Renewed soil erosion and remobilisation of radioactive sediment in Fukushima coastal rivers after the 2013 typhoons

O. Evrard (1, 2) , Caroline Chartin (3) , Yuichi Onda (4) , Hugo Lepage (1, 2) , Olivier Cerdan (5) , Irène Lefèvre (1, 2) , Sophie Ayrault (1, 2)

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 GEDI - Géochimie Des Impacts
3 ELI - Earth and Life Institute [Louvain-La-Neuve]
4 Université de Tsukuba = University of Tsukuba
5 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Summer typhoons and spring snowmelt led to the riverine spread of continental Fukushima fallout to the coastal plains of Northeastern Japan and the Pacific Ocean. Four fieldwork campaigns based on measurement of radioactive dose rates in fine riverine sediment that has recently deposited on channel bed-sand were conducted between November 2011 and May 2013 to document the spread of fallout by rivers. After a progressive decrease in the fresh riverine sediment doses rates between 2011 and early spring in 2013, a fifth campaign conducted in November 2013 showed that they started to increase again after the occurrence of violent typhoons. We show that this increase in dose rates was mostly due to remobilization of contaminated material that was temporarily stored in river channels or, more importantly, in dam reservoirs of the region during the typhoons. In addition, supply of particles from freshly eroded soils in autumn 2013 was the most important in areas where decontamination works are under progress. Our results underline the need to monitor the impact of decontamination works and dam releases in the region, as they may provide a continuous source of radioactive contamination to the coastal plains and the Pacific Ocean during the coming years.

Mots clés: Panoply

Domaines: Planète et Univers [physics]; Sciences de la Terre; Sciences de l'environnement; Sciences de l'environnement; Milieux et Changements globaux; Planète et Univers [physics]; Interfaces continentales, environnement; Planète et Univers [physics]; Sciences de la Terre; Géomorphologie; Planète et Univers [physics]; Sciences de la Terre; Hydrologie; Sciences du Vivant [q-bio]; Sciences agricoles; Science des sols

O. Evrard, Caroline Chartin, Yuichi Onda, Hugo Lepage, Olivier Cerdan, et al.. Renewed soil erosion and remobilisation of radioactive sediment in Fukushima coastal rivers after the 2013 typhoons. Scientific Reports, 2014, 4, pp.4574. ⟨10.1038/srep04574⟩. ⟨hal-01176528⟩