SINGAPORE – A $300 million upgrading project of the Bukit Timah First Diversion Canal – completed after seven years of work by national water agency PUB – will serve to strengthen Singapore’s flood resilience, said Environment and Water Resources Minister Masagos Zulkifli on Friday (Sept 13).

Speaking at a ceremony to mark the project’s completion, Mr Masagos added that it was one of the most expensive and complex drainage improvement projects that the agency has undertaken, but one that was a “necessary investment” in preparation for the extreme weather that climate change will bring.

“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 1m, an increase in daily mean temperatures as high as 4.6 deg C, and more extreme and intense weather events, which may lead to more frequent floods. The upgraded diversion canal will help us to better prepare for this.”

PUB said that the diversion canal, which is 3.2km in length, will now be able to convey 30 per cent more rainwater than before the drainage system was enhanced.

The upgrading works, which involved the deepening and widening of the canal as well as the construction of additional tunnels, will help alleviate the risk of flash floods along Bukit Timah and Dunearn Road, said PUB.

Landmarks in the area which will benefit from the enhanced flood protection include Ngee Ann Polytechnic, Beauty World Plaza and Bukit Timah Shopping Centre.

The entire project, which began in September 2012, was delayed a few times due to various engineering challenges faced by the agency.

Mr Yeo Keng Soon, PUB’s director of catchment and waterways, said that the drainage project was a “complex and challenging” one and was hindered by “several tough obstacles” throughout the three construction phases.

He added: “The hilly terrain and tough ground conditions due to the discovery of hard rock at shallower depths than anticipated meant that more time and effort was required for excavation works.”

PUB explained that the construction team had encountered hard rock in the ground at a depth of 20m, instead of 30m that they had expected during the third phase of the project, which involves constructing two tunnels across Military Hill.

The slopes at Military Hill also had to be stabilised using the soil nail method, which involved the insertion of reinforcing bars up to 10m in length into the slope on either side of the canal. This acted to stabilise the soil and ensure that the slope does not collapse during construction works.

PUB said that over 10,000 soil nails were used in the third phase of the project and it was the first time that the method was employed in drainage works in Singapore.

Mr Masagos said: “Despite PUB’s efforts and long-term planning to upgrade our drainage system, it is not possible to completely eliminate the incidences of flash floods. Even with the expanded diversion canal, a particularly heavy deluge could still exceed the canal’s drainage capacity.

“We will continue to upgrade the Bukit Timah Canal to better safeguard the area from flash floods.”

He added that works to widen and deepen a section of the canal, from Rifle Range Road to Jalan Kampong Chantek, will begin next month.

A 900m stretch of the canal will be widened from about 10m to 12m and deepened by about 1m to 2m.

Mr Yeo added: “Further downstream, road-raising works will be conducted along a 300m stretch, on either side of the canal.”

The project was awarded to Chan & Chan Engineering at a contract sum of $53.2 million. Works will commence in October this year and are expected to be completed by 2023.