ライシメータ裸地斜面を用いた降雨流出と侵食に関する研究

By applying a hydraulic analysis method to data of hydrology and sediment yield from 8 sloping lysimeters with a rain simulator, the following results could be obtained.<BR>1.The lysimeters were 10.0 m long (horizontally), 2.5 m wide and 2.0 m deep.Their slope angles were 5°, 7°, 10°and15°.Two types of soil: volcanic ash soil and sand, were put into the lysimeters and their surfaces were kept bare.<BR>2.The relationships between the mean flow rate and mean rate of transport, which were values of surface runoff and transport divided by the duration of each surface runoff, were improved to such an extent as to be expressed by power regression curves of each gradient for two types of soil.<BR>3.A bed load equation was able to be applied by treating the water-stable aggregate of volcanic ash soil as a single soil particle.The relationships between the mean dimensionless tractive force and mean dimensionless sediment transport based on the bed load equation were expressed by the power regression curves for each type of soil.<BR>4.The water depth at the end of downstream used in a bed load equation could be measured only in the experiment with a rain simulator.Therefore, the equation of the mean sediment transport rate substituting mean water flow for water depth as the variable was obtained as:<BR>q_b=AN^{P (B+0.5)} (sinθ) ^{(1-0.5p) (B+0.5)} q^{-P (B+0.5)} S^-Bd^1-Bg^0.5.<BR>Where q_b is the mean sediment transport rate (g/s/cm), A and B the regression coefficients, P the constant (=0.6), θ the slope angle in gradient, q the mean surface water flow of slope (cm³/s/cm), N the roughness, g the gravity acceleration, d the average diameter, s= (σ-ρ)/ρ, s the density of soil particles in water, σ and ρthe densities of soil particles and water.<BR>5.On the whole, these rate equations were in agreement with the observed sediment transport data obtained with natural and simulated rainfall.When the mean water flow was low and the slope was gentle, however, the application of the rate equation was limited.