Fluvial Redistribution of Chernobyl Fallout:Reservoir Evidence in the Severn Basin

Sediments in the Chelmarsh pump‐storage reservoir have provided a valuable record of the 137Cs levels associated with suspended particulates transported by the River Severn since 1965. The presence of Chernobyl‐derived 137Cs and 134Cs within the sedimentary record of the site, despite the absence of any direct fallout on the local area, confirmed that radiocaesium from the Ukrainian reactor accident has been mobilized from the upper reaches of the Severn basin where atmospheric deposition was relatively high. The incorporation of Chernobyl radiocaesium within these sediments can be used to date the 1986 fallout episode, and the established geochronology indicated variable rates of post‐1986 sediment accumulation. As radiocaesium is strongly bound to fluvial particulates, this mechanism of redistribution has not adversely affected the quality of the drinking‐water source at the site which was studied.