Evaluating Landslides and Sediment Yields Induced by the Chi-Chi Earthquake and Followed Heavy Rainfalls along the Ta-Chia River

10.6310/jog.2007.2(2).4

Shian-Jin Chiou；Chin-Tung Cheng；Shih-Meng Hsu；Yan-Hsiang Lin；Shu-Yeong Chi

Chi-Chi earthquake ； typhoon ； landslide ； sediment yields

Journal of GeoEngineering

2卷2期（2007 / 08 / 01）

73 - 82

英文

Chi-Chi (Taiwan) earthquake and the followed typhoons induced heavy landslides and debris flows in the watershed of Ta-Chia river, the sediment yields from landslides caused lots of damages on the infrastructures including dams, power plants, bridges, villages and recreative parks. In order to evaluate the geohazards due to landslides and sediment yields along Ta-Chia river, the quantitative evaluation was conducted by using remote sensing images obtained at 6 stages of major disastrous events. Furthermore, the HEC-6 program was adopted to simulate the condition of deposit of Ta-Chia river in the near future according to the case history in Japan. The results show the highest level of riverbed deposited around the Chingshan office would raise more than 20 m in addition. Among the branch creeks of Ta-Chia river, Pi-Ya-Sun creek and Ji-Ler creek brought the larger sediment yields from landslides in the sub-watershed than other creeks. The area and volume of new landslides induced by disastrous events from 1999-2005 were over 24 million m^2 and 50-70 millions m^3, respectively. The new landslide area induced by the rainfall with 200-year return period will be approximately 4 million m^2 in the future. If the great earthquakes no longer occur, the sediment yields in the Ta-Chia main river will reduce with time and the riverbed will be scoured after 30 years. Therefore, it seems that the geological condition will be gradually stable in the future.