Saturday, 11 June 2016

Orchard flood protection works expected to be completed by 2018; Stamford Diversion Canal and Detention Tank go operational on 28 September 2018

Diversion canal and detention tank will cut Stamford Canal's load by 30% once complete
By Jalelah Abu Baker, The Straits Times, 10 Jun 2016

Major works by PUB to improve flood protection in Orchard Road are about halfway done, the national water agency said yesterday.

The Stamford Diversion Canal and Stamford Detention Tank will reduce the load of the Stamford Canal - which flanks Orchard Road on both sides - by 30 per cent, a spokesman said.

The diversion canal, which will relieve Stamford Canal of a portion of water, is close to 50 per cent complete.

The detention tank, which will hold water temporarily so that less water flows into Stamford Canal during heavy rain, is more than 50 per cent complete.

The 2km diversion canal will divert rainwater from 240ha of the total 630ha catchment area into the Singapore River - through two underground tunnels and drains that are 6m to 14m wide, said Mr Ridzuan Ismail, director of PUB's catchment and waterways department.

He was speaking during a media briefing at the Environment Building in Scotts Road.

The construction of the diversion canal is expected to be completed by the first quarter of 2018. It will stretch from Tanglin Road to Grange Road and off Kim Seng Road.

For 1km of the stretch, works for two tunnels under Grange Road - measuring 4.5m in internal diameter - will start next month.

Stamford Canal, which stretches 4.7km under the Orchard Road shopping belt with malls such as Ion Orchard, Wisma Atria and Lucky Plaza, could not cope with heavy rain in several instances in 2010 and 2011, leading to floods in the area.

"Through these projects, the flood risk for the main Orchard Road area will be reduced, because we are diverting the flows from the upstream areas," Mr Ridzuan said.

He also pointed to data covering 35 years that shows that rainfall has become more intense, and heavy rainfall more frequent.

The detention tank, the second in Singapore after another in Opera Estate, can store as much water as 15 Olympic-size pools, or 38,000 cubic metres. It will sit 28m under the Singapore Botanic Gardens coach carpark.

Water flowing towards Stamford Canal from Holland Road will overflow from a drain along the road into a chamber where two pipes - measuring 2.5m in diameter internally - will channel the water into the tank.

Water sensors will alert the automated system to release the collected water when rainfall has subsided. The water will flow both ways, pulled by gravity.

Minister for the Environment and Water Resources Masagos Zulkifli visited the tank's construction site yesterday.

"The Stamford Detention Tank is both to help out and mitigate possible flooding in the Orchard Road area and, more importantly, in the longer term, we hope that it will also help to mitigate the variable weather pattern we are going to see," he told reporters.

The tank is expected to be ready by the first quarter of next year.

He also added that by law, developers are now required to include detention tanks in buildings with land sizes over 0.2ha, and that more than 30 buildings are now thus equipped.

PUB attributed a delay in the completion of the detention tank to hard rock that needed time to break down. As for the delay in completion of the diversion canal, a spokesman said: "We did a detailed investigation of the services, for example, cables and pipes alignment, to ensure that the tunnelling depth will not affect the services above."

Giving an update on the drainage improvement programme, Mr Ridzuan said that projects at 256 locations have been completed since 2013, projects at 92 locations are ongoing and those at 24 more are planned to start this year.


* Stamford Detention Tank (SDT) and Stamford Diversion Canal: Drainage projects to keep Orchard flood-free ready
$227 million diversion canal and detention tank will help detain, delay and divert storm run-off during intense downpours
By Jose Hong and Jolene Ang, The Straits Times, 29 Sep 2018

Two drainage projects aimed at keeping Orchard Road flood-free during intense downpours were unveiled yesterday. These projects by national water agency PUB cost $227 million and took more than two million man-hours across four years of construction.

The Stamford Diversion Canal (SDC) and Stamford Detention Tank (SDT) aim to ensure that should the same intensity of rain happen again over the Stamford Catchment area as it did in June 2010, June 2011 and December 2011, Orchard Road would not flood.

The two new drainage projects will ease the load on Stamford Canal, which is 4.7km long and runs from Tanglin to Marina Reservoir, by about 30 per cent.

The 2km-long SDC will divert excess rainwater from Holland Road, Napier Road and Grange Road - which are in the upstream section of Stamford Catchment - into the nearby Singapore River, which then merges with Marina Reservoir farther on.

PUB chief executive Ng Joo Hee said: "The same rain that led to the Orchard Road floods eight years ago should not threaten our famous shopping street again."

He added: "Building bigger and bigger drains to deal with more and more intense rain is not a good method. The SDT and SDC are better ways. By detaining, delaying and diverting storm run-off before it can do serious harm, the SDT and SDC offer long-term flood protection for Orchard Road."

The principal engineer of PUB's catchment and waterways department, Mr James Koh, said the point at which the SDC joins Stamford Canal is now blocked off, preventing rainwater run-off from these upstream areas from flowing towards Orchard Road.

During heavy rainfall, the detention tank will be able to store excess water from the drains. Its capacity is 38,000 cubic m, or 15 Olympic-sized swimming pools. It will take around four hours to completely empty the tank when it is full.

When the rain stops and sensors detect that the drains are less than 25 per cent filled, the water from the tank will be pumped back and released.

Orchard Road Business Association executive director Steven Goh said they welcomed the two projects "very, very much". "There was some inconvenience during the eight-year planning and construction, such as taking two minutes longer to get from one building to another due to traffic diversions, but all of our stakeholders were supportive because they understood why this project was being done."

Speaking at the opening of the two drainage projects, Environment and Water Resources Minister Masagos Zulkifli said one of the key challenges was minimising disruption to users of the Orchard Road area.

"PUB engineers had to exercise great care to protect the structural integrity of nearby buildings and roads," he said, adding: "Throughout the four years of construction, motorists remained unaware that they were driving on top of major tunnelling works, as the roads above remained open and safe to use."

Mr Masagos said: "The Government has invested $1.2 billion in drainage improvement works since 2012, and will spend another $500 million in the next two to three years... We have to prioritise our investments and look for cost-effective and practical solutions to meet our needs. The SDT and SDC are key outcomes of (this) pragmatic approach."

Experts welcome Orchard Road drainage system, but say flood management is very difficult
By Jose Hong, The Straits Times, 29 Sep 2018

Experts have described the Stamford Diversion Canal (SDC) and the Stamford Detention Tank (SDT) as welcome moves in lowering the risk of floods in the Orchard Road area, though they added that the science of flood management remains extremely difficult.

For instance, Assistant Professor Aron Meltzner of Nanyang Technological University's Earth Observatory of Singapore (EOS) said it is almost impossible to calculate how much worse the rainfall would have to be - than that in 2010 and 2011 - to overwhelm the two new works and lead to floods.

Even the same levels of rain with slightly different conditions would completely change the drainage patterns. "If a similar deluge happens say even 1km away from where it happened in 2011, the water would take a different path and the details would be different."

Singapore should also expect more intense rain because of climate change, and the country's highly developed urban landscape adds to its flood risk, he added.

Speaking at the launch of the SDC and SDT yesterday, Minister for the Environment and Water Resources Masagos Zulkifli said: "We cannot expect zero flash floods as the design capacity of the drains may be exceeded during extreme rainfall."

PUB chief executive Ng Joo Hee said that with the SDC and SDT in place, floods should not inundate the premier lifestyle district again if the area receives the same heavy rainfall as it did in 2010 and 2011.

Mr James Koh, principal engineer of PUB's catchment and waterways department, also said the SDC completely diverts storm water away from the upper Stamford Catchment area. This would prevent the water from flowing into the Stamford Canal that goes through the Orchard Road area.

He added that if the area now receives heavy rainfall which matches that of 2010 and 2011, and if water from both the Stamford Canal and SDC flows into the Singapore River at the same time, it would not lead to flooding because of the river's high carrying capacity.

Associate Professor Adam Switzer, principal investigator at EOS, said the PUB has good reason to be confident, given the scope and size of the project. "I am fairly confident this system would handle any contemporary flood, and it almost certainly takes into account modelled future rainfall and changes in the climate system.

"That said, this is only one location, and preparing the whole city and region for an uncertain climatic future remains an immense task." Jose Hong

Stamford Diversion Canal and Stamford Detention Tank Go Operational -28 Sep 2018

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