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Jun 16, 2010

What causes flash floods?

The PUB is investigating the cause of the flood, especially in the worst-hit Orchard Road/Scotts Road intersection, where the flood waters reached 300 mm high, flooding basement carparks and shops, destroying goods and disrupting businesses. -- PHOTO: KHALEEL RAHMAN

THIS question was asked by scores of Singaporeans as they battled one of the worst flash floods which wrought havoc in many areas on Wednesday after a heavy early morning downpour.

The PUB is investigating the cause of the flood, especially in the worst-hit Orchard Road/Scotts Road intersection, where the flood waters reached 300 mm high, flooding basement carparks and shops, destroying goods and disrupting businesses.

The last known major flooding in the area was in 1984. But the investigations can only be carried out when the water level in the drains have fully subsided, said the PUB in an udpate on the flooding situation late Wednesday afternoon. It also warned that the flash floods may still occur in the event of heavy storms and urged the public to exercise caution.

PUB said about 100 mm of rain fell from 9am to 11am over many parts of central Singapore, with two peaks at 9.30 am and 10.30 am. The amount of rain recorded was 'more than 60 per cent of the average monthly rainfall for June,' said a PUB statement. The average rainfall for June is 162 mm.

When the rain first started at about 8am, PUB mobilised its contractors and staff on standby at hotspots and flood-prone areas, including Cuscaden Road, Wilby Road, Jalan Haji Alias and Little India.

When the torrent intensified at about 9.15am, the Traffic Police were alerted. PUB also despatched its officers and contractors to help stranded motorists, residents whose homes were flooded and owners of premises at affected locations.

'At the Upper Bukit Timah area, our men operated the flood gate and this helped to mitigate flooding in that area. PUB also sent sms alerts to the management of condominiums located in the area when the water level sensor reached 75 per cent at about 9.30am,' said PUB.

A second more intense storm fell over the central part of Singapore at about 10.30am. The worst-hit was the Orchard Road/ Scotts Road intersection, where the flood waters rose to almost knee-high. The deluge subsided within one hour, at about 11.30am.

PUB officers and contractors are clearing up the debris on the roads as well as assisting premise owners to pump out water from their basements.

The public can obtain the latest weather reports, including heavy rain warnings, by tuning in to radio broadcasts, calling NEA's weather forecast hotline at 6542 7788, visiting the NEA website atwww.nea.gov.sg or accessing the mobile weather service (Weather@SG - weather.nea.gov.sg).

The public can also call PUB's 24-hour Call Centre at 1800-284 6600 to report obstructions in drains or to check the flood situation.