Morphological and dynamic characteristics of abrasion on drainage structures in response to debris flow

Abrasion, a complex physical phenomenon prevalent in natural and engineered structures, frequently causes significant functional failures in drainage channels under the debris flow impact force. This underscores critical knowledge gaps regarding abrasion effects on debris flow-scoured drainage structures. Through multi-stage field investigations and data analysis across four representative areas, this study proposes a classification system for abrasion phenomena and analyzes morphological characteristics across different drainage structures and debris flow types (rainy vs. glacial). Further, the study methodically uncovers the long-term spatiotemporal distribution, development, and progression of abrasion in drainage channels and check dams. Dynamic abrasion characteristics were evaluated using three key parameters per debris flow: average gully vertical drop, watershed relative cutting degree, and soil sample data. The findings indicate that rainy debris flows exhibit higher average vertical drops (max: 0.933) compared to glacial debris flows (max: 0.621). Glacial debris flows show greater relative watershed cutting degrees (range: 0.15–0.3) than rainy types (range: 0.075–0.2). Multiple influencing factors were compared to identify critical controls on abrasion intensity. Debris flow velocity distribution and particle gradation within channels emerged as the primary determinants of abrasion distribution. Notably, a higher proportion of viscous particles (grain size D < 2 mm) leads to a significant increase in abrasion capacity (> 20%). These findings quantitatively inform the optimization of debris flow mitigation, providing a critical foundation for improving structural design, wear repair techniques, and channel configuration.