08 June 2011

Flood Alert System and Lessons for Nuclear Power Preparedness

Tanglin Mall and St Regis Residences, both located along Orchard Road, were flooded following a short period of intense rain on 5 June 2011.

As part of its flood warning system, Public Utilities Board has sensors installed in drains and canals.  The sensors monitor the water level every two minutes when it rains, and every ten minutes during dry conditions.  When the water level reaches the 75 per cent mark (which indicates moderate flood risk) or 90 per cent mark (which indicates a high flood risk), the sensors send SMS alerts to the owners of the buildings in areas prone to flooding.

It appears that intense rain on 5 June caused the water level to rise so fast that it bypassed the trigger points of 75 per cent and 90 per cent, according to PUB.  As a result, the SMS alerts were not sent.

It is not clear why the system was not designed to trigger an SMS alert when the water level exceeds the 75 per cent mark or the 90 per cent mark at the time of measurement or monitoring.  For example, what triggers the alert at the 75 per cent mark should be the water level being at 75 per cent or higher (or water level not less than 75 per cent, which is the same thing) at the time of measurement or monitoring.

PUB has now modified the system so that it will send SMS alerts if the water level rises beyond the 100 per cent mark.

It is not clear why the system was not originally designed to trigger another SMS alert when the water level reaches or exceeds the 100 per cent mark, which is when water overflows from the drain or the canal.

PUB will also look into reducing the two-minute interval for monitoring the water level when it rains.  The two-minute interval was based on past records (presumably of the rate at which the water level rose).  What happened on 5 June was that the water level was rising about three to four times as fast as that in its worst-case scenario, according to PUB.  Ideally, the interval for monitoring the water level should be dynamic, shortening as the water level rises.

PUB should also ensure that the sensors are able to trigger SMS alerts not only when the water level has reached any predetermined mark but also (more importantly) when the water level has risen past any predetermined mark since the last time the water level was measured or monitored.  Otherwise, whether the marks are set at 75 per cent, 90 per cent or 100 per cent may not make much difference to the efficacy of the SMS alert system.

The flood was distressing and painful for everyone affected — the occupants of the shop space, the building owners and the insurers.

Now, suppose it was not a flood, but a nuclear accident such as that at Fukushima Daiichi.

I am convinced that Singapore should never have a nuclear power plant.


1. Public Utilities Board ("PUB") is Singapore's national water agency under Ministry of the Environment and Water Resources.

2. PUB Tweaks Flood Alert System TODAY (8 Jun 2011).

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