Wed, Oct 06, 2010 - Page 8 News List

Empty talk reigns after the flooding

By Shern Jian-chuan 沈建全

As Typhoon Fanapi swept across eastern and southern Taiwan on Sept. 19, it brought extremely heavy rainfall of 500mm to 800mm or more in six hours to Gangshan (岡山) and Ciaotou (橋頭) townships in Kaohsiung County and Nanzih (楠梓) and Zuoying (左營) districts in Kaohsiung City. That is well in excess of the 480mm deluge that can be expected to occur once every 200 years. In fact, we could expect this kind of volume to occur in these areas only once every 500 years. Such heavy rainfall is bound to cause flooding, whatever city it falls on.

Various media pundits and academics, however, have failed to judge this objectively. Instead, for their own political purposes, they have chosen to lash out at the Kaohsiung City Government. Such emotional criticism is hardly reasonable. It would have been better to have taken a more scientific approach.

When rain falls on a plain, it has to run through a drainage system, converging in streams and rivers before finally flowing into the sea. On this occasion, the flooded area included the aforementioned four townships and districts and spread over half of Kaohsiung City, about 210km2 in total. The drainage system for this lowland plain consists of just four rivers — the Agongdian (阿公店溪), Dianbao (典寶溪), Houjin (後勁溪) and Love (愛河) rivers. The discharge capacity of these four rivers, measured in cubic meters per second, is about 500 for the Love River, 600 for the Houjin River, 340 for the Agongdian River and 250 for the Dianbao River, adding up to 1,690m3 in all. If the average rainfall over six hours for the 210km2 that were flooded was 600mm, then the total amount of rain that fell on that area in that time must have been 126.3 million cubic meters.

Over the same period, all the drainage rivers in that area could only discharge 36.5 million cubic meters of floodwater — just 29 percent of the total — while the remaining 71 percent (89.8 million cubic meters) had nowhere to go. It could only sit there, flooding the area to an average depth of 43mm, or flow into low-lying areas where the flood would then be even deeper.

Another factor to be considered is that, as the center of Typhoon Fanapi moved out to sea near Tainan in the afternoon, powerful winds blowing in a counterclockwise direction drove a storm surge at least 1m high onto the coast of Kaohsiung. That, combined with the high tide that came in at dusk, blocked the floodwater from discharging into the sea.

With such a heavy rainfall and given the accompanying conditions, there was going to be a flood no matter who happened to govern Kaohsiung city and county at the time. The city and county governments must bear some responsibility for failing to dredge the drains beforehand and to provide plenty of sandbags to keep floodwater out of basements, as well as extractor pumps to pump out water when it got in. But other than that, it was a matter of waiting calmly in the emergency operations center, ready to handle any situation as it arose.

Indeed, at 6am on the day after the typhoon, the Kaohsiung City Environmental Protection Bureau’s garbage collection teams were fully mobilized to clear away fallen branches and shop signs. That task kept them working late into the night and they spent three days clearing trash until the job was done. They should be commended for their perseverance and efficiency.

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