Present Situation and Cause Analysis of Diversion Dam Disasters

导流坝建在河床上，洪水期间沙石在河床上移动严重。大坝结构、附着物和护岸工程有时会因大坝下方的河床冲刷而遭到破坏。2001年，分析了大量的导流坝灾害实例。在这些分析的基础上，对2001年9月再次被洪水摧毁的塔玛河几座导流坝的破坏情况进行了调查，并与以往的灾害进行了比较。这些调查表明，准确准确地预测河床形态和水道的自然和人为变化是非常重要的。导流坝因下游交替沙洲的迁移而改变航道，以及由溢流床开采造成的人为改变，都会给导流坝带来麻烦。2002年，采用了以下两种方法来研究这些问题。河床形态和河道现状及年际变化的调查方法研究…的机理是非常困难的由于在洪水期间缺乏直接的观测和测量，河流灾害，包括引水大坝灾害，更多和更多的原因。因此，这些研究的第一步是掌握洪水前后河床形态和水道的变化。调查长期的变化也很重要，因此野外工作方法，如航空照片的比较调查和对河床变化的调查结果的分析，是非常有用和富有成效的。小比例尺模型试验洪水演进预报方法研究一种在小比例尺模型水槽上模拟河床形态和水路的试验方法。要获得河流与水槽之间的相似性，最重要的一点是表现交替沙洲的形状和连接方式。根据木下的方法，上松-荒川河的小规模模型试验取得了成功。这一成功表明，有可能进行小规模模型试验，以调查灾害的原因和预防措施。较少

Diversion dams are constructed on riverbeds over which sand and gravel move seriously during floods. Dam structures and attaching and bank protection works are sometimes destroyed due to riverbed scouring below dams. In 2001, many examples of diversion dam disasters were analyzed. In addition to these analyses, failures of several diversion dams on the Tama River that were destroyed again by the flood in September 2001 were investigated, comparing them with past disasters.These investigations clarified that it was very important to predict natural and artificial change of riverbed form and watercourse precisely and accurately. Channel changes according to downstream migration of alternate bars and man-made changes by rierbed mining could cause troubles on diversion dams. In 2002, the following two methods were applied for studying these problems.1. Investigating method for present situation and yearly changes of riverbed form and watercourse It is very difficult to study the mechanisms … More and causes of river disasters, including diversion dam disasters, because of lack of direct observations and measurements during floods. For this reason, the first step of these studies is to grasp the changes in riverbed form and watercourse before and after a flood. It is also important to investigate long-term changes, so fieldwork approaches, such as comparison investiagtions of aerial photographs and analyses of survey results on riverbed changes, are very useful and fruitful.2. Prediction method for flood-flow route and its future change on a small-scale model experiment An experimental method to simulate riverbed form and water route on a small-scale model flume was studied. The most important point for obtaining similarity between the river and the flume is to represent the shape and connecting pattern of alternate bars. A small-scale model experiment for the Uetsu-Arakawa River succeeded according to Kinoshita's method. This success revealed the possibility of small-scale model experiment in order to investigate the causes of disasters and preventive measures. Less