March 14 was the International Day of Action for Rivers, having been declared as such in 1997 by anti-dam and environmental concern groups from dozens of countries, including Taiwan. Dams have a profound effect on ecosystems, and when they are built in geologically unstable areas, there is a danger that they may collapse and cause disastrous floods downstream. Indeed, such disasters have frequently occurred in the past. This is why the construction of dams must be approached with great caution in Taiwan, where the ecology and geology are both very fragile.
Following Typhoon Morakot last August, the bed of the Laonong River (荖濃溪) in southern Taiwan rose in some places by more than 23m, and the cross-watershed transfer project built to supply water to the Zengwen Reservoir (曾文水庫) in Taipei County was almost completely ruined. That was followed on March 4 by the Jiasian earthquake, after which environmentalist groups found that the transfer conduit tunnel was crossed by four geological faults, presenting the danger of collapse in case of a powerful earthquake.
As a result of multiple typhoons and earthquakes, Taiwan’s reservoirs are silting up faster than they can be cleared. Information published by the Water Resources Agency shows that the Zengwen Reservoir is so silted up that its capacity is just 37 percent.
These examples, along with the demands of river ecology and the impact on the national treasury, show why there needs to be a rethink about reservoir construction in this country. The government, however, appears not to have noticed, since it is now thinking of building even more reservoirs in places such as Pingsi (平溪) in Taipei County and Hsinchu County’s Bilin (比麟) and Gaotai (高台).
The most common response when environmentalists speak out against dam construction is: “If we don’t build dams, where will we get our water from?”
Despite the limitations posed by Taiwan’s natural conditions, there are many other ways to ensure sufficient water supply. These include protecting mountain forests that conserve water, more frugal water use and reducing leakage. There are also alternative sources that can be tapped. We should confront the water crisis by learning from the standards applied in arid countries, such as developing seawater desalinization and technologies that reuse and recycle water. There is scope for extending groundwater replenishment and building relatively low-cost and low-risk underground and riverbed wells. These are all options worthy of consideration.
The nearly century-old Erfeng Ditch (二峰圳) is a riverbed filtration system built in Pingtung County during the Japanese colonial period. The cost of its construction, when calculated at today’s rates, was only about 1 percent of the cost of building the Meinong (美濃) Reservoir and associated cross-watershed transfer project, but the Erfeng Ditch still provides 100,000 tonnes of clean water per day. It was water reclaimed and purified by the Dashu (大樹) sewage treatment facility that ensured an adequate supply for everyday use in the Kaohsiung region after Morakot.
Taiwan ranks 18th among nations most lacking in water, yet 24.6 percent of our water is lost through leakage from pipes, and we have the second-highest consumption of water per person in the world. Clearly, there is much scope for water-saving efforts. Reservoirs have irreversible effects on mountain, forest and river ecosystems. From both engineering and management points of view, governments should first employ water-saving measures and alternative sources such as those described above, while reservoirs should be the last option on the list.
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