I REFER to last Tuesday's report ("Past flood assumptions might
not hold water"). While I agree that people should refrain from
littering, I do not think littering alone can clog our large
drainage and canal systems.
The report did not address the crux of the flood problem -
drainage clogging. I believe our drainage and canal system can cope
with most heavy rains, and flooding is caused only by chokes.
The PUB has done an excellent job of keeping the island
practically flood-free for many low-lying areas. It was very
unfortunate that it was caught off guard by the Orchard Road
flood.
Fast-flowing rainwater usually flushes drains and carries away
floating material along its path. In torrential rainfall, a greater
volume of water rushes through the drains and canals, creating a
more powerful flush at a higher speed to carry away small floating
litter to the sea.
When large items like logs, leaves and branches get caught at
certain spots in the drains, clogging takes place and this chokes
water flow. The PUB has taken effective measures to screen large
floating debris to facilitate the free flow of rainwater. More such
screening and constant clearing should be implemented at
flood-prone drainage systems around the island.
Since we live in a tropical city, we may face the prospect of
flash floods occasionally. It does not help to re-examine data and
update models and parameters. Only physical measures, like
increasing the gradient or deepening drains and canals, as well as
vigilant clearing of debris, will minimise the chances of
flooding.
Paul Chan
