Measuring and Modeling Runoff, Soil Erosion and Sediment Yields to
assess Management Options in the Post-Fallout Watersheds of Iitate
Village, Fukushima, Japan
Abstract
Following the radioactive fall out of the 2011 Fukushima Daiichi Nuclear
Power Plant (FDNPP) accident, radiocesium (Cs-137) contaminated soils of
forests, uplands, rice paddies and other land uses released contaminated
sediments onto neighboring areas and into the creeks and rivers in
Iitate Village, Japan. The study used conventional and Cs-137
fingerprinting techniques to determine runoff and suspended sediment
discharges to assess the small and large-scale soil redistribution
dynamics within contributing areas in two watersheds. Also, we attempted
to use Cs-137 fingerprinting to identify spatial and temporal patterns
of erosion, transport and sedimentation on hillslopes within those
watersheds. Tributaries near the outlet of the 30 km2 Hiso watersheds
were simulated at the hillslope and watersheds using the process-based
Water Erosion Prediction Project (WEPP) model and the Geospatial
Interface for WEPP (GeoWEPP). Besides the simulation of historic soil
redistribution events, a particular emphasis was the identification and
assessment of various land use and cover changes on the past soil
redistribution. Results of the analysis in the post-fallout landscapes
enables scientists and farmers as well as natural resources and disaster
managers to investigate the consequences of active and passive land use
and cover changes on the runoff and sediment dynamics at the plot,
hillslope and watershed scales. Especially the behavior of Cs-137
contaminated clay particles in soils and sediments seem to be the key
for the success of the measurement, modeling and management techniques.
The result of this study has the potential to assist decision and
policymaking for stakeholders not only in areas that were impacted by
the contamination through radioactive fallout.