| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系碩士在職專班 === 102 === Taiwan has steep landscape and fractured rock layers. Hence, human development, frequent earthquakes and rainfall from typhoon events are likely to cause landslide on mountain slope, silt sediment and loss of soil and water resources. The occurrences of earthquake and typhoon usually cause disaster in downstream area. This research takes Tsengwen reservoir basin as the area under study. The research objects are landslides in the watershed caused by induced earthquakes and rainfall events since 1974, the year when reservoir operation begun. The interpretation results of aerial survey and satellite images, field investigations and measurement data of river course and reservoir sediments are the main data for this research; data before and after typhoon flood and earthquake events are integrated with factors like landscape and geological distribution to perform source and tendency analysis of sediment yield. The analysis results are described below: (1) in the case of flood events, events of accumulated rainfall over 840mm cause heaviest topsoil erosion and vegetation destruction. Events of accumulated rainfall over 840mm are the most important cause of reservoir sediments. (2) in the case of earthquake events, loose soil and gravel are piled at the cliff foot or in the river course. Without strong currents for transportation, apparent sediment difference will not immediately occur. (3) in the case of the effects of typhoon flood and earthquake are joined, the average sediment yield of recent 10 years are 3.46 times higher than the average sediment yield of past 26 years. (4) in the case of the turbidity increases from 7~9 NTU to 500 NTU, the chlorine mixture dosage in purified water rises from 1.74 (mg/L) to 2.34 (mg/L); the liquid aluminum sulfate mixture dosage also rises from 22.41 (mg/L) to 84.72 (mg/L). The increases of water purification costs are linearly multiple rises. (5) the initial plan expected the reservoir remains in operation until 2120. However, sediments seriously shorten the reservoir life span. Now the reservoir can only operate until 2086.
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