A research team led by University of Tsukuba has developed a new method to estimate long-term debris supply from steep slopes by measuring debris accumulated on decades-old abandoned roads using a drone equipped with LiDAR. This approach provides a practical means of quantifying debris input to debris-flow source areas.

Tsukuba, Japan—Debris supplied by rockfall and related slope processes is a key factor controlling the frequency and magnitude of debris flows. However, estimating the amount of debris supplied over several decades has been technically challenging. In this study, the research team focused on abandoned mountain roads and successfully estimated decadal-scale debris supply by measuring deposits accumulated on these road surfaces using UAV-LiDAR technology.

The team conducted a high-resolution topographic survey along a closed section of Shizuoka Prefectural Road 288 near the Shizuoka-Nagano prefectural border. The road became impassable after a disaster in 1991, and rockfall-derived debris has accumulated steadily since then. By dividing the surveyed road into segments, the researchers analyzed the relationship between slope topography and debris supply. The results showed that debris supply increases with steeper mean slope angles and larger contributing areas. Based on these analyses, headwater slopes in the region were estimated to supply approximately 70-93 m3 of debris per year, indicating that a sufficient volume of material to trigger a debris flow can accumulate within several decades.

Across Japan's mountainous regions, the number of abandoned roads is increasing due to route realignment. These unused roads have rarely been utilized for scientific observation. This study demonstrates that UAV-LiDAR surveys of abandoned roads can provide valuable baseline data to support forecasting and risk assessment of debris-flow and landslide hazards.

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This study was financially supported by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (JP19H01371 and JP22H00750, PI: T. Hattanji).

Original Paper

Title of original paper:

An abandoned road as a debris trap: Estimating debris-supply rate from steep slopes based on UAV-LiDAR DEMs

Journal:

Geomorphology

DOI:

10.1016/j.geomorph.2026.110193

Correspondence

Associate Professor HATTANJI Tsuyoshi
Institute of Life and Environmental Sciences, University of Tsukuba

HARADA Shunsuke
Graduate School of Life and Environmental Sciences, University of Tsukuba (Current affiliation: PASCO Corporation)

Associate Professor OGURA Takuro
Graduate School of Education, Hyogo University of Teacher Education

Associate Professor HAYAKAWA Yuichi S
Faculty of Environmental Earth Science, Hokkaido University

Related Link

Institute of Life and Environmental Sciences