Logjam controls the fluvial channel morphology: Interception and blockage characteristics of large wood and its influence on sedimentary dynamics

Abstract

Large pieces of wood can be seen everywhere in vegetation-developed gullies, whose transportation, deposition, and logjam in channels significantly affect the processes of debris flows. However, little is known about the characteristics of sediment deposition induced by the accumulation of large amounts of wood in naturally blocked wood, check dams, and bridges. In this study, small-scale experimental tests were carried out to investigate the characteristics of the interception rates, sediment deposition volume, and energy dissipation. The results revealed that the obstacles in the channel changed the large wood transport process, and the large wood interception rate gradually increased with increasing large wood relative length among the three obstacles; however, different characteristics of different obstacles were also observed. In addition, logjam and fluid density caused changes in channel morphology, and the length and depth of the sediment deposition volume gradually increased with increasing fluid density. Moreover, different trends in the depth change rate (ΔH/H₀) and Froude number (F₀) were observed. ΔH/H₀ was significantly influenced by the dimensionless large wood accumulation factor and fluid density, and the greater the fluid density was, the faster the growth rate was. Furthermore, stable logjams can dissipate fluid energy, but this effect is almost negligible for relatively large wood lengths, and natural and engineering logjams are conducive to reducing erosion in gullies.