Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.2,2005
Determining the sources of sediment using radionuclides in Nagasawa Reservoir
Catchment,
Upper Yoshino River
Hiroaki KATO Yuichi ONDA Shinya HIRAMATSU
Fumiko KASHIWAGI Kuniaki MIYAMOTO
Abstract
The concentrations of Cs]137 and Pb]210ex in fluvial sediment and soil were analyzed
to determine the sources of fine sediment collected at 9 tributaries located in
Nagasawa reservoir catchment, Shikoku Island, Japan. The major sediment source
was identified as subsoil derived from landslide scar or channel bank, but sediment
production from forest floor was also identified from the existence of Cs]137
and Pb]210ex/Cs]137 ratio. It was indicated that sediment production caused by
past landslide dominated in subcatchments with high percentage of landslide area,
but sediment production from forest area was also estimated in subcatchments with
small landslide area. The surface soil of landslide scars were characterized by
high concentration of Pb]210ex. The concentrations of Pb]210ex in sediment collected
in Tebako]dani catchment increased with downstream distance. This implied that
residence time of sediment could be estimated by comparison with direct deposition
rate of Pb]210ex. It was concluded that the sources of fine sediment could be
determined by analyzing the concentrations of Cs]137 and Pb]210ex in channel bed.
Key words:Cs]137, Pb]210ex, sediment sources, landslide area, residence time
Japan Society of Erosion Control Engineering
Sabo Kaikan, 2-7-5 Hirakawa-cho, Chiyoda-ku,
Phone +81-3-3222-0747 Fax +81-3-3230-6759
http://www.jsece.or.jp/
Mail jimu@jsece.or.jp