Modelling the extent of Cs-137 soil contamination patterns at the Kostica River basin (Bryansk Region, Russia)
Authors: Linnik Vitaly , Sokolov Alexander , Ivanitsky Oleg , Saveliev Anatoly 
Published: March 2020

&lt;p&gt;Digital terrain analysis may be a useful tool for modeling the extent of Cs-137 soil contamination patterns after the Chernobyl disaster. The test area of the &amp;#160;Kostica River basin (Bryansk Region, Russia)&amp;#160; covers an area of 19,4x11,6 km and is characterized by relatively low levels of &lt;sup&gt;137&lt;/sup&gt;Cs contamination after the Chernobyl accident&amp;#160; in the range of&amp;#160; 2.4&amp;#160; to 33 kBq/m&lt;sup&gt;2&lt;/sup&gt;. It is just 4-18 times higher than the global fallout which was equal to 1,75 kBq/m&lt;sup&gt;2&lt;/sup&gt; in 1986.&lt;/p&gt;&lt;p&gt;The purpose of&amp;#160; the research was to obtain estimates of the transformation of initial &lt;sup&gt;137&lt;/sup&gt;Cs patterns as in&amp;#64258;uenced by different landscape factors (DEM attributes) with a grid resolution of 100, 50 and 25 m. Different kinds of DEM&amp;#160; curvatures calculations&amp;#160; may be done by using SAGA, Whitebox GAT and Grass for each grid size model.&lt;/p&gt;&lt;p&gt;In the case under study two informational layers were made use of&amp;#160; to evaluate processes of &lt;sup&gt;137&lt;/sup&gt;Cs redistribution in the River Kostica basin. These are: 1) SRTM&amp;#160; layer with a resolution of 90 m&amp;#160; and&amp;#160; 2) the data of air-gamma survey with a resolution of 100 m.&amp;#160; The total watershed area of the Kostica River occupies 225 km&lt;sup&gt;2&lt;/sup&gt;. SRTM data were resampled in a coordinates and georeference system of AG (air-gamma survey was represented in the Gauss-Kruger coordinate system) lay&amp;#160; with a resolution of 100 m.&lt;/p&gt;&lt;p&gt;The results of the air gamma survey conducted in the summer of 1993, give clear evidence that the processes of &lt;sup&gt;137&lt;/sup&gt;Cs lateral migration took place due to nearly a fourfold increase of &lt;sup&gt;137&lt;/sup&gt;Cs in the lower slope as compared to the surface of the watershed during a seven-year period after the Chernobyl accident.&lt;/p&gt;&lt;p&gt;We examine the effect of grid size of the &amp;#160;digital elevation model (DEM) on the erosion simulations. For resampled grid data with a resolution &amp;#160;of 50 and 25 m &amp;#160;we apply SAGA-GIS Module &amp;#8220;Resampling&amp;#8221; and compare the results with those of &amp;#160;the original method of simplicity versus fitting (SvF). &amp;#160;The method SvF is devoted to finding a compromise between simplicity of the model and precision of replication of experimental data. The integral in the range of squared second derivatives was used as a measure of simplicity, with usual standard deviation being applied as a measure for replication of experimental data.&lt;/p&gt;&lt;p&gt;The study is based on the concept of sediment and hydrological connectivity. We apply GIS-based models considering lateral soil migration to analyze sediment cascade systems. Soil erosion was evaluated based on an analysis of Cs-137 migration determined using the LS factor implemented by GRASS GIS.&lt;/p&gt;&lt;p&gt;The reported study was funded by RFBR according to the research project &amp;#8470; 20-07-00701A&amp;#160;&lt;/p&gt;