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Preferential flow and non-equilibrium solute transport in the critical zone

Preferential and non-uniform flows are induced by biotic (e.g. earthworms and roots) and abiotic factors and processes (e.g. wet-dry and freeze-thaw cycles, lithology and structure) as well as anthropogenic activities (e.g. tillage and cultivation methods in agricultural land, man-made landforms from waste rock dumping and disposal strategies in mining). The understanding of preferential flow is of premium importance in relation to soil hydrology, as it can move a considerable amount of water and solutes in porous media. Preferential flows can occur spatially from the pore scale, to entire catchments, across large regions. Temporally, the preferential processes can change during hydrological events, from within hours to seasonal events, and across inter-annual variations of years.
This session welcomes studies on experimental and theoretical challenges to identify, quantify, and model the key physical factors and processes that are responsible for preferential flows in porous media across scales (from pore scale to catchment scale). Contributions are welcome to reflect on experimental studies, novel approaches and advances in solutions to:
• Understand the geometry and connectivity, formation and dynamics of fissure, fractures and macropores and its effect on preferential flow;
• Understand the effect of physical processes and geochemical processes on the dynamics of macropores and fracture networks;
• Unpacking the pore structure of soil using new methods and approaches, including the use of non-Newtonian fluids, for improved characterization of heterogeneous soils and the advancement of flow and transport modeling.
• Effects of preferential flows within the soil-plant-atmosphere continuum and their consequence for solute, nutrient, or contaminant transport in the saturated and unsaturated zone;
• Coupling the physical processes of preferential flows and geochemical processes for improving the understanding of solute sorption and desorption, mineral precipitation and dissolution;
• Modelling of the effect of preferential flow on mass transport across scales, from pore scale to pedon scale and entire catchments and landscapes.

Convener: Laurent Lassabatere | Co-conveners: Majdi R. Abou Najm, Thomas Baumgartl, Jannes KordillaECSECS, Mandana ShayganECSECS
| Tue, 24 May, 08:30–10:00 (CEST)
Room -2.47/48

Tue, 24 May, 08:30–10:00


Preferential flow at field scale

Roman Juras et al.

The distribution of rainwater and subsurface runoff formation in forest soil can be strongly affected by soil disturbance and microrelief. This study analyses preferential pathways of dyed water after artificial rainfall on a forested slope with pits and mounds formed by historical tree uprooting.

Two heavy rain experiments were carried out using a special tailored rainfall simulator. The first plot was situated above the pit-mound transition. The second (control) plot was situated at a nearby undisturbed surface. The soil profiles were excavated after the rainfall simulation and the dyed stained patches indicating preferential flow were photographed. Subsequently, advanced image analysis was performed to assess differences in water flow patterns in both soil profiles.

The results show contrasting dyed patterns in soil, indicating significant differences in the preferential flow and runoff formation at each plot. The dye-stained patches revealed in image analysis indicated much higher water entry into subsoil of pit profile (31 % of area) than in control plot (8 %). These findings support our previous hypothesis about the significant impacts of terrain depressions formed by tree uprooting on preferential flow and subsurface runoff formation. These terrain disturbances may redirect shallow subsurface flow and force the redistribution of water into deep subsoil layers.  The effects of pit-mound microrelief on the hydrology of forested slopes should be considered in future hydrological modelling and land management.

How to cite: Juras, R., Valtera, M., and Jačka, L.: How does pit-mound microrelief affect preferential flow and runoff formation in forest soils? A case study using rain simulator and dye tracer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4724, https://doi.org/10.5194/egusphere-egu22-4724, 2022.

Jasmina Defterdarović et al.

Soil vadose zone is one of the most complex terrestrial systems due to various processes occurring within its boundaries. The first Croatian critical zone observatory SUPREHILL was established to specify subsurface preferential flow and nonlinear agrochemical transport processes. Combining laboratory and numerical methods with extensive sensor-based equipment will result in a wide range of data allowing us to accurately estimate heterogeneities on a local scale. The presented study includes estimation of soil hydraulic properties (SHP) and water flow experiments under controlled conditions. Undisturbed soil cores (250 cm3) were taken in three repetitions at the top, middle and the bottom of the hillslope to estimate SHP using the HYPROP and WP4C techniques. Undisturbed soil columns were taken at the hilltop, middle, and the bottom of the vineyard hillslope from the row and interrow area. Soil columns are 25 cm high and 16 cm in diameter with soil moisture sensors and tensiometers set inside each column. Each soil column was irrigated three times per day during two-week period. Results obtained using HYPROP showed very similar SHP in the investigated depth which indicates uniform soil structure along the hillslope (top soil layer). HYPROP derived SHP showed very low values of hydraulic conductivity, but the sensors in columns reacted shortly after irrigation which indicates higher hydraulic conductivity. Since soil cores for HYPROP are relatively small compared to the soil columns, the presence of preferential flow is minimal, and some flow pathways present on the larger scale are not accounted for. Therefore, preferential flow will be further identified and quantified using a dye tracer, and experimental results will be shown. For additional preferential flow identification and quantification, later in the research, we will combine CT-scanning of undisturbed soil columns and numerical simulations.  

How to cite: Defterdarović, J., Filipović, L., Kovač, Z., Krevh, V., Han, L., Kodešová, R., Gerke, H. H., and Filipović, V.: Estimation of soil hydraulic properties and preferential flow at agricultural hilllslope under controlled conditions , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7218, https://doi.org/10.5194/egusphere-egu22-7218, 2022.

Felix Abayomi Ogunmokun and Rony Wallach

Soil water repellency has a substantial effect on soil-water retention and flow. Typically, soils are denoted water repellent when they resist spontaneous wetting by water for more than five seconds. Soil water repellency reduces infiltration capacity, increases surface runoff, soil erosion, and induces uneven distribution of water content, including preferential flow pathways. We describe an in-situ study aiming to remediate these soils by surfactant application using a commercial drip system.

The study was carried out on a commercial citrus orchard irrigated with secondary treated wastewater, which usage has been shown to induce soil water repellency over time. To relieve the adverse effects of soil water repellency, different concentrations of a nonionic surfactant were applied to the soil using a drip system for three years. The spatial variation of the soil's wettability was characterized by the sessile drop method (contact angle) and water drop penetration time (WDPT) test. The spatial soil-water content distributions and flow were monitored undisturbedly by electrical resistivity tomography (ERT) surveys. Spatial soil-agrochemical distributions along transects where the ERT surveys took place were determined by intensive soil sampling at two depths: 0-20 and 20-40 cm.

The ERT results indicated that while the surfactant application via drippers improved the water repellent soil's wettability, it enhanced the development of preferential flow pathways. Although preferential flow pathways associated with treated wastewater irrigation existed in all soil profiles, they were exacerbated by the surfactant application. Additionally, increased leaching of mobile elements, like Cl, N, and EC, was measured for the surfactant-treated plots. Contrarily, P adsorption to the soil particles was increased in the surfactant plots compared to the untreated plots. While the contact angle along the soil surface showed no difference between the untreated and surfactant treated plots, the WDPT decreased in the latter. These findings indicate that aside from the foreknown causes of preferential flow in soils like earthworms, wet and dry cycles, aliphatic hydrocarbons, etc., localized surfactant application by drippers (point sources) for water repellent soils remediation enhances preferential flow and chemicals leaching. Therefore, a different method for surfactant application that remediates soil water repellency without enhancing agrochemicals leaching should be considered and examined.

How to cite: Ogunmokun, F. A. and Wallach, R.: Surfactant application via drippers for water repellent soil remediation enhances agrochemicals leaching through preferential flow pathways, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2034, https://doi.org/10.5194/egusphere-egu22-2034, 2022.

Ryan Stewart and Jesse Radolinski

Organic contaminants such as antibiotics are being applied to soils in increasing loads. These chemicals can be rapidly transported via preferential flow, making it important to understand and quantify soil-solute interactions under bypass flow conditions. In this study we applied deuterium-labeled rainfall to field plots containing manure spiked with eight common antibiotics, and collected pore water samples from 48 suction cups spread along a hillslope. In total we collected more than 700 measurements across the eight antibiotics. Our results indicated that solute transport to lysimeters was similar between antibiotics when preferential flow was less than 15%. When preferential flow exceeded 15%, however, compounds with relatively low affinity for soil were sampled in higher concentrations, suggesting that preferential flow mobilizes compounds that are more easily released from the soil matrix. Our findings show that extensive preferential flow can enhance, rather than reduce, the influence of chemical properties. These data provide new insight into how flow heterogeneity affects pollutant mobility in soils and can be used to build more accurate process-based transport models.

How to cite: Stewart, R. and Radolinski, J.: Assessing interactions between preferential flow and antibiotic transport in soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13015, https://doi.org/10.5194/egusphere-egu22-13015, 2022.

Yusong Wang et al.

Temperate Highland Peat Swamps on Sandstone (THPSS) are ecological communities that consist of either ephemeral or permanent swamps developed in peat overlying Triassic sandstone formations in the Sydney Basin Bioregion of eastern Australia. THPSS with distinctive vegetation play an important role in biodiversity, carbon capture and storage, and the regional hydrological cycle. Some THPSS of Sydney Basin have underlying sandstone with cracks potentially formed over the past decades by human intervention. These cracks may create preferential flow paths that may accelerate the drainage process at the bottom of the swamps and may affect the soil moisture conditions of the swamps with ecological consequences. In order to understand and predict the impact of cracks on the swamps’ soil moisture and provide information to guide the management and restoration of the THPSS, 2D numerical simulations have been carried out using dual-porosity hydraulic models or explicit fast flow paths to represent the preferential flow paths. The models are calibrated and validated against historical soil moisture data and then used to evaluate the effect of cracks on soil moisture.

How to cite: Wang, Y., Shaygan, M., McIntyre, N., and Baumgartl, T.: The impact of preferential flow on Temperate Highland Peat Swamps on Sandstone soil hydrology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12859, https://doi.org/10.5194/egusphere-egu22-12859, 2022.

Thomas Baumgartl et al.

Environmental impacts of open-pit coal mining include issues such as fire risk, large-scale slope instability and groundwater contamination. Because of the man-made landforms used to cover open-pit mines and the coal material itself, soil hydrology can be affected in a way that non-uniform fluxes and preferential flow may occur. The aim of this study was to evaluate soil hydraulic properties of open-pit mines and coal material and to implement dual porosity approach into numerical experiments to quantify non-uniform fluxes and slope stability. Water retention and hydraulic conductivity curves were estimated for both coal and clay (overlaying material) using the combination of Dewpoint potentiometer WP4C and HYPROP devices. Mechanical properties were determined additionally using the Unconfined Compressive Strength test. Numerical simulations have been performed using HYDRUS 2D/3D and associated SLOPE CUBE module to assess the hydrological and mechanical behavior of coal-cover slope models under different climatic scenarios. Results showed that coal has very different hydraulic properties from the soil, with three to four orders of magnitude smaller saturated hydraulic conductivity, two orders of magnitude larger air entry point, and larger material strength parameters. The effects of present cracks/fractures on hydraulic properties of both, soil cover and coal have been taken into account by the bimodal properties determined using an extended van Genuchten-Mualem (Durner) model. Comparison of hydraulic conductivity curves indicates that the identified cracks/macropores play an important role in increasing hydraulic conductivity when the material is close to saturation. Therefore, 5% and 10% crack-weighting factors were adopted in numerical simulations for coal and topsoil/cover, respectively. The underlying coal changes its pore size distribution dramatically, depending on the degree of drying, which was confirmed during evaporation experiments. Numerical experiments showed higher risk to slope stability during the wetter years, albeit still on an acceptable level. The challenge remains on how to adequately quantify water balance in coal material with present preferential flow, and with the additional complexity of changing pore size distribution properties over time.

How to cite: Baumgartl, T., Shao, Q., and Filipović, V.: Using the Dual Porosity Approach to Quantify Non-uniform Fluxes for the Estimation of Hydrological and Stability Performance of Sloped Covers over Coal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10859, https://doi.org/10.5194/egusphere-egu22-10859, 2022.

Synthetsis and questions

Preferential flow from pore to REV scale

Luis Alfredo Pires Barbosa and Horst H. Gerke

Biopore walls are often coated with exudates and finer soil particles such that the soil in the vicinity displays altered hydro-mechanical properties resulting in distinct wettability, permeability and diffusivity when compared to the soil matrix. The mechanical properties in the coating surface (i.e. stiffness and pore structure) may change rapidly during wetting or drying, thus affecting the biopore-matrix mass exchange of water and solutes during preferential flow and local non-equilibrium dynamics.

Since the combined effects of hydro-mechanical properties on the soil structure dynamics are still poorly explored, we developed a cohesive structural model of the biopore - soil matrix interface and varied particle size and stiffness (i.e. Young’s modulus) in Discrete Element Method (DEM). Pore Finite Volume (PFV) was coupled in order to simulate water and air phases during pore scale drainage in 3D. Thus, the model take into account structural responses (i.e. deformations and stresses) during the change from saturated to funicular state. Considering water tension surface constant (0.0728 Pa) and the spherical particles perfectly wettable, four coated surfaces were simulated using a combination of particle radius of 0.1 and 0.2 mm and Young’s modulus of 700 GPa and 1100 GPa. The soil matrix particle properties were constant with radius of 0.3 mm and Young’s modulus of 700 GPa. Lateral drainage was simulated by decreasing the pressure head at the external coated surface, then the air phase invaded soil matrix in direction to the coated area. The retention curve showed higher dependence on particle size rather than particle stiffness. Simulated drainage started relatively slow followed by a rapid saturation decrement. For smaller particles with coated surfaces, the change from slow to rapid drainage was observed twice, for the soil matrix and for coated biopore surfaces. The shrinkage behavior was linear during slow drainage followed by swelling effect in rapid saturation decrement. With the combination of smaller particles and higher Young’s modulus, the plastic deformation and water retention was higher. This coupled effect of heterogeneous mechanical properties on shrinkage-swelling dynamic of biopore-matrix mass exchange bring about a new approach for more complex and realistic models.

How to cite: Pires Barbosa, L. A. and Gerke, H. H.: Shrinkage-swelling effect on mass transfer through a pore-scale model of the biopore - matrix interface coupling Discrete Element and Finite Volume, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4962, https://doi.org/10.5194/egusphere-egu22-4962, 2022.

Ishaan Markale et al.

Bacterial biofilms can form in porous media that are of interest in industrial and particularly environmental applications such as in situ groundwater remediation. The presence of biofilms modifies pore-scale and bulk hydrodynamics and consequently solutes transport and reaction kinetics. Porous media consist of highly heterogeneous flow fields and thus biofilm growth is also highly variable resulting in spatially variable biofilm permeabilities. Random processes are often invoked in hydrogeology to model variable quantities. Geo-statistical simulations require numerous realizations of a stochastic process over a grid. Our study leverages highly resolved three-dimensional X-ray computed microtomography images of bacterial biofilms in a tubular reactor to numerically compute pore scale flow and solute transport on a fine grid by considering various realizations of the biofilm permeability field. Using a conservative tracer experiment we first validate our flow and transport model which is then used to understand the impact of a heterogeneous permeability field on fluid-fluid and biologically driven reactions.

How to cite: Markale, I., Carrel, M., Kurz, D., Morales, V., Holzner, M., and Jimenez-Martinez, J.: Effect of biofilm permeability on flow and transport in three-dimensional porous media: A geostatistical study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6202, https://doi.org/10.5194/egusphere-egu22-6202, 2022.

Soheil Safari Anarkouli and Martin Lanzendörfer

Zbraslav sand has been used as a testing material in many former soil mechanics studies. It is a poorly graded sand with almost no fines and with grains of subangular shape. We will be interested in predicting the variation of its pore structure, in particular the pore size distribution (PSD), as a result of the oedometric compaction of the sample. Apart from the derived unsaturated hydraulic properties, we will be particularly interested in predicting its saturated permeability with respect to non-Newtonian (shear-thinning) fluids.

Clarifying and quantifying the dynamics of the PSD due to compaction will be a difficult undertaking owing to the instability of soil structure and variation of PSD over time. In this study, we will follow the discrete approach during the sand compaction process introduced by Mahmoodlu et al. [1] and later studies. Discrete element method (DEM) can directly trace the motion of individual particles and explicitly consider the particle–particle interactions without the need of macroscopic constitutive correlations. We will use this method to generate a packing of idealized particles for a certain porosity and particle size distribution, and simulate the movement of grains during the compaction process. Subsequently, having the simulated configuration of grains at each observed state, the pore network will be extracted to obtain the pore connectivity and morphology [2]. In the next step, the flow of various shear-thinning fluids through the media (the pore network) will be simulated [3, 4]. In this way, we are preparing for a subsequent study focused on the experimental measurement of the effective PSD directly during the oedometric test. We are particularly interested in how the observed variations in pore structure will be represented by the effective PSD obtained by the method, introduced by Abou Najm et al. [5], i.e. computed from the observed permeabilities with respect to shear-thinning fluids.

This research is supported by Czech Science Foundation under grant 21-27291S.



[1] Mahmoodlu, M. G., Raoof, A., Sweijen, T., & Van Genuchten, M. T. (2016). Effects of sand compaction and mixing on pore structure and the unsaturated soil hydraulic properties. Vadose Zone Journal, 15(8).

[2] Li, G. Y., Zhan, L. T., Hu, Z., & Chen, Y. M. (2021). Effects of particle gradation and geometry on the pore characteristics and water retention curves of granular soils: a combined DEM and PNM investigation. Granular Matter, 23(1), 1-16.

[3] de Castro, A. R., Agnaou, M., Ahmadi-Sénichault, A., & Omari, A. (2020). Numerical porosimetry: Evaluation and comparison of yield stress fluids method, mercury intrusion porosimetry and pore network modelling approaches. Computers & Chemical Engineering, 133, 106662.

[4] Hauswirth, S. C., Abou Najm, M. R., & Miller, C. T. (2019). Characterization of the pore structure of porous media using non‐Newtonian fluids. Water Resources Research, 55(8), 7182-7195.

[5] Abou Najm, M. R., & Atallah, N. M. (2016). Non-Newtonian fluids in action: Revisiting hydraulic conductivity and pore size distribution of porous media. Vadose Zone Journal, 15(9).

How to cite: Safari Anarkouli, S. and Lanzendörfer, M.: Predicting the hydraulic properties of Zbraslav sand, as affected by compaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11649, https://doi.org/10.5194/egusphere-egu22-11649, 2022.

Synthetsis and questions

Developping methods for characterizing PF and soil hydraulic properties

Laurent Lassabatere et al.

Sorptivity is a crucial parameter for modeling water infiltration into soils. Many works have related sorptivity to the soil hydraulic functions, i.e., the water retention and unsaturated hydraulic functions. Parlange's  (1975) formulation is one of the most used to relate sorptivity to the soil hydraulic functions, allowing the direct computation of sorptivity as a function of the soil hydraulic parameters and initial and final water contents. On this basis, several works investigated the possibility of direct analytical relationships between sorptivity and the hydraulic shape and scale parameters  (e.g., Lassabatere et al., 2021). So far, most of the studies have focused on single permeability soils with monomodal water retention and unsaturated hydraulic functions. However, the use of dual- or multi-permeability approaches is increasing in relation to the necessity to account for preferential flows in soils. The approach developed by (Gerke and van Genuchten, 1993) or (Pollacco et al., 2017) are examples of dual-permeability approaches and allow the modeling of preferential flows in soils. In the proposed study, we apply the formulation proposed by Parlange (1975) for the computation of sorptivity for dual-permeability soils, considering the approaches proposed by Gerke and van Genuchten (1993) and Pollacco et al. (2017). Our developments lead to a relation between the bulk sorptivity of the dual permeability soils to those of the matrix and the fast-flow compartments, plus additional terms. We end with the scaling of the proposed relation for investigating the effects of the matrix and fast-flow shape and scale parameters and the volumetric content occupied by the fast-flow compartment.


Gerke, H. H. and van Genuchten, M. T.: A dual-porosity model for simulating the preferential movement of water and solutes in structured porous-media, 29, 305–319, 1993.

Lassabatere, L., Peyneau, P.-E., Yilmaz, D., Pollacco, J., Fernández-Gálvez, J., Latorre, B., Moret-Fernández, D., Di Prima, S., Rahmati, M., Stewart, R. D., Abou Najm, M., Hammecker, C., and Angulo-Jaramillo, R.: Scaling procedure for straightforward computation of sorptivity, 2021, 1–33, https://doi.org/10.5194/hess-2021-150, 2021.

Parlange, J.-Y.: On Solving the Flow Equation in Unsaturated Soils by Optimization: Horizontal Infiltration, 39, 415–418, 1975.

Pollacco, J. A. P., Webb, T., McNeill, S., Hu, W., Carrick, S., Hewitt, A., and Lilburne, L.: Saturated hydraulic conductivity model computed from bimodal water retention curves for a range of New Zealand soils, 21, 2725–2737, https://doi.org/10.5194/hess-21-2725-2017, 2017.

How to cite: Lassabatere, L., Yilmaz, D., Di Prima, S., Abou Najm, M., Stewart, R. D., Fernández-Gálvez, J., Pollacco, J., and Angulo-Jaramillo, R.: Sorptivity of dual-permeability soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4713, https://doi.org/10.5194/egusphere-egu22-4713, 2022.

Deniz Yilmaz et al.

In the last decade, the development of methodologies based on Beerkan infiltration (ring or disk infiltrometry technique with null constant water head) analysis allows today to estimate the hydraulic properties of surface soils with increasing accuracy. In particular, the 3D model of Haverkamp et al. (1994) and its two-term (BEST methods) and four-term (4T) expansions (Moret-Fernández et al., 2020) have demonstrated their robustness. The analysis of the transient part of cumulative Beerkan infiltration allows the simultaneous estimation of the sorptivity S and the hydraulic conductivity at saturation Ks. Very recently presented, the sequential analysis (SAI) of Beerkan data (Moret and Fernandez et al., 2021) applied to stratified soils columns allows delimiting the part of the Beerkan infiltration curve governed by the upper layer and estimating its thickness. This approach opens new perspectives for using Beerkan water infiltration, especially for estimating the conductivity of the underlying porous medium. Numerical Beerkan infiltration of layered soils combination in 1D were produced using van Genuchten-Mualem model and Hydrus 1D software.  Numerical curves were subject to SAI method to estimate the upper horizon soil hydraulic properties and the regime state of the infiltration flow allowed the estimation. Therefore, it is possible under certain assumptions to estimate the hydraulic conductivity of the underlying soil in 1D. This is the first step towards the determination of stratified soils hydraulic properties. This approach will allow new theoretical development for the extension to three-dimensional water infiltration into layered soils and relative hydraulic characterization of soil layering.

Moret-Fernández, D., Latorre, B., López, M.V., Pueyo, Y., Lassabatere, Angulo-Jaramillo, R., Rahmati,M., Tormo, J., Nicolu, J.M. (2020). Three- and four-term approximate expansions of the Haverkamp formulation to estimate soil hydraulic properties from disc infiltrometer measurements. Hydrological Processes, 34 (26), 5543-5556.  

Haverkamp, R., Ross, P. J., Smettem, K. R. J., & Parlange, J. Y. (1994). Three‐dimensional analysis of infiltration from the disc infiltrometer: 2. Physically based infiltration equation. Water Resources Research, 30(11), 2931-2935.

Moret-Fernández, D., Latorre, B., Lassabatere, L., Di Prima, S., Castellini, M., Yilmaz, D., & Angulo-Jaramilo, R. (2021). Sequential infiltration analysis of infiltration curves measured with disc infiltrometer in layered soils. Journal of Hydrology, 126542.

How to cite: Yilmaz, D., Moret-Fernandez, D., Latorre, B., Angulo-Jaramillo, R., and Lassabatere, L.: Saturated hydraulic conductivity estimation of layered soil in 1D from Beerkan Experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5937, https://doi.org/10.5194/egusphere-egu22-5937, 2022.

Kunwar Mrityunjai Sharma et al.

In well-test analysis, the generalized radial flow (GRF) model uses the non-integer flow dimension to describe the change in flow area with respect to radial distance from borehole due to non-uniform flow (Barker, 1988). But the flow dimension not only depends on the change in flow area but also on the permeability variance in the flow medium. Therefore, in our present study, the flow dimension, due to the combined effect of change in flow volume and permeability variance, is termed AFD, the apparent flow dimension.  AFD can be determined as the second derivative of the drawdown-time plot from pressure transient testing and can have variable non-integer values as a function of time. This study presents a comprehensive set of analyses using rectangular channel networks representing multidimensional porous medium, starting from 1D (where the flow volume remains one-dimensional) and proceeding to 3D systems. We investigate the effect of conductance variance between the connected flow channels in a constant flow transient well test with the objective of formulating a relationship between conductance variance and AFD. Results in the one-dimensional case demonstrate that the AFD changes substantially as a function of channel conductance variation. Thus, the AFD increases abruptly when the propagating pressure reaches a high conductance channel, and it decreases when the pressure finds a channel with a lower conductance. The impact of conductance contrast on apparent flow dimension variation is summarized as a generalized plot of AFD upsurge/drop and conductance contrast between successive flow channels. In 2D and 3D systems, the channeling or preferential flow effect of the heterogeneous porous medium is also studied with the help of flow dimension analyses. The heterogeneity is introduced into the 2D network statistically through conductance distributions with varying variance values. The calculated flow dimensions, smaller than the corresponding dimension values, indicate the presence of flow channeling in the network (Verbovšek, 2009).  Channelization in a 2D porous heterogeneous system is examined as a function of the conductance variance, and it is found that channeling tends to result from the larger variance of the conductance distribution. Following the investigation of the 1D and 2D porous media, similar ideas are applied to the 3D channel networks representing 3D systems in order to investigate both steady-state and transient flow problems. Results from this study provide new insight and the possibility of using transient pressure tests to supplement multiple single well tests, interference tests, and tracer transport tests for the characterization of the heterogeneous porous medium.


Barker, J. A. (1988). A generalized radial flow model for hydraulic tests in fractured rock. Water Resources Research, 24, 1796–1804.

Verbovšek, T. (2009). Influences of Aquifer Properties on Flow Dimensions in Dolomites. Groundwater, 47(5), 660–668. https://doi.org/https://doi.org/10.1111/j.1745-6584.2009.00577.x

How to cite: Sharma, K. M., Dessirier, B., Tsang, C.-F., and Niemi, A.: Use of apparent flow dimension in transient pressure analysis to evaluate non-uniform flow in heterogeneous porous media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9617, https://doi.org/10.5194/egusphere-egu22-9617, 2022.

Gersende Fernandes et al.

Stormwater management zones must enable water to infiltrate easily, primarily due to macropores, but little is known about the transport of pollutants through these macropores. Some coupled methods using, for example, dyes, disc, or ring infiltrometers were developed to give insight on the respective contributions of the macropores versus the matrix to the bulk infiltration. However, these methods do not visualize where and how water infiltrates. Besides, no information is given on the solute transfer in soils, whereas this issue is crucial regarding the quality of soils and groundwater. One of the goals of the national program INFILTRON (https://infiltron.org) project granted by the French national research agency is to develop superparamagnetic iron oxide nanoparticles (SPIONs) which mimic both pollutant and bacteria flow behavior in soils (Raimbault et al., 2021) and are detectable by ground-penetrating radar (GPR). Within its framework (Lassabatere et al., 2020), we aim to show how nano-tracers can help detect preferential treatment flows (lithological heterogeneity, root system) and quantify or qualify the pollutant transfer in heterogeneous soils. A specific device was designed and presented for the concomitant monitoring of water infiltration and nano-tracer injection. This specific infiltrometer involves two water supply reservoirs and a ring diameter of 50 centimeters. This device maintains a constant depth of water (10 cm) above the soil and delivers the water infiltration into the soil. Two rules posed on the reservoirs allow monitoring the water drop and computation of the cumulative infiltration. Fifty volumes of SPIONs solutions (5 mL of 3.35g/l SPIONs solution) were injected into the ring to maintain a constant concentration in the ring. GPR monitors the bulb of infiltrated water and SPIONs. GPR data is treated with ReflexW (©Sandmeier geophysical research) and RockWorks (RockWare®) software. Combining this specific prototype with the use of GPR for the detection of water and the SPIONs gives insight into the processes of infiltration and SPIONs transfer and localization in the soil. These data allow us to understand and model pollutant transfer into the vadose zone.

Raimbault, J., Peyneau, P.-E., Courtier-Murias, D., Bigot, T., Gil Roca, J., Béchet, B., and Lassabatère, L.: Investigating the impact of exit effects on solute transport in macropored porous media, 2020, 1–20, https://doi.org/10.5194/hess-2020-494, 2020

Lassabatere, L., De Giacomoni, A.-C., Angulo-Jaramillo, R., Lipeme Kouyi, G., Martini, M., Louis, C., Peyneau, P.-E., Rodriguez-Nava, V., Cournoyer, B., Aigle, A., and others: INFILTRON package for assessing infiltration & filtration functions of urban soils, in: EGU General Assembly Conference Abstracts, 11269, 2020. https://doi.org/10.5194/egusphere-egu2020-11269

How to cite: Fernandes, G., Di Prima, S., Lipeme Kouyi, G., Angulo-Jaramillo, R., Martini, M., and Lassabatere, L.: A new method to determine filtration of pollutants in urban soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7174, https://doi.org/10.5194/egusphere-egu22-7174, 2022.

Asra Asry et al.

Sustainable Urban Drainage Systems (SuDs) have grown in popularity in recent decades as an efficient and effective solution for urban drainage systems, with the aim of reducing flood risk, improving urban amenity and reducing negative impacts on receiving waters. Infiltration is a critical factor in both the management and modelling of SuDs. Predicting infiltration behaviour is rendered difficult by the inherent heterogeneity of substrate characteristics. Much research has been devoted to understanding the physical processes responsible for preferential flows in soils and developing simplified and physically-based infiltration models for predicting preferential flows and water infiltration into heterogeneous soils. In this study, INFILTRON-mod, a generic physically-based package, is proposed. This package involves infiltration models for uniform and non - uniform flows in soils, considering the Darcian approach and mass balance. Uniform and non-uniform flows are modeled using the single and dual permeability approaches, respectively. The dual permeability concept assumes that the soil comprises two regions, i.e., the general matrix and the fast-flow regions, each obeying the Darcian approach. Then, different sets of infiltration models can be considered for the description of water infiltration into the single permeability soils and, by analogy, into each region of the dual-permeability soils. In this study, we investigate different sets of infiltration models, including the Green and Ampt model and other specific custom-made models. The different sets combined with either single or dual permeability approaches were tested against numerically generated data and real experimental data obtained with INFILTRON-exp, a specific large ring infiltrometer deployed on several experimental sites.

 First, we validated the proposed sets against numerically generated data for six different synthetic soils representing contrasting behaviors (sand, loam, silt, etc.). The synthetic data were generated with HYDRUS. The cumulative infiltrations were then compared, and the performance of the proposed sets of models was assessed. The results confirm that some sets fit well, whereas others are less accurate. The results also depended on the considered initial conditions.

Then, INFILTRON-mod was extended to the modeling of bioretention systems with the implementation of all the components of the hydrologic cycle (evapotranspiration, overflow, exfiltration to surrounding soils, water storage in the filter, and underdrain discharge). The different sets of models were then compared to observations from the Wicks Reserve Bioretention Basin (Melbourne, Australia), including the height of water in the filter layer and the outflow fluxes. The sets of models were then calibrated using two rainfall events before being validated over 20 rainfall events. The model performance was assessed for both the single and dual permeability approaches. We obtained very good fits of the experimental data with a median NSE above 0.8 for outflows, particularly for two infiltration models with the dual permeability approach, demonstrating the benefit of including preferential flows in the model. Our findings will help to develop the INFILTRON-mod package for modeling water infiltration into heterogenous soils and modeling bioretention systems.

How to cite: Asry, A., Lipeme Kouyi, G., Bonneau, J., Fletcher, T. D., and Lassabatere, L.: Modeling bioretention systems using different sets of simplified preferential infiltration models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9245, https://doi.org/10.5194/egusphere-egu22-9245, 2022.

Synthesis and discussion