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HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue.

The introduction of cash crops and the evolution of farming practices in the uplands of Southeast Asia have drastically changed the agricultural landscape of the region during these last decades. This evolution has significantly increased soil erosion leading to important on and off-site effects. A long-term multi-scale monitoring of soil erosion was initiated in the early 2000's in the Houay Pano catchment located near the city of Luang Prabang in Northern Laos to assess these effects and propose sustainable land management solutions. We report here the analysis and the modelling of the soil erosion measurements made during the whole period on 1m 2 plots for different land uses. As expected, land use has an important impact on runoff production and soil erosion. The mean annual runoff coefficient increased from 0.05 for established fallow (4 years) to 0.45 for old teak trees plantation (14 years) with intermediate values for crops. The mean soil loss followed the same trend with respect to land use, from − − 25 g m y 2 1 to − − 3765 g m y 2 1. These measurements confirm that established fallow promotes infiltration and reduces erosion and, at the opposite, teak tree increases soil crusting, lowers the infiltration rate and enhances soil detachment. The splash and wash erosion component of a process-oriented model developed for terrace erosion was used. This model describes the soil loss after a rainfall event as the product of an effective soil detachability, the rainfall kinetic energy, the runoff coefficient and different attenuation factors linked to soil surface features. The agreement is good, both at the event and the yearly scales. When aggregated by land use, surface features percentages have low standard deviations and soil detachability variability may be described by a log-normal distribution. This suggests that each land use has a unique signature in the erosion process given by the percentages and the distribution. We conclude that: (i) leaving the litter layer and an understorey in crops and trees plantations is the best way to minimize soil erosion, and (ii) the splash and wash model may be helpful to set up optimal agronomic strategies for a sustainable land use of Southeast Asia uplands.