Prevention of flooding in Singapore

Transient Dams

Dr Seow Onn Choong

As we are all aware the recent floods have caused a great deal of discomfort  and loss of money in the areas affected. To make matters worse the recent  flooding of Tanglin Mall and St. Regis Residences coincided with the anniversary of the flooding of Orchard Road just last year.  PUB is at a loss on how these disasters can be prevented. Orchard road 's level was raised at a great cost with buildings installing flood barriers. This had now shifted the floods further up the drainage system thus affecting Tanglin Mall area.

Many suggestions have been put forth. These include building additional canals running parallel to the existing canal or building underground storage tanks near these flood prone areas. AS PUB has put the blame on climate change would these measures be successful. Furthermore the construction of such devices at such built up areas will not only be very expensive but extremely  destabilising to the surrounding businesses. At best we are only trying to treat the symptoms.

What is the real cause behind the floods?

Climate change may be the cause but we cannot blame nature. We have no control over it and at best  must adapt to it.

The most important factor is also a man made problem. I would  like to call it the increase concretetisation of Singapore. As you can see there is rapid development in Singapore with construction of ever bigger shopping malls and homes. All these structures and the associated land are contributors to the floods we see. The rain does not just fall on the flooded areas but also on every inch of land.

Many government policies have also contributed to the sudden deluge of water. The most obvious is the efficient drainage of  water. When we see things locally we want to build drains that can drain away all the water as swiftly as possible so that the area does not flood. Recently one can see that most drains have been covered up.  This has brought us more walking space and also more greenery. However I was told it was meant to prevent leaves from falling into drains and thus do not end up in the reservoirs.  In addition gutters have been banned and the traditional water storage tanks for watering gardens have now been abandoned.

My proposal is very simple. Every building or land owner is a stakeholder and contributor to this flooding  problem we are now facing. We must now make every stakeholder hold on to the rain water that falls on their compound and release it at a rate that does not affect other stakeholders further down the drainage system. This would prove to be a cheaper and faster method to be implemented. It can be also used in all areas that was flooded  not just those prime areas.

Methodology.

The function of transient dams can be likened to fire rated doors. These doors are meant to delay the spread of fire in buildings so that not only can it give the occupants time to escape, It also enable the fire brigade to do its job without the building being gutted. The design of these dams is very unique.  When there is no rain  or during light rainfall water flows through this dams without any resistance.  This is possible by allowing an opening at the  base of the barrier. Thus there will be no stagnant pools of water or silting at the barriers. When heavy rain occurs, the amount of water reaching the barrier is now restricted by the flow rate through the opening. Thus water will build up behind the barrier . The top of the barrier is lower than the height of the drain . When the volume of water is too much for this section  water will overflow the dam into the next section . As such excess water is released . This prevents flooding at the vicinity of that dam. Technically speaking if many such dams are built in a drain , the whole  drain can  be converted into  a temporary reservoir. Now if you can imagine if all the drains in any drainage area is dam up , a giant reservoir can be created. Once the rainfall slows or when the rain stops, water will slowly drain away from this temporary reservoir.   Please see diagram to understand the construction of the dam.

The most important task is  to make a survey of all our drainage system with priority given to those areas affected by the floods recently.  With the information obtained  we can  outline all the contributors of the water to the flood prone areas .Next we must build transient dams in all  the drains involved.

Every building must install such dams at  their outlet which connect to the public drains. In addition they can construct water features to enhance the retention of water. These  water features can contribute to watering of plants in their compounds thus avoiding the present wasteful system of using tap water. In public areas which are relatively lightly developed existing  drains can be enlarged and deepened to create a bigger volume to hold the rain water. A good example is Dempsey area which in all  probabilities contributed to the recent Orchard Road floods.

In comparison  to those suggestions on prevention measures as outlined earlier, my proposal of creating transient dams could be the most effective  both in cost and the  quick delivery of the system  The dams are simple and cheap to construct. The existing infrastructure can be converted without any interference to the existing stakeholders

  Initially one  would need only  angled  metal bars and wooden planks. Since the dams are made of wood their effectiveness can be easily adjusted and the dams can be removed once better or more permanent flood prevention methods are introduced.

In future the design of drains must be changed not to drain water swiftly away but also to hold on the water for a period of time. We must also encourage homes and buildings to store rainwater not only for watering their gardens but also to use in their toilets. It does  not make sense for us to send our rainwater down the drain to be process and then bought  back to water our gardens. The fear of mosquitoes infestation can very easily be overcome as there are many  preventive measures.

The priority now is  to stop flooding in Singapore. We will never know when the next big storm will arrive.

Dr Seow Onn Choong   19 june 2011