NUS conducts study on permeable road surface

Monica Kotwani Channel NewsAsia 7 Jul 13;

SINGAPORE: Porous surfaces could be another means of controlling flash flooding in Singapore.

For instance, concrete slabs with hole in neighbourhood carparks is among the many methods adopted by urbanised countries like Singapore to mitigate flooding after heavy rains. The little grass patches in them absorb rainwater.

Channel NewsAsia understood the National University of Singapore has been studying the concept of permeable surfaces for minor roads and pavements in a bid to slow down the flow of water into drains after heavy rainfall.

When it rains, the water will be absorbed through a layer of porous concrete and flow through a layer of gravel to store water temporarily.

The gravel has about 30 to 40 per cent space in between to store water.

An overflow channel will drain water from the gravel layer during heavy storms or long periods of rain.

Below the gravel, a layer of geotextiles, or permeable fabrics, filters the water further into the ground.

Weep holes are present throughout the subsoil layer for water to seep through to the drains.

This whole process could result in holding up to a few hours of rainfall and take up to 24 hours to slowly seep into the ground.

However, an engineering expert said challenges could still exist.

Associate Professor Tan Soon Keat, deputy executive director at Nanyang Environment and Water Research Institution, elaborated: "Maintenance will be an issue. If water can go through, it also means debris will be trapped between the pebbles. This type of practice coupled with proper design of base layer, can be used in pedestrian walkways or perhaps pathways in parks, or pedestrian malls."

Prof Tan said such porous surfaces would be most feasible in areas that don't carry heavy loads such as trucks and cars.

The national water agency PUB recently imposed stricter flood prevention requirements on new developments.

From June this year, developers will need to implement on-site measures to slow down the flow of stormwater into public drains.

This rule will apply to new projects that are of size 0.2 hectares or more.

Green roof is one of such on-site measures designed to control stormwater runoff.

Made up of plants and green spaces, these popular features on top of commercial and residential developments serve two functions - treating water for it to be reused and slowing the release of water into drains after a heavy downpour.

Experts said it makes sense for developments to play their part.

Chong Kee Sen, vice president of The Institution of Engineers in Singapore, said: "In Singapore, what we experience is short duration, high intensity rainfall. We are designed for that situation that happens once in every 10 years. It would be relatively costly for us to have storm drainage for public drains to be sized to cater to such situations. In land scarce Singapore, this may not be a viable solution.

"What could be a good solution in this case, where each small little development plays their part in reducing the maximum rainfall into the drainage system, thereby preventing a flood situation and at the same time, reducing the cost in terms of construction of public drains."

- CNA/fa

A flood prevention idea ... using porous road surfaces
Monica Kotwani Today Online 8 Jul 13;

SINGAPORE — The National University of Singapore is studying the idea of using permeable surfaces for minor roads and pavements, which could help prevent floods by slowing down the flow of water into drains after heavy rainfall.

These surfaces would allow water to be absorbed into a layer of porous concrete and flow through a layer of gravel, to be stored temporarily.

About 30 to 40 per cent of the space in between the gravel is used to store the water, which will then flow through a layer of geotextiles, or permeable fabrics, before it exits through small openings into the drain.

The whole process could hold up to a few hours of rainfall.

However, an engineering expert said challenges still exist.

Associate Professor Tan Soon Keat, Deputy Executive Director at Nanyang Environment and Water Research Institute, said: “Maintenance will be an issue. If water can go through, it also means debris will be trapped between the pebbles.

“This ... practice, coupled with proper design of the base layer, can be used in pedestrian walkways or perhaps pathways in parks, or pedestrian malls.”

Assoc Prof Tan added that such porous surfaces would be most feasible in areas that do not carry heavy loads such as trucks and cars.

National water agency PUB recently imposed stricter flood prevention requirements on new developments.

From last month, developers are required to implement on-site measures to slow down the flow of stormwater into public drains. This rule will apply to new projects with land sizes of 0.2 hectares and above.

A green roof is one such on-site measure. Made up of plants and green spaces, these popular features on top of commercial and residential developments serve two functions — treating water for it to be reused and slowing the release of water into drains after a heavy downpour.

Experts said it makes sense for developers to play their part.

Mr Chong Kee Sen, Vice-President of the Institution of Engineers Singapore, said: “What we experience is short-duration, high-intensity rainfall. It would be relatively costly for us to have public drains to be sized to cater to such situations. In land-scarce Singapore, this may not be a viable solution.

“What could be a good solution will be for each developer to play its part (in slowing the release of water into drains), thereby preventing a flood and, at the same time, reducing the cost of the construction of public drains.”