Human impacts on erosion and deposition in Onga river basin, Kyushu, Japan

Human disturbances on the ground surface cause erosion and deposition in difference types of landscape. Research on erosion and deposition will understand the magnitude of these impacts in the past and now. In this paper, sediment volume stored in channel for long-term (Holocene) is calculated and erosion model (RULSE) is applied to estimate erosion in short-term (few decades). These values are compared with the one of denudation model established in Japan. As a result, it has clarified that an amount of 47% of total sediment yield from denudation is discharged to the channel for long-term sediment storage in Onga River basin. The RULSE model has indicated that 48% of the total sediment yield comes from erosion processes as sheet and rill erosions, and 52% comes from mass movement such as slope failure. Currently, the sediment yield from forest and agriculture activities is considered to be about 69,000 ton/year which is higher consists of 28% of long-term annual erosion for whole basin.