Mitigating Debris Flows: The Role of In-Channel Forests
DOI:
https://doi.org/10.64862/Keywords:
Debris flow, Wooded channels, Sediment trapping, Deposition slope, Impact forceAbstract
Although channel forests are recognized for their potential to mitigate debris flows, their effectiveness in trapping sediment remains inadequately quantified. This research examines, through physical modeling, how the trunk volume fraction—defined as the ratio of total trunk cross-sectional area to forested area, varying between 0.9×10-3 and 88.6×10-3—affects deposition behavior and impact dynamics of debris flows. When debris flow enters the forested channel, a sharp rise in the energy slope of flow resistance initially disrupts the balance with the channel bed slope. This leads to reduced flow velocity, increased flow depth, and a subsequent decline in the energy slope. Concurrently, substantial sediment deposition occurs within the forested segment, raising the bed slope until a new equilibrium is established with the energy slope. The attenuation rate of the peak impact force was measured between 15.8% and 79.0%, while sediment retention rates varied from 3.0% to 31.7%. The attenuation of peak impact force correlated most strongly with relative opening, whereas sediment retention was most closely associated with the initial resistance energy slope of the forest. Viscous debris flows showed a moderately lower peak force attenuation compared to diluted flows, but higher sediment retention. Sediment deposition increased the bed slope by 0.002 to 0.089, a change proportional to the initial resistance energy slope, with proportionality coefficients of 2.3% for viscous and 3.4% for diluted debris flows. Additionally, this study proposes new methodologies for estimating deposition slope and potential sediment retention volume in wooded channels. For more details on this study, please refer to Wang et al. (2025).
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