On June 3, Changhua, Yunlin and Chiayi counties and Greater Tainan were hit by a series of thunderstorms. Most streets in Chiayi City are supplied by the high-lying Lantan Reservoir (蘭潭水庫) on the east side of the city toward lower areas on the west side. Given that Chiayi is built on hilly land about 100m above sea level and considering its geological composition of red soil and gravel beds, it is not an area in which floods should easily occur.
The main cause of the floods is connected to the rising property prices over the past decade. Before development, most of the land was hilly terrain that effectively drained and held back floods. The hinterland around Chiayi Park and the Chiayi Botanical Garden performed a similar function. However, almost all of these hills have been developed into luxury homes and non-agricultural village estates for the rich. These commercial developments are paved with impermeable surfaces.
Consequently, even Chiayi University’s Lantan campus is awash with mud. When rain fell on Fenci Lake (奮起湖) and the upper reaches of the Bajhang River (八掌溪) 20 years ago, it took about eight hours to reach the south side of Chiayi City 40km away. Now it takes little more than two hours to arrive.
A policy should be adopted of redefining and rescaling the drainage of urban areas that lie in the path of rivers throughout Taiwan, and checking if the drainage areas are sufficient. This could be the basis for adjusting national land planning and the division of administrative districts.
Global sea surface temperatures have been rising about twice as fast since the 1970s. With this in mind, drainage and flood control channels should be planned according to rainfall figures for the past 20 years and projecting the scale of floods in the next 50 or 100 years, rather than relying on statistical data from the past 100 years. We have recently experienced a succession of rainstorms that have repeatedly broken records.
Stormwater retention and drainage systems for densely populated areas and large and influential public construction projects in downstream areas should be improved, expanded and made more effective, section by section and year by year. As for upstream mountainous areas, they should be properly regulated to stop the cycle of commercial development and accompanying public works.
These measures would reduce the risk of landslides and floods following heavy rainfall. They would also prevent the constant menace of pollutants such as pesticides and fertilizer, not to mention excrement, running into reservoirs where they are stored up and supplied as toxic drinking water to people living downstream.
In places where flood prevention and drainage systems have been insufficient to handle the torrential rainstorms of past decades, it may be necessary to employ rigid enforcement measures to limit the intensity of land use in urban areas, cutting the amount of artificial surfacing used so as to make land more permeable. Building more flow barriers between sections and areas upstream would also be an effective short term measure.
The documentary Beyond Beauty: Taiwan From Above (看見台灣) has made many people more aware of the dangers to our environment. This awareness must be turned into action to prevent floods, improve the quality of drinking water, break the cycle of disasters in mountainous areas and stop the waste caused by the mistaken allocation of resources. The starting point is national land planning, waterway and drainage basin management, and controlling the development and use of the nation’s land and rivers.