Two typhoons hit Taiwan last weekend, causing flooding in the coastal and low-lying areas in Chiayi and Pingtung counties and in Tainan. While many expressed disappointment at the effectiveness of the government’s flood control measures, others have proposed that the flooded areas be given priority in the water infrastructure part of the Forward-looking Infrastructure Development Program.
Due to overpumping of groundwater, land subsidence and inferior drainage in the western coastal areas, it is unavoidable that typhoons and torrential rain will result in flooding there.
The main cause this time was the incredibly heavy rain, with Jiadong Township (佳冬) receiving 182mm of rain per hour — more than four times the definition of “heavy rain” by the Central Weather Bureau.
Such levels would cause great damage anywhere in the world. In Chiayi, where rainfall exceeded 200mm in two hours, storm sewers were overwhelmed. Luckily, unlike the catastrophic floods caused by Typhoon Morakot in 2009, flooding this time only occurred in a few areas.
The highest flood reached waist-high this time. Although the floods have caused great inconvenience and financial losses to many people, there have been much worse floods in the past.
Controlling floods in low-lying coastal areas is difficult, as available methods are restricted to building embankments and pumping stations, and other traditional means.
However, these make it difficult to avoid flooding once rainfall exceeds capacity.
For example, the drainage system in Jiadong and Linbian Township (林邊) is designed to handle 400mm of rain per day. The latest flooding in Jiadong was not a result of flawed engineering — it was a natural disaster, pure and simple.
The only way to improve flood prevention is to install larger pumps. However, where will the pumped water go? Discharging it in other areas could worsen flooding there.
To protect urban and high-value industrial areas from flooding, nearby rice paddies were used as temporary retention basins, as they can survive a few days of flooding, while flood control infrastructure costs could be kept lower.
However, rice farmers today might be less willing to cooperate. That would add to the cost of flood control infrastructure and lead to more land expropriation.
If you were a landowner, would you prefer occasional flooding or having parts of your land expropriated for infrastructure such as drainage canals and detention ponds?
Before engineers propose a flood control plan, they have to consider a variety of factors, including society, the environment and costs, with the most important factor being a project’s cost-benefit ratio.
From the public’s perspective, cost-benefit ratios might not always make sense, as people tend to prioritize their own interests and do not hesitate to protest when they feel that these have been tread on.
Since the government has limited resources, infrastructure projects must be cost-effective and prioritized according to their urgency. The government cannot and should not prioritize flood control infrastructure in an area just because of one extreme weather event.
A more difficult problem is that as the nation keeps seeing record-breaking rainfall, the public must be prepared to live with natural disasters as a part of their lives. If people are unable to adapt, the cost of flood prevention investment might become prohibitive as disaster prevention measures fail to keep up with changing hydrological conditions.
Chang Yen-ming is a former deputy director of the Taichung branch of the Water Resources Agency.
Translated by Tu Yu-an
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