Longshore transport modeling of the contaminated sediment in the Fukushima area

The cesium-contaminated sediment in the Fukushima mountain area is expected to be transported by the river flow to the downstream region, and eventually to the ocean. The contaminated sediment discharged from the river to the ocean settles down to the seabed of the coastal area around the river mouth. Some part of the settled sediment is transported to the offshore region and the contamination of the coastal area is expected to decay gradually. Estimation of the environmental half-life of the contaminated sediment is important for the assessment of the safety of the edible fish in the Fukushima coastal area. Thus we need to calculate the sediment transport in the coastal area induced by various ocean phenomena, such as tidal current, river current, wave and wind-induced current. We have estimated the effect of several kinds of ocean phenomena on the coastal sediment transport, and found that the wind-induced current and the wave-induced suspension are the most dominant phenomena, while contributions from tidal current and the river flow is negligible.