, the more foundation works required. We wanted to avoid piling to minimise disturbance to the seabed and keep the water clear, even though traditionally you need to pile down larger marine structures for stability,” explains John Kiong, JTC’s deputy director for Engineering and Operations.

The A-framed reef structures are anchored to the seabed by their own weight, with additional weighted ballasts providing extra stability. As the design slopes upwards, rectilinear fibreglass panels protrude out at different depths to maximise the surface area for coral growth. This multi-level configuration also takes advantage of the varying amount of sunlight penetration to encourage the growth of different species. To increase texture complexity and support a diverse marine life, JTC even embedded the structure with fibreglass pipes and rocks recycled from the creation of its underground storage facility, the Jurong Rock Caverns.

“When you increase complexity (in the design), you attract different types of animals,” explains Dr Tun. “By creating that, you encourage a more complex ecosystem that is more resilient.”

While it will take years of monitoring to assess the impact of this structure, marine life has begun moving in. Less than a month after its installation, algae and barnacles have appeared, and to the surprise of the team, schools of fishes have also sought shelter in it. By closely studying the way various elements of the structures interact with the environment, Kiong hopes the knowledge gained can benefit how JTC approaches the design of marine structures.

“There are a lot of thoughts right now about designing with nature,” he says. “Having knowledge in coral growth will help us take that into consideration when designing future developments.”

Dr Tun adds that projects like this demonstrate how development projects can incorporate nature to achieve a “win-win” situation. This will become even more important as Singapore becomes more built-up in the future.

“Working with nature is learning from nature,” she says. “Even though we always say development is going to have an impact, there’s also an opportunity that we can benefit from, but we need to be conscious that nothing can ever replace a natural environment, and interventions should only be implemented to complement and not replace them.”

➜ Read “A City for Nature”

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