| Summary: | 碩士 === 國立中央大學 === 應用地質研究所 === 100 === The major portion of sediment yield in Shihmen reservoir was contributed from landslide caused by extreme storm events. Water turbidity of reservoir was often affected due to heavy rainfall that includes plum rain (March to May), typhoon (July to September), and northeast monsoon (November to January) in Taiwan. This study is focused on surface erosion after heavy rainfall in the past three years, so as to assess the relationship between heavy rainfall and water turbidity in the watershed of Shihmen Reservoir. Upper montane catchments of Shihmen Reservoir, from 2008 to 2010 were used to construct hydrological conditions and time series of turbidity. The effects of seven typhoon events namely Kalmaegi, Fung-Wong, Sinlaku, Jangmi, Morakot, Fanapi, and Megi were examined. It was found that the relationship between discharge and turbidity was related to the antecedent rainfall, rainfall characteristics, and the timing of the events in the typhoon season. In contrast, typhoons which took place right after others showed clockwise hysteretic loops in the upstream of catchment area, indicating signs of sediment depletion. Sometime the turbidity- discharge relations exhibit counterclockwise or figure eight attributed to different rainfall characteristics. On the other hand, typhoons showed counterclockwise hysteretic loops in the downstream of fully supplied catchment area, indicating signs of sediment supply. Furthermore, some of the turbidity- discharge relations exhibit clockwise or figure eight can be attributed to different rainfall characteristics. The correlation of hydrological conditions and turbidity is expected to be beneficial in the mitigation of sediment yield of Shihmen Reservoir for future typhoon events.
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