Abstract
The Varaždin aquifer represents the main source of water for public supply, agricultural, and industrial purposes in the Varaždin County in NW Croatia. In the last decades, this area has experienced contamination of groundwater with nitrates. This study describes the conceptualization of the Varaždin aquifer for the purpose of developing numerical model of groundwater flow and nitrate transport. Within the study, three important elements are defined: aquifer geometry, recharge from precipitation, and other boundary conditions. 3D aquifer model revealed that Varaždin aquifer consist of three layers: upper aquifer, semipermeable interlayer, and lower aquifer. The Wetspass-M model was used for the assessment of spatial and temporal distribution of water balance components for the period 2008–2017. Results of the model indicate that the average annual precipitation is distributed as 34% groundwater recharge, 21% surface runoff, and 45% actual evapotranspiration. The maps of equipotential lines show the behavior of the aquifer system and define boundary conditions, i.e., recharge and discharge areas of the aquifer: an inflow boundary from Drava River and accumulation lake Varaždin on the northwest and north, no flow boundary on the west and south, and an outflow boundary on the east.
Highlights
The Varaždin aquifer is a vital source of water for public supply, agricultural, and industrial purposes in the Varaždin County in NW Croatia
About 50% of the average annual surface runoff occurs during the colder period from November to February
The hydrogeological conceptual model will be used for setting up a numerical groundwater flow and nitrate transport model
Summary
The Varaždin aquifer is a vital source of water for public supply, agricultural, and industrial purposes in the Varaždin County in NW Croatia. According to its hydrogeological characteristics, it represents one of the strategic groundwater resources in Croatia. In the last few decades, this area has experienced high nitrate concentrations caused by anthropogenic sources, such as manure, synthetic fertilizers, septic systems, and other wastewaters. This paper is part of a broader study being conducted in Varaždin alluvial aquifer with the aim of assessing the origin, fate, and the transport of nitrate within the study area. A detailed survey of hydrodynamic characteristics of the aquifer was undertaken to develop hydrogeological conceptual model, which will be used as a foundation for setting up a numerical groundwater flow and nitrate transport model. Preparation of conceptual model involved identification of the study area, creation of 3D model of hydrogeological system, estimation of recharge from precipitation, and defining boundary conditions are shown
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