Should developers incorporate stormwaters control systems within developments?

13 October 2020

Topic
The developers in a city should incorporate stormwaters control systems within their developments. This will obviate the need for the city authority to expand public drainage infrastructure to discharge the increased runoffs from their developments.

Background of Topic
Stormwater collection system in HDB Towns
Public Utilities Board (PUB) is the national water agency that manage water supply, drainage and sewerage.[1] Housing and Development Board (HDB) is the planner and developer of public housing. HDB has always collaborate with PUB to build infrastructure to drain surface runoff and channelled the collected rainwater into reservoirs.

PUB is constantly exploring options to expand the water catchment area to maximize Singapore's water sources. The Bedok – Sungei Seletar water scheme was completed in 1986 and it is the first urban water catchment in Singapore.[2] Under this scheme, rainwater are collected in the urban catchments of Bedok, Tampines, Pasir Ris, Ang Mo Kio and Yishun New Towns through a comprehensive network of drains and 9 stormwater collection facilities.[2] Rainwater are either drain directly into Bedok or Lower Seletar Reservoirs, or collected in stormwater collection facilities.[2] As there is a capacity limit for drains and reservoirs, the stormwater collection facilities act as additional storage space to drain surface runoff and rainwater collected will be pumped into the reservoirs when capacity permits. The Bedok – Sungei Seletar water scheme can collect 47,000m³ of water a day.[2] The water scheme won the Environmental Engineering Honour Award in the United States' National Competition in 1987.[2]

Initially, the 8 stormwater collection facilities at Bedok, Tampines and Loyang are utilitarian square concrete tanks that does not blend well with the residential surroundings. Subsequent stormwater collection facilities like Yishun Pond and Pang Sua Pond are landscaped ponds that collects stormwater and drains it to the respective reservoirs in their catchment.[2] In addition, existing ponds in Pasir Ris Town Park, Punggol Park and Woodlands Town Garden were adapted into stormwater collection facilities. The natural drainage network at Bukit Panjang, Woodlands and Sembawang New Towns were transformed into new urban water catchment during public housing development under the Seletar Streams water scheme.[2] These strategies are win-win solutions for both HDB and PUB, as Singapore lacks the space to collect and store rainwater, solve issues of excessive surface runoff and drainage capacity limit, and the waterbodies beautify the landscapes of HDB New Towns.

The latest instalment is Alkaff Pond, an artificial lake in Bidadari Park that is inspired by the former Alkaff Lake Gardens.[3] HDB designed Alkaff Pond to create a tranquil urban oasis within Bidadari Estate, its latest public housing estate.[3] Alkaff Pond also double as a flood control facility to slow surface runoff from the flood-prone Potong Pasir vicinity.[4]

Stormwater collection facility under flyover
Besides HDB, Land Transport Authority (LTA) built a stormwater collection facility under the junction of Bukit Timah Expressway (BKE) and Seletar Expressway (SLE) when constructing the interchange.[2] Besides collecting surface runoff, this reinforced concrete stormwater collection pond also maximized under-utilized space under flyover.[2]

Great Orchard Flooding
On the morning of 16 June 2010, Orchard was flooded by the infamous "Great Orchard Flood".[5] PUB's hydraulic analysis reported that intense rain and heavy accumulation of debris in the covered Stamford Canal drainage system caused the flood at Singapore's prime shopping district.[5] Debris trapped in a culvert obstructed water flow and reduced the draining efficiency of Stamford Canal, resulting in rainwater overflowing onto Orchard Road.[5] Furthermore, the construction of new malls (e.g. Ion Orchard, 313 Somerset and Orchard Central) on previously vacant greenfields might increase surface runoff beyond the maximum capacity of Stamford Canal.[22]

Many buildings, including Liat Tower, Tangs Plaza, Lucky Plaza and Ion Orchard, were severely affected by the "Great Orchard Flood".[6] While then Minister for the Environment and Water Resources Yacob Ibrahim described the June 2010 flood as an 'once in 50 years' freak event,[7] Orchard Road was flooded again by at least 6 flash floods in July 2010, June 2011, October 2011, December 2011,6 November 2012, and May 2018.[8]

After the June 2010 flood, PUB increased the frequency of clearing debris and maintenance of the Stamford catchment.[5] PUB also constructed the Stamford Detention Tank and Stamford Diversion Canal to improve the drainage capability of Stamford Canal and protect Orchard against floods.[9] Completed in September 2018, the Stamford Detention Tank under Botanic Gardens will temporary store excessive surface runoff, before pumping the rainwater back to Stamford Canal when capacity permits.[9] The covered Stamford Diversion Canal divert stormwater from the upstream of Stamford catchment into Singapore River.[9] Similar underground stormwater storage tank was built in Greater Tokyo (i.e. The Metropolitan Outer Area Underground Discharge Channel).[10]

PUB worked with building owners (e.g. Liat Tower, Tanglin Mall, Lucky Plaza, Wisma Atria) to install flood protection barriers.[9] In December 2010, Liat Tower spent $200,000 to install 19 anti-flood panels to form a 54m long barrier against floodwater of 80cm high.[11] In addition, the basement shops (i.e. Hermes, Wendy's, Starbucks and Massimo Dutti spent more than $11,000 to install portable slide-in floodgates at their entrances. However, the flood protection measures at Liat Tower did not work and the basement shops were flooded by rainwater again in December 2011.[6, 12] In March 2013, Lucky Plaza spent $1,000,000 to construct a 150m long pop-up flood barrier around the building.[13] The 1.2m high concrete panel lies flat as part of the corridor, but will sprung up after sensors detect water and set off a siren to warn pedestrian to keep clear. However, the flood barrier has not been activated yet.[13]

Flood Control Measures at Kovan
Intense downpour on 17 November 2014 resulted in the worst flash flood at Kovan, Hougang.[14] The heavy rain caused water to overflow from the upstream canal of Sungei Serangoon, flooding landed houses and basement carparks of condominiums along Tampines Road and triggered power outages.[14] The water level is ankle-deep at ground level and reached the windows of cars parked in the basement carpark of Fortune Park condominium, located along Tampines Road.[14] Severe flash floods were reported at the area again on 14 July 2017 and 30 April 2020.[15, 16]

As Kovan is a flash flood hot spot, several measures were implemented to address the problem. PUB completed the drainage improvement works to the upstream of Sungei Serangoon in March 2019, where the canal is widened and deepened, and roadside drains in the vicinity were upgraded.[17] Hydraulic analysis showed the drainage improvement works reduced the flood-prone area by 86%, and the 30 April 2020 flood was confined to the depressed road junction of Tampines Road and Hougang Avenue 1.[17] PUB and LTA are studying the feasibility to raise the depressed road junction.[17]

In addition, PUB loaned portable flood protection barriers to residents staying at the landed properties along Tampines Road,[18, 19] which were built decades ago and do not meet the prevailing minimum platform level standard.[19] The flood protection barriers are inflatable panels to be installed at doorways and requires the owner to manually pump to inflate it.[18, 19] Although it is difficult to setup the barriers, residents feedback that it is better than having nothing to protect against the flood and hope that innovation would improve the design.[18, 19]

On 12 August 2020, PUB announced that Fortune Park condominium was chosen for experimentation of a new smart flood protection system.[20, 21] The flood barriers will be installed at the entrance of Fortune Park, which will prevent the basement carpark from being flooded again.[21] The system do not requires electricity or manual operation,[20] as it will be automatically activated in the event of a flash flood and it will be able to block floodwater of up to 1m high.[21] This is the first flood control project piloted by PUB at a private residential development and is expected to be completed in October 2020.[21]

Private Developments
In the context of private development, PUB imposed minimum platform level as conditions for Government Land Sales (GLS) site, Additions and Alterations work and redevelopment.[23]

Assessing the Topic
In my personal opinion, to a certain extent, developers should incorporate stormwater control system within their developments as a 'final line of defence' against flash flood. However, the drainage authority should continue to forecast, plan, expand, manage and maintain the drainage infrastructure to discharge increased runoffs from new developments.

Developers to Raise Platform Level
Currently, PUB mandated that the minimum platform level of a development must be at least 104mRL and 104.5mRL for developments along the southern coast and northern coast respectively; or 300mm above adjacent road or ground level; or 600mm above the highest recorded flood level; whichever is higher.[23]

The highest floodwater level Singapore ever experienced was 40cm high.[19] Perhaps, PUB should consider revising the minimum platform level requirements from 104mRL and 104.5mRL to 105mRL, which is above the highest floodwater level. In this way, the development will be less likely to be affected by flash flood and rising sea level.

Incorporate Water Features in Urban Design
While PUB already encourage developers to incorporate ABC Waters design features within developments, the authorities might wish to consider providing incentives (e.g. bonus GFA, property tax rebates) to developers that incorporated such features (e.g. bioswales, rain gardens, wetlands) within landscape to reduce surface runoff.

If developers are to incorporate advance stormwater control system within their developments, there will be opportunities to create innovative multi-functional spaces where utilitarian stormwater collection facility could blend into the urbanscape through urban design. These stormwater collection facility could take the form of landscaped pond, water plaza, fountain garden, aquaculture or hydroponic farming. In fact, Benthemplein Water Square at Rotterdam is a successful stormwater management facility that doubles as a public square when dry and becomes a pond after a storm.[24, 25]

PUB may also consider imposing the construction of underground stormwater detention tank as part of a GLS condition.

Who to Bear the Cost & Responsibilities?
However, let's not forget that the Great Orchard Flood was a mistake (lack of maintenance), misjudgement and oversight (increase surface runoff from new developments) by PUB.[5]

It is unfair for developers and owners of existing buildings to bear the cost of constructing stormwaters control and flood management systems. The flood protection barriers at Liat Tower and Lucky Plaza are funded and built by developers and owners of existing buildings. It is particularly insulting for Liat Tower to pump so much money on a system that did not work.

While getting the developers and building owners to implement and bear the cost will help PUB to save substantial cost and effort, this strategy is not ethical and reflects badly on the image and competency of PUB as the national water agency. Furthermore, developers and owners are not experts in stormwater management. This strategy is as bad as shifting the mistake and blame to the developers and owners, which will cost heavily in political opinions.

Therefore, conditions imposed needs to be moderated, so that it is fair and not too onerous for the developers and owners. Alternatively, PUB should provide grants to existing building owners who need to install flood protection barriers.

References
1. Public Utilities Board. (2020, July 28). About Us. Public Utilities Board. Retrieved October 9, 2020, from https://www.pub.gov.sg/about
2. Lee, J. (1997, June 16). Catchment areas coming up in urban sites. The Straits Times.
3. Xue, J. (2013, August 29). New Alkaff lake for Bidadari estate. Today. Retrieved October 9, 2020, from https://www.todayonline.com/singapore/new-alkaff-lake-bidadari-estate
4. Tan, C. (2020, March 14). Bidadari to have flood prevention lake. The Straits Times. Retrieved October 9, 2020, from https://www.straitstimes.com/singapore/environment/bidadari-to-have-flood-prevention-lake
5. AsiaOne. (2010, June 17). PUB: Heavy rain and debris likely cause of Orchard flood. AsiaOne. Retrieved October 11, 2020, from https://www.asiaone.com/News/AsiaOne%2BNews/Singapore/Story/
A1Story20100617-222707.html
6. Won, X. L. (2018, December 27). 4 Floods in Singapore You May Have Missed In The Past 10 Years. The Epoch Times Singapore Edition. Retrieved October 11, 2020, from https://epochtimes.today/4-floods-in-singapore-you-may-have-missed-in-the-past-10-years
7. Au Yong, J. (2013, September 17). Idea of the '50-year flood' has been misunderstood. The Sunday Times. Retrieved October 11, 2020, from https://www.asiaone.com/singapore/idea-50-year-flood-has-been-misunderstood
8. Lam, L. (2018, May 26). Heavy rain causes flash flood in Orchard Road; vehicles stuck in murky water. The Straits Times. Retrieved October 11, 2020, from https://www.straitstimes.com/singapore/flash-flood-in-orchard-road-pub-issues-high-flood-risk-alerts-in-central-region
9. Public Utilities Board. (2018, September 28). Stamford Diversion Canal and Stamford Detention Tank Go Operational. Public Utilities Board. Retrieved October 11, 2020, from https://www.pub.gov.sg/news/pressreleases/
stamforddiversioncanalandstamforddetentiontank
10. 江戸川河川事務所. 首都圏外郭放水路とは. 江戸川河川事務所. Retrieved October 11, 2020, from https://www.ktr.mlit.go.jp/edogawa/edogawa00402.html
11. Today. (2010, December 23). New pop-up anti-flood system for Liat Towers. Today. Retrieved October 11, 2020, from https://www.eco-business.com/news/new-pop-anti-flood-system-liat-towers
12. Tan, L., & Liang, A. (2011, December 27). Countermeasures fail to stop flooding at Liat Towers. The New Paper. Retrieved October 11, 2020, from https://www.asiaone.com/News/Latest%2BNews/Singapore/Story/
A1Story20111227-318299.html
13. Koh, H. T. (2013, March 8). Lucky Plaza goes from sandbags to concrete. The New Paper. Retrieved October 11, 2020, from https://www.asiaone.com/print/News/Latest%2BNews/Singapore/Story/
A1Story20130306-406696.html
14. Tan, A. (2014, November 18). Tampines Road hit by flash flood. The Straits Times. Retrieved October 9, 2020, from https://www.asiaone.com/singapore/tampines-road-hit-flash-flood
15. (2017, July 14). Heavy rain causes flood at Tampines Road. Channel News Asia. Retrieved October 9, 2020, from https://news.nestia.com/detail/-/93285
16. Lay, B. (2020, April 30). Flash floods in a few areas in S'pore as torrential downpour pounds island. Mothership. Retrieved October 9, 2020, from https://mothership.sg/2020/04/flash-floods-singapore-2020
17. Ministry of Environment and Water Resources. (2020, May 27). Parliament Q&A. Ministry of Sustainability & the Environment. Retrieved October 9, 2020, from https://www.mse.gov.sg/news/written-reply-by-mr-masagos-zulkifli--minister-for-the-environment-and-water-resources--to-parliamentary-question-on-flash-floods--on-26-may-2020
18. Hariz, B. (2019, November 22). PUB to lend new anti-flood devices to residents and businesses for monsoon season. The Straits Times. Retrieved October 9, 2020, from https://www.straitstimes.com/singapore/pub-to-lend-new-anti-flood-measures-to-residents-and-businesses
19. Ang, H. M. (2019, November 22). PUB to deploy new portable flood protection devices for northeast monsoon season. Channel News Asia. Retrieved October 9, 2020, from https://www.channelnewsasia.com/news/singapore/pub-portable-flood-protection-devices-northeast-monsoon-12117310
20. 黄, 贝盈. (2020, August 12). 公用局拟试用新自动防洪栅栏. 联合早报. https://www.zaobao.com.sg/realtime/singapore/story20200812-1076372?amp
21. 吴, 俍㬕. (2020, August 12). 政府拟装新防洪栅栏 阻水淹进私人公寓. 8视界. https://www.8world.com/news/singapore/article/pub-flood-barrier-trial-1217736
22. Chua, G. (2010, June 17). PUB probes Orchard Rd flood. The Straits Times. Retrieved October 11, 2020, from https://wildsingaporenews.blogspot.com/2010/06/pub-probes-orchard-rd-flood.html
23. Public Utilities Board. (2013, June). Code of Practice on Surface Water Drainage. Public Utilities Board.
24. C40. (2014, August 27). Benthemplein Water Square: An innovative way to prevent urban flooding in Rotterdam. C40 Cities. Retrieved October 1, 2020, from https://www.c40.org/case_studies/benthemplein-water-square-an-innovative-way-to-prevent-urban-flooding-in-rotterdam
25. Bokern, A. (2014, June 5). Water Square in Rotterdam by de Urbanisten. Uncube. Retrieved October 1, 2020, from http://www.uncubemagazine.com/blog/13323459

[This is an essay submitted for "DEP5105 Urban Infrastructure & Mobility Systems" module on 13 October 2020 for AY2020/2021 Semester 1. "DEP5105 Urban Infrastructure & Mobility Systems" is offered by National University of Singapore (NUS) Department of Architecture (DoA) Master of Urban Planning (MUP).]

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