Effect of land-use changes on sediment transportation in a small catchment during last 60 years

Abstract:

To investigate the effect of land-use changes on sediment transportation in a small catchment, a short core from reservoir was obtained. Reservoir sedimentation rate changes during last 60 years were reconstructed by radionuclides, exPb-210 and Cs-137, and land-use changes from 1960’s to 2000’s were estimated by analyzing aerial photographs. Reservoir sedimentation rate changes can be recognized in three periods. During first period (1940’s ~ early in 1950’s), reservoir sedimentation rate had increased since the construction of reservoir. During second period (early in 1950’s ~ early in 1990’s), reservoir sedimentation rates were stable relatively around 3 kg m^-2 a^-1, however, two higher sedimentation peaks occurred. During last period (early in 1990’s ~ 2003), reservoir sedimentation rate had increased sharply. Before 1990’s, the sediment transportations from a catchment to reservoir had been changed little although the increase of forest and grassland areas and the readjustment of rice fields had been occurred repeatedly and those land-use changes might not affect considerably the sediment transportation. The increasing of field area and bare area due to the reduction of forest area since early in 1990’s might be a dominant factor for the increasing the supply of sediment from a catchment, and gradually increasing rainfall amount in this study area since 1970’s would also assist the rapid increasing of sedimentation rate. Therefore, these results implied that land use changes and increasing rainfall caused by climate changes could be result in huge sediment transportation in the future.