Spatial distribution and transport characteristics of debris flow sediment using high resolution UAV images in the Ohya debris flow fan

Debris flows are significant geomorphic processes that can pose hazards to human settlements and infrastructure, making the understanding of their sediment transfer characteristics and impacts on the surrounding landscape crucial for effective land management and hazard mitigation strategies. This study investigates the distribution patterns of sandstone, vegetation, and shale classes within the Ohya debris flow fan, aiming to gain insights into the sediment characteristics, grain size variations, and vegetation cover trends along the flow path. Using a combination of field surveys and image processing we analyzed sediment characteristics and grain size variations a three study zones: upstream, transfer, and downstream. Statistical parameters such as mean, mode, skewness, and kurtosis were employed to quantify the grain size distribution and identify variations across the study zones. Results reveal distinct spatial variations in the distribution of sandstone, vegetation, and shale classes along the flow path. We observed a decrease in sandstone and vegetation cover from the upstream to the downstream sections, while the area covered by the shale class exhibited an increasing trend in the downstream direction. These findings suggest that debris flows selectively remove smaller particles downstream. The distribution of particle sizes within the sandstone class also exhibited variations, with a higher proportion of smaller pebbles downstream due to more effective removal of finer particles in the upstream zone. This study highlights the complex interplay between debris flow dynamics, sediment transport, and vegetation colonization. The findings contribute to the scientific knowledge of debris flow processes and can be used to inform land management decisions and mitigate the hazards associated with debris flows in similar environments.