Measurement of soil characteristics controlling runoff processes and model development

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1.Estimation of soil hydraulic properties based on the investigation of soil structuresWe develop a new method to estimate pore size distributions from microstructures of the soils. The microstructures are numerically generated by the distinct element method(DEM), which was originally proposed to describe rock block movement (Cundall and Strack, 1979). The distinct element method simulates how a group of discrete particles move collectively by tracing each particle on the basis of equation of motion. We use this method to pack soil particles with various radius in specific volume in random manner, and repeat this procedure to evaluate pore size distributions of soil packages.2.Development and applications of hydrological models incorporating soil propertiesWe developed several hydrological models which incorporate soil physical properties and applied to study catchments. First of all, we developed a flow routing model for forest hillslopes, on the basis of physical mechanics of water f … More low on and/or beneath the hillslope surface (Mouri et al. (2003), Tachikawa (2004)). Mouri et al.(2003) developed an algorithm to predict dynamic behavior of water and sediment in the basin scale. In their algorithm, a basin is divided into a number of hillslopes, and a kinematic wave model incorporating soil characteristics is applied to each hillslope to predict water and sediment movement. Tachikawa et al.(2004) developed a stage-discharge relationship equation incorporating saturated-unsaturated flow mechanism of hillslopes. This equation is able to describe a wide range of flow patterns from dry to wet periods. Secondly, we developed a soil runoff model based on water flow models which incorporate soil physical characteristics (Ichikawa et al.(2003), Ichikawa et al.(2003)). In this model, rate of soil erosion is calculated using friction velocity, which is determined from overland flow depth. Thirdly, we developed a coupled model of two dimensional shallow surface water flow and one dimensional saturated-unsaturated subsurface flow to precisely predict micro physics of rainfall-runoff processes, by incorporating soil hydraulic properties and micro topography of soil surface. Less