Felda Chay, Business Times 25 Nov 09;
ABOUT $20 million will be spent on the first stage of widening and deepening the Bukit Timah diversion canal to prevent a repeat of last Thursday's floods, national water agency PUB said yesterday.
Upgrading works on the stretch of the canal running from Wilby Road to the junction of Sixth Avenue will start in the third quarter of next year and will be completed in two years.
PUB will also install a water level sensor next week to give early warning of rising water levels in the Bukit Timah Canal near Blackmore Drive, said the director of its catchment and waterways department Tan Nguan Sen. PUB will notify traffic police and nearby condominiums if the water rises 'above a certain level'.
A second phase of upgrading works is also on the cards to expand the remaining stretch of the canal. This phase is set to start in 2011. When completed, the width of the canal, now 11 metres on average, will be expanded to 26m. It will be able to hold about twice the amount of water it can carry now. The three kilometre canal, stretching from Sixth Avenue to Sungei Ulu Pandan, overflowed last Thursday. Floodwater was knee-high in some places, and underground carparks in three buildings were flooded.
PUB is also working with Holland-Bukit Timah GRC to encourage the management of condos such as Corona Ville, where the basement carpark was flooded, to build physical crests to prevent water flowing in.
Mr Tan said that the flooding was caused by 'heavy and intense' rainfall over the Bukit Timah area, with 110 millimetres of rain - equivalent to about 115 Olympic-size pools of water.
The canal was built in 1972 as part of the Bukit Timah Flood Alleviation Scheme - a government project to divert water away from Bukit Timah, a low-lying area with a history of flooding.
Upgrading the canal is part of long-term planning for the area and has been planned even before the recent flood, Mr Tan said. This is in anticipation of increased storm water run-off - caused by a drop in grass-covered areas as a result of new developments in the area over the next 10 to 15 years.
Work to expand canals next year
Capacity of Bukit Timah Canal will be doubled from Wilby Road to Sixth Avenue
Amresh Gunasingham, Straits Times 25 Nov 09;
A DIVERSION canal which overflowed last Thursday and flooded parts of Bukit Timah Road will be expanded over two phases in the next three years, said the national water agency yesterday.
The tender has closed for the first phase, which will be a $20 million facelift to double the capacity of the main Bukit Timah Canal at its juncture with the diversion canal. This is the portion stretching from Wilby Road to Sixth Avenue.
A floodgate located at the Sixth Avenue junction to divert water from the main canal into the three-decade-old diversion was unable to contain rising water levels from 92mm of rain being dumped over half an hour. The rainfall is the second-biggest in the last two decades over the same period, following the 96mm in November 1995.
This caused water levels in the main canal to rise and breach the low-lying stretch from Third Avenue to Coronation Road.
PUB said construction would probably start in the third quarter of next year, and take two years.
The second phase will see the 3km diversion canal, stretching from Sixth Avenue to Sungei Ulu Pandan, widened in parts from 11m to more than 20m. It will also be deepened from the present 4m. Work on this phase is expected to start in two years.
The PUB will also install a sensor system along the Bukit Timah Canal near Blackmore Drive next week, to provide early warning to police and nearby developments if the canal's water level is rising.
Last Thursday, at the flood's height - between 1pm and 2pm - the floodwater was knee-deep, throwing traffic in Bukit Timah into chaos.
Property and cars were damaged as three underground carparks were partially submerged.
The diversion canal was built in 1972 and sized according to how much development there was in the area as well as economic considerations, said Mr Tan Nguan Sen, director of catchment and waterways at PUB, yesterday.
'We did not want to build oversized canals that would not be used to their full capacity.'
Since then, housing and infrastructure developments have burgeoned on the road, a key factor in the volume of water flowing over the surface.
Land scarcity limits the size of drainage systems so they cannot cater to every extreme event, said Mr Tan.
To cope with last week's volume of rainfall, the diversion canal would have to be 30m wide.
The buildings which had their basement carparks submerged are hoping to avoid a similar occurrence in future.
Corona Ville condominium, one of the three, has a drainage system linked directly to the diversion canal which overflowed.
PUB is in discussions with its management to install pump systems in the carpark. It is also talking to the Holland-Bukit Timah GRC about installing physical barriers such as sandbags to prevent water flowing into other developments.
The flood comes three years after one of Singapore's worst floodings in recent history. In December 2006, 345mm of rain fell over a 20-hour period, the third-highest in the last 75 years. Parts of the island from Thomson Road to Yio Chu Kang were submerged and landslides were triggered in Mandai Road and Bukit Batok West Avenue 2.
PUB to install water level sensors at affected flood areas at Bt Timah
Hoe Yeen Nie, Channel NewsAsia 24 Nov 09;
SINGAPORE : As a result of the massive flood along Bukit Timah Road last Thursday, PUB, the national water agency will install water level sensors next week to warn of potential floods.
PUB has also started widening canals along Bukit Timah Road.
On the November 19, a freak downpour dumped 92 millimetres of rain on the Bukit Timah area in 30 minutes, about half the amount Singapore sees in the entire month alone.
On regular days, a diversion canal off the main Bukit Timah canal helps to channel water into Sungei Ulu Pandan.
But last Thursday, PUB said the intensity of the storm meant that the diversion canal could not drain water away quickly enough, resulting in massive flooding along Bukit Timah Road.
PUB stressed that the problem does not lie with the canal system as floodwaters drained away within an hour.
Due to the rainy season, PUB had increased inspections of flood-prone areas. But Bukit Timah was not one of them.
PUB said that is because two diversion canals built in the last 30 years had been effective in draining water away from the low-lying areas. However, following the flood, PUB will install a water level sensor at the main canal near Blackmore Drive.
PUB will be alerted when the canal is 50 per cent full. It will then warn residents and traffic police of potential flooding.
It said the sensor "is enough" to alert residents of further floods, and comes on top of on-the-ground monitoring when there are heavy rains in the area.
PUB added that it will soon widen the diversion canal, from its current 11 metres on average to 26 metres. This will allow the diversion canal to cope with more intense downpours.
"We noticed that over the past few years, there have been a lot of new condominiums developed. This has changed the land surface type from grass areas to concrete surfaces. Because of that, the amount of run-off has increased," explained Tan Nguan Sen, director of Catchment and Waterways, PUB.
Upgrading works also include widening the stretch of the main canal between Wilby Road and Maple Avenue. Work will begin late next year and will be completed in 2012.
PUB said there are only about 80 hectares, or 160 football fields, of flood-prone areas in Singapore. This is down from over 3,000 hectares in the 1970s, after authorities carried out extensive works to improve drainage systems. - CNA /ls
Developers must bear cost of flood prevention steps
Straits Times Forum 25 Nov 09;
MR CHRISTOPHER de Souza, the MP overseeing Bukit Timah, was reported stating that he would be looking into getting the management of private buildings in the area to enhance measures to prevent flooding in their basement carparks ('Working on flood controls', Monday).
I am surprised that the residents and officials accompanying Mr de Souza did not discuss what could be done to eliminate the flooding problem to existing and future developments in the area.
Why must owners in these private buildings enhance measures? Should it not be the responsibility of the developers?
Developments alongside the Bukit Timah Canal are susceptible to flash floods judging from historical evidence. I am baffled that professional builders and developers did not take this fundamental problem into account when they started work on the projects. If they had done their due diligence, residents would not have been so unpleasantly affected by last Thursday's deluge.
We are told that widening of the canals has been ongoing for many years. Yet, the flooding problem has not stopped.
Ultimately, the people responsible for flood safety are the developers and their professional consultants. It is they, and not the residents, who should bear the cost of repairs and preventive measures.
Michael Yeo
