Straits Times Forum 5 Dec 09;
WE THANK Mr Narayana Narayana ('Floods a freak event, or could we have tracked it?', last Saturday) and Mr Thomas Lee ('Floods - I would have thought such events were well within our ability to prevent or minimise', Tuesday) for their letters on the Bukit Timah flood.
The heavy rain in the Bukit Timah area on Nov19 was exceptionally intense. In just two hours, 110mm of rain fell, of which 92mm fell from 1.20pm to 1.50pm. This was equivalent to about 40 per cent of the rainfall for the entire month of November falling within the half an hour.
The National Environment Agency (NEA) issued a warning at 12.45pm that day to alert the public to expect heavy rain in the afternoon over many areas of Singapore. However, the exact locations where exceptional rainfall is expected are difficult to predict in any weather forecast. PUB also issued flash-flood advisories to residents and shop owners in low-lying areas in October and to the media on Nov 16 as part of its monsoon preparations.
The huge amount of rain within such a short time that day caused Bukit Timah Phase 1 Diversion Canal to fill up and overflow. However, Bukit Timah Phase 2 Diversion Canal which channels stormwater from the middle part of Bukit Timah to Marina Reservoir via Kallang River did not overflow.
PUB had already initiated plans to deepen and widen Bukit Timah Phase 1 Diversion Canal before this incident. While this upgrading work was intended primarily to cater to increased stormwater runoff from new developments in the next 10 years, it will also help to mitigate the extent and severity of flooding of other intense storms. Works on the first stage are slated for completion by 2012.
Ten fast-track projects were also recently completed to alleviate flooding in flood-prone areas, and five major flood-alleviation projects are ongoing. Flood-prone areas in Singapore have been reduced from 3,200ha in the 1970s to about 79ha today.
In land-scarce Singapore, it will not be cost- effective to build a large and extensive drainage system that caters to all extremities. A balance is needed between setting aside more land for such infrastructure and other requirements for Singapore's development.
PUB will regularly review and improve drainage infrastructure across Singapore to ensure an effective drainage network. Such continuous efforts will help further mitigate the risk of floods.
Tan Nguan Sen
Director (Catchment and Waterways)
PUB
Ms Wong Chin Ling
Head (Operational Services Department)
Meteorological Services
National Environment Agency
Floods
Straits Times Forum 1 Dec 09;
'I would have thought such events were well within our ability to prevent or minimise.'
MR THOMAS LEE: 'I refer to last Saturday's letter, 'Floods a freak event, or could we have tracked it?' I would have thought such events were well within our ability to prevent or minimise. In this age of computer simulation, areas likely to be affected could easily be mapped out. When heavy rain occurs, with input from meteorological experts, such spots should be identified quickly and warnings sent out via telcos, TV and radio. That is total defence.'
