|Rain Areas Animation from the NEA website|
Minister Vivian posted this:
"This morning's heavy storm brought more than 100 mm of rain to the Kent Ridge area with major flash floods especially at AYE and Commonwealth Avenue. Both the Sungai Ulu Pandan and Sungai Pandan Kechil overflowed their banks.
Drainage improvement work at Commonwealth Avenue will be completed by June next year.
The flooding at AYE will require expansion of the Sungai Pandan Kechil which drains south to the sea and is subject to tidal influence. This is a major project that PUB has been considering. Will have to expedite this."
Where is Sungei Pandan Kecil?
I really can't figure it out from the online maps. If a reader knows more, please do leave a comment.
There is the very large Sungei Pandan, which at the upper reaches divides into Sungei Ulu Pandan and Sungei Pandan. Further upstream, these become merely 'canal'. 'Sungei Pandan Kecil' doesn't show up on the wikipedia entry of 'List of Rivers in Singapore'.
|Click on image for larger view.|
|Canal at the western end of West Coast Park|
from the NParks website.
What does "subject to tidal influence" mean?
It probably means that the level of the water in this "Sungai Pandan Kechil" goes up and and down with the tides. So at high tide, the water may not drain as rapidly into the sea. If there is heavy rain at high tide, then rainwater is likely to back up and result in flooding.
Today, the peak rainfall did NOT coincide with the highest tide. Peak rainfall was at about 0830hrs, when the tide was predicted to be about 1.5m. The highest tide today is predicted at nearly 3m at noon. In Singapore, the highest daily predicted tide is about 2.5 to 3m. [Why am I saying 'predicted'? Because the tide tables only give predicted tide heights. Actual tide heights as measured at various locations are a different thing altogether and may not match predicted tide heights (as I have found to my personal dismay on low tide trips).]
When a dam is placed across a canal/sungei, does it mean that it is no longer "subject to tidal influence"?
Hmm, good question. Hopefully, someone can help with a proper answer.
But looking at the issue from a logical ordinary person's point of view: I do know that all dams have a sluice gate, to release water from the dam so that the water doesn't back up and cause flooding upstream. I guess this is done now and then on some sort of schedule for all dams.
Obviously, to drain the dam water, the sluice gate can only be opened when the water outside the gate (in the sea) is lower than the water inside the gate (behind the dam). So if the tide is high, the water in the sea may be higher than the water inside the gate and the sluice gate can't be opened to drain the water, even if there is a huge flood of water incoming from rainfall.
So, to my mind, all our canals/sungei/river are subject to some sort of tidal influence even if there is a dam across it.
What is Singapore doing to prepare for flooding due to climate change?
Today's flooding was relatively short in duration. Resulting in some funny photos and comments. But things could get a lot worse with climate change.
|Photo from New Nation|
A recent study also found that coastal flooding in cities around the world could cause damage totaling $1 trillion annually by the year 2050 if no mitigating steps are taken. Although Singapore is not highlighted as one of the cities at high risk, the risk remains.
Already today, we experience severe if short-lived storms called the Sumatras. These tend to happen before dawn when most people are safely in bed and thus unaware of them. But a Sumatras happening at rush hour will probably be keenly felt by many people.
|Storm building up over Cyrene Reef.|
But it is melting ice, among others, that will contribute to global sea level rise. So what is being done to prepare for sea level rise in Singapore?
In June it was reported that the Building and Construction Authority (BCA), which is in charge of protecting the island nation's coasts, called a tender for a coastal adaptation study - the most extensive one done here yet - to come up with a framework to keep low-lying areas safe. I suggested that in protecting from rising seas, there might be a role for natural shores.
Update on 6 Sep:
Check out the awesome comments made by Pat to this post below which provides lots of fascinating and educational information, links and analysis. Thank you Pat!
Media articles report that authorities say the floods "were the result of the unfortunate coming together of two forces of nature - heavy rain and high tide". PUB says "upgrading of the canal in this problematic area will not happen immediately. It will take a further nine months to determine the scope of works needed, including how much the canal's capacity can be expanded and what construction method to use. At the earliest, work will only begin in the first half of 2015, and it may take a few years depending on the scale of work and site conditions"
|From Straits Times 6 Sep 13.|
Update on 7 Sep:
It was reported in the Straits Times that "PUB will build a tidal gate at the Sungei Pandan Kechil canal within six to nine months. The 2m-tall steel gate near West Coast Road prevents high tide from the sea from flowing into the canal, by creating a temporary storage area. "If we can cut out the influence of the tide, it helps buy some time during severe rain." PUB will also consider building a barrage - a larger version of a tidal gate - in the long term."
Pat shares MORE intriguing information and analysis about this PUB proposal in new comments below. Pat's points are also echoed in Development vs environmental protection: Public discussion needed by Tan Wee Cheng, Today Online 7 Sep 13.
Update on 8 Sep:
Chengming Wang shares photos of a survey of the Pandan waterways on facebook and says: "It is not convincing that high tide is a cause of the flooding at AYE. There is sufficiently wide area (about 380 meters by width) at the river mouth where Sungei Pandan Kechil discharges into Sungei Pandan. If the high tide is the reason, West Coast area which also received same amount of rain should have been flooded as well. Someone pointed out that chocking of inlet points to Sungei Pandan Kechil is the main reason for the AYE flooding. Flooding caused by high tide does not subside within short time in 40 minutes."
Update 13 Sep:
In Voices/TODAY, this flooding incident was discussed including mention of the possible impact to Singapore of rising seas which will result in higher tides, and more. This clip appears to be unedited and is very long.
- Changing weather patterns causing more flash floods Sumita d/o Sreedharan and Woo Sian Boon Today Online 13 Sep 13;
- Underground work may worsen floods Lim Hong Yin Today Online 12 Sep 13;
- Singaporeans must take climate change seriously Straits Times 9 Sep 13;
- Development vs environmental protection: Public discussion needed Tan Wee Cheng Today Online 7 Sep 13;
- Interim solution for AYE flood problem PUB will build tidal gate at canal in 6 to 9 months
Rachel Au-yong And Lim Yi Han Straits Times 7 Sep 13
- 'Not acceptable' for major expressway to close due to flooding: Minister Balakrishnan Yahoo Newsroom 6 Sep 13;
- Study finds cost of future flood losses in major coastal cities could be over $50 billion by 2050 e! Science News 19 Aug 13;
- Singapore will be able to cope with rising global sea levels: Experts Xue Jianyue Today Online 21 Aug 13;
- Singapore takes first steps on plan to protect its coasts Study to include dealing with rising sea levels and saving low-lying areas Grace Chua Straits Times 19 Jun 13;
- Singapore, polar politics and the melting Arctic Joseph Chinyong Liow Today Online 2 Aug 13;
- Singapore among those granted observer seat on Arctic governing council Alister Doyle PlanetArk 16 May 13;
- Singapore has interest in the Arctic region Esther Teo Straits Times 14 May 13;