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 had 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 this later flowed into rivers.
The rivers, in turn, become silted and shallower, carrying the teh tarik-coloured floodwaters, she said.
Kam quoted the late Kam U-Tee, who was former Penang Water Authority chairman, on the flash flood situation in Penang. She said U-Tee had foreseen the problem during the October 2008 massive floods in Penang.
“U-Tee said the Paya Terubong and Bayan Baru valleys were converted into concrete aprons, causing water to run straight into the streams and causing flash floods, even with moderate rainfall.
“U-Tee also attributed it to hill-cutting activities, which led to the erosion of slopes, carrying mud and silt into rivers and making them shallower.
“I think this observation is still accurate today,” she said.
Flood mitigation alone won’t help
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.
She said the authorities should look at the bigger picture when approving projects, adding that the environmental impact assessment (EIAs) by themselves would not suffice.
“EIA alone is looking at a project with blinkers on. You must look at the accumulated effects of the development.
“Dredging rivers and installing more pumps are reactive measures. It is repetitive and very costly.
“One should be looking at non-structural measures, such as having a drainage master plan, which the state Drainage and Irrigation Department has vowed to do. Prevention is better than cure.”