Abstract
Ulleung-do is a volcanic island located 130 km east of the Gangwon-do province of South Korea. It is characterized by steep slopes covered with effusive rocks released from multiple volcanic activities. Having accumulated deep colluvium, Ulleung-do Island manifests a high vulnerability to landslides frequently caused by heavy rains or typhoons, debris flow, rockfall, and other disaster hazards in mountainous areas. Therefore, facilities and residential areas located in the lower areas of the island sustain widespread damage. Hence, the installation of check dams designed to reflect the area’s local conditions is required to avoid further damage. In line with that, this study analyzes the disaster cases in Ulleung-do’s mountain areas and the effect of check dams in debris flow reduction for each type using the KANAKO-2D model. At observation point 1, the result shows that the maximum rate of debris flow is reduced by 48.5% with an open-type check dam installed and 62.9% with a closed-type check dam installed from the level without a check dam. For observation point 2, the maximum flow depth decreases by 49.7% with an open-type check dam and 77.4% with a closed-type check dam. Thus, this study suggests that the simple installation of check dams in a mountain stream that has experienced debris flow effectively mitigates damage brought by various disasters.
Highlights
Ulleung-do is a volcanic island covered with effusive rocks released from multiple volcanic activities, thereby showing a geologic characteristic with deep colluvium and residual soil layers
The island is vulnerable to falling rocks and landslides caused by heavy rains and typhoons. e accumulation of such sediments in a mountain stream has a high possibility of causing debris flow
In the “open-type check dam” condition, the maximum rate of debris flow was found to be reduced by about 48.5% from the level of the “no check dam,” while the “closed-type check dam” condition has the maximum rate of debris flow reduced by 62.9%, indicating that the closed-type was more effective than the open-type. e debris flow time capturing was counted, starting from its arrival at the check dam until it ended up overflowing. e time of debris flow captured in 130°53′0′′E
Summary
Ulleung-do is a volcanic island covered with effusive rocks released from multiple volcanic activities, thereby showing a geologic characteristic with deep colluvium and residual soil layers. For this reason, the island is vulnerable to falling rocks and landslides caused by heavy rains and typhoons. Diverse studies have been conducted using different methods for topics related to ground disasters occurring at steep slopes, such as landslides, debris flows, and rock slides caused by rainfalls. Studies on the assessment of debris flow susceptibility and hazard with rainfall distributions are widely referenced [1,2,3,4,5]. Skilodimou et al [8] produced assessment maps on hazards from landslides, floods, and earthquakes and subsequently combined them using an analytical hierarchy process and geographical information system (GIS)
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