Thu, Sep 06, 2018 - Page 8 News List

Flooding can only be mitigated

By Chang Yen-ming 張炎銘

Heavy rainfall has brought widespread flooding to southern Taiwan, where city and county governments blame the Central Weather Bureau for making inaccurate forecasts and not warning local authorities early enough.

The Tainan City Government has said it would need NT$65 billion (US$2.1 billion) more over 30 years to complete its flood control and prevention plans. This is not the right attitude.

Politicians brag about their political achievements in terms of “solving” or “eradicating” floods, but hydrologists know that floods can never be eliminated.

There are plans to invest several hundred billion New Taiwan dollars in everything from flood control plans in flood-prone areas and integrated flood management within drainage basins to the creation of water environments as part of the Forward-looking Infrastructure Development Program.

However, this investment can only alleviate ponding and flooding in certain areas, and reduce the damage and losses caused by disastrous floods, because the design standards and degree of protection of every water control project are limited. Even countries with the most advanced flood prevention technology can never be completely free of floods.

The government must still accept the blame and shoulder its responsibilities, but no one should harbor the illusion that anyone can guarantee safety forever.

Experts suggest mitigating floods by means of “sponge cities.” A few years ago, flood detention basins were popular in flood prevention; more recently, the trend has been the use of “intelligent rivers” to provide early warnings and prevent disasters.

Every method is right and effective in its own way, but even a multipronged approach using multiple methods has limits.

When a “sponge city” has absorbed as much water as it can, the excess water that it cannot absorb could cause a disaster. Flood detention basins are effective, but how big can they be and how much rainwater can they hold? If they overflow, it would cause ponding and flooding in nearby areas. Intelligent river management can provide early warnings, but that would not necessarily eliminate deaths, injuries and property damage.

Science and technology are limited, rendering weather forecasting a difficult task, but even more advanced technology and more accurate forecasts would not solve all the problems.

Standards for urban drainage in some localities only call for a five or 10-year return period, meaning that floods can be expected to recur every 10 years on average. It is useless to authorize pumps to deal with torrential rainfall if all the nearby waterways are overflowing and there is no place to pump the water.

Hoping that disastrous floods will never happen is wishful thinking. Even if the government were to spend huge sums of money to expropriate land and demolish buildings, with no concern for public opinion, and enlarge flood channels, the effect would be limited.

Perhaps the return period should be lengthened to 50 or 100 years. Even Taipei, with a return period of 200 years, had widespread flooding when Typhoon Nari struck in September 2001.

Countries with the most advanced flood prevention, such as the US and Japan, have also experienced disastrous floods in the past few years.

Climate change is causing ever-greater extremes of drought and flooding, and existing standards might not match real conditions.

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