Hi guys and welcome back to my blog! In my previous post, I wrote about how we could possibly replace our hard-engineering coastal defenses with replanted mangroves as part of Singapore’s coastal protection plan for the future. There is a popular saying though that goes, “If it ain’t broke, don’t fix it”. Our existing coastal protection infrastructures are relatively effective in protecting our coastlines against erosion, so why should we replace them with mangroves?

To answer this question, we can draw inspiration from the argument put forth by the ABC Waters programme. The PUB describes the programme as “a strategic initiative to improve the quality of water and life by harnessing the full potential of our water bodies” (PUB, 2006). Similarly, mangroves indeed have so much more to offer than just its shoreline protection capabilities, providing a whole range of ecosystem services ranging from biological to ecological ones as highlighted in my previous post, not to mention its immense beauty!

I have to admit that as I wrote these 2-part series of posts, there was always a niggling doubt at the back of my mind, and that is my inability to understand how our mangroves would be able to cope with rising sea levels and, ironically, Singapore’s plans to combat this issue. In his National Day Rally speech in 2019, PM Lee Hsien Loong highlighted that rising sea levels were an “existential threat” to our nation (Tan, 2019), before laying out possible strategies as part of a S$100 billion Coastal Protection plan as shown in the following infographic by Channel NewsAsia:

These solutions are further elaborated on in this infographic by The Straits Times below:

These 2 strategies involve either the construction of massive dykes or extensive reclamation respectively along the East Coast stretch, which is the area hardest hit by rising sea levels. If the polders or reservoirs were to be created, mangroves would be rendered obsolete there. I’ll come back to this later, but the bottom line is, I was left wondering how in the world mangrove restoration can fit into this picture?

So imagine my excitement when I found out that mangroves can actually keep up with sea level rise naturally! Mangrove soils can grow vertically through its ability to facilitate accretion of coastal sediment, its buildup of organic matter, and the soil-raising effects of mangrove root growth (Spalding et al., 2014). As a result, it is possible for mangroves to be able to keep up with rising sea levels, as observed in studies in Australia and Belize (Spalding et al., 2014). Isn’t that amazing? What can mangroves not do? However, it is essential that inland space be provided for these mangroves so that they can continue to serve their coastal protection functions as they will naturally retreat landwards in response to the rising waters (Spalding et al., 2014).

Would this be feasible in Singapore’s context? Unfortunately, this is a difficult question to answer. Playing around with Google Earth, I noticed that the majority of the 70% of coastline currently protected by hard-engineering infrastructure belongs to ports, shipyards or industrial estates. These include the Port of Singapore Authority (PSA) terminals in the South and Southwest, Tuas and Jurong Island industrial estates and shipyards, and Senoko fishery port and Sembawang shipyard in the North, among others. These are key infrastructure that realistically will not sacrifice some precious space for the sake of mangrove restoration, so this can be ruled out in these areas.

Now back to Singapore’s audacious coastal protection plan. After considering all these perspectives, I feel that the outlook for coastal mangrove restoration is pretty tough. Mangroves would not be able to exist within the polders along the East Coast, and their restoration is probably not feasible along the industrial areas.

But, I can still see some glimmers of hope for this idea. Take a look at Fig. 2 again. The 2^nd strategy involving reclamation of offshore islands from Marina East to Changi has potential for mangrove replanting along the southern banks. After all, reclaimed land is still subject to erosion and needs to be protected, and what better way to do that than to follow the example of Pasir Ris Park and replant mangroves there? Other than that, mangroves can be replanted sporadically along existing seawall-protected coastlines with some inland buffer space, for instance the stretch east of Coney Island, and along some parts of Changi Beach Park.

Looking at the big picture, it would be most ideal for Singapore to adopt a mix of both hard and soft engineering approaches towards the safeguarding of our shores against rising sea levels. This is contingent on the government’s plan for land-use as well, because fringe mangroves would require some space for landward retreat. Ultimately, we can only continue to do research, raise awareness and keep the ideas coming for local mangrove restoration. Hopefully, better ideas will be brought to fruition in the coming years!

References:

PUB. (2006). Active, Beautiful, Clean Waters Programme. PUB, Singapore’s National Water Agency. https://www.pub.gov.sg/abcwaters/about

Spalding, M., McIvor, A., Tonneijck, F. H., Tol, S., & van Eijk, P. (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. Wetlands International and The Nature Conservancy. 42 p. https://www.nature.org/media/oceansandcoasts/mangroves-for-coastal-defence.pdf

Tan, A. (2019, August 19). National Day Rally 2019: Major engineering works under consideration to tackle threat. The Straits Times. https://www.straitstimes.com/politics/major-engineering-works-under-consideration-to-tackle-threat

Infographic sources:

Fig. 1.: https://www.channelnewsasia.com/news/singapore/ndr-2019-singapore-climate-change-costs-rising-sea-levels-11819402

Fig. 2.: https://www.straitstimes.com/sites/default/files/attachments/2019/08/19/ST_20190819_AUSEA19AAA_5055577.pdf