Macropore flow in structured soils is an important process in relation to the transport of water, contaminants and nutrients in the soil. A close relation exists between hydraulic conductivity K(h) near saturation and the potential of macropore flow. At the same time, tracer breakthrough experiments in the laboratory can determine the degree of macropore flow. In this study, we aim to investigate a direct link between tracer breakthrough characteristics and soil hydraulic properties (SHPs) of structured soils, which may explain spatial variation of solute transport in soils. We used SHPs and tracer breakthrough characteristics for 71 undisturbed topsoil columns (19 cm height, 20 cm diameter) from Denmark. We defined K10 (near-saturated hydraulic conductivity) as K(h) at a matric potential (h) of −10 cm and used logarithmic transformation, logK10. On the same soil columns, we calculated the 5%, 25%, and 50 % arrival times (AT) as the percentage of the cumulative relative mass of tracer percolating through the bottom of the soil column. The regression analyses proved significant positive relation between logK10 and 5% AT, 25% AT, and 50 % AT. The saturated hydraulic conductivity appeared to be less critical for the shape of the tracer breakthrough curves. In addition, the 5% AT, 25% AT, and 5 0%AT correlated with soil pF values at 1.7, 2.0, and 2.5 (volumetric water content at h equal to −100 cm, −300 cm, and −500 cm, respectively) showing significant negative correlations.  Linking SHPs with tracer breakthrough characteristics on large intact columns thus proves highly useful for characterizing soil macropore functions.

How to cite: Xin, P., Pesch, C., Norgaard, T., Heckrath, G., Zhang, K., W.de Jonge, L., and V.Iversen, B.: The linkage between near-saturated hydraulic conductivity and tritium leaching, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3977, https://doi.org/10.5194/egusphere-egu23-3977, 2023.

Soil structure is a crucial component of soil health and quality that significantly impacts water infiltration. Natural or anthropogenic drivers, such as soil management practices, can drastically alter soil structure, which in turn can affect water infiltration. These changes in soil structure have opposing effects on water infiltration into soils and are often difficult to quantify. Here, we present a narrative systematic review (SR) of the impacts of soil structure on water infiltration. Based on inclusion and exclusion criteria, as well as defined methods for literature search and data extraction, our systematic review led to a total of 153 papers divided into two sets: experimental (131) and theoretical (22) papers. That implied a sizable number of in-situ and field experiments that were conducted to evaluate the effects of soil structure on water infiltration under the influence of different land uses and soil practices. Significant effects of soil structure on water infiltration were inferred from analyzing the metadata extracted from the collected articles. These effects were further linked to land use and management, where we demonstrated the influence of three distinct categories: tillage, crop management, and soil amendments. Additionally, significant correlations between infiltration rate and soil structural characteristics were established, with R² values ranging from 0.51 to 0.80, as well as between saturated hydraulic conductivity and soil structural characteristics, with R² values varying from 0.21 to 0.78. Finally, our review emphasized the significant absence of and the need for theoretical frameworks studying the impacts of soil structure on water infiltration.

How to cite: Basset, C., Abou Najm, M., Hao, X., and Daccache, A.: Does soil structure affect water infiltration? Global results from a meta-data systematic review, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4174, https://doi.org/10.5194/egusphere-egu23-4174, 2023.

Homogeneous soil and related darcean approaches are sometimes insufficient to describe flow processes in porous media. For this purpose, the double permeability (DP) approach was proposed by Gerke and van Genuchten (1993) and was then adapted by Lassabatere et al. (2014) to the quasi-exact implicit infiltration model of Haverkamp et al. (1994). The separation into two compartments called fast-flow and matrix regions with related volumetric fractions allows the modeling of preferential flow in soils. The inverting procedure from multiple-tension disc infiltration experiments proposed by Lassabatere et al. (2014) allows the estimation of DP hydraulic soil properties, i.e., the quantification of the volumetric fractions occupied by the two regions and their related hydraulic properties. This approach was applied to the studied experimental green roofs. Green roofs are structures known to play the role of buffer medium by absorbing the peak loads in the stormwater networks (thus reducing the risk of floods) and contributing to the attenuation of the urban heat island. The quantified hydrological contribution of these structures at the urban scale can be approached with the help of numerical modeling. In this study, we investigated the numerical modeling of the flow in vegetated roofs, which remain a challenging topic. In this study, multiple-tension infiltrometry tests were applied to experimental lysimeters simulating a vegetated roof (Yilmaz et al., 2016). These experimental infiltration data were inverted using the DP approach to estimate the properties of the material constitutive of the studied green roofs. Then Hydrus 1-D software was used to model the runoff produced by the experimental roof for several rainfall events. For this purpose, a summer period with three successive rain events was chosen, and the ability of DP to simulate the observed runoff was investigated. The results allow the validation of the proposed characterization and modeling method and provide material for understanding the hydraulic behavior of green roofs and the permanence of preferential flow in these structures. 

Gerke, H.H., van Genuchten, M.T., 1993. A dual‐porosity model for simulating the preferential movement of water and solutes in structured porous media. Water Resources Research 29, 305–319. https://doi.org/10.1029/92WR02339

Haverkamp, R., Ross, P.J., Smettem, K.R.J., Parlange, J.Y., 1994. 3-Dimensional analysis of infiltration from the disc infiltrometer .2. Physically-based infiltration equation. Water Resources Research 30, 2931–2935.

Lassabatere, L., Yilmaz, D., Peyrard, X., Peyneau, P.E., Lenoir, T., Šimůnek, J., Angulo-Jaramillo, R., 2014. New analytical model for cumulative infiltration into dual-permeability soils. Vadose Zone Journal 13, vzj2013.10.0181. https://doi.org/10.2136/vzj2013.10.0181

Yilmaz, D., Sabre, M., Lassabatère, L., Dal, M., Rodriguez, F., 2016. Storm water retention and actual evapotranspiration performances of experimental green roofs in French oceanic climate. European Journal of Environmental and Civil Engineering 20, 344–362. https://doi.org/10.1080/19648189.2015.1036128

How to cite: Yilmaz, D. and Lassabatere, L.: Estimation of dual permeability hydraulic properties and modeling the hydrological response of an experimental green roof, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2926, https://doi.org/10.5194/egusphere-egu23-2926, 2023.

In the Sahel region, agroforestry is a land-use system widely adopted as a more sustainable agricultural production system. In this type of system, woody perennials that are grown in association with agricultural crops and pastures, constitute spatially disconnected zones where microclimate and soil’s infiltrability, physical, chemical, and biological conditions are assumed locally improved. Particularly the stemflow concentrates a part of the intercepted rainfall from the canopies to the stems. Hence stemflow can induce preferential infiltration around the stem base and promote groundwater recharge.

In the West African Sahel, Faidherbia albida (Delile) A.Chev. is commonly adopted as multi-purpose woody perennial in agroforestry systems. It is a deciduous tree with an inverse phenology as it loses the leaves during the rainy season. Although, the absence of leaves during the rainy season is expected to decrease the interception and to consequently decrease stemflow, evidence of stemflow at the base of F. albida trees were reported in the literature when the stems were partially covered with green leaves (Chinen, 2007).

In this study, we carried out timelapse ground penetrating radar (GPR) surveys in conjunction with a simulated stemflow event to investigate stemflow-induced infiltration by an F. albida tree trunk and root system. We established a survey grid (2.1 m × 2.1 m) around an F. albida, consisting of twelve horizontal and ten vertical parallel survey lines with 0.3 m intervals between them. Two stemflow pulses, each of 20 L, were poured on the tree trunk using a PVC pipe with a 1-mm-diameter hole every 50 mm. The pipe was connected to a plastic funnel and positioned around the tree trunk at 0.4 m from the soil surface. One grid GPR survey was carried out before the stemflow simulation experiment. A total of 40 L of water was used during the experiment. A second survey was carried out after the injection of the first 20 L, while the last survey was carried out after the second stemflow pulse. We collected a total of 66 (3 GPR surveys × 22 survey lines) radargrams using a GSSI (Geophysical Survey System Inc., Salem, NH) SIR 3000 system with a 900-MHz antenna. We therefore obtained for each survey line a pre-wetting and two post-wetting radargrams. Next, we created other forty-four matrixes based on absolute differences between pre- and post-wetting amplitude values. Higher differenced values occurred because of amplitude changes and time shifts related to wave propagation.

The analysis of the differentiated radargrams provided evidence of deep infiltration along the tap roots. The wetted zone extended mainly in-depth providing evidence of the potential role played by the F. albida trees in groundwater recharge processes due to their deep rooting, preferably reaching the groundwater table. Put all together, this study shows a first signal of the importance of accounting for stemflow infiltration in the water balance of agroforestry systems with F. albida trees.

References

Chinen, T., 2007. An observation of surface runoff and erosion caused by acacia albida stemflow in dry savanna, in the south-western republic of Niger 10.

How to cite: Talla, S., Faye, W., Fernandez, G., Lassabatere, L., Angulo-Jaramillo, R., Roupsard, O., Di Prima, S., and Do, F. C.: Evaluating stemflow infiltration through time-lapse ground-penetrating radar surveys on a Faidherbia albida tree in Senegal's Sahel, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5271, https://doi.org/10.5194/egusphere-egu23-5271, 2023.

In Senegal, the groundnut basin is the main agricultural region under a semi-arid climate, heavily cultivated in an agrarian system combining agricultural rotation and agroforestry dominated by Faidherbia albida trees. The soils of the groundnut basin, essentially sandy, have a low water retention capacity. In this area, water is a limiting factor, and the climate variability represents an additional constraint on an already precarious agricultural production system. It is therefore essential to improve knowledge on water saving practices and soil humidity dynamics. The management of water resources in agricultural fields requires reliable information about soil hydraulic properties, which control the partition of rainfall into infiltration and runoff, and their spatio-temporal variability.

To investigate the variability of soil hydraulic parameters we have carried out infiltration measurement in open space without tree and below tree canopies. A total of 24 infiltration measurements were carried out using an automatic single-ring infiltrometer in the nearby of each plot (4 measurements × 6 plots), and after removing the first 10 cm of uncompacted sand. The infiltration tests were carried out in June, October and December, respectively before, during and after the crop season. We used the Beerkan Estimation of Soil Transfer Parameters (BEST) method to retrieve the soil hydraulic parameters from infiltrometer data and field measurements of soil porosity, initial and saturated soil water contents and soil bulk density.

The statistical analysis of the data showed a high variability during the cultivating period, both in time and space, especially of the saturated soil hydraulic conductivity Ks. However, the Ks seems higher under tree cover, around 0.186 mm/s, for 0.167mm/s without any tree canopy influence.  Despite the expected homogeneity of the investigated sandy soil, the presence of the perennials triggered a patchy distribution of soil hydraulic conditions. These preliminary results evidenced the importance of taking into account parameters variability and landscape structure when simulating soil water dynamics in the Senegalese groundnut basin.

How to cite: Faye, W., Orange, D., Talla, S., Do, F., Jourdan, C., Roupsard, O., Faty, A., Niang, A., Kane, A., Di prima, S., Angulo-Jaramillo, R., and Lassabatere, L.: Spatio-temporal analysis of soil surface hydraulic properties in a semi-arid agroforestry system of the Senegalese groundnut basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16621, https://doi.org/10.5194/egusphere-egu23-16621, 2023.

The hydrological response of steep slopes catchments is strongly conditioned by the connectivity of subsurface preferential flows. The objective of this research is to investigate the role played by stemflow infiltration in subsurface water flow dynamics, focusing on a forested hillslope located in an Aleppo pine Mediterranean forest (Pinus halepensis, Mill.) located at Sierra Calderona, Valencia province, Spain. We combined stemflow artificial experiments with ground-penetrating radar (GPR) techniques as a non-invasive method to investigate stemflow-induced preferential flow paths activated by different trees and the related hydrological connectivity at the hillslope scale. Our observations allowed us to identify different dynamics associated with the initiation of stemflow and then lateral preferential flow, including the activation of connected preferential flow paths in soils that received stemflow water from different trees. These observations provided empirical evidence of the role of stemflow in the formation of lateral preferential flow networks. Our measurements allow estimations of flow velocities and  new insight on the magnitude of stem-induced lateral preferential flow paths. The applied protocol offers a simple, repeatable and non-invasive way to conceptualize hillslope responses to rainstorms.

How to cite: Marras, E., Fernandes, G., Giadrossich, F., Stewart, R. D., Abou Najm, M. R., Winiarski, T., Mourier, B., Angulo-Jaramillo, R., Comegna, A., del Campo, A., Lassabatere, L., and Di Prima, S.: Evidence of hillslope connectivity on Aleppo pine plantation by artificial stemflow experiments and preferential flow pathways detection using time-lapse ground penetrating radar surveys, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2830, https://doi.org/10.5194/egusphere-egu23-2830, 2023.

The preferential flow and transport through unsaturated zones have received considerable attention in the soil and agricultural fields, particularly in increasing discharge rates and amounts and the subsequent transportation of pollutants to groundwater. Over the past century, traditional stormwater control has been replaced by a new low-impact development (LID) approach called " on-site alternative design strategy", which aims to restore or maintain the hydrological functions of urban watersheds by using the capacity of soil and vegetation to retain and filter wastewater pollution, such as bioretention facilities. Therefore, obtaining an accurate estimation of water Infiltration within Bioretention basins is crucial. The Bioretention modeling usually refers to the implicit reservoir base model, which is based on the mass balance and interaction between all the components of the hydrologic cycle (evapotranspiration, overflow, exfiltration to surrounding soils, infiltration through filter media or non-saturated zone, and underdrain discharge) during the time. Among the existing bioretention models, the unsaturated zone or filter medium is considered a homogeneous medium, and the flow is calculated with conceptual infiltration models, such as the Green-Ampt model, the Horton model, etc. Despite our knowledge that the soil reservoir medium is heterogeneous (e.g., coarse materials, plant root systems), it is, therefore, necessary to use a physics-based infiltration model that considers the impact of non-equilibrium and preferential flow on the hydrological and hydrogeochemical performance of bioretention facilities. The INFILTRON-mod, a generic physics-based package, has been proposed for this aim.

This package consists of infiltration models, including the Green-Ampt model and three other specific custom-made models, for uniform and non-uniform flows in soils based on the Darcian approach and mass balance. Uniform and non-uniform flows are modeled using the single and double permeability approaches, respectively. The dual permeability concept assumes that the soil consists of two reservoirs, i.e., the general matrix and fast flow regions, each obeying the Darcian approach. We assumed instantaneous exchange between the two regions. Consequently, we assumed that the wetting fronts in the two reservoirs advance at the same rate. Then the different sets combined with the single or double permeability approaches were tested against numerically generated data using HYDRUS and real experimental data obtained with INFILTRON-exp, "a specific large ring infiltrometer" deployed at several experimental sites.

The results show that the custom-made models lead to different results, with some being better. In addition, considering the dual permeability models improved the fits of the experimental data acquired with the infiltrometer. Then, the improved model was used to model the observations from the Wicks Reservoir bioretention basin (Melbourne, Australia), including the water head in the filter layer and outflow rates, and this led to satisfactory results. The results obtained from this study will be used to develop the INFILTRON-mod package that can be easily integrated into the LID modeling performance for calculating the infiltration element in the unsaturated filter medium.

How to cite: Asry, A., Lipeme Kouyi, G., Bonneau, J., Fletcher, T. D., and Lassabatere, L.: INFILTRON-mod, a simplified preferential infiltration model for modeling bioretention systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5608, https://doi.org/10.5194/egusphere-egu23-5608, 2023.

Time results in large changes to soil infiltration characteristics due to weather, mechanical stability and the action of biology.  Even as the water status changes in a wetting soil, swelling may alter infiltration characteristics. Our laboratory has developed several novel approaches to measure how soil water infiltration characteristics vary over time and are influenced by biological processes or weathering stresses.  The measurements are often combined with an assessment of mechanical properties and pore structure so that underlying processes driving soil structure dynamics can be disentangled. An overview and a discussion of the benefits and challenges of the approaches will be provided.

A small-scale infiltrometer (sub-mm size) was adapted to allow for measurements of water infiltration and repellency at aggregate or rhizosphere scale.  It has been applied in numerous studies exploring the impacts of biological exudates, plant roots and weathering.  More recent research has compared results from this infiltrometer with X-Ray CT imaging to determine the impacts of soil pore structure on infiltration characteristics.  A challenge with a small-scale infiltrometer is experimental error caused by tip contact with the soil and the shape of the wetting front.  This has been demonstrated from repeated tests on repacked sands and sieved soils.

If soil aggregates, spatial variability or hot spots like the rhizosphere are not of interest, conventional infiltration measurements with flow across the entire surface of a soil core offer less laboratory experimental error.  We used this approach to explore the dynamics of soil wetting and swelling as affected by a range of biological exudates.  Repacked soil discs were wetted by a sintered disc attached to a weighed water reservoir, with swelling measured dynamically in horizontal and vertical directions using infra-red sensors.  Whereas polygalacturonic acid (PGA) had no affect on sorptivity, increasing concentrations of lecithin and actigum decreased sorptivity, likely due to different mechanisms of surface tension and viscosity respectively.  Total swelling was positively correlated with water sorptivity for both lecithin and actigum, suggesting that an expanding pore structure in the unconfined soil discs may enhance water uptake rates.  Biological exudates therefore have dual impacts on decreasing wetting and swelling rates, which will affect soil structural stability.

Current research is exploring soil structural stability impacts on soil hydrological properties over time.  This includes field studies exploring the impacts of soil amendments and management practices, and laboratory studies with controlled structural changes from wetting/drying and mechanical stresses.  In this work, changes in water infiltration due to stresses are explained from pore structure analysis with X-Ray CT imaging and mechanical stability tests.

How to cite: Hallett, P., Marin, M., Balacky, H., Islam, M. D., Raffan, A., Salas Hernández, E., and Utin, U.: Swell ways to measure how plant roots, biological exudates and temporal weathering impact soil structure and infiltration characteristics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16729, https://doi.org/10.5194/egusphere-egu23-16729, 2023.

The aim of this research is testing a new statistical model able to describe the interaction between soil and atmosphere. The model is based on a robust parametric LTS (Least Trimmed Squares) method and harmonic functions. It has been developed taking into account field measurements of quantities involved in both infiltration and evapo-transpiration phenomena, such as volumetric water content, soil-water potential, air temperature, rainfall amounts and solar radiation. The proposed statistical model allows assessing the volumetric water content at different sites using only time series of daily rainfall amount as input data. The model was applied in different test sites, whose data were assumed by the International Soil Moisture Network (ISMN). In fact, ISMN allows getting free time series of soil and meteorological data from monitoring stations all over the world. This note shows how the proposed model is accurate with respect to field data in estimating the volumetric water content in different soils, climates and depths. Future implications of this research will regard water content predictions, especially in areas where field data are scarce. Since the proposed LTS algorithm is very efficient and the computational workload is rather low, the possibility of coupling it with a slope stability analysis over large areas will be investigated, in order to get a distributed real-time model for shallow landslides susceptibility.

How to cite: Sannino, G., Anello, M., Riani, M., Laurini, F., Bittelli, M., Bordoni, M., Meisina, C., and Valentino, R.: Assessment of long-time series of soil water content through an innovative robust statistical model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7099, https://doi.org/10.5194/egusphere-egu23-7099, 2023.

The macropore-matrix mass transfer of water and solutes is an important aspect of non-equilibrium-type of preferential flow in structured soils. For a representative soil volume, effective mass transfer parameters depend on heterogeneous local properties of the soil macropore structure, its geometry and shape, and on properties at macropore walls that can differ from those of the matrix with respect to texture, organic matter, bulk density, and porosity. These affect the soil pore system locally with respect to hydraulic, mechanic, bio-geo-chemical, and other processes. Clayey aggregate skins, for example, may be more due to plastic deformation but can restrict water exchange; solutes may become adsorbed along macropore surfaces and released under changing condition. Still relatively little is known about formation of such local biological hotspots in soil, on how to determine the local mass transfer parameters, and how to upscale to the scale of the soil volume, and on the interrelations between all the individual local properties and the combined effect on relevant bulk soil transport processes. The present contribution reviews recent experimental and modeling work including field and lab percolation experiments using the movement of bromide, Brilliant Blue, iodide, and Na-Fluorescein to identify the flow paths and parameter optimization approaches for determining such parameters. It seems that preferential transport of reactive solutes depends even more strongly on the geometry and properties at flow paths surface than the water flow itself or the movement of conservative solutes. The identification and determination of effective mass transfer parameters in two-domain models remains a challenge when considering that local changes in the soil structure are highly dynamic during the vegetation, the seasons, and due to soil management.

How to cite: Gerke, H. H.: Characterization of macropore-matrix mass transfer parameters in two-domain preferential flow models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8635, https://doi.org/10.5194/egusphere-egu23-8635, 2023.

In recent years, scientists & physicists faced a question about the macroscope boundary condition interacting with the capillary pressure related to fluid topology. How to integrate the relationship of mechanics between thermal physical quantities (e.g free energy, entropy, & pressure) and fluid topology variables (e.g surface area, mean curvature, & Euler-Characteristic) play a main role in Continuum Mechanics research on low Reynold number flow in porous media in the future. As well, developing the theory approach is our research purpose. The perspective of Newton's Mechanics can not fit the demand of dealing with multiphase porous media flow with a lot of complex and unknown constraints and cross-scoping variables. To build up the dynamic model containing the topology states for multiphase flow in porous media, we introduced two concepts to cross the barricade of Newton mechanics applying to multiphase porous media flow, the generalized coordination and Lagrangian mechanics based on Hamilton’s Principle (The Least Action Principle). The principle shows that any physical quantity changing path making the “Action” as a function(Lagrangian integration) of generalized coordination is holding the minimum. Lagrangian mechanics is widely used in many other frontal research regions depending on the Lagrangian quantity design and generalized coordination setting, including dynamical Structure Analysis, Automatic control theory, electrodynamic and Standard Models in Particle Physics.

We provide the approach from Lagrangian mechanics to describe the thermodynamic and topology changing path during the multiphase flow process. This study recognized the topology state variable as generalized coordination. Furthermore, the Lagrangian quantity and dissipation terms were designed in this research with the kinetic energy, Landau potential, and Rayleigh dissipation function. We combined Steiner’s formula as fluid geometric constraint, dissipation system, and Lagrangian Mechanics to develop the evolution dynamic equations for fluid topology properties. Then we derive the geometrical conservation equations for the topology state variables during the whole dynamics process. Also, the derivation of Darcy’s law finished from Lagrangian mechanics under saturated and steady conditions.

How to cite: Liu, C. Y. and Hsu, S. Y.: Thermodynamic and Topology path equations, Multiphase flow in porous media with Steiner’s Formula & Lagrangian Mechanics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7331, https://doi.org/10.5194/egusphere-egu23-7331, 2023.

Flow and mixing processes in porous media control many natural and industrial systems, such as microbial clogging, oil extraction, and effluent disposal. In many systems, the porosity may evolve during mineral precipitation, such as in rocks, and control fluid mixing and fluid transport properties. Here, we use three-dimensional in situ dynamic neutron and X-ray micro-tomography imaging to explore fluid transport into Berea sandstone core samples during in-situ carbonate precipitation. Neutron imaging can track fluid flow inside the rock, whereas X-ray imaging illuminates the regions where mineral precipitation occurs. We control the precipitation of calcium carbonate in the rock through reactive-mixing between solutions containing CaCl₂ and Na₂CO₃. By solving the advection-diffusion equation using the contrast in neutron attenuation from time-lapse images, we derive the 3D velocity field of the injected fluids and characterize the evolution of the permeability field into the rock during mineral precipitation. We also investigate the mixing between heavy water and a cadmium solution under the influence of mineral precipitation. Results show that, under the effect of mineral precipitation, a wide range of local flow velocities develop in the sample, under the same fluid injection rate, and we quantify the distribution of flow velocities in the sample. Moreover, we observe more efficient mixing between heavy water and a cadmium solution after mineral precipitation. The finding of this experimental study is useful in progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface.

How to cite: Shafabakhsh, P., Le Borgne, T., Mathiesen, J., Linga, G., Cordonnier, B., Pluymakers, A., Kaestner, A., and Renard, F.: Dynamic neutron and X-ray three-dimensional imaging of fluid flow and mixing during mineral precipitation in porous rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8089, https://doi.org/10.5194/egusphere-egu23-8089, 2023.

Wastewater management and treatment are key points in maintaining the quality and the sustainability of water resources. To preserve receiving water environments, efforts are being conducted to improve the treatment efficiency. Soil infiltration can therefore be used as a nature-based solution tertiary treatment, in some areas without surface water available, or with supplementary water bodies’ protection regulations. Secondary wastewater effluents (SWE) infiltration surfaces  mainly consist of infiltration trenches or flood-meadows. Among the main issues encountered with soil infiltration, two can be highlighted: the possible low hydraulic conductivity induced by soil clogging, on the one hand, and the use of non-renewable draining materials such as pebbles or gravel to ensure the distribution of water in trenches, on the other hand. In France, in order to overcome those issues, stakeholders are now considering the replacement of the gravel with woodchips, a renewable biodegradable material, also prone to biodiversity in soils. If there is no woodchip-filled soil infiltration surfaces downstream wastewater treatment plant in France, woodchips are however used for decentralized wastewater treatment, even though no study has quantified precisely their efficiency. The understanding of the flow processes and the risk of preferential flows in the woodchip-filled infiltration trenches is a prerequisite for a proper management of these works.

Our study aims at investigating flow regimes in woodchip-filled infiltration trenches. Several woodchip-filled infiltration trenches were studied and analyzed with regards to their infiltration capacity in four decentralized wastewater treatment sites, located in South-West of France on silty-clay soil. Measurements of infiltration capacity of the soil below the woodchips-filled trenches were conducted with infiltration tests according to the Beerkan method (Braud et al., 2005). On each site, two tests were conducted on the bottom of the infiltration trenches after extracting woodchips and two others in the soil at a lateral distance of 1 m from the infiltration trench at the same soil depth, in order to sample the same type of soil. The soil hydraulic functions, i.e., water retention and hydraulic conductivity curves, below the woodchips and in the natural soil profiles were then calculated using the BEST method (Angulo-Jaramillo et al., 2019) and compared. Our findings showed that the use of woodchips locally maintains or even enhances the infiltration rate in the soil below. Moreover, the hydraulic conductivity was 5 to 14 times higher (up to 8600 mm.d^-1) in soils under woodchip-filled infiltration trenches than in the reference soils. To explain such positive effects, several hypothesis were formulated and discussed against physical, biogeochemical and ecological factors (woodchips organic amendment, suitable moisture conditions, earthworm communities’ activity). Dye tracer experiment, soil pit, and soil samples (chemical tracings and analyses) revealed the presence of preferential pathways induced by macro fauna and roots plants. An earthworm count showed that the majority of earthworms in the woodchips were 10 times higher than in the natural soil profile. Experiments also showed an organic carbon enrichment in woodchip-filled infiltration trenches soils that could lead to an improvement and stabilization of soils structure.

How to cite: Louis, P., Delgado-Gonzalez, L., Dubois, V., Lassabatère, L., and Clément, R.: Impact of the use of woodchips as drainage material on infiltration in secondary wastewater effluents infiltration trenches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6752, https://doi.org/10.5194/egusphere-egu23-6752, 2023.

It’s known that certain soils surfaces may be subjected to water repellence, which prevents immediate water infiltration. With time, the water repellence vanishes and the water infiltration initiates. In such situation, the infiltration models developed for regular soils are not able to describe this early infiltration process. Recently, Abou Najm et al. (2021) proposed a simple corrector factor to deal with this problem and to account for water repellence at the beginning of the infiltration process in water-repellent soils. These authors applied their correction factor to the Philip two-term approximate transient expression. Recently, Di Prima et al. (2021) used this approach to adapt the BEST-slope algorithm (Lassabatere et al., 2006), based on the two terms transient expansion of the quasi-exact implicit (QEI) model for modelling water infiltration into regular soils for the estimation of the initial soil sorptivity (S) and the saturated hydraulic conductivity (Ks) of water repellent soils. The new model for the hydraulic characterization of soils regardless the degree of water-repellence, was named BEST-WR. It was validated using analytically generated data, involving soils with different textures and a dataset that included data from 60 single-ring infiltration tests. However, some points of the BEST-WR method deserved further investigations, especially concerning the validity time of the two-term approximate expansion used to fit the data. Indeed, if this validity time is defined for the BEST-Slope method, this is not the case for the BEST-WR method. To alleviate the issue of the limitation in time, Yilmaz et al. (2022) proposed an extension of the BEST-WR model by increasing the number of terms considered for the approximate expansions of the QEI model. They applied the correction factor to the three-term approximate expansion which is known to have a much wider validity time interval. This new formulation called BEST-WR-3T has the advantage of being valid on a very large time interval, allowing the modelling of the whole experimental datasets, without worrying about time limitations, for most practical applications. In this study, this new more robust formulation is evaluated on several examples using both analytical and field infiltration obtained with different approaches: the regular manual Beerkan method or using the automated infiltrometers developed by Di Prima et al. (2016). The robustness of the new method is observed when the BEST-WR method encounters difficulties in estimating soils parameters.  

References:

Abou Najm et al. (2021). A Simple Correction Term to Model Infiltration in Water‐Repellent Soils. Water Resources Research, 57(2), e2020WR028539.

Di Prima et al. (2016). Testing a new automated single ring infiltrometer for Beerkan infiltration experiments. Geoderma, 262, 20-34.

Di Prima, et al. (2021). BEST-WR: An adapted algorithm for the hydraulic characterization of hydrophilic and water-repellent soils. Journal of Hydrology, 603, 126936.

Lassabatère et al. (2006). Beerkan estimation of soil transfer parameters through infiltration experiments—BEST. Soil Science Society of America Journal, 70(2), 521-532.

Yilmaz et al. (2022). Three-term formulation to describe infiltration in water-repellent soils. Geoderma, 427, 116127.

How to cite: Yilmaz, D., Di Prima, S., and Lassabatere, L.: Assessment of the BEST-WR three-term formulation to estimate water repellent soil hydraulic properties, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4078, https://doi.org/10.5194/egusphere-egu23-4078, 2023.

Treated wastewater (TWW) has gained recognition as an alternative source for freshwater irrigation and is steadily expanding worldwide, particularly under the current climate change. Beyond its many advantages, it has been found that prolonged use of TWW renders the soil water-repellent to certain degrees. The flow in these soils has been known to take place in preferential flow pathways (unstable flow). This lecture presents the results of a study performed in a commercial citrus orchard grown on sandy-loam soil in central Israel that has been irrigated with TWW. Electrical resistivity tomography (ERT) surveys revealed that water flow in the soil profile is occurring along preferential flow paths, leaving behind a considerably nonuniform water-content distribution. The preferential flow in the soil profile led to uneven distribution of salts and nutrients, with substantially high concentrations in the drier spots and lower concentrations in the wetter spots along the preferential flow paths. The chemical's pore concentration, which depends on the local soil water content, is higher than paste-measured concentrations and may even reach toxic values. This could partially explain the negative effect that prolonged TWW irrigation has on soil and trees. The relationship between water-repellent soils and the spatially nonuniform distribution of nutrients and salts in the root zone was verified in a consecutive in-situ study where soil water repellency was eliminated by surfactant application to the soil. Repeated ERT surveys and chemical concentration measurements in disturbed soil samples along transects revealed that the surfactant application diminished the preferential flow pathways and rendered the soil water and dissolved chemicals uniformly distributed. The preferential flow elimination and increased chemical distribution uniformity result in a yield increase compared to the surfactant-untreated soil. The different aspects of the results will be further presented and discussed. 

How to cite: Wallach, R.: The effect of water-repellent soil-induced preferential flow on the spatial distribution of nutrients and salts in the soil profile of a commercial orchard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4692, https://doi.org/10.5194/egusphere-egu23-4692, 2023.

Abstract: Treatment wetlands (TWs) are complex ecosystems due to variable conditions of hydrology, soil hydraulics, plants and microbiological species diversity and mutual interactions. On the one hand, hydraulics plays a vital role on the treatment performance and on the life cycle of TWs, on the other hand, the vegetation substantially contributes to remove and to retain pollutants. As well known, the unavoidable and progressive clogging phenomenon in TWs affects their hydraulics. A lack of knowledge still remains to what extend hydraulic parameters variation can affect the vegetation developments in TWs. To answer to this question, the Phragmites australis development in comparison with hydraulic characteristics was monitored in a 8 years old - horizontal flow (HF) TW located in Mediterranean area (Eastern Sicily, Italy). Data were collected in nine observation points equally distributed along three transects established at 8.5 m (T1), at 17 m (T2) and at 25.5 m (T3) from the inlet. The falling head (FH) test was conducted to assess the hydraulic conductivity (K_s) variation in the HF-unit. Residence time distribution (RTD) analysis was performed to evaluate the real hydraulic retention time (HRT) and the hydraulic efficiency parameter (λ). Finally, the saturation method was applied for substrates porosity (φ) determination. In the HF-TW a morphological and chemical characterization of Phragmites australis above-ground biomass was carried out in 2022. In particular, plants density (in terms of culms number) and height (m) were measured at the end of the growing season (July). In each transect of the HF-TW, fresh weight (g), dry matter (DM, %), ash (%), volatile solids (VS, %), pH, Total Kjeldahl Nitrogen (TKN, % of DM) and fiber content (cellulose, hemicellulose and lignin) were estimated. Preliminary results showed a strong positive regression between DM and both K_s (R² = 0.78) and porosity values (R² = 0.97) observed in the HF-TW. This study could contribute to help plant operators to understand hydraulic characteristics effects on the biomass, to improve TWs treatment efficiency, system management and lifespan.

Keywords: Wastewater treatment, Phragmites australis, plants growth, hydraulic characteristics, substrate.

Acknowledgments: This research was funded by the University of Catania-PIAno di inCEntivi per la RIcerca di Ateneo 2020/2022—Linea di Intervento 3 “Starting Grant” and the PhD Course in Agricultural, Food and Environmental Science (Di3A, University of Catania).

How to cite: Sciuto, L., Sacco, A., Cirelli, G. L., Barbera, A. C., and Licciardello, F.: Could hydraulic parameters variation affect the vegetation development in treatment wetlands?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14883, https://doi.org/10.5194/egusphere-egu23-14883, 2023.