ABSTRACT
At present, the sediment became a serious problem to Shih-Men watershed, where its main river was called Ta-Han River. Since 1963, Shih-Men dam have been constructed mainly to provide the potable water to population of downstream area. It could also generate hydraulic power to industry and factories for promoting economic development. In 2004, Typhoon AERE assaulted northern Taiwan as shown in Figure 1, which its maximum rainfall intensity was 90 mm and accumulated up close to 1,600 mm recorded by the nearby rainfall gauge station, and it exceeded 200 year of return period. It caused many landslides and debris flows around the watershed. Accompanied with a series of landslides, some routes and roads had been interrupted to pass along. In the meantime, a mountain of rocks and soils had been taken into the main of Ta-Han River and became sediment. When the sediments had transported by the river flow from upstream to downstream and it had directly dropped to the Shih-Men dam. They made water of
the main river more turbid because fine content was the major component, which could not rapidly sink in the short term so that NTU excited up to high value. This critical situation could make no potable water to
drink about half of month. After Typhoon AERE, our government and research center had paid more attention and started to renovate the main and branch of Ta-Han River. Besides, they also wanted to find out which causes made the disasters happen.
