On the measurement of solute concentrations in 2-D flow tank experiments

Abstract

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.

Quantification of Uncertainties from Image Processing and Analysis in Laboratory-Scale DNAPL Release Studies Evaluated by Reflective Optical Imaging

“…The latter should be tested for different experimental setups (e.g., water-unsaturated soils, LNAPL compounds, saltwater intrusion), other non-consolidated porous media (e.g., silty sand, clay lenses, combinations of several sediment fractions), and fractured rock (e.g., sandstone, limestone) in order to point out the flexibility and transferability of the IPA framework presented here. [34,49,80] [ 56,62,66,68,76,78,79] Converting to gray scale [48] [ 82,83] Correction of spatially non-uniform illumination Correction using a reference image, either flat-field image or without tracer and then dividing, subtracting or normalizing to the image - [62,84,85] Converting by using adaptive thresholding algorithm using percent distance between peaks…”

“…Image normalization using black and white cards or grey cards [56] [ 66,76] Correction using white card or gray card or reference areas [29,30] [ 60,77,78] Standardization of image - [69,79] Color model change to uncover required information Conversion to HSI or YCbCr [42,49,68,80] -…”

Effects of tectonic structures, salt solution mining, and density-driven groundwater hydraulics on evaporite dissolution (Switzerland)

“…Fractured zones along the graben structures may provide a vertical hydraulic connection to the evaporites of the Middle Muschelkalk. The physical principle of resulting density-coupled flow in a deeper aquifer, which emerges along the fracture zone into a surficial aquifer has been recently investigated with a series of laboratory-scale experiments for benchmarking 2D numerical simulations (Konz et al 2008(Konz et al , 2009aYounes et al 2009).…”

“…Both the geological and the groundwater model were used to define boundary conditions for an approximately 1,000-mlong and 150-m-deep 2D cross section, where a series of 2D density-coupled solute-transport simulations were con-ducted. The size and complexity of the density-flow problem required the application of codes which had been recently tested on benchmark data of laboratory experiment, and which were set up to simulate the geological conditions found at the site (Konz et al 2008(Konz et al , 2009aYounes et al 2009). The 2D field-scale density-flow simulations allowed for evaluating both the effect of the anthropogenic groundwater withdrawal and the dip of the halite formation on salt dissolution rate.…”

Laboratory Experiments of Drainage, Imbibition and Infiltration under Artificial Rainfall Characterized by Image Analysis Method and Numerical Simulations

“…For our study, LRM was used because it can be conducted with non-transparent porous media and wide flow tanks; LTM is dedicated rather to transparent media of small dimensions, while MIAM is much more expensive to access saturation of different phases in porous media. Image analysis based on reflected light has largely been used for intermediate-scale experiments (e.g., [23,[25][26][27][28][29][30][31][32][33][34][35][36][37][38]). Application of quantitative photometric procedures for unsaturated flow characterization is less widespread, and even less so with the LRM.…”