Flash Floods in Singapore – An Act of God or Poor Planning?
In the past one year, Singapore had experienced numerous occasions of flash floods. During those episodes, people were inconvenienced and some of them suffered material losses. Recently, a 15 year old boy drowned as he unwittingly stepped into a drain which was concealed by the muddied water. Supporters for the Government had defended them by calling the complainers nasty names for blaming the Government instead of God for the heavy rain. The complainers insisted that the Government is at fault. Who should we really blame?
Let us examine the very nature of rain and drainage. In a normal piece of land, whenever there is rain, water would seep into the ground. There are permeable layers under the ground and water flow either downward or horizontally along certain routes till they merge with some streams and rivers. As our do not permit water to rush through it unopposed (think of pouring water through a basin full of sand or hot water through a coffee sock), the amount of water that the ground can collect before overflowing would be limited. Hence, it is correct to say that too much rain could cause flash floods which would be an act of God.
However, even if the rain volume is less than the volume that triggers flash floods, flash floods still can occur. That is the price we have to pay for urbanisation. Whenever we build roads concrete flooring, these artificial floors are unfortunately not permeable. Since water cannot seep underground or through the drainage (natural streams and rivers) that was formed through years of work by nature, they need to flow along the artificial flooring to the lowest point where they can escape. We can now do an experiment. If we pour a bucket of water into the sand, the water would most likely disappear without a trace in a second. If we instead pour water into an aluminium tray with a few holes (to simulate some amount of natural ground, water would flood the tray and escaping slowly into the ground through those holes. In this case, the same amount of water is used and emptied at the same rate but with very different result. This shows that poor planning can also result in flash floods.
As we widen more and more of our roads and build more and more pavements and other non-permeable flooring, we had effectively caused our areas to be prone to flash floods. Whenever we start developing the area without proper planning for drainage, this would occur. No doubt one could argue that such volume of rain would have caused a flash flood nonetheless as our canals (former streams and rivers) had also overflowed. I would like to point to the fact that our ground can actually hold a tremendous amount of water (thick of wet sand) and only excess water would seep through to the rivers in the past. With the built-up area, water were emptied into the canals and drains quickly from the non-permeable surfaces while a huge part of the land below the roads and buildings remained dry (it would take a while for them to soak up the water). That caused a bottleneck and hence flooded our canals and drains. We have to relook holistically at our drainage and not resort to some stop gap measures.
There had been several projects undertaken by the Government to raise the height of the roads (notably in Bukit Timah and Orchard Road) after the past couple of floods. However, if we do not address the drainage problem, the higher roads would only lead to flooding problem somewhere else as the water that were unable to escape to the ground previously would end up flowing downwards and cause flooding at newer locations (evident from the recent Tanglin flood).
To conclude, though the heavy rain can be attributed to Act of God, the flash floods themselves are probably a planning oversight and are totally preventable and regrettable.