Detention tank, diversion canal to enhance flood prevention

Olivia Siong Channel NewsAsia 19 Jul 12;

SINGAPORE: National water agency PUB has announced measures which it said will help prevent major flooding in Orchard Road from occurring again.

It plans to build a diversion canal and detention tank at the Stamford Canal Catchment to better deal with intense storms.

Prolonged heavy rains led to major flooding at Orchard Road in the last two years.

This was due to the Stamford Canal exceeding its capacity.

PUB is implementing two new measures after a nine-month study.

Firstly, PUB plans to build a new diversionary canal to ease the load on the existing Stamford Canal.

Storm water at the upper catchment, which serves areas like Napier Road and Holland Road, will flow to the Singapore River instead of the Stamford Canal.

So the new two-kilometre long canal will run beneath the surface starting from Grange Road, along Hoot Kiam Road, River Valley Road and off Kim Seng Road to the Singapore River.

The diversion canal along Bukit Timah Road is one of two existing diversion canals in Singapore. It was built in 1991 and diverts storm water to the Kallang River.

The new diversion canal will be about one third the size of the one along Bukit Timah Road.

A new underground water detention tank will also be built at Tyersall Avenue near Holland Road, opposite the Ginger Garden.

The tank will be built below a proposed nursery and coach park, which will be built by National Parks Board.

The tank will collect excess rainwater from drains along Holland Road during a heavy downpour.

The water will then be pumped back to the drains and discharged after a rain storm into the Marina Reservoir through the new diversion canal.

It will be able to hold about 15 Olympic-sized swimming pools of water - that's about 38,000 cubic metres of water.

The tank will also be about four-storey high. It will be the second water detention tank in Singapore. The first was built and completed in 2002 at Opera Estate.

The new water tank will be two-and-a-half times the size of the existing one.

PUB said while the new measures might not completely eradicate flash floods, they will help alleviate the situation.

Director of Catchment and Waterways for PUB, Mr Tan Nguan Sen, said: "Whatever structural design you build, engineering design you have, if you have a storm that's 'higher' than your design, you'll still have some residual flood risk. But definitely it'll be much less extensive and much less severe."

Mr Tan added motorists might be inconvenienced during the construction of the diversion canal and detention tank.

"It'll be something like what you see in typical road construction or drainage construction. The traffic may have to be diverted temporarily and then reinstated later.

"We will have to work together with the other agencies to make sure there's minimum traffic disruption and to ensure the traffic will continue to flow as per normal," Mr Tan explained.

Detailed design for the construction tenders for both measures will be carried out in the second half of this year.

Work on the diversion canal is expected to be done by the end of 2017.

And the detention tank is set for completion by the end of 2015.

-CNA/ac/ck

New canal to help ease Orchard floods
Detention tank also part of several measures to handle rainwater surge
Floodwaters in the carpark behind Orchard Building in the Orchard Road shopping belt on Dec 23, 2011. Singapore will build both a detention tank and a diversion canal to reduce flooding in the Orchard Road area. -- PHOTO: STOMP
Feng Zengkun Straits Times 20 Jul 12;

IN ONE of its most extensive efforts to fight floods, national water agency PUB will build a canal and a water detention tank to ensure Singapore's key shopping district and surrounding areas do not go under water again.

The 2km-long diversion canal will start at the same point as the Stamford Canal serving the Orchard Road area, but will steer rainwater towards the Singapore River. It will be ready in 2017.

The water detention tank, to be completed by 2015, will be built under a new carpark for coach buses near the Botanic Gardens. It will hold 38,000 cubic m - the volume of about 15 Olympic-sized swimming pools - and store rainwater from drains in the area temporarily during storms. The water in it will be pumped out to the drainage network after storms.

The two projects will reduce the Stamford Canal's catchment area by more than a third, easing the load on this canal, which runs from Grange Road through Orchard Road to the Marina Barrage.

This announcement comes after a series of high-profile floods along Orchard Road in the past two years, which caused millions of dollars in damage.

An expert panel appointed by the Government last June to look at ways to reduce flooding had concluded that the Stamford Canal was no longer big enough to handle the recent more intense rain.

News of the two projects yesterday came at the close of a nine-month study into long-term solutions to the floods. It looked at past floods and used a computer model to simulate even worse storms, such as one which lasts four hours and could dump 100mm of rain in an hour.

PUB chief executive Chew Men Leong said: 'The agency has put in place a multi-pronged plan to strengthen flood resilience across Singapore to cater to increasing weather uncertainty and urbanisation.'

Besides the two projects, the plan includes a more advanced forecasting system to be tested next year, and using building features to capture rainwater.

A weir, or barrier, will be built across the Stamford Canal to force upstream water to flow into the new diversion canal.

Professor Chan Eng Soon, who led the flood expert panel, said that with the diversion canal capturing water from about 40 per cent of the Stamford Canal catchment, it will be able to handle more intense storms.

'I think it would be able to handle the storms of 2010 and last year, except for some minor areas due to the local factors,' he said.

PUB will call for detailed design tenders for both projects by year-end; construction is likely to start next year. It declined to comment on the cost of the projects.

It said it will work with others such as the Land Transport Authority to minimise disruption during the works.

The new canal will run under only roads, not buildings. PUB said it will maintain the number of traffic lanes on affected roads.

The agency used computer models to check that the diversion canal will not transfer flood risk to other places.

Property consultant Colin Tan said property prices in flood-hit areas could recover because of these projects, although the construction work may drive down rentals in the meantime.

PUB previously built two diversion canals to ease the load on the Bukit Timah Canal. The first was completed in 1972; the second, twice as long and three times as large as the new canal, cost $240 million when it opened in 1990.

More measures to keep flooding at bay
PUB to build storage tank and under-road diversion canal to ease load on Stamford Canal
Woo Sian Boon Today Online 20 Jul 12;

SINGAPORE - Following a nine-month study on long-term anti-flood measures, national water agency PUB yesterday announced plans to build an underground detention tank and a 2-km diversion canal, which will ease the load on the Stamford Canal.

Detailed design for the construction tenders of both projects will be conducted this year.

The four-storey high detention tank is set for completion by the end of 2015. It will be built beneath a proposed nursery and coach park at Tyersall Avenue next to the Botanic Gardens. With an estimated capacity of 38,000 cubic metres - or 15 times that of an Olympic-sized pool - it will store excess stormwater from the existing drains along Holland Road. The excess stormwater will be pumped back into the drains for discharge into the Marina Reservoir via the proposed diversion canal after the rain subsides.

Work on the diversion canal is expected to be done by the end of 2017. It will divert rainwater from 38 per cent of the Stamford Canal catchment to the Singapore River.

About 3m to 4m deep, the new canal will run beneath the surface, starting from Grange Road, along Hoot Kiam Road, River Valley Road and off Kim Seng Road to the Singapore River.

As the projects will be up for tender, PUB said it is premature to estimate the cost. Nevertheless, it said the issues of cost and feasibility of solutions had been taken into consideration.

In January, Minister for the Environment and Water Resources Vivian Balakrishnan said in Parliament that building a diversion canal would cost between S$300 million and S$400 million, as he spoke about the possible options to alleviate future floods in the area.

PUB said it will work with the relevant agencies and stakeholder groups, such as the Land Transport Authority (LTA), to minimise disruptions during the construction.

At a media briefing yesterday, PUB Director of Catchment and Waterways Tan Nguan Sen said: "There will be operations where part of the road will be diverted, but the diversion will ensure that the number of lanes on the road will be maintained."

Speaking to TODAY, Professor Chan Eng Soon, who chaired an expert panel on drainage design and flood protection measures, said the duration of the construction of the diversion canal was understandable. He said: "You're looking at the diversion of a significant amount of rainfall runoff, so it'll be quite a sizeable canal to build.

"Naturally, the construction will need to take time."

PUB has previously rolled out several drainage improvement projects in the area to alleviate flash floods including the removal of sections of the NEWater pipeline in the canal and the smoothening of the canal wall with polymer lining.

Owners of buildings along Orchard Road, such as Lucky Plaza, Tanglin Mall and Wisma Atria, have also put in place measures to improve flood protection. For example, Wisma Atria has raised its platform to prevent floodwater from entering its basement.

Orchard Road Business Association executive director Steven Goh said that last week, PUB had informed his association of its plans.

Welcoming PUB's latest initiatives, Mr Goh acknowledged PUB's efforts in addressing the issue as well as engaging the stakeholders. "Right now, even without the canal, they are already trying to improve the flow of the water by installing the polymer lining in different pockets of Orchard Road," he noted.