Committee recommends flood control measures

Esther Ng Today Online 2 Jul 11;

SINGAPORE - Humps just before basement entrances of commercial and residential buildings should be raised from 15cm to 30cm, while the ground level of these buildings should be 60cm above the road or highest-recorded flood levels.

These are some of the recommendations of the Inter-Agency Drainage Review Committee released on the PUB website yesterday, which are now open to public consultation.

The cost involved in adopting these changes would be "negligible" for new buildings but could be "technically challenging" for existing building as some sites may not have "sufficient dimensions to achieve such compliances", said president of the Singapore Institute of Architects, Mr Ashvinkumar Kantilal.

For instance, raising the crest level will necessitate a steeper approach gradient, but not all sites may be able to accommodate this, said Mr Ashvinkumar.

Still, he said, "a one-off implementation cost" should not be seen as being prohibitive and can be defrayed by some form of grant or subsidy from the relevant authority similar to the Building and Construction Authority's current practice in defraying part of the overall costs in converting existing buildings to increase accessibility for users, he said.

Associate Professor Susanto Teng from Nanyang Technological University's School of Civil and Environmental Engineering said: "Raising the crest levels from 15cm to 30cm is quite high and likewise the platform level of buildings, but it sounds reasonable and practical."

The amount of rainfall drains can hold have been more clearly defined based on catchment area or importance of the development.

For instance, drains designed to accommodate a once-in-25-year flood should be able to serve catchments between 100 hectares and 1,000 hectares, while drains serving a once-in-50-years rainfall should have enough capacity to serve areas covering 1,000 hectares. Catchments can be car parks or other paved areas and verges.

"There are a lot more paved areas than, say, 15 years ago, so rainwater flows much faster into our drains. These recommendations are timely and prudent," said Associate Professor Vladan Babovic from the National University of Singapore's civil engineering department.

In addition, the minimum reclamation levels have been increased by 1m to 104m along the southern coast and 104.5m along the northern coast, to cater for rising sea levels due to climate change and storm surges.

For areas affected by high tides, the proposed platform level - the required minimum ground level of a development - would be raised to 104m from 102.5m along the southern coast.

The previous parameters were 75cm above 101.75m - the highest tide level along Singapore's southern coast.

The proposed ground level for the northern coast will rise to 104.5m up from 103m.

The expert panel on drainage design and flood protection measures have reviewed these proposals, and without providing specifics, have advised adopting an even higher level of flood protection for critical installations like airports and business district areas.

They also recommended incorporating "detention ponds" which can help to mitigate constraints such as limited land for widening.

Inter-agency committee proposes change in drainage design
Esther Ng Channel NewsAsia 1 Jul 11;

SINGAPORE: The PUB has released a set of recommendations to avoid flood situations in commercial and residential buildings.

Crest levels at the basement entrances of commercial and residential buildings are to be raised from 15 to 30 centimetres, while the ground level of these buildings should be 60 centimetres above the road or highest-recorded flood levels.

These are some of the recommendations of the Inter-Agency Drainage Review Committee (IADRC) released on the PUB website on Friday.

In addition, the amount of rainfall drains can hold have been more clearly defined based on catchment area or importance of the development. For instance, drains designed to accommodate a once-in-25-year flood must be able to serve catchments between 100 and 1000 hectares.

Drains serving a once-in-50-years rainfall must cover 1,000 hectares.

In addition, the minimum reclamation levels have been increased by one metre to 104 metres for the southern coast and 104.5 metres along the northern coast.

The minimum reclamation level was raised to cater for rising sea levels due to climate change and storm surges.

For areas affected by high tides, the proposed minimum ground or platform levels would be raised by about 1.5 metres from 102.5 metres to 104 along the Southern Coast and from 103 metres to 104.5 metres along the Northern Coast as additional safeguards from rising sea levels due to climate change.

-CNA/ac