Abstract
Based on the statistical analysis of the time series of data, the influence of the change of Sava River temperature and geothermal anomalies on the changes of the groundwater temperature of the Zagreb and Samobor-Zapresic aquifers is described. In the analysis, data were used from daily measurements of the Sava River temperature and from the quarterly measurements of the groundwater temperature. Statistical methods of correlation, cross-correlation and linear regression were applied and the maximum, mean and minimum groundwater temperatures were analysed. Obtained results are presented in the form of statistical parameters, diagrams and maps of isotherms. This data is indispensable for development of shallow geothermal applications related to open loop groundwater heat pump systems. Since efficiency of the heat pump is directly dependent source temperature, presented analyses is necessary for prefeasibility study of geothermal projects and comparison between different designs. Furthermore, currently operating projects in the Zagreb and Samobor-Zapresic are systematically elaborated, giving first approximation of energy consummation from this renewable energy resource.
Highlights
Geological and hydrogeological aspects of the Zagreb aquiferThe Zagreb and Samobor-Zaprešić aquifer systems are located in Northwest Croatia and include urban areas and their surroundings (see Figure 1)
The identification of temperature fluctuations of the Sava River and groundwater temperature oscillations of the Samobor-Zaprešić and Zagreb aquifers are needed for the development of shallow geothermal energy applications
A low frequency of groundwater temperature measurements results in the inability of recording actual temperature fluctuations during one hydrological year, as extreme temperatures are not recorded most of the time
Summary
The Zagreb and Samobor-Zaprešić aquifer systems are located in Northwest Croatia and include urban areas and their surroundings (see Figure 1). The aquifers are composed mainly of Quaternary sediments, i.e. Middle and Upper Pleistocene and Holocene, which are described in the explanatory notes for the Basic Geological Map of SFRY 1:100 000 (Basch, 1983; Šikić et al, 1979). Head contour map analysis (Posavec, 2006) showed that during high river water levels, infiltration to groundwater takes place throughout the whole Zagreb aquifer area. The hydraulic connection between the Sava River and the aquifer is very strong since the river is carved, along the entire flow through the Zagreb and Samobor-Zaprešić aquifers, into alluvial Holocene deposits with mainly high values of hydraulic conductivity. Identification of the Sava River temperature influence on the groundwater temperature This area has a marine west coast climate, with four separate seasons.
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