Experimental insights into the abrasion of large wood in rivers

When transported in rivers, large wood interacts with one another and with flow, sediment, and river boundaries, leading to their physical degradation. This degradation, causing mass of loss and changing of the geometry of the wood, is relevant to various fluvial processes, including bed morphology evolution, aquatic habitat variation, changes to the local environment, and the carbon cycle. The physical degradation of large wood can be categorized into two main types processes, based on wood types and the characteristics of the wood physical motion: abrasion and debranching. Field observations suggest that abrasion primarily occurs through collision and shearing during transport, affecting large trunks as well as fragmented branches. In contrast, debranching results from the rotation of large woods and collisions with the riverbed, with the extent of this process closely tied to the wood's structural properties.

Previous studies have largely focused on large wood transport, the formation of logjams, and the bio-chemical degradation of smaller wood components (such as sticks and leaves) within aquatic habitats. While these studies have deepened our understanding of wood characteristics and their interactions with the environment, physical wood degradation during transport remains underexplored. This degradation affects wood transportation, logjam formation and failure, and aquatic habitats. Therefore, a more detailed understanding of the physical degradation process is crucial for advancing research on large woods in rivers.

Here we introduce a laboratory-based tumbling machine experiment to investigate the abrasion process of large woods during river transport. Preliminary tests examine the relationship between wood abrasion and the potential energy of water flow. Wood samples, with diameters of 10–15 cm and a diameter-to-length ratio of 0.5, were selected from various tree species. Experiments were conducted under different water depths and flow velocities. Our methodology includes measuring the basic physical properties of the wood samples, using motion sensors, and combining 3D printed sensors to monitor their movement characteristics. Additionally, Surface from Motion (SfM) is employed to capture changes in the wood samples' Digital Elevation Models (DEMs) before and after the experiments, enabling precise quantification of degradation volume and patterns.

Preliminary results will be discussed considering the level of observed wood abrasion, size alterations, and debarking of the wood surfaces. Specifically, the influence of water depth and relative flow velocity on wood abrasion will be discussed. Wood abrasion will be quantified using specific indicators, allowing us to define distinct degradation patterns and their mechanisms. The potential findings will highlight the connection between river flow energy and physical wood abrasion, offering preliminary insights into the mechanisms underlying wood abrasion in rivers. 

Keywords: Large wood; wood abrasion; debarking process; experimental design; wood abrasion pattern