page_title: Shihmen Dam
section_title: Later history
hierarchical_section_title: Shihmen Dam / History / Later history
caption_attribution_description: 中文（台灣）‎: 興建中的石門水庫大壩及溢洪道。
context_page_description: Shihmen Dam is a major rock fill dam across the Dahan River in northern Taoyuan City. It forms the Shihmen Reservoir, Taiwan's third largest reservoir or artificial lake. It provides irrigation in Taoyuan, flood control for the Taipei Basin, and hydroelectricity and domestic water supply for more than three million people in northern Taiwan.
  Completed in 1964 after nine years of construction, Shihmen was Taiwan's first multi-purpose water project and a major step towards the island's economic independence after World War II. Year-round water releases from the dam enabled additional rice harvests and doubled Taoyuan's annual agricultural output, while the reservoir became a major tourist destination due to its scenic beauty and plentiful fisheries. However, the project was criticized for its high cost and its impact on local communities, as more than 2,000 people were displaced to make way for the reservoir.
  Like many other reservoirs in Taiwan, Shihmen has suffered from sedimentation, reducing its capacity by over a third. Efforts to reduce the rate of sediment accumulation, including dredging, check dam construction and watershed restoration work, have had a limited effect.
context_section_description: Engineers estimated that the natural sedimentation rate would give the reservoir a useful life of at least 71 years without any sediment removal. However, just four months after the reservoir began filling, Typhoon Gloria struck Taiwan, and the resulting floods washed 19 million cubic metres (670 million ft³) of sediment into the reservoir – taking 23 years off its expected lifespan. As the reservoir filled, it also inundated several historic landmarks, including the former summer villa of Chiang Kai-shek, the Amuping Stone Bridge and a nearby Earth God shrine.
  Irrigation was the primary goal of the Shihmen reservoir; about 22,000 hectares (54,000 acres) of new farmland came into production after the dam was built, bringing the total to 57,000 hectares (140,000 acres). The annual crop was more than doubled due to an increased water supply for pre-existing farmland. Individual farmers' income rose by almost 20 percent. About 27 kilometres (17 mi) of canals were added to the existing irrigation system, including the new Shihmen Canal, bringing the total to 175 kilometres (109 mi), and a treatment plant with 30,000 tons per day capacity was constructed to provide municipal water supply. Despite the scale of the project, the increase in agricultural production was estimated to feed 500,000 people, or less than two years of population growth. The importance of the dam for irrigation has been decreasing since the 1990s as Taoyuan County saw significant urbanization; in the meantime, demand for cleaner domestic water has risen.
  The government allocated NT$21 million to develop the Shihmen Reservoir as a recreational area. Boating facilities and about 31 kilometres (19 mi) of new roads were constructed to improve access to the reservoir. The reservoir would also be stocked with game fish, and its shores would eventually be developed with "temples, museums, monuments, pagodas, hostels and residences." After the dam was completed, it brought prosperity via tourism to this rural area, helping to diversify its economy from one solely reliant on agriculture. However, due to the project's high capital cost, the actual annual return on investment was only 1.5 percent: "It stands as an engineering monument of which the Chinese people may be proud. But it was purchased at far too high a cost in terms of tens of millions of dollars of alternative developmental opportunities foregone."
caption: The spillway, nearing completion in 1964
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