Numerical modeling of heavily polluted fine-grained sediments remobilization in northern Czech Republic

摘要

The northern part of the Czech Republic is regarded as significantly polluted by antecedent or ongoing heavy industrial production mainly concentrated in the riparian zones of the Elbe River and its tributaries. Toxic pollutants tend to persist in the environment for a long time bound with fine-grained sediments. Nevertheless, a high-flow event can induce a remobilization of those deposits and lead to secondary pollution of downstream aquatic ecosystems. Numerical modeling was used as a tool for remobilization probability assessment under local hydrodynamic conditions within 113 km of Elbe and Bílina river beds and riparian zones. The assessment was based on statistical evaluation of causal discharge, the actual discharge observed at the evaluated cross section at the time of remobilization defined as significant erosion of observed sediment depositions. MIKE modeling software by DHI was used with different levels of horizontal plan schematization according to site-specific flow conditions and available data sources. MIKE 11 and MIKE 21 were used for Bílina River and MIKE 21 C was used for the Elbe River. Sediment transport was calculated simultaneously with hydrodynamic simulation of the unsteady synthetic boundary conditions based on observed flood properties (MIKE 21 C, MIKE 21 MT). Remobilization assessment of Bílina River sediment was based on the shear stress map evaluation verified with the results obtained by 2D model of the experimental site. The study contributes to risk-based assessment of polluted sediment management of the Elbe and extends the current scope of remobilization prediction within a reasonable timeframe using a numerical modeling method.