PUB veteran helped design drainage system that has reduced such areas by 98%
Chang Ai-Lien, Straits Times 18 Oct 10;
PUB veteran Yap Kheng Guan knows Singapore's extensive network of drains like the back of his hand - after all, he built many of them.
Drains have been his passion in his 35-year career at the Environment Ministry and the national water agency PUB, which is responsible for drainage issues.
He has stood beside floodwaters as pig and water buffalo carcasses floated past in the 1970s. He has blasted through granite to build underground drainage tunnels.
But the seeds of his career in drainage were planted much earlier.
His secondary school, St Andrew's near Potong Pasir Village, was built on elevated ground, he said. It would be closed during bad floods that happened during the rainy season so that it could serve as a refugee centre for people in the area whose homes were sometimes flooded up to the roof.
As a boy scout, he helped to distribute blankets and food to these people.
Said the soft-spoken 58-year-old: 'This really brought home to me the impact of flooding, and shaped my decision later when I had the chance to improve the situation for Singapore.'
Starting off as an engineer handling drainage projects in 1975, he has witnessed some of the nation's most devastating floods, including the December 1978 deluge which holds the record for the highest amount of rainfall in a day in the last 60 years - 512 mm.
Seven people died, including five who drowned, and about 1,000 people had to be rescued and evacuated.
'The moment the waters subsided, we would be there to make sure that debris was cleared. We were on call 24/7 and we wouldn't have had it any other way,' he said.
'There was a sense of urgency for myself and my colleagues, especially because all the new towns were coming up and this industrialisation would only make the flooding situation worse unless we expanded and enlarged our drainage systems.'
Singapore, with its high-intensity rainfall and an average of 240cm of rain each year, as well as its low-lying land surrounded by the sea and its high tides, was already a flood zone waiting to happen. With more buildings coming up, the situation was only set to get worse.
Part of the challenge then was to convince other agencies in charge of public housing and transportation, for instance, that land had to be set aside for drains and also kept in reserve for future flood alleviation systems.
'When the country expands and urbanises, you have only one chance. All that we have in place now, including Marina Barrage, was mapped out 20 to 30 years ago,' he said.
By doing so, engineers and planners have managed to reduce flood-prone areas to 62ha this year, 98 per cent less than the 3,178ha in 1970. With ongoing efforts, the figure is set to go down to 40ha by 2013.
Over the last 30 years, the Government has spent $2 billion on upgrading drainage infrastructure. About $150 million is spent each year on such works.
Transforming the system from that of natural streams and smaller canals to the comprehensive network of drains and canals of today came with its own set of demands.
Marine clay in catchment areas such as the Geylang River and Marina Barrage posed one huge challenge. 'The soil was like toothpaste and the piles just sank right into it,' said Mr Yap.
'In Geylang, we had to devise a chemical treatment to strengthen the soil by pumping pressurised cement into it.'
At Marina Barrage, piles had to be driven 60m deep to reach firm soil.
Special care was spent on roads, tunnels, the MRT system and other crucial areas. Ground openings, ventilation ducts and access to underground facilities were built at least 1m higher than the highest recorded flood levels. At MRT stations, for example, stairs at the entrance were built to prevent water from entering.
'That's why the MRT system has been dry since it started,' said Mr Yap.
Now a senior director at PUB, he still has a mental map of the more than 7,000km of drainage fanning across the island. Stretched out end to end, the drains would extend from Singapore to Sydney, Australia, and beyond.
He was among the first at Stamford Canal in Orchard Road after freak floods hit on June 16 and July 17 this year.
'Doing this has become second nature, although I'm no longer in charge of drains,' he explained.
He said there can never be a zero-flood situation because it would be too expensive and land-intensive to create monster drains big enough to handle freak weather.
'The question is, do you design for the mother of all storms, or can you strike a practical balance?'
Generally, drains are designed to cater to the heaviest rainfall to hit an area every five years, based on factors such as run-off, rain intensity and the size of the catchment area.
For sensitive areas such as the airport, the calculation is based on the heaviest rainfall over 50 to 100 years.
'Of course an engineer's wish is to be super kiasu (Hokkien for 'afraid to lose') but the result would be huge, extremely expensive canals that come at the expense of other things such as the roads and trees. And most of the time, these drains would be empty.
'Yes there will still be floods, but I am proud to say we have a sound system in place which will see us through for many, many years.'
Did Marina Barrage make Orchard Road floods worse?
Straits Times 18 Oct 10;
AFTER floods hit Orchard Road on June 16 and July 17 this year, various theories were floated by people wondering why the shopping district had been deluged. Chang Ai-Lien puts these questions to the PUB.
# Did Marina Barrage contribute to the flooding because water levels at the barrage were too high and not pumped out fast enough, causing a backlog?
The barrage keeps seawater out, acting as a tidal barrier to reduce flash floods in low-lying city areas. Its nine crest gates are lowered if there is excess water in the basin. If heavy rains coincide with high tide, seven drainage pumps are activated to remove excess storm water.
During the highest tides, some parts of Singapore can be flooded even in the absence of rain. Marina Barrage makes sure that this is not a problem in the surrounding 26ha of flood-prone areas because it keeps water at a constant mid-tide level, shaving 1.5m to 1.7m off high-tide levels.
Weather conditions and water levels are monitored constantly, and the moment set levels at the barrage are exceeded by around 10cm or so, water is discharged. This has been done many times and there has been no case where water has not been released fast enough.
In addition, the section of Orchard Road which was flooded is too far away to be affected by the barrage. During heavy rain, the influence of Marina Barrage at Stamford Canal does not go beyond Handy Road near The Cathay Cineplex. At such times (heavy rains), water levels in the canal beyond this point have remained the same with or without the barrage.
# Could new developments along Orchard Road, such as Ion Orchard, have contributed to the flooding because they have depleted green space which would previously have soaked up the water?
Of three major developments in the vicinity, one - Ion Orchard - used to be 1.86ha of green space. Orchard Central and 313@Somerset both used to be carparks.
PUB has a comprehensive drainage masterplan drawn up in the mid-1970s, which guides the provision of drainage systems and sets aside drainage reserves for future requirements, while planning flood alleviation projects to target known flood-prone areas.
Drainage capacity is planned for even before the bulldozers come in. Developments such as Ion Orchard and the effect of the potential increase in surface run-off were factored in when building and upgrading the Stamford Canal in Orchard Road.
All the new buildings in Orchard Road did not flood because they had prevention measures in place such as ramps at basements.
PUB is now helping older buildings such as Liat Towers and Lucky Plaza, which were hit by the recent floods, to do the same. Prior to this year, the last time Orchard Road was flooded was in 1984.
