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When a landslide dam collapses, the overflow discharge increases sharply. In addition, it is known that in landslide dams, high-concentration sediment flows down due to rapid vertical erosion and side bank collapse. However, when there is a large amount of wood debris in the flooded area of a landslide dam, there are many unexplained points re-garding the collapse characteristics of landslide dams. In this study, we experimentally investigated the effects of wood debris deposited in the flooded area when a landslide dam collapses. As a result, it was confirmed that in the situation where the wood debris block stopped, the wood debris block was caught in the sediment on the downstream slope of the landslide dam, and the sediment on bank downstream of the landslide dam collapsed and was covered. Also, as the amount of wood debris increased, the maximum overflow discharge decreased, sediment concentrations increased, and tended to be the starting point for erosion channel collapse. Furthermore, it was suggested that the regime theory applies to the relationship between the erosion channel width and the overflow discharge during the overflow period.Key words: landslide dam, wood debris, over topping water, erosion, regime theoryAkira ODA, Michiaki NAKAMURA, Hirokazu SUMI, Takeshi TAKEMURA and Minoru OCHIAI 　天然ダムの越流決壊時には急激に越流流量が増加する．また，決壊時に発生する急激な縦侵食と側岸崩壊により高濃度な土砂が流下することが知られている．しかし、天然ダムの湛水域に流木が多量に存在する場合の天然ダムの決壊特性については不明な点が多い．本研究では湛水域に集積した流木が天然ダムの決壊時に及ぼす影響を実験的に検討した．その結果，流木塊が停止するときの状況として，天然ダム下流法面の土砂に流木塊が引っかかる場合と，天然ダム下流法面の土砂が流木塊の下流側に覆い被さるように崩れる場合が確認された．また，流木本数が多いほど越流流量の最大値は低下し，土砂濃度は高くなり，侵食流路の崩壊の起点となる傾向が示された．さらに，越流流量の増水期における侵食流路幅と越流流量の関係はregime理論が成立することが示唆された．キーワード：天然ダム，流木，越流決壊，侵食，regime理論Journal（掲載誌）Proceedings of the Japanese Conference on Hydraulics(Jsce),Vol77,No.2,I_661-I_666,2021.－　　－13流木を伴う天然ダムの越流決壊特性に関する実験的研究Experimental Study on Failure of Landslide Dam with Wood DebrisPublished Paper