Flood Resilience in Singapore

Singapore is an independent island nation located at the southern tip of the Malaysian peninsular, at a busy crossroad of world shipping lanes. The 716 square kilometre country thrives on international financial trade and in 2012 its 5.3m population was one of the world’s five richest populations per capita in terms of GDP. It also has the fifth largest port in the world. Its people have a reputation for hard work and strict discipline, and Singapore was one the ‘Asian Tigers’ of the late 1990’s and has an unemployment rate of only 1.9%. Yet there is one problem this rich island nation is still struggling with; flash-flooding during the annual monsoon seasons.

Although Singapore has experienced only four major floods in the last 60 years, and was ranked the least vulnerable to climate impact of 11 major Asian coastal cities in the 2009 Asian Mega-Cities Report, the cost of damage during localised flooding is increasing, and with sea-level increases becoming a real threat, the city is investigating ways of addressing the issue. The National Environment Agency has reported that the number of rain days per annum has increased by 1.5 days per decade, with average rainfall per month increasing from 96mm in 1980 to 117mm in 2012.

At a population density of 7,540 people per square kilometre, the country is considered 100% urbanizediv with 80% of Singaporeans living in high rise apartments. Rapid urbanization in the form of high rise buildings with associated paved areas and roads has led to increasing run-off of Singapore’s average rainfall of 2,400mm per annum, whereas previously most of it would have soaked into the soil. The majority of the rain falls during the two monsoon seasons, November to March and May to September. In an attempt to manage all this surface runoff, Singapore now has 7000km of roadside drains running into canals and 32 main rivers.

Construction of drainage systems started in 1914 as a means of draining stagnant pools to prevent breeding of malaria-carrying mosquitoes. In 1951 a Joint Committee on Flood Prevention was established, and this body promoted the widening, deepening and concrete-lining of canals to alleviate flooding in densely developed and flood-prone areas such as Queenstown, Geylang, Bedok, Potong Pasir, Whampoa, Jurong, Tampines and Seletarv.

In addition, a tidal-gate system was designed in the 1960’s for the Central Business District and other areas in central Singapore that were below the high tide level and faced frequent flooding during high tides.

Urbanization along the Singapore River resulted in severe pollution of the waterway, with concentrations of refuse impeding its flow, but a 10-year campaign in the 1980’s saw it cleaned up significantly and cleared of blockages that exacerbated flooding. Today the river is a popular recreational and cultural venue.

According to PUB, Singapore’s water supply and management authority, concerted efforts and careful land development planning have reduced Singapore’s flood prone areas from 3,200ha in the 1970s to the 56ha currently. This has been at a cost of S$2bn (US$1.6bn) over the last 30 years. PUB is now targeting its flood-prone projects in areas where flash-flooding and ponding still occur. 22 canals were identified in 2010 as requiring upgrading to cater for increased run-off volumes.

floods singapore 1970s
Flood prone areas of Singapore in the 1970s
floods singapore
Flood prone areas of Singapore today

In 2011, however, Singapore’s Expert Panel on Enhancing Flood Protection released a report noting that, although Singapore’s storm-water drainage system compared favourably with those of other major metropolitan cities, all drainage systems have a finite capacity and the design and network of canals and drains in Singapore was no longer adequate to handle higher rainfall levels. Professor Chan Eng Soon, the panel’s chairman stated that “Conventional design approach and standards are not sufficient to secure an adequate drainage system for the future, especially given global climate changes”, and that “PUB needs to consider a wider range of measures that mitigates the effects of urbanisation. I think it could look at solutions in a more holistic way”.

As a result, PUB has adopted a multi-pronged ‘Source-Pathway-Receptor’ approach to addressing storm-water managementvi, aimed at Source Areas (the 1976 Code of Practice on Surface Water Drainage – COP – was revised in 2013 to require new developments to slow down run-off that would be discharged into the public drainage system by incorporating features such as roof gardens, water gardens, porous pavements and detention tanks); Pathways (PUB is increasing canal capacities by 30% to 45%); and Receptors (the 2013 COP requires entrances to new and redeveloped buildings in low–lying areas likely to receive floodwaters to have minimum platform and crest protection levels or install alternative flood protection measures)vii. PUB has also implemented strategies for increasing public preparedness for floods, using SMS alerts on heavy rains, live CCTV images of flood-prone areas, and updates through social media

Implementation of these measures will be over a relatively lengthy time period and, as the numerous recent events in different parts of Singapore have shown, flash-flooding may be a part of urban life for some time to come so, if you visit Singapore in monsoon season, don’t forget to find out how to receive SMS flood alerts.

Sources: Channel News Asia; PUB; Singapore Business Review

Images / Maps: PUB