DEVELOPMENT OF RUNOFF MODEL FOR ROTATIONAL PADDY FIELDS AND EVALUATION AT A WATERSHED SCALE

Abstract

 In this study, we have developed a model to evaluate the influence of runoff from paddy fields used for upland crop cultivation （rotational paddy fields）on the basin scale. For the modeling, a field survey was conducted to confirm the outflow mechanism and characteristics of the rotational paddy fields. The results showed that the runoff from the rotational fields responded sharply to the rainfall pattern, the peak runoff was large compared to the rice paddy fields. We considered that the cause of the increase in runoff was the inundation between the ridges. To reproduce the runoff, a model was constructed that represent changes in the surface inundation depth by expressing the ridge shape with a cosine function. This model reproduced the observation results well. As a result of applying this model to the case watershed, it was suggested that the inundation damage would increase greatly through increase in the area of rotational paddy fields.