Abstract
Production and transport of suspended materials from agricultural fields possibly cause serious water pollution and degradation of the soils, however, there are few attempt on the precise modeling of soil loss properties during surface drainage from clayey soils. In the present study, we developed a process-based model for the precise estimation of unit load of suspended materials from agricultural fields. The model includes two-dimensional transport equations of water and suspended solids, a set of bedload equations based on the liquid limit of surface soil, redeposition of dispersed soil, and shear retardation by scouring. The model was tested against the erosion data obtained by (1) a deep (50 cm) lysimeter with a 9 cm-width sluice gate and (2) a ditch of variable length (10-90 cm). The amount of soil loss during surface drainage was measured at varied solid ratio (0.25-0.34). Investigation of surface draining paddy fields was also conducted. The model could simulate the increase of soil discharge by lowering solid ratio, but the model required modification of critical friction velocity for aggregated volcanic soil. Two-dimensional distribution of soil scouring in paddy fields could be predicted by the model, but the precise estimation of soil discharge at field should be confirmed by a development of sampling methodologies.
