Flash Floods in Orchard Road

Mr Ang Wei Neng asked the Minister for the Environment and Water Resources in view of the flash floods which occurred on 23 December 2011 (a) whether the recently completed flood management strategies such as the raising of Orchard Road helped to prevent the flash floods; (b) whether the SMS alert service had adequately alerted shop owners and shoppers at Liat Towers and Lucky Plaza of the water "ponding"; and (c) what additional measures would PUB take to mitigate similar occurrences in the Orchard area.

Mr Yaw Shin Leong asked the Minister for the Environment and Water Resources (a) what are the reasons for the "ponding" phenomenon in Orchard Road and what are the technical differences between "flash floods" and "ponding"; (b) whether the drainage improvement projects scheduled for 2012 would have any impact on the flooding/ponding situation in Orchard Road; and (c) to what extent was due diligence done to ensure that Orchard Road's drainage systems were clear of debris that could obstruct the flow of water.

The Minister for the Environment and Water Resources (Dr Vivian Balakrishnan): Mr Speaker, Sir, may I have your permission to answer both Question Nos 4 and 5 together?

Mr Speaker: Yes, please.

Dr Vivian Balakrishnan: I thank both Members for their questions. Over the last six months, I have spent a lot of time walking the ground, looking at plans, maps and peering into drains. With the indulgence of the House, I propose to give a detailed answer and to take all supplementary questions thereafter.

Stamford Canal drains a catchment area of 631 hectares – that is quite a significant chunk. It starts upstream at the Botanic Gardens and Dempsey Hill. It extends downstream to Bras Basah and City Hall areas and ultimately drains into the Marina Reservoir. Orchard Road is a valley in the mid-section of this catchment area. It is bounded by higher ground to the north of Orchard Road, characterised by the Mount Elizabeth area. To the south is the Leonie Hill area. If Members would look even more closely, they would realise that there are two smaller hills Cuscaden in the west and Cairnhill in the east. What this means is that not only is there a valley, there is also – superimposed on this – a basin between Cuscaden and Cairnhill Roads. This explains why this particular stretch of Orchard Road is of special concern with regard to flooding.

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There have been three episodes of flooding in the Orchard Road area over the past 18 months. On 16 June 2010, some 100 millimetres (mm) of rain fell in the area over two hours. This resulted in the stretch of Orchard Road between Cuscaden Road and Cairnhill Road being flooded to a depth of up to 300 mm. On 5 June 2011, a few days after I moved to the Ministry, some 124 mm of rain fell on those areas over about four hours, and caused the Tanglin area to be flooded to a depth of some 100 mm. Most recently, on 23 December 2011, even heavier rainfall occurred – this time, some 153 mm of rain over three hours was recorded over the same catchment area.

I have taken pains to state the numbers, but I want to remind Members of the trend that for these three episodes, each time, there has even been higher rainfall falling on the catchment area. These three episodes are really part of a larger and longer pattern of rainfall change that is occurring in Singapore. If Members would look at the second slide [ indicating ], we have plotted the maximum one-hour intensity of rain in each of these 30 years over the past three decades. I had the expert panel review this together with the scientists in the university. Their conclusion was that Singapore is experiencing, on a secular basis, increasing intensity of rainfall. Whether this continues into the future is something which will be measured and proven over time.

The point is that we are facing a situation of increasing rainfall intensity, together with increasing urbanisation, and Orchard Road is a case in point. Nevertheless, over the past three to four decades, PUB has invested very heavily in drainage infrastructure. They have spent about $2 billion over the past three decades. This has, in fact, reduced the low-lying flood-prone areas in Singapore from 3,200 hectares (ha), which was the situation in the 1970s, to today's 49 ha. These are low-lying flood-prone areas. Prolonged extensive floods that some of us in this House – I think anyone who is above the age of 40 here – will remember that in our childhood, when floods inundated large areas and stayed for many hours, when traffic, services and many other things were disrupted, fortunately, no longer occur. What we are confronted by today are transient localised episodes, typically lasting up to about half an hour or so, and they occur in areas where the rainfall intensity has temporarily overwhelmed the local drainage systems.

There was a question that I think Mr Yaw asked about: the technical difference between a flash flood and a pond. Let me just say that as far as I am concerned, PUB should not have used the word "ponding". As far as I am concerned, I call a spade a spade – a flood is a flood. As long as there is water accumulating somewhere where it is not supposed to be, as long as it has implications on human safety or business operations, that is a flood, and it is a problem that needs to be resolved. PUB and the building owners must resolve it.

Let me now return to the episode on 23 December last year. What PUB actually intended to highlight was the fact that despite this being the third episode, and despite the fact that there had been even heavier rainfall, Orchard Road itself – the arterial road for traffic – remained passable at all times. To a large extent, this was because of the completion of the road-raising works which began last year and was completed by June 2011. This slide [ indicating ] attempts to show several things. The lowest line shows the profile of the bottom of the canal. You have a blue line above that, which is based on data derived during this heavy storm, together with a computer model, to indicate the level at the top of the canal. What this slide will show is that the section which we have indicated, had we not raised the road by June 2011, in December we would almost certainly have faced flooding on Orchard Road itself and traffic would have been impacted.

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As far as the buildings were concerned, because all the building owners along this stretch of Orchard Road had been placed on alert and had taken extensive measures to mitigate the impact of flooding, the net result was that, in fact, the problems were confined primarily to the basements of Liat Towers and Lucky Plaza.

I met the building owners and the management of both these buildings. And I can assure the House that they are taking their mitigation and prevention measures seriously. For instance, Liat Towers has now completed building a 60 cm-high wall to prevent rainwater from overflowing from an internal drain into its basement. Lucky Plaza is in the process of installing new flood barriers to prevent water from the pavement flowing into its basement. In addition, they have also described that they are going to build some new sumps and pump systems so that they will be better able to cope with the flow of water. But it is noteworthy, and I think we should all remember, that Liat Towers and Lucky Plaza are very old buildings. They have been there for more than 30 years, and their basements really make them vulnerable. So, we may need both short-term and long-term measures.

There has also been much speculation by various people about the role of Marina Barrage. It is worth highlighting to the House that I instructed PUB to maintain the water level in Marina Reservoir during the entire month of December at below mean sea level. Even in the midst of the storm, with a heavy inflow of water from Stamford Canal and Bukit Timah Canal into Marina Reservoir, we were still able to maintain the level of water in Marina Reservoir below mean sea level. This is only possible because we have a barrage and we have gates and very large pumping systems. If we did not have a barrage, then we would not have a reservoir in the first place, and secondly, the water level in the lower reaches of the Singapore River, Stamford Canal and Kallang River would then be subject to tidal influences.

The point I am making is that, in fact, having a barrage, having pumps and having gates gives us more control, not less control. Having said all that, I should also point out that the level of water in Marina Reservoir does not affect the hydraulic situation of water in the upper reaches of Orchard Road, and this is simple physics. At Grange Road, the platform level is 108 metres; in other words, it is 8 metres above mean sea level. So, the real reason for keeping and controlling the water level in Marina Reservoir is to protect the low-lying areas like Chinatown and other areas in the city centre, which are the true low-lying flood-prone areas that we will recall from the days of our childhood.

Having said all that, in the long run, we do need to increase the capacity of Stamford Canal. I have set this very simple challenge to PUB. I said: let us assume that we will continue to have storms exactly similar to what we had in the last three episodes. In fact, let us assume further that they may even be worse than that. Within reasonable limits, in order to cope with such an incident, what kind of enhancement do we need to make to Stamford Canal? And the reply that the engineers came back to me with was that if we wanted to be able to be almost guaranteed that we could cope with similar storms of the last 18 months, then in the long run we needed to increase the capacity of Stamford Canal by 30%.

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Well, here comes the next problem. I think many Members will be familiar that whenever PUB has a drain, we have a drainage reserve. In other words, we always have space where, if we need to – to deepen or widen the drain – we will take them from the owners of a public utility. In the case of Stamford Canal, which Iies under Orchard Road, we have run out of drainage capacity. Secondly, to now embark on further surgery on Stamford Canal would cause enormous disruption to the services and operations, and pedestrian and vehicular flows along Orchard Road.

I put all these to the House because I want Members to understand that we are constrained on the ground and, as I will explain later, there will also be major financial and fiscal factors that we have to take into account.

PUB is evaluating other options to increase the overall capacity of Stamford Canal. In fact, there is an ongoing consultancy study, which I think will only be completed in May this year. Some of the ideas they are studying include building storm water detention ponds upstream. In the past, whenever we had to deal with the floods, the answer was very simple – increase the flow rate. You increase the flow rate by widening and deepening drains. I think we will need a more sophisticated approach in the future and it may involve, in fact, retaining water upstream, so that you reduce the peak flow rate during the peak of the storm. As I said earlier, we are trying to deal with flash floods, and not with prolonged periods of inundation like what we see in Thailand or other places of the world.

These detention ponds are not going to be cheap. To give Members again an idea of scale, they have a capacity of 40 to 50 Olympic-size pools. We will need land two to three times the size of a football pitch. Putting aside land like that in precious real estate in the Orchard Road area – I think Members will agree – is something which you do not enter into lightly.

There is also another idea which they are studying, which is to build a diversion canal to divert water from the upper third of the Stamford catchment, cut across the Grange Road highlands and ultimately to reach the Singapore River, somewhere around Zion Road. That will be another major engineering project which will cost $300 million to $400 million. Again, it is not something which we enter into lightly. PUB has built diversion canals and again for those who are old enough, you will remember that the Bukit Timah stretch used to flood very regularly and very severely. In fact, there are two diversion canals which divert some water from Bukit Timah Canal into Pandan Reservoir, and another part into the Kallang River. I am just giving Members an idea, so that you will understand the level and intensity, and the costs of these major projects. In the long run, these do need to be done. In the short run, there are also things which we need to do.

For instance, it is important for us to ensure that every single drain and canal that currently exists is free-flowing, not choked by litter and is performing according to specifications. PUB and its contractors have intensified their daily cleaning and inspection routine. In certain portions, they have even installed underground closed circuit television so that we can continuously monitor the performance of these canals. In preparation for the ongoing northeast monsoon, PUB has also stepped up the frequency of cleaning and inspection of drains, especially in flood-prone and litter-prone areas, and in areas with heavy leaf shedding.

The public also has a role to play. If Members should notice any drain that is clogged or dirty, please let us know. We have made it very convenient for you to call through to our 24-hour call centre or post a message on the PUB Facebook or through the iPhone application which we have also published for free.

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We checked the drains in Orchard Road on 23 December 2011, including those in St Regis Residences, Orchard Towers, Liat Towers, and we did not find any drains to be blocked.

Let me now turn to building owners. PUB cannot solve this problem alone. It is necessary, at least in the short to medium term, that building owners take the initiative to protect themselves and take additional preventive measures. We will also review their SOPs with them because whenever things go wrong, it is not just a matter of infrastructure. It is also a matter of operational procedure. Does everybody who needs to know, know the facts, and to know the facts in real time? And has everyone taken appropriate action? This is a whole level of additional training and collaboration which we will need to go on with the building owners. Of course, we will make sure that building and renovation plans conform to drainage regulations. Members will also recall that just last month, we had, in fact, upgraded our draining regulations, raising platform levels, having crest-protection for basement carparks in order to ensure that we do everything possible in the medium term to reduce the impact of floods.

Beyond that, it is information. Last year, we made a free SMS alert system available to members of the public information on weather, rainfall, the level of water flowing within the canals. Over the last few months, we have continuously increased the number of sensors. Nowadays, fortunately, sensor technology is not as prohibitive as it was in the past and, depending on your area of interest, you can indicate to PUB which times you want to be alerted. For those who just enjoy a Twitter cascade, well, look for the hashtag #sgflood. I can assure you, PUB floods that hashtag because I believe that we need to ensure that accurate real-time information is available to everybody so that they can take appropriate measures.

Let me conclude by saying that the weather has changed. Increasing urbanisation has changed and although we are not dealing with prolonged periods of inundation, even flash floods in a built-up dense city like ours do have an impact. Therefore, we have to have plans for the long term to deal with this eventuality. In addition to that, we are embarking on both short-term maintenance as well as medium-term preventive and mitigative measures, and we are working with building owners and members of the public to deal with this.

Mr Ang Wei Neng (Jurong): Mr Speaker, Sir, I would like to thank the Minister for his comprehensive reply. We understand that it is going to be difficult to widen Stamford Canal, but could the Ministry perhaps also consider deepening it as one of the measures? Is it just a matter of costs? The second supplementary question is that we understand that PUB has also announced that it will do an enhancement on some 10 canals to handle the future flood situation. But we also learn from the Minister that the rainfall intensity in Singapore has increased quite tremendously. So for these 10 projects, how much of the capacity is PUB increasing? Would this increased capacity be able to handle the flash floods that we experienced in Orchard Road and more?

Dr Vivian Balakrishnan: If I could get the third slide back up, which will show Members the profile of the drains. Members should have a copy of it. Members will notice that, in fact, the Stamford Canal is already very deep. If we go any deeper, we will create a Stamford basin, which is not the objective. So the point is: we need to either slow down the rate of inflow into Stamford Canal through detention ponds, or have an alternative bypass. The example I can give from the medical perspective is, if our coronaries are choked, we do a bypass. It increases the total capacity of the system. Equally related to that, something which I did not have time to explain is that we are examining the flow dynamics within Stamford Canal. For example, even without widening – basically reducing the friction to fluid flow within the canals – whether that can also buy us a few percentage points of increase in the transmission. We also have to make sure that there are no obstacles in there and, if there are services and other pipes which need to be moved, we will do so. In other words, I am trying to maximise the current utility of Stamford Canal without taking more land and without disrupting traffic and business any further.

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The other point was intensity. The Member is absolutely right. It is also the reason the Ministry is investing more in climate science and in our ability to predict weather changes and to have some reasonable projections on the type of intensity we have to deal with. What I do know is that we do need to increase and enhance our planning norms, but this cannot be a blank cheque for PUB. Well, Singapore does not intend to be Venice, with canals everywhere. So there has to be a reasonable limit to how much we prepare for the future. The assurance I will give is that we will do so on the basis of evidence, science and discipline as far as fiscal expenditure is concerned.

Mr Yaw Shin Leong (Hougang): I thank the Minister for his comprehensive reply. It is heartening to hear the Minister share his candid response on the ponding versus flooding debate. I have three supplementary questions. One, would the Minister agree that the introduction of large scale developments in Singapore has resulted in an acute loss of open space that is open to absorb rainwater into ground water table, reducing excess run-off that could contribute to flooding. Two, would the Minister also consider going further upstream to treat the problem at the source by requiring developers to submit environmental impact assessments prior to each construction? This is a common best practice in developed cities around the world. Three, is MEWR integrating and coordinating such studies as part of its routine and ongoing system in view of PUB's drainage masterplan?

Dr Vivian Balakrishnan: Sir, I thank the Member for those three supplementary questions. The expert panel will be publishing its findings sometime later this week. In fact, this was also one question which we posed to them. As we urbanise Singapore, as there are more concrete and pavements everywhere, we would expect that there would be greater run-off or rapidity of flow of rain that has fallen on our pavements. What this means is that our drainage norms which were good enough in the past may not be good enough to cope with it. This is being taken into account.

The Member has quite rightly said therefore that future developments in Singapore need to take into account the impact on the environment. But it is in a larger sense of it. Every new building, road and new development makes a difference to drainage, pollution, traffic and health. It has multiple facets to this. So I agree with the Member's third point that, in fact, this calls for greater collaboration and integration among all the planning agencies and the approving authorities to ensure that future developments are sensitive, rational and enable us to cope with the changing climate.

Mr Speaker: Ms Irene Ng. Last question.

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Ms Irene Ng Phek Hoong (Tampines): Sir, the Minister spoke about the twin trends of increasing rainfall intensity and increasing urbanisation. Can I ask the Minister if he will conduct a review of all the masterplans for construction projects and land use to see whether there has been over-construction, and how we reserve land to put in place more protection for green areas? For instance, the Bukit Brown cemetery, whether it is really necessary to build over it. To just look over it with a fresh eye, given the information that we are affected by these twin trends. May I also ask the Minister whether the increasing rainfall intensity is due to climate change and, if so, what are the wider implications of this in Singapore, given that we are a low-lying flat island?

Dr Vivian Balakrishnan: I am not the Minister for National Development although I did spend some time there. Firstly, on the Masterplan. In fact, if we actually look at the map of Singapore, or the next time you fly in or out of Singapore, look out of the plane. You will realise that despite us being so crowded and dense, we still have a lot of green areas which MND and URA have deliberately sought to preserve. So we are not a concrete jungle. And I will take the risk of speaking on behalf of Minister Khaw Boon Wan to say that I am sure he does not intend for Singapore to become a concrete jungle where all rain that falls will flow along drains. That is not the case. The Member is absolutely correct that we need to get the balance right between development on the one hand and its impact on the environment on the other hand. I can give the Member the assurance that both the Ministry of the Environment and Water Resources, and the Ministry of National Development work very closely on this.

The point on Bukit Brown, I believe, should be a separate Parliamentary Question.

On climate change, this is a source of long-term worry. At this point in time – I will give some examples – there have been different models, and the model which we are paying special attention to is the one which projects a rise in sea level. There have been some reports that have suggested that Singapore needs to prepare that, by the end of this century, sea levels could rise by 65 mm or more. When I was in Durban in December 2011, I met a senior scientist from the World Meteorological Association. He said, "No, no, you need to be worrying about more than one metre of rise", which is highly worrying for a low-lying city state like ours. We hope that these are changes which will take a few decades to unfold and, therefore, we will have time to prepare for it now.

For instance, last year, we made a decision that for all future reclamation projects, we will raise the platform level by an additional metre. This will cost us a lot of money in the short term because it means getting more sand. But we are buying insurance for the future. Similarly, if any of you are developing new buildings, for example homes and so on, you will often find that PUB will insist that you raise the platform level. Typically, in a specific area, if there has been a flood before and we know what the high level of flood is, we will insist that new developments start at a platform level of at least 600 mm above that.

Again, it is buying insurance for the future. So the point I am trying to make is that there are potential worrying long-term trends for us which we need to prepare for today. We need to do so in a careful, calibrated and rational way because, otherwise, you end up taking the risk of either spending too much money in the short term or, worse, taking the risk of not being prepared for the future. I suppose most of us will not be here at the end of the century, but I think we still owe a responsibility to our children and grandchildren.

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