Canalisation is used to manage floods however we now know that canalisation can increase the risk of floods if the canals are not sufficiently large. PUB worked with NParks to remove concrete and expose the surface below to sunlight and restore a section of Kallang River in BAMK to a more naturalised state. The restored river ecosystem provides a diversity of benefits for man and the main benefit is the reduced impact of floods resulting from heavy rainfall. This is a remarkable start for Singapore as our rivers are mostly canalised. This area is a great site to visit as people can learn about the importance of naturalising canals while enjoying recreational activities in BAMK, just as my class did on our NUS GE3255 Aquatic, Riparian and Coastal Systems field trip in September 2023.
One feature of these restored rivers is the removal of the concrete (daylighting) and widening of the floodplains. This increases the area the water travels through and water flow through the channel is slower. Such reduction in speed also applies to flood waters. Additionally, there is an increase in channel capacity which means that the channel can carry more water. This helps to account for a possible increase in the volume of water that occurs because of heavy rainfall as Earth’s climate changes.
Moreover, the vegetation around the channel helps in water filtration, sediment retention and trapping of carbon. Plants can excel in eliminating nitrates, phosphates and metals from water. These chemicals can be stored in plant tissue or used for growth. Studies in the United States observed drop of 88% and 76% in nitrate and phosphorus respectively after runoff from farms passed through a forest. Plants also augment sediment trapping by lowering water flow and forming barriers and uptake carbon dioxide from the surroundings and use them in photosynthesis.
Figure 1: Pickerel weed (Monochoria vaginalis) (Picture taken by Genevieve Fong on 29 August 2023) Conservation status: Least concern (Native) |
Additionally, we observed an increase in biodiversity due to the restoration efforts as there is a wider variety of habitats for animals to use. The air in the park is also fresher as there is more production of oxygen. People can enjoy the fresh air and the wildlife while taking part in a variety of activities like playing in the water and kite flying.
Figure 2: White-breasted waterhen (Amaurornis phoenicurus) (Picture taken by Shreeyaa Subramanian on 12 September 2023) Conservation status: Least concern (Native) |
| Figure 3: Grey heron (Ardea cinerea) (Picture taken by Gretchen Coffman on 12 September 2023)
Conservation status: Least concern (Native) |
Last but not least, similar restoration can be done in canals alongside parks and housing estates in Singapore with appropriate earth control measures implemented. Canalisation of rivers should be a last resort.
Links
https://extension.psu.edu/the-role-of-trees-and-forests-in-healthy-watersheds
https://www.nparks.gov.sg/-/media/cuge/ebook/citygreen/cg5/cg5_09.ashx
https://www.eea.europa.eu/publications/why-should-we-care-about-floodplains
https://wetlandact.org/sediment-trapping-another-vital-role-of-wetlands/
https://www.nccs.gov.sg/singapores-climate-action/drainage-and-flood-prevention/
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