The Jinbu debris flow experiment in South Korea – GWC Mag

The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.

South Korea has a substantial challenge from debris flows in upland areas, generally triggered by heavy rainfall. For example, in 2011 a debris flow struck an urban area of Mt. Umyeon in Seoul, causing heavy losses, including 16 fatalities. As a result, there has been an active programme in South Korea to simulate debris flows, to understand their dynamics and to determine appropriate mitigation strategies.

One approach that has been used is real world measurement of debris flows, which is helpful for the calibration of models. A number of groups are active in the area, including the well-known flume at the USGS, the experimental facilities at HKUST in Hong Kong, the under-construction large-scale flume at Kunming in China and the famous Illgraben site operated by WSL. Flumes tend to use comparatively volumes of material on linear channels.

In South Korea a different and novel approach has been adopted. Here, a site was identified at Jinbu in Gangwon Province for experimental work. The site consists of a natural channel, with six tributaries, with a total main channel length of 824 m. This is considered to be typical of a debris flow channel in an upland area of South Korea. There is a check dam at the end of the channel to ensure an experiment does not have downstream consequences.

The facility, and one of the experiments, is described in a new paper published in the Journal Landslides (Yune et al., 2023). Their paper includes this image that shows the configuration of the site:-

At the head of the main channel, a large concrete box with a gate has been constructed, which allows 346 m³ of soil and 268 m³ of water to be stored and then released down the channel. In the upper, steep part of the channel, the bed has been reinforced with a geotextile to prevent erosion (and thus to protect the channel); thereafter the flow is allowed to travel down the gully naturally. The channel is extensively instrumented, including sensors and cameras, and the channel is surveyed with lidar before and after an experiment.

Yune et al. (2023) have descried an experiment using the Jinbu facility. Interestingly, in this experiment, logs were placed along the channel that were entrained into the flow to explore the role of timber in the dynamics.

The supplementary information for the paper provides videos of the debris flow as it travelled down the channel at Jinbu. Sadly, these do not seem to have been posted online. The image below shows the debris flow front just below the initiation zone, giving an indication of the sped of the flow:-

In the experiment, the debris flow accelerated in the upper, steep portion of the channel, reaching a peak velocity of 16.6 metres per second. As the gradient reduced downslope, the debris flow velocity also reduced. The flow eroded the bed in the high velocity sections.

There is a need for a variety of approaches to the modelling of debris flows. This approach is novel but invaluable, providing insight into the ways in which flows interact with the topography and with bedforms. The shear scale of the flows that can be simulated is remarkable.

This is great science that is also great fun.

Reference

Yune, CY., Kim, BJ., Jun, KJ. et al. 2023. Real-scale experiment of debris flow in a natural gulley: key findings and lessons learned. Landslides. https://doi.org/10.1007/s10346-023-02134-3

Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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