A 3D geological model of the area east of Basel on the southeastern border of the Upper Rhine Graben, consisting of 47 faults and six stratigraphic horizons relevant for groundwater flow, was developed using borehole data, geological maps, geological cross sections, and outcrop data. This model provides new insight into the discussions about the kinematics of the area between the southeastern border of the Upper Rhine Graben and the Tabular Jura east of Basel. A 3D analysis showed that both thin-skinned and thick-skinned tectonic elements occur in the modeled area and that the Anticline and a series of narrow graben structures developed simultaneously during an extensional stressfield varying from E-W to SSE-NNW, which lasted from the Middle Eocene to Late Oligocene. In a new approach the faults and horizons of the 3D geological model were transferred into discrete elements with distributed hydrogeological properties in order to simulate the 3D groundwater flow regime within the modeled aquifers. A three-layer approach with a horizontal regularly spaced grid combined with an irregular property distribution of transmissivity in depth permitted the piezometric head of the steady-state model to be automatically calibrated to corresponding measurements using more than 200 piezometers. Groundwater modeling results demonstrated that large-scale industrial pumping affected the groundwater flow field in the Upper Muschelkalk aquifer at distances of up to 2 km to the south. The results of this research will act as the basis for further model developments, including salt dissolution and solute transport in the area, and may ultimately help to provide predictions for widespread land subsidence risks.

[1] The Henry semianalytical solution for salt water intrusion is widely used for benchmarking density dependent flow codes. The method consists of replacing the stream function and the concentration by a double set of Fourier series. These series are truncated at a given order and the remaining coefficients are calculated by solving a highly nonlinear system of algebraic equations. The solution of this system is often subject to substantial numerical difficulties. Previous works succeeded to provide semianalytical solutions only for saltwater intrusion problems with unrealistic large amount of dispersion. In this work, different truncations for the Fourier series are tested and the Levenberg-Marquardt algorithm, which has a quadratic rate of convergence, is applied to calculate their coefficients. The obtained results provide semianalytical solutions for the Henry problem in the case of reduced dispersion coefficients and for two freshwater recharge values: the initial value suggested by Henry (1964) and the reduced one suggested by Simpson and Clement (2004). The developed semianalytical solutions are compared against numerical results obtained by using the method of lines and advanced spatial discretization schemes. The obtained semianalytical solutions improve considerably the worthiness of the Henry problem and therefore, they are more suitable for testing density dependent flow codes.Citation: Zidane, A., A. Younes, P. Huggenberger, and E. Zechner (2012), The Henry semianalytical solution for saltwater intrusion with reduced dispersion, Water Resour. Res., 48, W06533,

Abstract. In this study we describe and compare photometric and resistivity measurement methodologies to determine solute concentrations in porous media flow tank experiments. The first method is the photometric method, which directly relates digitally measured intensities of a tracer dye to solute concentrations, without first converting the intensities to optical densities. This enables an effective processing of a large number of images in order to compute concentration time series at various points of the flow tank and concentration contour lines. This paper investigates perturbations of the measurements; it was found both lens flare effects and image resolution were a major source of error. Attaching a mask minimizes the lens flare. The second method for in situ measurement of salt concentrations in porous media experiments is the resistivity method. The resistivity measurement system uses two different input voltages at gilded electrode sticks to enable the measurement of salt concentrations from 0 to 300 g/l. The method is highly precise and the major perturbations are caused by temperature changes, which can be controlled in the laboratory. The two measurement approaches are compared with regard to their usefulness in providing data for benchmark experiments aimed at improving process understanding and testing numerical codes. Due to the unknown measurement volume of the electrodes, we consider the image analysis method more appropriate for intermediate scale 2D laboratory benchmark experiments for the purpose of evaluating numerical codes.

[1] A series of laboratory-scale two-dimensional porous medium tank experiments was conducted to study stable-layered variable density flow problems using well-defined experimental parameters and boundary conditions. The experiments were carried out both in a rectangular flow tank and in a more complex geometrical setup aimed at studying variable density flow in geometries similar to geological formations of aquifers and aquicludes connected via fault zones. An impermeable layer within the porous medium tank forced the solutes to pass through a vertical channel, representing a geological fault zone, to reach the outlet of the tank. Flow through the porous medium occurred through a single inflow opening and an outflow opening on the opposite edge of the domain. An image analysis technique delivered 2%, 10%, 50%, and 80% salt concentration isolines at distinct times. Breakthrough curves of the dyed saltwater with an initial density of 1063 g/L were available at any location within the tank. The experimental data are presented as benchmark problems to evaluate numerical codes. A numerical model based on mixed finite elements for the fluid flow problem and a combination of discontinuous Galerkin finite element and multipoint flux approximation methods for the transport turned out to be adequate for the simulation of the physical experiments. The high data availability makes the proposed benchmark experiments a valuable tool for assessing the performance of density-coupled flow models.Citation: Konz, M., P. Ackerer, A. Younes, P. Huggenberger, and E. Zechner (2009), Two-dimensional stable-layered laboratoryscale experiments for testing density-coupled flow models, Water Resour. Res., 45, W02404,

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