Typhoon Morakot unleashed record rainfall on the south and wrought the worst damage of any typhoon in the past 50 years. Areas of Pingtung County affected by land subsidence — in which the land sinks below sea level — that had never flooded before ended up under water.
Flooding is a very real risk for areas affected by land subsidence and residents in these areas should have been aware of this. Flooding in upstream areas of Pingtung County was caused by a buildup of water that could not be naturally redirected into the ocean in time, which had dire consequences.
Apart from the record rainfall, there were two main reasons for the flooding. First, poor upstream soil conservation meant that the land was unable to absorb the rainwater effectively. Second, downstream, sea walls that had been built in the hope of protecting areas affected by land subsidence actually impeded the drainage of floodwater.
Many coastal areas are affected by land subsidence and the next time Taiwan experiences record rainfall, a similar disaster could occur.
I visited Pingtung in April for a forum on water management. While there, I noticed that many water control projects were under way in the area, such as increasing the height of sea walls, building pumping stations, widening drains, building underground reservoirs, recharging groundwater and conducting lowland afforestation.
These measures will only be effective for approximately 30 years and the aim is to minimize the amount of damage done by floods during those 30 years. However, the real problem is that residents are willing to put up with floods a few days out of a year but unwilling to leave areas affected by land subsidence.
For example, one residential building too close to the Chiang Yuan pumping station floods every time it rains. Other houses in the area have had special pumps installed.
Current strategies for water control are merely aimed at solving today’s problems because residents are unwilling to leave flood-affected areas, while the problems that make these areas susceptible to floods are getting worse.
For example, land subsidence in Linbian (林邊) and Jiadong (佳冬) townships, which are crammed full of cultivation farms, is on average 3m per century. Combined with the possibility that sea levels could rise 1m in the future, it has been estimated that land in these areas could drop another 3m between next year and 2040.
Land subsidence will continue to be a problem. Water control measures aim to solve local floods but do not solve the broader problems posed by inclement weather over large areas. The combination of these two realities means rescue work will become more important than water control projects as more areas sink below sea level.
The best way to adapt to these problems would be to make plans for Linbian and Jiadong townships for 30 years from now and to cooperate with the townships.
Since we cannot stop land subsidence in these areas, we should look at ways to relocate people from areas that will clearly continue to suffer from land subsidence over the next 30 years. We should also remove sea walls that are no longer necessary to allow excess water to flow freely into the ocean.
If we can meet these challenges, we could perhaps slow down the pace of land subsidence over the next 30 years and help minimize future disasters caused by heavy rainstorms.
Liu Chung-ming is director of the Global Change Research Center at National Taiwan University.
TRANSLATED BY DREW CAMERON
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