A ‘weighted’ 137Cs inventory calculation of Reservoir 11, Mayak P.A., Russia with the novel use of remotely sensed information and sample data in a GIS

The objective of this study was to make a robust 137Cs inventory calculation for Reservoir 11 in the Mayak Production Associations industrial cascade of reservoirs. High resolution satellite photographs provided information about the original Techa River and floodplain environment before, during and also after Reservoir 11 was constructed. The images provided important clues about the old Techa River system and also showed the extent of the contaminated area. Sediment cores were sampled along a transect in Reservoir 11, and perpendicular to the Techa River in 1996. 137Cs contamination densities were in the range 344–4030 kBq m−2 and appear to exhibit a strong dependence on relative position along the transect, with more central positions exhibiting the highest actual levels. The contamination densities derived from the seven cores were combined with (published) data from four core samples collected in a 1994 field campaign. Sample data and images were integrated in a geographical information system (GIS). The GIS aided in the definition of distinctive floodplain classes, the so-called sediment ‘facies’, area calculations and in the positioning of 1994 and 1996 sample profiles in the reservoir. The resulting inventory estimate for Reservoir 11, is a factor 4–10 lower than earlier calculations. Analysis of the uncertainty in the calculations has been carried out and provides support for the integrity of the new method.