Kristijan Posavec

Fully automated objective-based method for master recession curve separation.

The fully automated objective-based method for master recession curve (MRC) separation was developed by using Microsoft Excel spreadsheet and Visual Basic for Applications (VBA) code. The core of the program code is used to construct an MRC by using the adapted matching strip method (Posavec et al. 2006). Criteria for separating the MRC into two or three segments are determined from the flow-duration curve and are represented as the probable range of percent of flow rate duration. Successive separations are performed automatically on two and three MRCs using sets of percent of flow rate duration from selected ranges and an optimal separation model scenario, having the highest average coefficient of determination R(2), is selected as the most appropriate one. The resulting separated master recession curves are presented graphically, whereas the statistics are presented numerically, all in separate sheets. Examples of field data obtained from two springs in Istria, Croatia, are used to illustrate its application. The freely available Excel spreadsheet and VBA program ensures the ease of use and applicability for larger data sets.

Conceptual model for groundwater status and risk assessment - case study of the Zagreb aquifer system

This paper presents a conceptual model of the Zagreb aquifer system. The conceptual model can be applied to groundwater status risk assessment and pollution risk assessment at the local scale, thus satisfying both environmental and preventative/limitation objectives of the Water Framework Directive (WFD) and Groundwater Directive (GWD). Its main purpose is to apply a risk assessment procedure, according to the WFD requirements, and to serve as a foundation for setting up a numerical model of flow in both the saturated and unsaturated zones in order to identify pressure and impact effects on groundwater quality. The model is divided into two parts, taking into account the WFD requirement to assess a risk for a wide range of source-pathway-receptor relationships. The Global Conceptual Model (GCM) provides insight into the processes and pressures at the level of the groundwater system. It contains the geological and hydrogeological characterization of the Zagreb aquifer system and the description of the most significant point and diffuse sources and pathways of pollution and processes influencing pollutant behaviour in saturated and unsaturated zone of the groundwater system. The main pollutants of the Zagreb aquifer system are potentially toxic metals, nitrates, pesticides, pharmaceuticals and chlorinated aliphatics. A Local Conceptual Model (LCM) supports parameterization of the whole groundwater system through the description of heterogeneities and flow and solute parameters of the system components at two sites representing local conditions in the saturated (Stara Loza) and unsaturated (Kosnica) zones. This concept can be regarded as an effective tool for groundwater management of the groundwater system and its compartments and for communicating the conditions in complex groundwater systems with experts, policy makers and general public in an understandable way.

Analysis of mountain springs discharge time series in the Tennacola stream catchment (central Apennine, Italy)

The mountain portion of the Tennacola stream basin, which is located in the northeast sector of the Sibillini Mountains (Central Apennines, Italy), has a large number of springs exploited for drinking water. The presence of lithotypes with different hydraulic conductivity allowed the formation of two main groups of springs with different discharge and regime. This paper aims to provide new insights about the groundwater circulation within carbonate and karst complexes. In detail a study based on spring hydrograph analysis using the MRC method and on the main statistical parameters has been carried out, in order to evaluate the main features related to the flow paths and the main hydrogeological properties of the aquifers studied. The results allowed to characterize the main hydrogeological features of the aquifers and to evaluate the dimension of the recharge areas.

Groundwater recharge estimation using spring hydrographs: the case of the Tennacola carbonate aquifer (central Apennine, Italy)

The recharge of an aquifer is fundamental to evaluate the availability of the resource and for planning its use over the time.In general, indirect methods are widely used, because these are based on the rainfall, evapotranspiration and runoff data. These three parameters are not always simple to evaluate in relation to the possible presence of errors in the available data, malfunction of instruments or difficulty to make a monitoring in relation to the complexity of the area, with consequent uncertainty on the results. In such situations, the use of a direct method could be useful to estimate more accurately the aquifer recharge.A common direct method is based on the analysis of the spring hydrographs, i.e. the discharge monitored at the spring. In this work, a spring hydrograph from the central Apennines of Italy has been analysed in order to estimate the average recharge value feeding the aquifer.

Method and Excel VBA Algorithm for Modeling Master Recession Curve Using Trigonometry Approach

A new method was developed and implemented into an Excel Visual Basic for Applications (VBAs) algorithm utilizing trigonometry laws in an innovative way to overlap recession segments of time series and create master recession curves (MRCs). Based on a trigonometry approach, the algorithm horizontally translates succeeding recession segments of time series, placing their vertex, that is, the highest recorded value of each recession segment, directly onto the appropriate connection line defined by measurement points of a preceding recession segment. The new method and algorithm continues the development of methods and algorithms for the generation of MRC, where the first published method was based on a multiple linear/nonlinear regression model approach (Posavec et al. 2006). The newly developed trigonometry-based method was tested on real case study examples and compared with the previously published multiple linear/nonlinear regression model-based method. The results show that in some cases, that is, for some time series, the trigonometry-based method creates narrower overlaps of the recession segments, resulting in higher coefficients of determination R2 , while in other cases the multiple linear/nonlinear regression model-based method remains superior. The Excel VBA algorithm for modeling MRC using the trigonometry approach is implemented into a spreadsheet tool (MRCTools v3.0 written by and available from Kristijan Posavec, Zagreb, Croatia) containing the previously published VBA algorithms for MRC generation and separation. All algorithms within the MRCTools v3.0 are open access and available free of charge, supporting the idea of running science on available, open, and free of charge software.

Application of the MRC method to the study of some mountain springs in the Tennacola stream catchment (central Apennine, Italy)

The study concerns part of the plain sector of Aosta Valley (NW Italy). The investigated area is located between the cities of Sarre-Gressan and Pollein-Saint Christophe and is characterized by the presence of hexavalent chromium in the main shallow unconfined aquifer. The pollution is probably related to the negative environmental effects induced by the industrial steel production that since 1915 is present over the area. Since 1990 the industrial area was subjected to a number of direct investigations aimed to assess the contamination intensity. A preliminary remediation activity has been developed in last decades but the contaminants have been still observed in the groundwater monitoring network. This study highlights the set-up of a groundwater conceptual and numerical model of the shallow aquifer aimed to better understand and analyze the transport dynamics of hexavalent chromium in the local aquifer. The simulation is performed using the specific finite element software Feflow for groundwater flow and mass transport modeling. The hydrogeological setting of this area is related to the different sedimentary glacial, lacustrine and fluvial processes which characterized the bottom of the Aosta valley during the Quaternary. The shallow 80m-width aquifer is constituted by sandy to gravelly deposits and presents rare silty lens while its bottom is characterized by a decametric lacustrine silty level. The main aims of the numerical model are to give a more unequivocal explanation of the origin of the contamination and to support the predictive analyses in order to design an efficient site remediation for soil and groundwater. This represents a fundamental task in order to preserve the safety of the public water uses supplied by the aquifer. The preliminary hypothesis about the source of contaminations are still uncertain and referred to different scenarios that have to be further investigated by comparing monitoring data and transient flow simulation conditions.