5:15 PM - 6:30 PM
[HTT16-P07] Variations in sedimentation rates of Tsuya River in the western Nobi Plain, central Japan over the last decades
Keywords:sedimentation rate, flood history, Pb-210 dating, Tsuya River
The Nobi Plain has been formed with the fluvial processes of the Kiso Three Rivers (composed of the Kiso, Ibi and Nagara rivers), central Japan. Tsuya River, a branch of the Ibi River is flowing at the eastern foot of Yoro Mountains, Gifu prefecture, in the western margin of the plain with abundant groundwater. Because the current main channel of Tsuya River has the modern continuous levee only on its eastern side, it flows across ends of their alluvial fans with receiving a lot of spring water and sediment via its western side derived from the Yoro Mountains. This study is conduced to describe the environmental changes of Tsuya River from the viewpoints of sedimentation dynamics with natural and artificial impacts.
Sediment dynamics over the last decades in the Tsuya River are evaluated with the lead (Pb) -210 dating method. The sedimentation rates were determined by applying CIC (Constant Initial Concentration) and CRS (Constant Rate of Supply) models to the sediment cores in the pond linked to the right/western bank of main channel. The CRS model mostly agreed with the Cs-137 dating, which the CIC model was not applicable because of fluctuations in the lead 210 profiles. The average sediment rates of 0.24 - 0.44 g cm-2 yr-1 were obtained, which were larger than the reported values in most of the lakes in Japan. Furthermore, the higher sedimentation rates with the maximal values such as 0.59, 0.71 and 2.62 g cm-2 yr-1 were obtained from 1961 to 1984, which could respectively correspond to flood events and construction works in Tsuya River watershed during the same period by according to conventional literatures. Consequently, these results might clarify the river sediment dynamics also be explained with the classical lead-210 method (CRS model).
Sediment dynamics over the last decades in the Tsuya River are evaluated with the lead (Pb) -210 dating method. The sedimentation rates were determined by applying CIC (Constant Initial Concentration) and CRS (Constant Rate of Supply) models to the sediment cores in the pond linked to the right/western bank of main channel. The CRS model mostly agreed with the Cs-137 dating, which the CIC model was not applicable because of fluctuations in the lead 210 profiles. The average sediment rates of 0.24 - 0.44 g cm-2 yr-1 were obtained, which were larger than the reported values in most of the lakes in Japan. Furthermore, the higher sedimentation rates with the maximal values such as 0.59, 0.71 and 2.62 g cm-2 yr-1 were obtained from 1961 to 1984, which could respectively correspond to flood events and construction works in Tsuya River watershed during the same period by according to conventional literatures. Consequently, these results might clarify the river sediment dynamics also be explained with the classical lead-210 method (CRS model).