In the previous studies, high turbidity is revealed to occur in Tokoro River and to affect social economical and environmental activity in Okhotsk area. Also, it is demonstrated that turbidity from fields is one of the most influential factors on high turbidity in Tokoro River. However, it is not clarified how high turbidity is provided from fields and forests areas. Therefore, this study attempted to understand the mechanisms of the occurrence of high turbidity and the role of fields and forests areas on the occurrence of high turbidity. In 2 hectors field and forest areas, SS concentration due to the impact of rainfall is investigated in 2009, which reveals that SS concentration is associated with rainfall intensity by using exponential function. Also, it is found that SS concentration in field tends to increase with rainfall intensity more rapidly than forest areas. The proposed equation for evaluating SS concentration is confirmed to have high applicability by using distributed hydrological model.
