In 1972, PUB finished constructing a canal that runs from Bukit Timah Road/Dunearn Road near Sixth Avenue to Clementi Road, to contain the frequent floods in the areas.

Just 19 months ago, in September 2019, the canal underwent an upgrading completed at a cost of $300 million to prepare for more frequent floods till 2100.

It was one of the most expensive and complex drainage improvement projects that the agency had undertaken.

Despite this recent upgrading of the Bukit Timah canal, the Bukit Timah and Dunearn Road areas were hit with a massive flood last Saturday.

Singapore's drainage network plan may not have taken into consideration the increase in urban developments.

Rapidly, over the years, forests have been cleared for more buildings and road developments, making Singapore a bigger concrete jungle.

In forests and grasslands, rainfall permeates through the soil, which stores water in the sub-surface layer and below.

As forests and grasslands are cleared for infrastructure developments, the permeable soil is replaced by the impermeable surfaces of roads, parking spots and concrete paths, which result in flooding when the drainage system and canals are full.

The increase in underground deep tunnel developments - such as underground MRT networks, the Deep Tunnel Sewerage System, and underground ammunition storage facilities - results in more flooding, as these concrete structures replace the earth where rainfall used to be absorbed before the earth was removed.

The same thing happens with earth being excavated for deep basement shopping levels and carparks.

In developing sustainable drainage plans, national water agency PUB needs to work closely with the Land Transport Authority, Building and Construction Authority, National Parks Board and other relevant government agencies.

Aaron Ang Chin Guan