Change of topography and prediction of sediment disaster after the Chi-chi earthquake in Taiwan

1999年9月21日发生的台湾集集大地震，造成了巨大的财产损失和人员伤亡。此外，它还引发了山区的许多边坡失稳和泥石流。由此产生的泥沙运动在每次大雨中都造成泥沙灾害。本研究目的在探讨地震后泥沙灾害与地形变化之预测。主要研究结果如下：1.定量地阐明了台湾中部10.76km^2研究区地震后斜坡地形和河道地形的变化。通过航空摄影判读，已经确定了131多个边坡破坏疤痕。滑坡面积为1.35km^2，占研究区面积的12.5%。每次大雨时，滑坡产生的沉积物都流向下游。在研究区主要河道布设了19条高程800 ~ 1100 m的导线，每年对河道地形变化进行监测。根据调查结果，定量地阐明了地震后地形的长期变化.虽然地震前研究区每年发生一次泥石流，但地震后发生了20多次或更多。在研究区，沿沿着观察到较老和较新的泥石流阶地。台湾过去曾多次发生强烈地震，地震引起的泥沙运动被认为是造成山川地形变化的主要原因。为了研究地震后泥石流的特征，利用摄像机对泥石流进行了观测。2007年还观测到大规模泥石流。

The Chi-Chi Taiwan Earthquake on September 21, 1999 killed many people and involved great property loss. Also, it triggered many slope failures and debris flows in the mountainous regions. The resulting sediment movement caused sediment disasters at every heavy rain. This study aimed to examine the prediction of sediment disaster and the change of topography following the earthquake based on the field investigations. The results are summarized as follows :1. Changes of topography of slopes and river channels following the earthquake ware clarified quantitatively in the study area (10.76km^2)in central Taiwan. More than 131 slope-failure scars have been identified through aerial photographic interpretation. The slope-failure area is 1.35km^2, representing 12.5% of the study area. The sediment from slope failures flows out to the lower reaches of the river at every heavy rain. The outflow of the sediment changes the river topography at the same time as it causes sediment disasters.2.19 courses of traverse were installed in altitude 800m-1100m, and change of the topography was surveyed every year in the main river channel of the study area. The long-term topography changes following the earthquake were quantitatively clarified based on the survey results.3. Although debris flows had occurred about once per year in the study area before the earthquake, they occurred 20 times or more after the earthquake. Older and more recent debris-flow terraces are observed along the river in the study area. In Taiwan, severe earthquakes have occurred repeatedly in the past, and sediment movement resulting from earthquakes is considered to be the main cause of change in mountain and river topography.4. In order to research the characteristics of debris flows after the earthquake, debris flow was observed using the video camera. The big debris flow was observed also in 2007.