engleski

Developing a Conceptual Model for Groundwater Flow and Transport Model of Nitrate in the Varaždin Alluvial Aquifer

Groundwater contamination with nitrate is a major concern in the Varaždin alluvial aquifer. Increased concentrations of nitrate in groundwater are predominantly caused by intensive agricultural activities where synthetic nitrogen fertilizers and manure are being used. For better understanding of distribution and fate of nitrate, it is necessary to develop a conceptual model of the Varaždin aquifer, which will be used as a foundation for setting up a numerical model of groundwater flow and transport model of nitrate. A conceptual model is a simplified representation of the site to be modelled and requires identification of three key elements: model domain and aquifer geometry, aquifer parameters and boundary conditions. The research area (model domain) is located upstream of the town of Varaždin and includes the catchment area of the pumping sites ‘’Varaždin’’ and ‘’Vinokovščak’’. The aquifer of the research area is unconfined and represented by Pleistocene and Holocene alluvial deposits, which are primarily composed of gravel and sand with variable portions of silt. Groundwater generally flows from northwest to the southeast, parallel to the Drava River. The covering layer of the aquifer is not continuously developed and there is a high risk of contamination from the surface. The aquifer is recharged by precipitation infiltration through unsaturated zone and by surface water percolation. Aquifer geometry will be determined from geological maps, existing boreholes, geophysics data and geological cross sections. Aquifer parameters will be obtained from available results of field measurements and parameters for which is lack of field data will be estimated from the literature. Determination of appropriate boundary conditions will be based on analysis of head contour maps for high, medium and low groundwater levels. For the research purposes, a monitoring network of ten observation wells and four surface water locations has been established. Water sampling is conducted on a monthly basis for chemical analyses. Results of chemical analyses can identify the zones with elevated nitrate content in groundwater and combined with land use analysis, can help to locate the surface sources of nitrate for the model. The research is performed as part of the TRANITAL project that is funded by the Croatian Science Foundation (HRZZ) and supported by Young Researchers Career Development Project - Training of New PhDs – HRZZ & ESF.

nitrate, groundwater modelling, Varaždin aquifer

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