SINGAPORE - National water agency PUB will spend $500 million over the next two to three years to upgrade existing drains as a safeguard against floods given that extreme weather conditions have become more common.
This adds to the $1.2 billion it has already spent on drain improvement works since 2011.
Drains and canals in 75 locations are currently being expanded including the Bukit Timah First Diversion Canal, which runs from Bukit Timah Road near Sixth Avenue to Clementi Road.
PUB said it plans to upgrade drains and canals at 16 additional locations in 2018.
At a briefing held at the Ulu Pandan segment of the Bukit Timah First Diversion Canal on Thursday (Nov 30), PUB said the expansion of the 3.2km diversion canal, which cost $280 million, is expected to be completed by the end of next year.
The canal was at first expected to be ready by 2016. The first phase of the canal, across Ulu Pandan Road, was completed last year, with the second phase, between Bukit Timah Road and Holland Green, 95 per cent complete. But the third phase, between Holland Green and Clementi Road, is only 70 per cent complete.
Asked about the delay in the completion of the third phase at the briefing, Mr Simon Chin, principal engineer of catchment and waterways at PUB, cited the difficult terrain, hard rocks in the ground and a redesign to their initial plans as reasons for the delay.
The area's hilly terrain required the works to be done in phases rather than at one go, and the existing granite in the ground also required more time to excavate, he said.
When fully completed, the diversion canal will be able to take in 30 per cent more rainwater, which would help to prevent floods in the upper Bukit Timah catchment, which includes areas such as Ngee Ann Polytechnic, Beauty World Plaza, Bukit Timah Shopping Centre and Sime Darby Centre.
In 2009 and 2010, heavy rain flooded the basements of buildings in the area.
Expansion works are also ongoing at Sungei Pandan Kechil, Bedok Canal and Kallang River.
The drain works at the 75 locations are expected to be completed over the next two to three years. The PUB said it has upgraded drains and canals at 325 locations since 2012.
Also giving an update on the Stamford Diversion Canal and Stamford Detention Tank, which are being constructed to protect Orchard Road against floods, and which flank the shopping belt on both sides, PUB said they are almost completed.
The diversion canal, which will relieve Stamford Canal of a portion of water, will be completed in the third quarter of next year.
Meanwhile the detention tank, which will hold water temporarily so that less water flows into Stamford Canal during heavy rain, will be completed by the middle of next year.
PUB said it will be testing the pumps for the detention tank next month.
The detention tank, which sits 28m under the Singapore Botanic Gardens coach carpark, will be able to store as much water as 15 Olympic-size pools, or 38,000 cubic metres.
PUB said it has a "holistic stormwater management approach", which goes beyond drainage upgrading to also manage stormwater where it falls through "source" solutions, such as on-site detention tanks in buildings and also through "receptor" solutions such as flood barriers.
Said Mr Ridzuan Ismail, PUB's director of catchment and waterways: "With climate change, we expect more intense storms to occur more frequently in Singapore. PUB will continue to implement 'pathway' measures by deepening and widening drains.
"However, due to competing demands for land use, there is a limit to this measure. A more sustainable approach is a collective effort involving developers to put in 'source' and 'receptor' measures to slow down runoff into public drains and to protect developments from floods."
