Flash floods expected to worsen and become more intense

PENAMPANG: The Penang government on Nov 5 conceded that the floods currently affecting more than 100 areas in five districts in the state since Nov 4 was due, in part, to its drainage system.

State local government, traffic management and flood mitigation committee chairperson, Chow Kon Yeow, admitted that the existing drainage system could not accommodate the huge flow of water during heavy rain.

“The existing natural and man-made drainage systems could not cope with the flow of rain, especially since the very strong rainfall in all five districts, causing many areas to be flooded,” he told reporters.

The extraordinarily heavy rain since 2.00pm on Nov 4, which coincided with the peak of the high tide phenomenon, also contributed to the flash floods, he told reporters.

A scientist says flash floods on Penang Island are expected to worsen and become “more intense,” based on a study of past rainfall and increased development.

Kam Suan Pheng, an expert in soil science, said the island was now more likely to experience flash floods even after a short period of rain.

She said the heavier-than-usual rainfall these days doubled the likelihood of flash floods.

She said this was because the island has a complex mix of terrains and river systems compared with mainland Seberang Perai and, due to development, it had been unable to cope with excess rainwater.

“If you look at what the Penang state is like in terms of topography and hydrology, the island and mainland Seberang Perai’s rivers are different.

“The island has a more complex terrain and the natural drainage system is complex. With more hilly land down the spine of the island, rivers are shorter and faster flowing.

“Seberang Perai has a larger floodplain and fewer high lands. On the island, the population is denser, so we can expect floods to be felt more intensely,” she told a dialogue hosted by the Penang Forum today.
Kam said the natural system was once able to cope with increased rainfall but this was no longer true as more land had been developed.

She said the system was akin to a “sponge” that stores rainwater. It fed trees and evaporated to aid the natural rain cycle.

“When places get urbanised, the sponge gets smaller. So when there is development, the excess rainwater gets less absorbed into the ground and comes off as flash floods,” she said.

She said these “sponges” were usually the hill land, farmlands and riverbanks, which were mostly developed.

Kam said, after the hills were cut, rainwater came down these hills with mud and later flowed into rivers.

The rivers, in turn, became silted and shallower, carrying the teh tarik coloured floodwaters, she said.

Kam said the Penang government should have better planning of its land use and control development to prevent more intense flash floods in the future.

She said more trees should be planted, more large-scale parks created and the island’s rivers should be given space to widen.

She also said development projects should not be allowed on riverbanks.

Kam said the current flood mitigation projects by the state were fine but they merely treated the symptoms instead of curing the root cause of flash floods.

Article reproduced from Herald Malaysia online