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

1999年9月21日发生的台湾集集地震造成多人死亡，财产损失巨大。它还引发了许多山区的边坡破坏和泥石流。由此产生的泥沙运动在每次暴雨时都会造成泥沙灾害。本文在野外调查的基础上，探讨了地震后沉积物灾害和地形变化的预测方法。研究结果总结如下：1。台湾中部研究区（10.76km^2）地震后斜坡及河道地形变化的定量厘清。通过航空摄影判读，已经确定了131多个边坡破坏疤痕。边坡破坏面积为1.35km^2，占研究面积的12.5%。每次下大雨时，斜坡上的泥沙就会流向河流的下游。泥沙的外流在造成泥沙灾害的同时，也改变了河流的地形。2.19条导线在海拔800 ~ 1100m处敷设，每年对研究区主河道进行地形变化调查。根据调查结果，定量地阐明了地震后的长期地形变化。虽然地震前研究区每年大约发生一次泥石流，但地震后泥石流发生了20次或更多。在研究区沿河流可观察到较古老和较近代的泥石流阶地。台湾过去多次发生强烈地震，地震引起的泥沙运动被认为是山川地形变化的主要原因。为了研究地震后泥石流的特征，采用摄像机对泥石流进行了观测。2007年也观测到了大的泥石流。

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.