Study on the development of fluvial landforms after large landslides

1984年9月，日本Ontakesan发生了一次体积为3400万立方米的大型边坡崩塌。这次破坏的规模在日本历史上发生的大型斜坡破坏中排名第八。断裂产生的沉积物沿着Otaki河谷向下沉积，并在中游沉积。随后，这些沉积物被切割，以复制被输送到下游的沉积物。这次崩塌和随后的地貌变化为分析大崩塌后河流地貌的发育和水文过程的变化提供了很好的范例。为此，我们在Otaki河流域进行了综合研究。我们的研究主要集中在五个问题上：a)河道形态的变化，b)河流泥沙的输送，c)侵蚀和沉积的速率，d)阶地陡坎和河谷形态的发育，e)河流径流的变化。还研究了相关问题，如地质、气候和流域内的植被。为了涵盖如此广泛的科学领域，在各个领域具有经验和知识的研究人员参加了这个小组。在该组织成立之前，一些成员已经在Otaki河流域工作过。本研究也使用了前人的研究数据。从而对流域地貌、沉积学、水文学、气候、植被等方面有了一些新的认识。这份出版报告包含10篇论文来介绍我们的结果。此外，我们的团队还在日本其他地区进行了研究，以提高对河流地貌、坡面破坏、河流径流、斜坡和植被的了解。尽管这些研究的结果没有包括在本报告中，但它们在期刊、科学报告和会议上发表了。这份报告列出了这些论文的清单。

A large slope failure with a volume of 34 million cubic meters took place at Ontakesan, Japan, in Sept.1984. The volume of the failure is the eighth largest among historical large slope failures in Japan. The sediments produced by the failure went down along the valley of the Otaki river, and were deposited in the middle reach. Subsequently the deposits were incised to reproduce sediments which have been transported downstream. This slope failure and subsequent geomorphic changes provide a good example to analyze the development of fluvial landforms and changes in hydrological processes after big slope failures. For this reason, synthetic research were performed in the drainage basin of the Otaki river.Our research focuses mainly on five issues : a) change in channel forms, b) transportation of river sediments, c) rates of erosion and deposition, d) development of terrace scarps and valley forms, and e) change in river runoff. Related issues such as geology, climate, and vegetation in the river basin were also examined. To cover such broad scientific fields, researchers with experiences and knowledge in various fields took part in the group. Some of the members had already worked in the Otaki river basin before the group foundation. The preceding research data were also used in this study. As a result, some new insights were obtained regarding geomorphology, sedimentology, hydrology, climate, and vegetation in the river basin. This publishing report contains ten papers to present our results.Furthermore, our group performed research in other areas of Japan to improve the understanding of fluvial geomorphology, slope failure, river runoff, clinate, and vegetation. Although the results of these studies are not included in this report, they were presented in journals, scientific reports, and conferences. The list of these papers is carried in this report.