Japan Geoscience Union Meeting 2021

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[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG42] Water and sediment dynamics from land to coastal zones

Thu. Jun 3, 2021 1:45 PM - 3:15 PM Ch.11 (Zoom Room 11)

convener:Shinichiro Kida(Research Institute for Applied Mechanics, Kyushu University), Yuko Asano(The University of Tokyo), Keiko Udo(International Research Institute of Disaster Science, Tohoku University), Dai Yamazaki(Institute of Industrial Sciences, The University of Tokyo), Chairperson:Dai Yamazaki(Institute of Industrial Sciences, The University of Tokyo), Keiko Udo(International Research Institute of Disaster Science, Tohoku University), Yuko Asano(The University of Tokyo), Shinichiro Kida(Research Institute for Applied Mechanics, Kyushu University)

2:00 PM - 2:15 PM

[ACG42-02] Interpreting the sediment dynamics from mountains to the sea in the Saru River souce-to-sink system using radionuclide tracers

★Invited Papers

*Shigeru Mizugaki1, Junichi Otsuka1, Yasuhiro Murakami1, Keiko Iwakura1 (1.Civil Engineering Research Institute for Cold Region, Public Works Research Institute)

Keywords:sediment fingerprinting, natural radionuclides, particle size

Coastal erosion has been a nationwide problem in Japan since the 1950s, and there is a need for comprehensive sediment management in stream systems from mountains to coasts. In addition to understanding the sediment dynamics in the stream-sediment system, it is an extremely important basic issue to understand the source of sediment production. To clarify the sediment dynamics in the source to sink sediment transport system, we collected a variety of sediments such as suspended sediment, fluvial material, beach sand, and coastal sediment from the mountains to the sea in the Saru River basin in Hokkaido, and conducted the fingerprinting sources of those sediment using radioisotope tracers. The results show that coastal sand and sediment are mainly composed of sand, and that the contribution of accretionary sedimentary rocks, melange substrates, and plutonic rocks in the upstream region is high. On the other hand, suspended sediment is mainly composed of silt and clay, and sedimentary and metamorphic rock areas are the main sources of production. Since the riverbed material contains little silt and clay, the suspended sediment could be originated from the mountain slopes in the mid- and down-stream areas of the Saru River basin. Sand components may contribute to the coastal and littoral sediments not only from the mountain slopes but also from the re-migration of the fluvial materials. These results suggest that countermeasures against coastal erosion and beach loss require in-channel storage and continuity from the upper reaches of mountainous areas to the sea to supply sufficient quantities of sand to the sea.