Drainage projects to keep Orchard flood-free ready

$277m diversion canal and detention tank will help detain, delay and divert storm run-off during intense downpours

The interior of the Stamford Detention Tank, which lies 30m beneath the Botanic Gardens. The tank is part of the PUB works to prevent flooding of the scale that hit Orchard Road in 2010 and 2011.
The interior of the Stamford Detention Tank, which lies 30m beneath the Botanic Gardens. The tank is part of the PUB works to prevent flooding of the scale that hit Orchard Road in 2010 and 2011.ST PHOTO: MARK CHEONG

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."

A version of this article appeared in the print edition of The Straits Times on September 29, 2018, with the headline 'Drainage projects to keep Orchard flood-free ready'. Subscribe