Abstract
Large wood (LW) disasters, which often accompany sediment-related disasters, occur worldwide. To prevent and mitigate such disasters, we developed a unique LW trap featuring horizontal rods aligned with the flow. When LW enters the trap, it is scooped up by the rods and thus separated from water and sediment. We explored trapping efficacy using a flume of slope 0.087. Water circulated at a constant rate of 1.8 L/s, LW was added to the flow, and the trapping rates were measured. We focused on the relative wood length (Lw) with respect to the horizontal rod spacing (Sr), the number of LW units supplied, and the supply rate. A longer relative length (Lw/Sr) of LW was associated with a higher trapping rate. The trapping rate was also high when the LW number or supply rate was high. The critical Lw/Sr value was 1.5; below this value, LW was not trapped. This study yields the basic information needed to design traps featuring horizontal rods to mitigate LW-related disasters.
Highlights
A tree of trunk diameter >0.1 m and length >1.0 m is here defined as Large wood (LW), in line with previous studies [1,2,3]
The concept of capturing LW in traps featuring horizontal rods that we propose here is very similar to the use of the inclined racks proposed by Schalko [21]
The LW trapping rate was determined by Equation (1): Rt = nt /n where n is the number of LW units fed into the flume and nt is the number of units trapped
Summary
A tree of trunk diameter >0.1 m and length >1.0 m is here defined as LW, in line with previous studies [1,2,3]. Research in recent decades has revealed that LW in rivers affects river morphology and sediment dynamics, e.g., [4], increasing the variety of river habitats and conserving fluvial ecosystems, e.g., [5]. Despite such benefits, trees that fall from forest slopes after heavy rainfall become LW that accumulates in rivers, posing hazards to people and property, e.g., [6]. City (both in Hiroshima Prefecture) during heavy rainfall in 2018 [11] (Figure 1). Large amounts of LW flow into dam reservoirs during heavy rainfall compromises dam function [12,13]
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