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PUB completes Bukit Timah drainage project to reduce risk of flash floods

PUB completes Bukit Timah drainage project to reduce risk of flash floods

The drain at Holland Green after construction. (Photo: PUB)

SINGAPORE: Work to expand the Bukit Timah First Diversion Canal has been completed after seven years, and it will better protect the flood-prone area.

The S$300 million project is one of Singapore’s most expensive and complex drainage improvement works.

The 3.2km canal can now take in 30 per cent more rainwater than before, said national water agency PUB on Friday (Sep 13), easing the risk of floods along Bukit Timah Road and Dunearn Road.

This area includes places such as Ngee Ann Polytechnic, Beauty World Plaza, King Albert Park and Sime Darby Centre.

First built in 1972, the canal diverts stormwater from the upstream section of the Bukit Timah Canal to Sungei Ulu Pandan.

However, areas around it experienced frequent flooding due to rapid urbanisation and the “under-sized” canal, said PUB.

In November 2009, it was overwhelmed by the equivalent of 115 Olympic-size pools of water which drained into the canal after intense rainfall. Knee-level floodwaters caused major traffic congestion and partially submerged basement car parks.

Last year, another bout of intense rainfall caused flashfloods in Bukit Timah, affecting the stretch from Blackmore Drive to Wilby Road.

A screenshot of a video taken of a flood at Toh Tuck Avenue after Pan Island Expressway exit on Tuesday (Jun 26). (Screengrab: YouTube/Vins & Annette Singh)

READ: 'Intense rain' caused flash floods in central, western Singapore: PUB

The reconstruction of the canal has freed up about four hectares of land - the size of seven football fields - as two-thirds of the canal is now covered.

Previously, the Bukit Timah First Diversion Canal consisted mainly of an open drain along its entire 3.2km length. According to PUB, some of the land has already been used for recreational purposes. 

View of the completed tunnel underneath Military Hill. (Photo: PUB)


At a ceremony on Friday to mark the completion of the upgrading works, Environment and Water Resources Minister Masagos Zulkifli said the project was an “important and necessary investment”, as climate change is expected to bring about more extreme weather in future. 

He highlighted a recent study by Swiss-based research group Crowther Lab, which identified Singapore as one of the major cities that could experience a dramatically different climate by 2050. 

READ: Climate research centre to study how sea level rise could impact Singapore

"You have probably already noticed some of the impacts of climate change such as more intense rainfall and prolonged dry spells," said Mr Masagos.

"By 2100, we could experience mean sea level rise of up to 1 metre, an increase in daily mean temperatures as high as 4.6 degree Celsius, and more extreme and intense weather events which may lead to more frequent floods," he said, adding that the upgraded diversion canal will help Singapore to better prepare for this. 

A view of Railway Corridor after construction. (Photo: PUB)

READ: NDR 2019: Climate change one of the 'gravest challenges facing mankind', impact on Singapore to worsen, says PM Lee

The project, which was carried out over three phases, started in 2012. It was originally expected to be completed in 2016 but the date was pushed back three times due to engineering challenges and difficult ground conditions.

As parts of the canal pass through hilly terrain and forested areas, more than 10,000 reinforcing bars of at least 10m in length were inserted into the slope along an 825m stretch of the canal.

Aerial view of Military Hill tunnelling. (Photo: PUB)

This helped to stabilise the slope and ensure that it did not collapse during construction works. It is the first time PUB has used this “Soil Nail” method in a drainage improvement project. 

"This was a complex and challenging drainage project that required PUB's engineers and contractors to surmount several tough obstacles throughout the three construction phases," said Mr Yeo Keng Soon, PUB’s director of Catchment and Waterways. 

"Extensive efforts such as multi-stage traffic diversions were also needed to minimise inconvenience and disruption to motorists and the public," he added. 


Other flood protection measures for the area are in the pipeline. 

In October, PUB will start upgrading works on a 900m upstream section of the Bukit Timah Canal.

The section, which stretches from Rifle Range road to Jalan Kampong Chantek, will be widened to around 12m, up from its current width of about 10m. It will also be deepened by an additional 1m to 2m.

Further downstream, work will be carried out along a 300m stretch to raise the road on either side of the canal by up to 20cm. 

The project was awarded to Chan & Chan Engineering at a contract sum of S$53.2 million and works are expected to be completed by 2023.

A view of Garlick Avenue after construction. (Photo: PUB)

PUB said this will further boost flood protection in the area, preventing a repeat of the flash floods that occurred in recent years. 

Since 2011, the Government has invested S$1.8 billion on drainage improvement works. Another S$400 million will be spent over the next two years.

READ: Singapore to spend S$400 million upgrading, maintaining drains over two years

PUB has, since 2014, completed upgrading works at 254 locations to increase the capacity of drains and canals.

Expansion works at another 66 locations are ongoing.

Source: CNA/aa


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