Can we turn protective seawalls into new natural habitats?

As the world’s climate gets warmer, the ice sheets will melt, and storm events will increase in frequency and intensity. This alone will raise sea levels around the world and increase the risk of storm surge flooding in coastal communities. Add to that the thermal expansion of water as it absorbs the heat from the atmosphere, and we can expect to witness sea levels rise by 0.8 meters by the end of the century. Therefore, to protect our cities and island communities, many nations have adopted seawalls to act as a barrier between the land and the ocean. These are quite effective, yet they have several environmental impacts. For example, they isolate habitats from the wider ocean and change ocean currents causing coastal erosion where none was apparent before. And significantly, if you take a look at the sparse life growing on a seawall compared to the abundance of life in a natural rocky shore environment, you can clearly see that natural marine communities do not share our appreciation of the seawall.

To tell us more, we spoke to Dr Stephen Summers, senior research fellow at the Singapore Centre for Environmental Life Sciences Engineering (SCELSE) and a climate change research cohort member for the Association of Commonwealth Universities.

To start off Stephen, could you tell us what you do?

I have two main roles. One of my larger ones is working on a seawall project, which isn’t so much about building seawalls to protect but rather mitigating against seawalls. Whenever low-lying island states such as Singapore build a seawall for protection from rising water levels, typically the seawall has a detrimental effect on the environment, decreasing sediment stability and flora and fauna biodiversity. I work on an eco-engineering project, in which we’re trying to change the design of the seawall and maintain the structural aspects that we see today, while reducing the negative environmental impacts. To give you an example, we’re working with different materials to see which ones are adapted to certain environments.

The best way of describing my second role is to say that it concerns marine pollution, meaning everything from oil spills to plastic pollution. What impacts do these anthropogenic contaminants in the ocean have on ecosystem function? And what impact can we have on the pollution? How can we mitigate it, clean it up, get it to biodegrade? Things like that.

Could you tell us more on what your seawall project involves? Are you working on new designs with different materials?

Let me start by saying that while we have looked at new materials and new designs, the current designs of seawalls are functionally very good. By changing the materials of a seawall to be more beneficial to certain environments, we can’t really improve on the function. In other words, we don’t want to lower function to make it more aesthetically pleasing. What we have really looked into is replacing one material for another to see if it has any impact. For instance, with “business as usual”, very little grows on seawalls, which can be good for commercial environments, for instance. Another material may promote corals and other organisms, which can be good for tourist areas. And in a more general sense, certain materials could promote higher biodiversity and be beneficial to ecosystem health.

What we see is that there is some small impact at the level of larger organisms, such as corals and algae. For example, corals appear to prefer calcium-based rock rather than volcanic rock like granite or basalt. Unfortunately, seawalls made out of limestone are not effective because they tend to just crumble away. While we did consider these elements initially, it was more of a blue-sky approach to find out how different materials have different impacts. How we’re utilizing this now is in cladding. This is where we take the existing structure and clad it with concrete tiles. The idea we have at the moment is having different materials within the concrete tile, so we still get the properties of a material and keep the structural integrity of the granite seawall.

Are there any of these tiles in situ at the minute? 

There are many hundreds of tiles throughout the world. We see some in the United Kingdom, some in the Sydney Harbour, and also some on the east coast of Singapore in a place called Changi. They exist in various shapes and sizes, mathematical complexities, and materials, to see what the impact is on a large scale. It’s one thing to do a small experiment on a scale of a few meters but having these larger kilometre scales will help us see the effects from a very different perspective.

Are you seeing any early indications of what’s happening to the local ecology where the tiles are in place?

The material has a very small effect, but what we are seeing is an effect of complexity. With these various tiles, we’ll have holes of different sizes drilled into them, and we’ll even have small wells moulded in to have pockets of water retained inside the tiles when the water level drops at low tide. What we’re tending to see is that we’re getting a higher range of biodiversity growing on the seawalls because of this more diverse niche environment.

Are the civil engineering community or the companies that are installing seawalls interested in these developments? Do you think they might want to take them up?

In Singapore, the national government looks after all the seawalls, and they’re working with us to aid in this installation. Their interest lies within wanting improved water and improved aesthetics, but they also want improved seawalls. Two things are very interesting to them from an engineering standpoint. Firstly, if you clad a seawall in concrete tiles, the cladding actually protects the seawall. There’ll be less erosion on the seawall, so it’ll last longer. You may have to go through every few years and replace the cladding, but that’s far easier than replacing the seawall. Secondly, in the case of storm surge, as a wave comes up the seawall it can cause significant flooding. If you’ve got a series of bumpy tiles that have got clams and barnacles growing on them, it breaks up the wave. It dissipates the power in the storm surge, meaning that the seawall is more effective. In other words, we can somewhat improve the functionality of the seawall using this cladding.

Thank you. Finally, what do you want policy-makers attending the COP26 to most understand about your research or about climate change more generally?

My research only exists because politicians, policy-makers, and industry people have been kicking the can down the road for so long that we’re no longer at the point where we can prevent the effects of climate change. My entire research career is now based on mitigating the problems that are already in existence. I’d prefer to have a different job, rather than picking up the mess of previous decision-makers. I’d prefer to be snorkelling on the coral reef for fun rather than for the reasons I currently do. If there is one point that I’d like to hammer down it’s that there is no more time to waste, action is long past due.

Dr. Stephen Summers

Dr Stephen Summers is a senior research fellow at the Singapore Centre for Environmental Life Sciences Engineering (SCELSE), a climate change research cohort member for the Association of Commonwealth Universities, and a member of the Commonwealth Futures Climate Research Cohort established by The Association of Commonwealth Universities and the British Council to support 26 rising-star researchers to bring local knowledge to a global stage in the lead-up to COP26. In addition, he is a resident researcher for the St John’s National Marine Laboratory, a national infrastructure facility.

Dr Summers completed his PhD with the Centre for Ecology and Hydrology (Oxford, UK) and the Open University (UK) investigating the impacts of biofilms on pedogenesis from volcanic environments. Since then, he has been investigating the complexities of marine microbial communities. These can range from crude oil pollution through to the impacts of plastic waste on the natural bacterial communities in the ocean. Most recently, Dr Summers has been assessing the impacts of man-made seawall structures on the biological health of Singapore coastal areas.

He has contributed to various governmental waste management policy discussions, in the UK, Australia and more broadly to the World Economic Forum in Dalian, China. Additionally, he has participated in an international Blue Charter marine waste programme with the ACU.

@micro_steve

Header photo by Karl Moran on Unsplash.