Transferts d'eau et de soluté en milieu non saturé hétérogène à l'échelle d'un pilote de laboratoire (expériences et modélisations)

L hétérogénéité de la zone non saturée joue un rôle important dans le transfert d eau et de soluté car elle accentue à la fois le développement des zones de stockage temporelles et les écoulements préférentiels. Par conséquent, la validation des modèles prédictifs nécessite le développement des outils expérimentaux spécifiques afin d observer et de quantifier les mécanismes de transport impliqués dans un système non saturé hétérogène. Cette thèse vise à étudier l effet combiné de la vitesse d infiltration, de la barrière capillaire et l angle de la pente d interface entre deux matériaux sur les processus de l écoulement de l eau et du transport de soluté dans un modèle physique, le lysimètre de laboratoire 1x1x1.6 m3, nommé LUGH (Lysimeter for Urban Groundwater Hydrology) et un modèle numérique 3D de ce lysimètre. Le lysimètre LUGH est rempli par un sable fin et un mélange bimodal (50 % sable fin et 50 % gravier) en deux configurations: un profil uniforme de matériau bimodal ou un profil avec deux couches avec une pente de 14o. Ces agencements figurent l hétérogénéité structurale et texturale observée sur un des sites expérimentaux de l OTHU (Observatoire de Terrain en Hydrologie Urbaine) : le bassin d infiltration d eaux pluviales Django Reinhardt géré par la ville de Lyon (France). Le lysimètre est alimenté en eau et avec un traceur inerte (bromure de potassium, KBr) sur une partie de la surface par un système d arrosage automatique. Les effluents ont été recueillis dans quinze sorties différentes en bas du lysimètre. La forte hétérogénéité des flux des sorties et des courbes de percée souligne la mise en place des écoulements préférentiels résultant à la fois de l effet de barrière capillaire et de l effet de fond du lysimètre. A partir des résultats expérimentaux, la modélisation numérique à l aide de logiciel COMSOL MultiphysicsTM a permis de mieux comprendre les mécanismes responsables de ces transferts hétérogènes. Lorsque le modèle numérique validé, un test de sensibilité a été conduit pour étudier les effets de la vitesse d infiltration et de la pente de l interface sur l écoulement. Les résultats montrent que la diminution de la vitesse d infiltration ou l augmentation de la pente de l interface favorisent le développement des écoulements préférentiels. Notre étude a donné également des renseignements pertinents sur le couplage entre les processus hydrodynamiques et le transfert des solutés dans les sols non saturés hétérogènes en soulignant le rôle de la géométrie des interfaces ainsi que celui des conditions aux limites comme des facteurs clés pour la quantification des écoulements préférentiels.The heterogeneity of the unsaturated zone plays an important role in the water and solutes transfer as it accentuates both the development of stagnant zones for water and preferential flow. Therefore, the validation of predictive models requires the development of specific experimental tools to observe and quantify the transport mechanisms involved in a heterogeneous unsaturated system. The aim of this thesis is to describe the combined effect of infiltration, capillary barrier and sloping layered soil on both flow and solute transport processes in a large physical model (1x1x1.6 m3) called LUGH (Lysimeter for Urban Groundwater Hydrology) and a 3D numerical flow model. Sand and a soil composed of a bimodal sand-gravel mixture were placed in the lysimeter represent one of the commun structural and textural elements of the heterogeneity observed in the vadose zone under an infiltration basin of Lyon (France). The soil was compacted in two configurations: a uniform profile and a profile with two layers having a slope of 14. Water and an inert tracer (KBr) were injected from the top of the lysimeter using a specific water sprinkler system and collected at 15 different outlets at the bottom. The 15 breakthrough curves obtained presented high heterogeneity, emphasising the establishment of a preferential flow resulting from both capillary barrier and soil layer dip effects. Numerical modelling led to better understanding of the mechanisms responsible for these heterogeneous transfers and it was also used to perform a sensitivity analysis of the effects of water velocity (water and solute flux fed by the sprinkler) and the slope interface. The results show that decreasing velocity and increasing the slope of the interface can lead to the development of preferential flows. In addition, the offset of the centre of gravity of the flow distribution at the output increases linearly as a function of the slope angle of the layered soil. This paper allows coupling the hydrodynamic approach with the transfer of pollutants in unsaturated heterogeneous soil and highlighting preferential flow by flow modeling.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Analysis of the Role of Tortuosity and Infiltration Constants in the Beerkan Method

It has recently been proposed to couple the Beerkan method with the Beerkan Estimation of Soil Transfer parameters (BEST) algorithm to facilitate the estima- tion of soil hydraulic parameters from an infiltration experiment. Although this simplified field procedure is relatively rapid and inexpensive, it has been doubt - ed if the Beerkan method can represent a valid and reliable alternative to other conventional methods. This study explored the impact of the tortuosity param- eter (p) and two infiltration constants included in the BEST algorithm using a sensitivity analysis applied to three experimental soils. The analysis that was validated using the numerical model HYDRUS 2D/3D indicates that the tortuosity is relatively insignificant compared to parameters b and g that have a large impact on the estimation procedure

BEST-2K Method for Characterizing Dual-Permeability Unsaturated Soils with Ponded and Tension Infiltrometers

This study presents a new method (BEST-2K) that extends the existing BEST methods for use in characterizing the water retention and hydraulic conductivity functions of matrix and fast-flow regions in dual-permeability soils. BEST-2K requires input information from two water infiltration experiments that are performed under ponded (Beerkan) and unsaturated (tension infiltrometer) conditions at the surface. Other required inputs include water content measurements and the traditional BEST inputs (particle size distribution and bulk density). In this study, first, a flowchart of the BEST-2K method was developed and illustrated with analytically generated data for a synthetic dual-permeability soil. Next, a sensitivity analysis was performed to assess the accuracy of BEST-2K and its sensitivity to the quality of the inputs (water contents and cumulative infiltrations, and the prior estimation of the volume ratio occupied by the fast-flow region). Lastly, BEST-2K was applied to real experimental data to characterize three soils that are prone to preferential flow. BEST-2K was found to be a particularly useful tool that combines experimental and modeling approaches for characterizing dual-permeability soils and, more generally, soils prone to preferential flows

Inverse modelling of two-dimensional water infiltration into a soil containing macropores

Two series of axi-symmetric laboratory infiltration experiments were carried out in homogeneous sand and in sand containing artificially made vertical macropores. In the first case the results are compared with numerical solution of the Richards equation. In the second case the results are compared with the double-porosity model obtained by homogenization. The constitutive relations between the capillary pressure, saturation and unsaturated hydraulic conductivity for the sand and macropores are identified via numerical inverse analysis of cumulative infiltration. The applicability of several types of constitutive functions available in the literature is tested. The saturated conductivity and air-entry pressure fitted for the macropores are compared with theoretical predictions. The cumulative infiltration curves fitted by numerical inversion show reasonable agreement with observations for both types of porous media

Comparing Beerkan infiltration tests with rainfall simulation experiments for hydraulic characterization of a sandy-loam soil

[EN] Saturated soil hydraulic conductivity, K-s, data collected by ponding infiltrometer methods and usual experimental procedures could be unusable for interpreting field hydrological processes and particularly rainfall infiltration. The K-s values determined by an infiltrometer experiment carried out by applying water at a relatively large distance from the soil surface could however be more appropriate to explain surface runoff generation phenomena during intense rainfall events. In this study, a link between rainfall simulation and ponding infiltrometer experiments was established for a sandy-loam soil. The height of water pouring for the infiltrometer run was chosen, establishing a similarity between the gravitational potential energy of the applied water, E-p, and the rainfall kinetic energy, E-k. To test the soundness of this procedure, the soil was sampled with the Beerkan estimation of soil transfer parameters procedure of soil hydraulic characterization and two heights of water pouring (0.03m, i.e., usual procedure, and 0.34m, yielding E-p=E-k). Then, a comparison between experimental steady-state infiltration rates, i(sR), measured with rainfall simulation experiments determining runoff production and K-s values for the two water pouring heights was carried out in order to discriminate between theoretically possible (i(sR)K(s)) and impossible (i(sR)3.0.co;2-vCerdà, A. (1999). Seasonal and spatial variations in infiltration rates in badland surfaces under Mediterranean climatic conditions. Water Resources Research, 35(1), 319-328. doi:10.1029/98wr01659Cerdà, A. (2000). Aggregate stability against water forces under different climates on agriculture land and scrubland in southern Bolivia. Soil and Tillage Research, 57(3), 159-166. doi:10.1016/s0167-1987(00)00155-0Cerdà, A. 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Journal of the American Statistical Association, 62(318), 399-402. doi:10.1080/01621459.1967.10482916Liu, H., Lei, T. W., Zhao, J., Yuan, C. P., Fan, Y. T., & Qu, L. Q. (2011). Effects of rainfall intensity and antecedent soil water content on soil infiltrability under rainfall conditions using the run off-on-out method. Journal of Hydrology, 396(1-2), 24-32. doi:10.1016/j.jhydrol.2010.10.028Mualem, Y., Assouline, S., & Rohdenburg, H. (1990). Rainfall induced soil seal (A) A critical review of observations and models. CATENA, 17(2), 185-203. doi:10.1016/0341-8162(90)90008-2Mubarak, I., Angulo-Jaramillo, R., Mailhol, J. C., Ruelle, P., Khaledian, M., & Vauclin, M. (2010). Spatial analysis of soil surface hydraulic properties: Is infiltration method dependent? Agricultural Water Management, 97(10), 1517-1526. doi:10.1016/j.agwat.2010.05.005Nunes, A. N., Lourenço, L., Vieira, A., & Bento-Gonçalves, A. (2014). 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Impacts of thinning of a Mediterranean oak forest on soil properties influencing water infiltration

In Mediterranean ecosystems, special attention needs to be paid to forest-water relationships due to water scarcity. In this context, Adaptive Forest Management (AFM) has the objective to establish how forest resources have to be managed with regards to the efficient use of water, which needs maintaining healthy soil properties even after disturbance. The main objective of this investigation was to understand the effect of one of the AFM methods, namely forest thinning, on soil hydraulic properties. At this aim, soil hydraulic characterization was performed on two contiguous Mediterranean oak forest plots, one of them thinned to reduce the forest density from 861 to 414 tree per ha. Three years after the intervention, thinning had not affected soil water permeability of the studied plots. Both ponding and tension infiltration runs yielded not significantly different saturated, Ks, and unsaturated, K-20, hydraulic conductivity values at the thinned and control plots. Therefore, thinning had no an adverse effect on vertical water fluxes at the soil surface. Mean Ks values estimated with the ponded ring infiltrometer were two orders of magnitude higher than K-20 values estimated with the minidisk infiltrometer, revealing probably soil structure with macropores and fractures . The input of hydrophobic organic matter, as a consequence of the addition of plant residues after the thinning treatment, resulted in slight differences in terms of both water drop penetration time, WDPT, and the index of water repellency, R, between thinned and control plots. Soil water repellency only affected unsaturated soil hydraulic conductivity measurements. Moreover, K-20 values showed a negative correlation with both WDPT and R, whereas Ks values did not, revealing that the soil hydrophobic behavior has no impact on saturated hydraulic conductivity

Comparing transient and steady-state analysis of single-ring infiltrometer data for an abandoned field affected by fire in Eastern Spain

Este estudio tenía por objeto determinar la conductividad hidráulica del suelo saturado de campo, Kfs, de un campo no controlado afectado por el fuego mediante recorridos con infiltrómetro de anillo único y el uso de procedimientos de análisis de datos en estado transitorio y estacionario. El muestreo y las mediciones se llevaron a cabo en 2012 y 2017 en un campo afectado por el fuego (sitio quemado) y en un sitio vecino no afectado (sitio de control). Se investigó el potencial de predicción de los diferentes procedimientos de análisis de datos (es decir, de estado transitorio y de estado estacionario) para obtener estimaciones adecuadas del Kfs. En particular, se compararon el método WU1 transitorio y los métodos BB, WU2 y OPD. Se utilizó el método de linealización acumulativa (CL) para aplicar el método WU1. Se obtuvieron valores de Kfs que oscilaban entre 0,87 y 4,21 mm.h-1, dependiendo del método de análisis de datos considerado. El método WU1 no arrojó estimaciones de Kfs significativamente diferentes entre los sitios muestreados a lo largo del período de cinco años, debido al desempeño generalmente deficiente del método CL, que echó a perder la caracterización hidráulica del suelo. En particular, sólo se obtuvieron buenos ajustes en el 23% de los casos. Los métodos BB, WU2 y OPD, con una caracterización basada exclusivamente en un proceso de infiltración estabilizado, produjeron una variabilidad apreciablemente menor de los datos de Kfs en comparación con el método WU1. Se llegó a la conclusión de que los métodos de estado estacionario eran más apropiados para detectar cambios leves de Kfs en las caracterizaciones hidráulicas del suelo después del incendio. Nuestros resultados mostraron un cierto grado de degradación del suelo en el lugar quemado con una reducción inmediata de la materia orgánica del suelo y un aumento progresivo de la densidad aparente del suelo durante los cinco años siguientes al incendio. Este empobrecimiento general dio lugar a una ligera pero significativa disminución de la conductividad hidráulica del suelo saturado por el campo.This study aimed at determining the field-saturated soil hydraulic conductivity, Kfs, of an unmanaged field affected by fire by means of single-ring infiltrometer runs and the use of transient and steady-state data analysis procedures. Sampling and measurements were carried out in 2012 and 2017 in a fire-affected field (burnt site) and in a neighboring non-affected site (control site). The predictive potential of different data analysis procedures (i.e., transient and steady-state) to yield proper Kfs estimates was investigated. In particular, the transient WU1 method and the BB, WU2 and OPD methods were compared. The cumulative linearization (CL) method was used to apply the WU1 method. Values of Kfs ranging from 0.87 to 4.21 mm.h-1 were obtained, depending on the considered data analysis method. The WU1 method did not yield significantly different Kfs estimates between the sampled sites throughout the five-year period, due to the generally poor performance of the CL method, which spoiled the soil hydraulic characterization. In particular, good fits were only obtained in 23% of the cases. The BB, WU2 and the OPD methods, with a characterization based exclusively on a stabilized infiltration process, yielded an appreciably lower variability of the Kfs data as compared with the WU1 method. It was concluded that steady-state methods were more appropriate for detecting slight changes of Kfs in post-fire soil hydraulic characterizations. Our results showed a certain degree of soil degradation at the burnt site with an immediate reduction of the soil organic matter and a progressive increase of the soil bulk density during the five years following the fire. This general impoverishment resulted in a slight but significant decrease in the field-saturated soil hydraulic conductivity.• POSTFIRE Project CGL2013-47862-C2-1 y 2-R • POSTFIRE-CARE Project CGL2016-75178-C2-2-RpeerReviewe

On Infiltration and Infiltration Characteristic Times

In his seminal paper on the solution of the infiltration equation, Philip (1969), https://doi-org.proxy.library.uu.nl/10.1016/b978-1-4831-9936-8.50010-6 proposed a gravity time, tgrav, to estimate practical convergence time and the time domain validity of his infinite time series expansion, TSE, for describing the transient state. The parameter tgrav refers to a point in time where infiltration is dominated equally by capillarity and gravity as derived from the first two (dominant) terms of the TSE. Evidence suggests that applicability of the truncated two-term equation of Philip has a time limit requiring higher-order TSE terms to better describe the infiltration process for times exceeding that limit. Since the conceptual definition of tgrav is valid regardless of the infiltration model used, we opted to reformulate tgrav using the analytic implicit model proposed by Parlange et al. (1982), https://doi-org.proxy.library.uu.nl/10.1097/00010694-198206000-00001 valid for all times and related TSE. Our derived gravity times ensure a given accuracy of the approximations describing transient states, while also providing insight about the times needed to reach steady state. In addition to the roles of soil sorptivity (S) and the saturated (Ks) and initial (Ki) hydraulic conductivities, we explored the effects of a soil specific shape parameter β, involved in Parlange's model and related to the type of soil, on the behavior of tgrav. We show that the reformulated tgrav (notably urn:x-wiley:00431397:media:wrcr26009:wrcr26009-math-0001 where F(β) is a β-dependent function) is about three times larger than the classical tgrav given by urn:x-wiley:00431397:media:wrcr26009:wrcr26009-math-0002. The differences between the classical tgrav,Philip and the reformulated tgrav increase for fine-textured soils, attributed to the time needed to attain steady-state infiltration and thus i + infiltration for inferring soil hydraulic properties. Results show that the proposed tgrav is a better indicator of time domain validity than tgrav,Philip. For the attainment of steady-state infiltration, the reformulated tgrav is suitable for coarse-textured soils. Still neither the reformulated tgrav nor the classical tgrav,Philip are suitable for fine-textured soils for which tgrav is too conservative and tgrav,Philip too short. Using tgrav will improve predictions of the soil hydraulic parameters (particularly Ks) from infiltration data compared to tgrav,Philip