17:15 〜 19:15
[HGG01-P04] Numerical Modelling of Pumice Deposits for Soil Erosion Control in Agricultural Fields
キーワード：数値計算、土壌侵食制御、軽石堆積物、農地管理
Pumice, a type of pyroclastic material with high vesicularity, is widely distributed in volcanic regions due to large-scale eruptions such as Plinian eruptions. Widespread pumice deposits play a significant role in soil properties. While the accumulation of pumice may initially cause slope instability, their long-term effects include improved soil water retention, leading to providing fertile agricultural conditions for plant root growth. Although previous research has examined slope stability and erosion in pumice-rich environments, few studies have considered the effect of pumice’s low density and variable density characteristics. The authors aim to evaluate the impact of pumice deposits on soil erosion in agricultural settings.
A simulation-based approach was conducted to analyze soil infiltration, surface runoff and erosion. Two soil conditions were compared: one with a clay-based layer and the others with an additional pumice deposit layer. Soil infiltration was modeled using the Horton equation, with pumice absorption simulated using a diffusion equation. The diffusion coefficient was determined from water absorption experiments using pumice samples (En-a, originating from Mount Eniwa) collected from an outcrop in Atsuma, Hokkaido in Japan. Surface runoff dynamics were analyzed using shallow water equations based on the continuity equation and momentum conservation principles to determine depth and velocity. Lastly, erosion due to surface runoff was quantified using the Meter-Peter-Müller equation to estimate the bed load transport rate. Experiments were conducted under different conditions of pumice particle size, layer thickness, saturation levels, rainfall intensity and slope gradient to examine the effect of pumice deposits on surface runoff depth, velocity and erosion volume.
The results showed that when surface runoff occurred, both the depth and velocity of the water flow were reduced in the presence of pumice deposits. However, erosion volume varied depending on the particle size, the saturation levels and layer thickness of the pumice. Smaller particle sizes, thinner layers, and higher soil saturation levels resulted in less erosion, indicating that while water retention of pumice can reduce runoff depth and velocity, pumice itself can be more susceptible to erosion due to its low density. These findings suggest the necessity of selecting appropriate particle sizes and layer thickness in erosion control strategies. Moreover, the Meyer-Peter-Müller equation applied in this contribution showed limitations when pumice density is closed to or lower than that of water, indicating that as erosion progresses and reaches the unsaturated layer, alternative sediment transport models, such as suspended load models, may be required to account for low-density sediment behaviors.
A simulation-based approach was conducted to analyze soil infiltration, surface runoff and erosion. Two soil conditions were compared: one with a clay-based layer and the others with an additional pumice deposit layer. Soil infiltration was modeled using the Horton equation, with pumice absorption simulated using a diffusion equation. The diffusion coefficient was determined from water absorption experiments using pumice samples (En-a, originating from Mount Eniwa) collected from an outcrop in Atsuma, Hokkaido in Japan. Surface runoff dynamics were analyzed using shallow water equations based on the continuity equation and momentum conservation principles to determine depth and velocity. Lastly, erosion due to surface runoff was quantified using the Meter-Peter-Müller equation to estimate the bed load transport rate. Experiments were conducted under different conditions of pumice particle size, layer thickness, saturation levels, rainfall intensity and slope gradient to examine the effect of pumice deposits on surface runoff depth, velocity and erosion volume.
The results showed that when surface runoff occurred, both the depth and velocity of the water flow were reduced in the presence of pumice deposits. However, erosion volume varied depending on the particle size, the saturation levels and layer thickness of the pumice. Smaller particle sizes, thinner layers, and higher soil saturation levels resulted in less erosion, indicating that while water retention of pumice can reduce runoff depth and velocity, pumice itself can be more susceptible to erosion due to its low density. These findings suggest the necessity of selecting appropriate particle sizes and layer thickness in erosion control strategies. Moreover, the Meyer-Peter-Müller equation applied in this contribution showed limitations when pumice density is closed to or lower than that of water, indicating that as erosion progresses and reaches the unsaturated layer, alternative sediment transport models, such as suspended load models, may be required to account for low-density sediment behaviors.