Bangkok’s city centre may be spared from heavy floods, but suburban residents want to open up the dikes to allow water out. Anger grows, but officials can do little to help.
The first thing Professor Han Vrijling does is open up an atlas, showing Thailand’s geography: a horseshoe of mountains with an elongated flat plain in the middle. Three majors streams join into the Chao Phraya River, which flows southward to the Gulf of Thailand. “All the water from the surrounding mountains collects in the flood plain and swells the river. And right there, at the mouth of the river, is Bangkok.”
No wonder then that the monsoon, which has been going on since July, has brought high waters to the Thai capital. What makes matters worse is that about 9 million people live there and that retrieval of groundwater has caused significant subsidence of the street levels there. In other words: the floods are not new, but the densely populated capital has become more vulnerable to them.
“There’s an important difference with the Dutch situation,” explains Prof. Vrijling. Holland has to be protected from water from the sea and from rivers. In Thailand, however, the rains are so strong that the water produced within an area surrounded by dikes can no longer be neglected. Indeed, suburban citizens have forced officials to open up barriers to allow the water out of their neighbourhoods at the risk of an adjacent industrial estate.
Prof. Vrijling, a hydraulic expert (Civil Engineering and Geosciences), has conducted a flood management study for Vietnam, where the situation is comparable. Unlike the Dutch situation, where dikes are designed to reduce the risk of flooding to once in 10,000 years, floods are a fact of life in Southeast Asia. Prof. Vrijling advised the Vietnamese authorities to attribute different levels of flood protection to designated areas. A flood every year for the flood plains, once in three years for low value crop fields, once in six years for high value crops, and once in 50 years for the cities. Required dike heights are proportional to the level of protection they offer. In Thailand, there’s one more issue: the Chao Phraya River meanders quite a bit near Bangkok. Dredging the river and opening a by-pass would help to discharge the river more quickly.
Professor of water management, Nick van de Giesen (CEG), agrees with Prof. Vrijling on the compartmentalisation in high, medium and low-risk areas. But he also observes that people have been building very close to the river, as if floods were something from the past. Moreover, he recalls that houses on the flood plains were traditionally built on poles, which kept the living space a meter or so above the ground. Modern houses in the suburbs do not offer the same protections.
Last year’s monsoon was exceptionally heavy, as is this year’s. Still, one cannot say if the events are related to climate change. What can be said is that climate change is expected to bring more rain to these areas. Air contains about 7 percent more moisture for every degree that it is warmer. Research shows that recirculation may boost that figure to 10 percent more rain for every degree warmer. Until now, hydrological aspects of climate change have been underexposed, Prof. Van de Giesen says.
Link to article in Delta
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