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Irvine D.J.,National Center for Groundwater Research and Training | Irvine D.J.,Flinders University | Brunner P.,Center for Hydrogeology and Geothermics | Franssen H.J.H.,Julich Research Center | And 2 more authors.
Journal of Hydrology

A common approach in modeling surface water-groundwater interaction is to represent the streambed as a homogeneous geological structure with hydraulic properties obtained by means of model calibration. In reality, streambeds are highly heterogeneous, and there are currently no methodical investigations to justify the simplification of this geologic complexity. Using a physically based numerical model, synthetic surface water-groundwater infiltration flux data were generated using heterogeneous streambeds for losing connected, losing transitional and losing disconnected streams. Homogeneous streambed hydraulic conductivities were calibrated to reproduce these fluxes. The homogeneous equivalents were used for predicting infiltration fluxes between streams and the aquifer under different hydrological conditions (i.e. for different states of connection). Homogeneous equivalents are shown to only accurately reproduce infiltration fluxes if both the calibration and prediction are made for a connected flow regime, or if both the calibration and prediction are made for a disconnected flow regime. The greatest errors in flux (±34%) using homogeneous equivalents occurred when there was a mismatch between the flow regime of the observation data and the prediction. These errors are comparatively small when compared with field measurement errors for hydraulic conductivity, however over long river reaches these errors can amount to significant volumes of water. © 2011 Elsevier B.V. Source

Falco P.,Center for Hydrogeology and Geothermics | Negro F.,Center for Hydrogeology and Geothermics | Szalai S.,Geodetic and Geophysical Research Institute of HAS | Milnes E.,Center for Hydrogeology and Geothermics
Near Surface Geoscience 2013

The term "geoelectric null-array" is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger nullarray in response to a fracture. The main objective is to determine which array(s) best localise vertical structures. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately. The numerical analysis served as basis to interpret the field results too. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. This study shows that geoelectrical null-arrays are better than classical arrays for localisation of fractures. Source

When implementing remediation programs to mitigate diffuse-source contamination of aquifers, tools are required to anticipate if the measures are sufficient to meet groundwater quality objectives and, if so, in what time frame. Transfer function methods are an attractive approach, as they are easier to implement than numerical groundwater models. However, transfer function approaches as commonly applied in environmental tracer studies are limited to a homogenous input of solute across the catchment area and a unique transfer compartment. The objective of this study was to develop and test an original approach suitable for the transfer of spatially varying inputs across multiple compartments (e.g. unsaturated and saturated zone). The method makes use of a double convolution equation accounting for transfer across two compartments separately. The modified transfer function approach was applied to the Wohlenschwil aquifer (Switzerland), using a formulation of the exponential model of solute transfer for application to subareas of aquifer catchments. A minimum of information was required: (1) delimitation of the capture zone of the outlet of interest; (2) spatial distribution of historical and future pollution input within the capture zone; (3) contribution of each subarea of the recharge zone to the flow at the outlet; (4) transfer functions of the pollutant in the aquifer. A good fit to historical nitrate concentrations at the pumping well was obtained. This suggests that the modified transfer function approach is suitable to explore the effect of environmental projects on groundwater concentration trends, especially at an early screening stage. © 2015 Springer-Verlag Berlin Heidelberg Source

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