Modélisation des écoulements en milieu poreux hétérogènes 2D / 3D, avec couplages surface / souterrain et densitaires

Dans ce travail, on considère la modélisation des écoulements dans des hydro-systèmes comprenant des sols et des aquifères géologiquement complexes et hétérogènes. On considèrera par exemple le cas d’un aquifère côtier soumis à l’intrusion saline, avec couplage densitaire (eau douce / eau salée), phénomène auquel peuvent se greffer d’autres couplages (écoulements à saturation variable, couplages surface / souterrain). On choisit une approche ayant les caractéristiques suivantes : - le modèle est spatialement distribué afin de représenter l’hétérogénéité du milieu ; - le modèle est fortement couplé afin d’appréhender les écoulements dans leur complexité physique. On utilise dans ce but un modèle fortement intégré, à une seule équation générique de type EDP, basée sur une loi de Darcy généralisée permettant de décrire différents "régimes" d’écoulements la co-existant dans un même domaine, tout en conservant robustesse et efficacité. Le travail est divisé en trois parties : dans une première partie on élabore un nouveau modèle numérique 3D, pour la modélisation des écoulements en milieux poreux à densité variable dans l’hypothèse d’une interface abrupte. Ce nouveau modèle est basé sur des relations ‘effectives’ non linéaires de saturation et de perméabilité, dans une équation d’écoulement de type Richards modifiée. La seconde partie correspond à l’élaboration et l’implémentation d’un modèle verticalement intégré d’intrusion saline en aquifère côtier, permettant d’étudier l’effet de l’hétérogénéité stochastique de l’aquifère. Le modèle, basé sur l’hypothèse ‘interface abrupte’, est implémenté comme un module ‘2D’ dans le code volumes finis BigFlow2D/3D. Le nouveau module 2D est utilisé pour analyser la variabilité de l’interface eau douce / eau salée par simulations stochastiques de type Monte Carlo à échantillonnage spatial (réalisation unique). Ces résultats sont comparés à nouvelle théorie, où l’interface aléatoire auto-corrélée est analysée par transformation de variable, combinée à une méthode de perturbation et à une représentation spectrale (Fourier / Wiener-Khinchine). Dans la troisième et dernière partie, on présente un modèle de couplage fortement "intégré" pour la modélisation des écoulements de surface et souterrain en hypothèses d’écoulement plan, verticalement hydrostatique. On s‘intéresse au cas d’une vallée fluviale avec cours d’eau, plaine d’inondation, et nappe d’accompagnement. L’écoulement en surface est modélisé par l’équation d’onde diffusante et l’écoulement souterrain par l’équation de Dupuit-Boussinesq. Ce modèle couplé est appliqué à la vallée fluviale de la Garonne dans la région de Toulouse - Moissac (France). Cette application a nécessité l’élaboration d’une méthode d’interpolation géostatistique adaptée à l’élaboration d’un Modèle Intégré Numérique de Terrain (‘MINT’), de façon à inclure le fond de la rivière au MNT topographique en haute résolution. Enfin, au-delà de cette application particulière, le modèle d’écoulement couplé surface / souterrain est généralisé au cas d’un couplage densitaire eau douce / eau salée, lorsque la nappe est sujette à l’intrusion saline au voisinage d’une embouchure ou d’un estuaire. ABSTRACT : In this work, we consider water flow modeling in hydro-systems that include geologically complex and heterogeneous soils and aquifers, e.g., a coastal aquifer undergoing seawater intrusion, with density coupling (freshwater / saltwater), along with other coupled phenomena (variable saturation, surface / subsurface coupling). The selected approach has the following characteristics: - the model is spatially distributed in order to represent the heterogeneity of the medium ; - the model is strongly coupled in order to apprehend the physical complexity of flow systems. We use for this purpose a strongly integrated model, governed by a single generic equation (PDE) based on generalized Darcy law, to describe different flow ‘regimes’ co-existing in the same domain, while conserving robustness and efficiency. The work is divided into three parts: in the first part, we develop a new 3D numerical model for variable density flow in porous media under the sharp interface approximation. This new model is based on non-linear ‘effective’ saturation and conductivity relations, in a modified Richards flow equation. The second part corresponds to the development and implementation of a vertically integrated saltwater intrusion model, to study the effect of stochastic heterogeneity in a coastal aquifer. The model, based on the sharp interface hypothesis, is implemented as a 2D module in the finite volumes code BigFlow 2D/3D. The new module is used for analyzing the variability of the salt / fresh interface through Monte Carlo simulations with spatial sampling (single realization). These results are compared to a new theory where the random field interface is analyzed via a transformation combined to a perturbation method and a spectral representation (Fourier / Wiener-Khinchine). In the third and last part, we present a strongly integrated model to simulate coupled surface / subsurface plane flows, such as a river valley with stream, floodplain, and free surface aquifer. Surface flow is modeled via the diffusive wave equation, and subsurface flow is modeled using the Dupuit-Boussinesq equation. This coupled model is applied to the Garonne river valley in the Toulouse-Moissac region (France). This application has required the elaboration of a geostatistical interpolation technique that produces an Integrated Digital Elevation Model (‘IDEM’). The IDEM incorporates a high resolution representation of river channels into the topographic DEM. Finally, beyond this specific application, the coupled surface / subsurface model is generalized to the case of salt / fresh density coupling, where the aquifer is subject to saltwater intrusion near a river mouth or an estuar

Model Coupling for Environmental Flows, with Applications in Hydrology and Coastal Hydrodynamics.

The aim of this paper is to present an overview of “model coupling” methods and issues in the area of environmental hydrodynamics, particularly coastal hydrodynamics and surface/subsurface hydrology. To this end, we will examine specific coupled phenomena in order to illustrate coupling hypotheses and methods, and to gain new insights from analyses of modelling results in comparison with experiments. Although this is to some extent a review of recent works, nevertheless, some of the methods and results discussed here were not published before, and some of the analyses are new. Moreover, this study is part of a more general framework concerning various types of environmental interactions, such as: interactions between soil water flow (above the water table) and groundwater flow (below the water table); interactions between surface and subsurface waters in fluvial environments (streams, floodplains); interactions between coastal flow processes and porous structures (e.g. sea‑driven oscillations and waves through sand beach or a porous dike); feedback effects of flow systems on the geo‑environmental media. This paper starts with a general review of conceptual coupling approaches, after which we present specific modelling and coupling methods for dealing with hydrological flows with surface water / groundwater interactions, and with coastal flows involving the propagation of seawater oscillations through a porous beach (vertically and horizontally). The following topics are treated. (1) Coupled stream‑aquifer plane flow in an alluvial river valley (quasi‑steady seasonal flow regime), assuming aquifer/stream continuity, and using in situ piezometric measurements for comparisons. (2) Water table oscillations induced by sea waves, and propagating through the beach in the cross‑shore direction: this phenomenon is studied numerically and experimentally using a wave canal with an inclined beach equipped with capacitive micro‑piezometers. (3) Tidally driven vertical oscillations of water flow and capillary pressure in a partially saturated / unsaturated sand beach column, studied numerically and experimentally via a “tide machine” contraption (described in some detail): the goal is to apprehend the role of capillary effects, and forcing frequency, on the hydraulic response of a beach column forced by tides from below. At the time of this writing, some of the results from the tide machine are being reinterpreted (ongoing work). We also point out a recent study of vertical flow in the beach, which focuses on the effect of intermittent waves in the swash zone, rather than tidal oscillations

Coronavirus Disease-2019 in Heart Transplant Recipients in Southeastern Michigan: A Case Series

BACKGROUND: Since coronavirus disease 2019 (COVID-19) was first identified in Wuhan, China, in December 2019, the number of cases has risen exponentially. Clinical characteristics and outcomes among patients with orthotopic heart transplant (OHT) with COVID-19 remain poorly described. METHODS: We performed a retrospective case series of patients with OHT with COVID-19 admitted to 1 of 2 hospitals in Southeastern Michigan between March 21 and April 22, 2020. Clinical data were obtained through review of the electronic medical record. Final date of follow-up was May 7, 2020. Demographic, clinical, laboratory, radiologic, treatment, and mortality data were collected and analyzed. RESULTS: We identified 13 patients with OHT admitted with COVID-19. The mean age of patients was 61 ± 12 years, 100% were black males, and symptoms began 6 ± 4 days before admission. The most common symptoms included subjective fever (92%), shortness of breath (85%), and cough (77%). Six patients (46%) required admission to the intensive care unit. Two patients (15%) died during hospitalization. CONCLUSIONS: Black men may be at increased risk for COVID-19 among patients with OHT. Presenting signs and symptoms in this cohort are similar to those in the general population. Elevated inflammatory markers on presentation appear to be associated with more severe illness

Pathophysiological Correlation between Diabetes Mellitus Type-II and Chronic Obstructive Pulmonary Diseases

INTRODUCTION: Diabetes Mellitus, a chronic disease is usually associated and linked to many other conditions and complications. Chronic Obstructive Pulmonary Disease (COPD); a life threatening progressive inflammatory lung disease associated with chronic bronchitis and emphysema; when associated with Diabetes Mellitus generates a huge burden on patients quality of life as well as on health care systems. OBJECTIVE: Although link between DM and COPD is not scientifically established or confirmed yet, however evidence suggest a pathophysiological correlation between both conditions might be present. This study focuses upon impact of DM on the onset of COPD and to find if there is any evidence of the suggested pathophysiological correlation. METHODOLOGY: We retrospectively analyzed 120 cases of Chronic Obstructive Pulmonary Disease (COPD), data collected from General Medical Units and Pulmonary Ward of Liaquat University Teaching Hospital, Jamshoro / Hyderabad from January till June, 2016. RESULTS: The majority of cases with COPD were male representing 81.6% of the sample population, almost 90% of patients were smokers or ex-smokers, 42.50% of COPD patients were suffering from DM and 76.47% were either non-compliant or had a very poor control over their blood glucose level. Blood glucose levels of most of the patients was from 140 mg/dl to 500 mg/dl and 19.60% of patients reached diabetic ketoacidosis (DKA) once at least. CONCLUSION: DM increases the risk for occurrence of COPD and cause rapid decline in clinical state of the patient. Unlike cardiovascular complication of diabetes in case of diabetic patients with COPD the lower the BMI the higher the risk of mortality

An evaluation of SMOS L-band vegetation optical depth (L-VOD) data sets:high sensitivity of L-VOD to above-ground biomass in Africa

The vegetation optical depth (VOD) measured at microwave frequencies is related to the vegetation water content and provides information complementary to visible/infrared vegetation indices. This study is devoted to the characterization of a new VOD data set obtained from SMOS (Soil Moisture and Ocean Salinity) satellite observations at L-band (1.4 GHz). Three different SMOS L-band VOD (LVOD) data sets (SMOS level 2, level 3 and SMOS-IC) were compared with data sets on tree height, visible/infrared indexes (NDVI, EVI), mean annual precipitation and above-ground biomass (AGB) for the African continent. For all relationships, SMOS-IC showed the lowest dispersion and highest correlation. Overall, we found a strong (R > 0.85) correlation with no clear sign of saturation between L-VOD and four AGB data sets. The relationships between L-VOD and the AGB data sets were linear per land cover class but with a changing slope depending on the class type, which makes it a global non-linear relationship. In contrast, the relationship linking L-VOD to tree height (R = 0.87) was close to linear. For vegetation classes other than evergreen broadleaf forest, the annual mean of L-VOD spans a range from 0 to 0.7 and it is linearly correlated with the average annual precipitation. SMOS L-VOD showed higher sensitivity to AGB compared to NDVI and K/X/C-VOD (VOD measured at 19, 10.7 and 6.9 GHz). The results showed that, although the spatial resolution of L-VOD is coarse (similar to 40 km), the high temporal frequency and sensitivity to AGB makes SMOS L-VOD a very promising indicator for large-scale monitoring of the vegetation status, in particular biomass

Synergistic calibration of a hydrological model using discharge and remotely sensed soil moisture in the Paraná river basin

Hydrological models are useful tools for water resources studies, yet their calibration is still a challenge, especially if aiming at improved estimates of multiple components of the water cycle. This has led the hydrologic community to look for ways to constrain models with multiple variables. Remote sensing estimates of soil moisture are very promising in this sense, especially in large areas for which field observations may be unevenly distributed. However, the use of such data to calibrate hydrological models in a synergistic way is still not well understood, especially in tropical humid areas such as those found in South America. Here, we perform multiple scenarios of multiobjective model optimization with in situ discharge and the SMOS L4 root zone soil moisture product for the Upper Paraná River Basin in South America (drainage area > 900,000 km2), for which discharge data for 136 river gauges are used. An additional scenario is used to compare the relative impacts of using all river gauges and a small subset containing nine gauges only. Across the basin, the joint calibration (CAL-DS) using discharge and soil moisture leads to improved precision and accuracy for both variables. The discharges estimated by CAL-DS (median KGE improvement for discharge was 0.14) are as accurate as those obtained with the calibration with discharge only (median equal to 0.14), while the CAL-DS soil moisture retrieval is practically as accurate (median KGE improvement for soil moisture was 0.11) as that estimated using the calibration with soil moisture only (median equal to 0.13). Nonetheless, the individual calibration with discharge rates is not able to retrieve satisfactory soil moisture estimates, and vice versa. These results show the complementarity between these two variables in the model calibration and highlight the benefits of considering multiple variables in the calibration framework. It is also shown that, by considering only nine gauges inst

Comparison of SMOS and SMAP Soil Moisture Retrieval Approaches Using Tower-based Radiometer Data over a Vineyard Field

The objective of this study was to compare several approaches to soil moisture (SM) retrieval using L-band microwave radiometry. The comparison was based on a brightness temperature (TB) data set acquired since 2010 by the L-band radiometer ELBARA-II over a vineyard field at the Valencia Anchor Station (VAS) site. ELBARA-II, provided by the European Space Agency (ESA) within the scientific program of the SMOS (Soil Moisture and Ocean Salinity) mission, measures multiangular TB data at horizontal and vertical polarization for a range of incidence angles (30-60). Based on a three year data set (2010-2012), several SM retrieval approaches developed for spaceborne missions including AMSR-E (Advanced Microwave Scanning Radiometer for EOS), SMAP (Soil Moisture Active Passive) and SMOS were compared. The approaches include: the Single Channel Algorithm (SCA) for horizontal (SCA-H) and vertical (SCA-V) polarizations, the Dual Channel Algorithm (DCA), the Land Parameter Retrieval Model (LPRM) and two simplified approaches based on statistical regressions (referred to as 'Mattar' and 'Saleh'). Time series of vegetation indices required for three of the algorithms (SCA-H, SCA-V and Mattar) were obtained from MODIS observations. The SM retrievals were evaluated against reference SM values estimated from a multiangular 2-Parameter inversion approach. The results obtained with the current base line algorithms developed for SMAP (SCA-H and -V) are in very good agreement with the reference SM data set derived from the multi-angular observations (R2 around 0.90, RMSE varying between 0.035 and 0.056 m3m3 for several retrieval configurations). This result showed that, provided the relationship between vegetation optical depth and a remotely-sensed vegetation index can be calibrated, the SCA algorithms can provide results very close to those obtained from multi-angular observations in this study area. The approaches based on statistical regressions provided similar results and the best accuracy was obtained with the Saleh methods based on either bi-angular or bipolarization observations (R2 around 0.93, RMSE around 0.035 m3m3). The LPRM and DCA algorithms were found to be slightly less successful in retrieving the 'reference' SM time series (R2 around 0.75, RMSE around 0.055 m3m3). However, the two above approaches have the great advantage of not requiring any model calibrations previous to the SM retrievals