SINGAPORE - While seawalls are the traditional defence for Singapore's coasts against rising sea levels, scientists at the National University of Singapore (NUS) are re-engineering them to ensure they do not come at the cost of life underwater.
Despite the ability of the undersea parts of some man-made defences to support coral communities, intertidal seawalls do not support biodiversity of the same richness as natural coastlines, said Associate Professor Peter Todd at NUS' Experimental Marine Ecology Lab.
More than 65 per cent of natural shorelines here have been transformed into hard coastal structures such as seawalls and rock slopes.
This is expected to increase in extent by the end of the century. In 2019, Prime Minister Lee Hsien Loong announced that $100 billion or more may be needed over the long-term to protect Singapore against rising sea levels, including plans to strengthen coastal defences .
To reduce the impact of existing seawalls on marine creatures, NUS scientists have developed an assortment of tiles that can be retrofitted onto seawalls to mimic natural habitat features.
The concrete tiles, from wedge-shaped "rock pools" to domes depending on the surface they are placed on, act as homes that are optimised to improve the variety of marine life.
Findings from their studies show that they can double the diversity of marine organisms on grey marine infrastructure, said Prof Todd.
He added: "The tiles can support between 20 and 25 species as compared to a traditional granite seawall, which has about 10 species. These organisms include algae, bivalves, quite a lot of marine snails and some crustaceans."
While these organisms may not appear to be charismatic, they are important food sources to sustain larger organisms such as fish in the shoreline ecosystem, he said.
Currently, 350 tiles are installed at Changi Bay and another 60 at Sentosa, according to Prof Todd.
After 12 years of experimentation with different designs and materials, the tiles have also been engineered to withstand Singapore's tropical climate, which can see seawall temperatures soaring to 50 deg C, Prof Todd said.
Going forward, the team is refining the tiles to be more environmentally friendly, experimenting with various types of green concrete.
The tiles are designed to last 20 years, but this may vary depending on how exposed the shore is to waves, said Prof Todd.
Responding to queries on whether the National Parks Board (NParks) plans to install the tiles outside of Changi Bay Point, its group director for the National Biodiversity Centre, Mr Ryan Lee, said it is still too early to see the results of these microhabitats in enhancing marine biodiversity as they were installed only recently.
Regarding protection of coral communities along seawalls, he said that the board advises developers to take precautions to minimise damage to the corals in the event of coastal development.
"Where coral communities are large and established, NParks may require for the corals to be transplanted to other sites to prevent destruction," Mr Lee added.
While the current focus is to transform existing seawalls here into better homes for marine life, Prof Todd has hopes the team will ecologically engineer greener seawalls for Singapore in the future.
He said: "Building a hybrid seawall that softens hard coastal defences with green elements might be a bit more expensive and complicated than building a regular sea wall, but this will come with biodiversity and cultural benefits."
The director of PUB's coastal protection department, Ms Hazel Khoo, said the national coastal protection agency will look beyond "hard" utilitarian engineering solutions by incorporating nature-based elements to enhance Singapore's coastal and marine environment.
Designing with nature is a key consideration as PUB conducts ongoing site-specific studies along the City-East Coast and north-west coast, where the proposed design of coastal protection solutions will target to maintain or even enhance biodiversity, she added.