Major works by PUB to improve flood protection along Orchard Road are about halfway done, the national water agency said yesterday.
The Stamford Diversion Canal and Stamford Detention Tank will reduce the load of the Stamford Canal - which flanks Orchard Road on both sides - by 30 per cent, a spokesman said.
The diversion canal, which will relieve the Stamford Canal of a portion of water, is close to 50 per cent completed.
The detention tank, which will hold water temporarily so that less flows into Stamford Canal during heavy rainis more than 50 per cent completed.
The 2km diversion canal will divert rain water from 240ha of the total 630ha of catchment into the Singapore River through two underground tunnels and drains 6m to 14m wide, said Ridzuan Ismail, PUB's director of the Catchment and Waterways Department.
He was speaking at a media briefing at the Environment Building in Scotts Road.
The diversion canal is expected to be completed by the first quarter in 2018. It will stretch from Tanglin Road to Grange Road and off Kim Seng Road.
For 1 km of the stretch, works for two tunnels under Grange Road - measuring 4.5m in internal diameter - will start next month.
Stamford Canal, which stretches 4.7km under the Orchard Road shopping belt which includes malls such as Ion, Wisma Atria and Lucky Plaza, could not cope with heavy rain in several instances in 2010 and 2011, leading to floods in the area.
"Through these projects, the flood risk for the main Orchard Road area will be reduced, because we are diverting the flows from the upstream areas," Mr Ridzuan said.
He also pointed to data covering 35 years that shows that rainfall has become more intense, and heavy rainfall is more frequent.
The detention tank, the second in Singapore after one in Opera estate, can store as much water as that of 15 Olympic size pools, or 38,000 cubic metres.
It will sit 28m under the Singapore Botanic Gardens coach park.
Water flowing towards Stamford Canal from Holland Road will overflow from a drain along the road into a chamber where two pipes measuring 2.5m in diameter internally will channel the water into the tank.
Water sensors will alert the automated system to release the collected water when rainfall has subsided. The water will flow both ways by gravity.
Minister for the Environment and Water Resources Masagos Zulkifli visited the construction site of the tank yesterday.
The tank is expected to be ready by the first quarter of next year.
Mr Masagos said that by law, developers now have to include detention tanks in buildings over 0.2 ha, and that more than 30 buildings are now equipped.
PUB attributed a slight delay in the completion of the detention tank to a hard rock that needed time to break down.
As for the delay in the diversion canal, a spokesman said:"We did a detailed investigation of the services, for example, cables and pipes alignment to ensure that the tunnelling depth will not affect the services above."
In an update on the drainage improvement programme, Mr Ridzuan said that projects at 256 locations have been completed since 2013, 92 are ongoing, and 24 more are planned to start this year.
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