Effect of the conditions of landslide dam formation
and rivers on peak discharge at landslide dam outburst

Osamu YOKOYAMA, Taro UCHIDA and Atsuhiko KINOSHITA

During sediment disasters, landslide dams rarely form compared to landslides and debris flows. However, when a landslide dam forms and an outburst occurs, it incurs significant damage to downstream residential areas. Therefore, researchers need to estimate the area and degree of damage to develop effective countermeasures. Recent research has revealed that peak discharge at landslide dam outbursts varies depending on the conditions of landslide dam formation, such as constituent materials, their shape and grain size. River conditions such as slope and width also affect peak discharge. It has been reported that multiple landslide dams have formed continuously in one valley stream, for example, Imokawa basin after the Niigata Chuetsu earthquake. However, most of the recent studies and reports have considered only a single landslide dam, and have not taken the water saturation of landslide dam materials into consideration. In this study, we performed a channel experiment considering the conditions of landslide dam formation and riverbed conditions focusing on the number of landslide dams, and observed the difference in peak discharge. The results showed that landslide outburst process was different in single and two landslide dam condition. In different grain size condition, the water saturation of landslide dam affected erosion process and peak discharge. Some cases of two landslide dams showed larger peak discharges compared to cases of one landslide dam. However, it was difficult to indicate the factor controlling the discharge ratio, such as height ratio or amount of submerged water.