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Floods – are we prepared?

By James Ong

Case Study 1:

On 2 December 1978, a total of 512.4mm of rain fell, the highest ever recorded for the month of December on a single day, according to NEA, resulting in one of the worst floods in Singapore's history. In fact, it is the highest single day rainfall for Singapore in NEA records. (NEA)

Monsoon rain contributed to this disaster. There were seven casualties, and more than a thousand residents were evacuated from their homes by the army and police boats from five affected areas. Total damage reached S$10 million. It was the worst flood since the Hari Raya floods that hit the island in December 1969. (Source)

PUB Chief Khoo Teng Chye said on 18 June 2010, "Even if we have very well-maintained drains... given the amount of rain that fell on that day - as I said, it's 60 Olympic-sized pools - I think it would have washed down into the culverts huge amounts of debris." (CNA)

Historical data has shown that as much as 300 Olympic-sized pools of rain fell on 2 December 1978. Are we prepared for 300 Olympic-sized pools of rainfall, which killed 7 in 1978? Was Mr Khoo caught off guard in June this year because he failed to learn from history?

Case Study 2:

On 5 June 1984, a total of 121.1mm of rain fell, the highest ever recorded for the month of June on a single day, according to NEA. This was probably the one quoted by the PUB after describing the Orchard Road flood as the worst in the area since 1984. (NEA)

Did Yaacob Ibrahim learn anything from 1984, when he said, “Every event is a new learning experience for us.”? (ST)

Case Study 3:

On 28 August 2007, Channel NewsAsia reported, “There was flooding in some parts of the island on Tuesday due to heavy rain, leading to traffic chaos. The rainfall recorded over a period of seven hours, from 7am to 2pm, hit 143mm – about 80 percent of what Singapore gets in a whole month.” (CNA)

On 7 August 2008, a total of 133.9mm of rain fell, the highest ever recorded for the month of August on a single day, according to NEA.

This, however, seems to contradict what CNA and TNP confirmed - that there was a 143mm rainfall for 28 Aug 2007. How then could the highest single one day rainfall be 133.9mm for August, as indicated on NEA’s record (see chart below), when 143mm is reported to be the highest instead? Did TNP and CNA report incorrectly or did NEA present the data incorrectly?

Recent floods, published by The New Paper on 20 Jun 2010, page 21:
19 December 2006, there was mayhem after 365mm of rain – third-highest recorded in the last 75 years – fell over 20 hours. (YouTube)

28 August 2007, 143mm of rain fell in seven hours, roughly 80 per cent of the average for the month, again there were flash floods.

28 November 2007, 99mm of rain was dumped in Orchard Road in just a few hours. Basement stores in Lucky Plaza and Liat Towers were flooded.

5 April 2009, 97.6mm fell, more than half of the average rainfall for the entire month, causing flash floods in MacPherson and Upper Paya Lebar.

19 November 2009, 110mm of rain – about six times that of a normal storm – fell in two and a half hours, leading to flash floods in Bukit Timah that caused at least $1 million in damage to cars alone.

TNP: “When there is at least one major instance of downpours causing flash floods every year for the last four years, such events can no longer be labelled ‘freak’.”

Conclusion:

Historical data do not seem to favour Yaacob Ibrahim and Khoo Teng Chye. Blaming the floods on clogged canals or debris simply showed how poorly our drainage systems were designed or managed.

Furthermore, according to news reports, the 100mm of rainfall which fell on both 16 June 2010 and 25 June 2010 were 60 per cent of the 140-year period of recorded average of 162.2mm for the month of June, according to the NEA. (NEA)

If they are using this 140-year record to explain to the public regarding the June 2010 floods, surely they should be prepared for floods like the 512.4mm of rainfall in 1978. Even if we added up the total rainfall on 16 June 2010 and 25 June 2010, it is not even half of the 512.4mm rainfall record set in 1978 (picture above). (Read about 1978's flood here.)

Did MEWR just joined MND, MOM, MHA and MCYS - the group of Ministries which have disappointed Singaporeans in recent years?

Part 2 - Climate Change and Marina Barrage

Singapore’s National Climate Change Strategy, March 2008 Chapter 2:

For Southeast Asia, the IPCC AR4 projects a warming similar to global mean warming.

Annual rainfall in Southeast Asia is also projected to increase by about 7 per cent by around 2100.

The development of drainage infrastructure in Singapore over the last 30 years has also reduced flood-prone areas from 3200 ha in the 1970s to 124 ha today.

PUB will reduce it to less than 66 ha by 2011 through: (Source)

  1. The development and improvement of drainage infrastructure in Singapore (e.g. widening and deepening of drains and canals),
  2. The completion of the Marina Barrage,
  3. As well as other flood alleviation projects. This will reduce the possibility of increased inland flooding due to climate change.

PUB said over the last 30 years, it has invested S$2 billion to upgrade Singapore's drainage infrastructure. It added that it will invest S$150 million each year for the next five years on upgrading works. (CNA)

The 100mm of rainfall which caused serious flooding on both 16 June 2010 and 25 June 2010 are no where close to the 512.4mm of rainfall set in 1978.

Interestingly, the highest ever recorded rainfall by NEA on a single day for the months of July (149.1mm), October (91.4mm) and December (512.4mm) which were recorded in 1941, 1952 and 1978 respectively have yet to be broken. (NEA)

From the above, large amount of taxpayers’ money has been spent with a goal to reduce flood-prone areas to less than 66 ha by 2011. Looking at the widespread flooding which happened due to just 100mm of rainfall on 25 June 2010, flood-prone areas seem to have increased dramatically in size.

The Three Objectives of Marina Barrage:

Water Supply: The Marina Barrage will increase our local water supply source, which is one of the four national taps. With the Barrage in place, the Marina Basin will turn into a body of freshwater through natural flushing in one to two years, similar to the Kranji and Lower Seletar Reservoir schemes. The new Marina Reservoir will add to the local water supply and increase the water catchment from half to two-thirds of Singapore.

Flood Control: The Marina Barrage is also part of a comprehensive flood control scheme to alleviate flooding in the low-lying areas in the city, such as Boat Quay, Shenton Way, Geylang, Chinatown and Jalan Besar. The barrage will separate the seawater from the freshwater and act as a tidal barrier to keep out the high tides.

Lifestyle Attraction: The Marina Basin will become a scenic water body no longer subjected to tidal variations. The entire reservoir is envisioned to be a lively, vibrant and exciting place where people can enjoy themselves not only on land but the waters. In addition to the cruises and water taxis today, the new Marina Basin can be the venue for many international and local sporting events and activities, adding to the vibrancy of the Basin.

The recent list of floods since 2006, published by The New Paper on 20 June 2010 and the widespread flooding on 25 June 2010, seem to suggest that Marina Barrage, which began construction in 2005 and was opened in 2008, has failed to serve one of its three objectives.

From National Library Article:

The barrage works using a system comprising gates and pumps. It has nine 30m-wide and 5m-high steel crest gates spanning the 350m-wide Marina Channel, and seven drainage pumps capable of displacing a combined total of 280 cubic metres of water per second. Each gate weighs 70 tonnes and each pump 28 tonnes.

Under normal conditions, the hydraulically-operated gates will be closed. When there is heavy rain but the tide is low, the gates will open to release excess water into the sea. When heavy rain coincides with high tide, the gates will remain closed while the pumps will be activated to pump the excess water out to sea.

Using the 2 December 1978 flood as a benchmark, the Marina Barrage pump system requires at least 44 minutes to pump out 512.4mm of rainfall or 300 Olympic-sized pools of water from the reservoir during high tide. For the recent 100mm of rainfall  or 60 Olympic-sized pools of water, the pumps need only 9 minutes, if my calculations are correct.

I am no expert but I am very curious to know if the Met Service and PUB have coordinated well enough whenever there was heavy rainfall in recent years.

During high tides, should the Met Service inform PUB to pump out water from the reservoir to the sea in advance, an amount equal to the projected rainfall? Was the system too slow to mitigate the effects of island-wide heavy rainfall, which resulted in overflowing canals and rivers which lead to the Marina Reservoir, in many parts of Singapore on 25 June 2010?

If this is not how the system works, would the Ministry explain how the barrage failed to meet one of its three objectives since its completion in 2008?

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Headline picture courtesy of Nicholina Chua

Picture of 1978 flood courtesy of MINDEF website

Picture of Marina Barrage courtesy of Asia Is Green

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