Oscillatory flows and capillary effects in partially saturated and unsaturated porous media: applications to beach hydrodynamics

In this thesis, we study hydrodynamic oscillations in porous bodies (unsaturated or partially saturated), due to tidal oscillations of water levels in adjacent open water bodies. The focus is on beach hydrodynamics, but potential applications concern, more generally, time varying and oscillating water levels in coupled systems involving subsurface / open water interactions (natural and artificial beaches, harbor dykes, earth dams, river banks, estuaries). The tidal forcing of groundwater is represented and modeled (both experimentally and numerically) by quasi-static oscillations of water levels in an open water reservoir connected to the porous medium. Specifically, we focus on vertical water movements forced by an oscillating pressure imposed at the bottom of a soil column. Experimentally, a rotating tide machine is used to achieve this forcing. Overall, we use three types of methods (experimental, numerical, analytical) to study the vertical motion of the groundwater table and the unsaturated flow above it, taking into account the vertical head drop in the saturated zone as well as capillary pressure gradients in the unsaturated zone. Laboratory experiments are conducted on vertical sand columns, with a tide machine to force water table oscillations, and with porous cup tensiometers to measure both positive pressures and suctions along the column (among other measurement methods). Numerical simulations of oscillatory water flow are implemented with the BIGFLOW 3D code (implicit finite volumes, with conjugate gradients for the matrix solver and modified Picard iterations for the nonlinear problem). In addition, an automatic calibration based on a genetic optimization algorithm is implemented for a given tidal frequency, to obtain the hydrodynamic parameters of the experimental soil. Calibrated simulations are then compared to experimental results for other non calibrated frequencies. Finally, a family of quasi-analytical multi-front solutions is developed for the tidal oscillation problem, as an extension of the Green-Ampt piston flow approximation, leading to nonlinear, non-autonomous systems of Ordinary Differential Equations with initial conditions (dynamical systems). The multi-front solutions are tested by comparing them with a refined finite volume solution of the Richards equation. Multi-front solutions are at least 100 times faster, and the match is quite good even for a loamy soil with strong capillary effects (the number of fronts required is small, no more than N10 to 20 at most). A large set of multi-front simulations is then produced in order to analyze water table and flux fluctuations for a broad range of forcing frequencies. The results, analyzed in terms of means and amplitudes of hydrodynamic variables, indicate the existence, for each soil, of a characteristic frequency separating low frequency / high frequency flow regimes in the porous system

Ecoulements oscillatoires et effets capillaires en milieux poreux partiellement saturés et non saturés : applications en hydrodynamique côtière

Dans cette thèse, on étudie les écoulements oscillatoires en milieux poreux (non saturés ou partiellement saturés) dus à des oscillations tidales des niveaux d'eau dans des milieux ouverts adjacents aux milieux poreux. L'étude est centrée sur le cas des plages de sable en hydrodynamique côtière, mais les applications concernent, potentiellement et plus généralement, les problèmes d'oscillation et de variation temporelle des niveaux d'eau dans des systèmes couplés, lorsque ceux-ci mettent en jeu des interactions entre les écoulements de sub-surface (milieux poreux) et les eaux de surface (milieux ouverts) : plages naturelles et artificielles; digues portuaires; barrages en terre; berges de fleuves; estuaires. Le forçage tidal des écoulements souterrains est représenté et modélisé ici, tant expérimentalement que numériquement, par une oscillation quasi-statique du niveau d'eau dans un réservoir externe ouvert, connecté au domaine poreux. On s'intéresse plus particulièrement aux écoulements verticaux forcés par une pression oscillatoire imposée au bas d'une colonne de sol. Sur le plan expérimental, ce type de forçage est obtenu par une machine à marée équipée d'un arbre rotatif. Au total, on utilise dans ce travail trois types d'approches (expérimentale, numérique, analytique), l'objectif étant d'étudier le mouvement vertical de la surface "libre" et l'écoulement non saturé sus-jacent, de façon à prendre en compte aussi bien les pertes de charge dans la zone saturée que les gradients de pression capillaire dans la zone non saturée. […] ABSTRACT : In this thesis, we study hydrodynamic oscillations in porous bodies (unsaturated or partially saturated), due to tidal oscillations of water levels in adjacent open water bodies. The focus is on beach hydrodynamics, but potential applications concern, more generally, time varying and oscillating water levels in coupled systems involving subsurface / open water interactions (natural and artificial beaches, harbor dykes, earth dams, river banks, estuaries). The tidal forcing of groundwater is represented and modeled (both experimentally and numerically) by quasi-static oscillations of water levels in an open water reservoir connected to the porous medium. Specifically, we focus on vertical water movements forced by an oscillating pressure imposed at the bottom of a soil column. Experimentally, a rotating tide machine is used to achieve this forcing. Overall, we use three types of methods (experimental, numerical, analytical) to study the vertical motion of the groundwater table and the unsaturated flow above it, taking into account the vertical head drop in the saturated zone as well as capillary pressure gradients in the unsaturated zone. Laboratory experiments are conducted on vertical sand columns, with a tide machine to force water table oscillations, and with porous cup tensiometers to measure both positive pressures and suctions along the column (among other measurement methods). Numerical simulations of oscillatory water flow are implemented with the BIGFLOW 3D code (implicit finite volumes, with conjugate gradients for the matrix solver and modified Picard iterations for the nonlinear problem). In addition, an automatic calibration based on a genetic optimization algorithm is implemented for a given tidal frequency, to obtain the hydrodynamic parameters of the experimental soil. Calibrated simulations are then compared to experimental results for other non calibrated frequencies. Finally, a family of quasi-analytical multi-front solutions is developed for the tidal oscillation problem, as an extension of the Green-Ampt piston flow approximation, leading to nonlinear, non-autonomous systems of Ordinary Differential Equations with initial conditions (dynamical systems). The multi-front solutions are tested by comparing them with a refined finite volume solution of the Richards equation. Multi-front solutions are at least 100 times faster, and the match is quite good even for a loamy soil with strong capillary effects (the number of fronts required is small, no more than N 4810 to 20 at most). A large set of multi-front simulations is then produced in order to analyze water table and flux fluctuations for a broad range of forcing frequencies. The results, analyzed in terms of means and amplitudes of hydrodynamic variables, indicate the existence, for each soil, of a characteristic frequency separating low frequency / high frequency flow regimes in the porous system

Moving Multi-Front (MMF): A generalized Green-Ampt approach for vertical unsaturated flows

A Moving Multi-Front (MMF) method is developed and tested for solving the Richards equation governing unsaturated flow in vertical homogeneous porous columns. The MMF model is a gridless method. It can be viewed as a generalization of the Green-Ampt piston flow approach, which models flow as a single abrupt moving front separating saturated and dry regions during infiltration. The MMF model further generalizes this concept, using a parametrization of unsaturated water retention and conductivity-pressure curves. It reduces the Richards PDE to an ODE system governing “M” moving front positions. Different tests are developed to validate this approach for 1D transient downwards/upwards flows submitted to constant and time-varying pressure boundary conditions. They include: (i) infiltration to deep water tables; (ii) infiltration to shallow water tables; (iii) capillary rise from fixed water tables; (iv) gradual water table rise (partially saturated column with evolving pressure condition at bottom). The MMF results are compared favorably to finely discretized fixed grid solutions of Richards PDE. Analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes (e.g. infiltration rate)

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

Leukemic Infiltration of the Esophagus, a Rare Etiology for a Common Disease

Introduction: The etiology of esophagitis in patients with acute leukemia is usually related to infections, reflux, or chemotherapy toxicity. Infiltration of esophagus by leukemic cells is rarely considered in the differential diagnosis.Presentation of Case: Here we present a case of 87-year-old male patient with a recent diagnosis of acute myelocytic leukemia who was found to have severe diffuse esophagitis secondary to leukemic infiltration.Conclusion: Leukemic infiltration of the esophagus is a rare potential etiology of severe esophagitis in patients with disseminated leukemia. Esophageal biopsy is needed to identify the exact cause of esophageal lesions in leukemia patient

Case Report Acute Cholangitis following Biliary Obstruction after Duodenal OTSC Placement in a Case of Large Chronic Duodenocutaneous Fistula

Over-the-Scope Clip system, also called "Bear Claw, " is a novel endoscopic modality used for closure of gastrointestinal defect with high efficacy and safety. We present a patient with history of eosinophilic gastroenteritis and multiple abdominal surgeries including Billroth II gastrectomy complicated by a large chronic duodenocutaneous fistula from a Billroth II afferent limb to the abdominal wall. Bear Claw clip was used for closure of this fistula. The patient developed acute cholangitis one day after placement of the Bear Claw clip. Acute cholangitis due to papillary obstruction is a potential complication of Bear Claw placement at the dome of the duodenal stump (afferent limb) in patient with Billroth II surgery due to its close proximity to the major papilla

Oscillatory flows and capillary effects in partially saturated and unsaturated porous media : applications to beach hydrodynamics

Dans cette thèse, on étudie les écoulements oscillatoires en milieux poreux (non saturés ou partiellement saturés) dus à des oscillations tidales des niveaux d'eau dans des milieux ouverts adjacents aux milieux poreux. L'étude est centrée sur le cas des plages de sable en hydrodynamique côtière, mais les applications concernent, potentiellement et plus généralement, les problèmes d'oscillation et de variation temporelle des niveaux d'eau dans des systèmes couplés, lorsque ceux-ci mettent en jeu des interactions entre les écoulements de sub-surface (milieux poreux) et les eaux de surface (milieux ouverts) : plages naturelles et artificielles; digues portuaires; barrages en terre; berges de fleuves; estuaires. Le forçage tidal des écoulements souterrains est représenté et modélisé ici, tant expérimentalement que numériquement, par une oscillation quasi-statique du niveau d'eau dans un réservoir externe ouvert, connecté au domaine poreux. On s'intéresse plus particulièrement aux écoulements verticaux forcés par une pression oscillatoire imposée au bas d'une colonne de sol. Sur le plan expérimental, ce type de forçage est obtenu par une machine à marée équipée d'un arbre rotatif. Au total, on utilise dans ce travail trois types d'approches (expérimentale, numérique, analytique), l'objectif étant d'étudier le mouvement vertical de la surface "libre" et l'écoulement non saturé sus-jacent, de façon à prendre en compte aussi bien les pertes de charge dans la zone saturée que les gradients de pression capillaire dans la zone non saturée. […]In this thesis, we study hydrodynamic oscillations in porous bodies (unsaturated or partially saturated), due to tidal oscillations of water levels in adjacent open water bodies. The focus is on beach hydrodynamics, but potential applications concern, more generally, time varying and oscillating water levels in coupled systems involving subsurface / open water interactions (natural and artificial beaches, harbor dykes, earth dams, river banks, estuaries). The tidal forcing of groundwater is represented and modeled (both experimentally and numerically) by quasi-static oscillations of water levels in an open water reservoir connected to the porous medium. Specifically, we focus on vertical water movements forced by an oscillating pressure imposed at the bottom of a soil column. Experimentally, a rotating tide machine is used to achieve this forcing. Overall, we use three types of methods (experimental, numerical, analytical) to study the vertical motion of the groundwater table and the unsaturated flow above it, taking into account the vertical head drop in the saturated zone as well as capillary pressure gradients in the unsaturated zone. Laboratory experiments are conducted on vertical sand columns, with a tide machine to force water table oscillations, and with porous cup tensiometers to measure both positive pressures and suctions along the column (among other measurement methods). Numerical simulations of oscillatory water flow are implemented with the BIGFLOW 3D code (implicit finite volumes, with conjugate gradients for the matrix solver and modified Picard iterations for the nonlinear problem). In addition, an automatic calibration based on a genetic optimization algorithm is implemented for a given tidal frequency, to obtain the hydrodynamic parameters of the experimental soil. Calibrated simulations are then compared to experimental results for other non calibrated frequencies. Finally, a family of quasi-analytical multi-front solutions is developed for the tidal oscillation problem, as an extension of the Green-Ampt piston flow approximation, leading to nonlinear, non-autonomous systems of Ordinary Differential Equations with initial conditions (dynamical systems). The multi-front solutions are tested by comparing them with a refined finite volume solution of the Richards equation. Multi-front solutions are at least 100 times faster, and the match is quite good even for a loamy soil with strong capillary effects (the number of fronts required is small, no more than N≈ to 20 at most). A large set of multi-front simulations is then produced in order to analyze water table and flux fluctuations for a broad range of forcing frequencies. The results, analyzed in terms of means and amplitudes of hydrodynamic variables, indicate the existence, for each soil, of a characteristic frequency separating low frequency / high frequency flow regimes in the porous system

Partially saturated oscillatory flow under tidal conditions in homogeneous and layered soil columns (experiment and simulations)

Surface/subsurface flow interactions concern a wide range of applications, from beach morphodynamics (swash zone), coastal aquifers (seawater intrusion and tidal effects), to harbour engineering and hydrology (e.g., man-made structures such as porous dykes and earth dams). The aim of this paper is to study numerically and experimentally the oscillatory flow in a sandy beach under tidal/low frequency forcing. In this short paper, we only describe the principle of the experiments, and then we focus on numerical simulations and analysis. For the numerical simulation, we use Richards's equation for variably saturated/unsaturated flow in a 1D porous column, with oscillatory pressure boundary conditions at the bottom of the column. Numerical simulations and analyses are conducted for the following cases: (1) homogeneous column, (2) heterogeneous 2-layer column (currently being extended to other heterogeneities)

Groundwater Quality Assessment Using Water Quality Index (WQI) Approach: Gaza Coastal Aquifer Case Study

Water resources in arid and semi-arid regions, such as the Gaza Strip (GS), are generally under increasing stresses in terms of water quality and quantity. Therefore management of these valuable resources is one of the crucial concerns and challenges facing researchers and specialists worldwide. In these areas, there is a pressing need to evaluate the water situation in terms of its quality using the available limited data. The Water Quality Index (WQI) helps managers and planners working in the water sector to qualitatively map water quality; which in turn enables them to propose the possible management options, and to prioritize the capital investment for the water sector. Being the only source of water for the GS population of more than 1.8 million, the Gaza Coastal Aquifer (GCA) is in a disastrous quality situation. It represents an extreme prototype model on how several negative factors (unstable political environment, disastrous economic situation, decaying environmental conditions, unplanned & disorganized human activities), are combined together to further deteriorate the groundwater quality. The objective of this paper is to assess and map the spatial distribution of groundwater quality of the GCA using the WQI approach. Research results indicate that severe water quality deterioration has occurred in the GS. The area fraction that is classified as "not good" based on the WQI jumped from about 30% to 55% over 10 years (between 2000 and 2010). The WQI maps developed in this research work assisted in forming a simple yet comprehensive view about groundwater quality in the GS. This, in turn, helps spotting critical locations in terms of water quality, and setting management priorities accordingly. In summary, the space-time analyses of WQI provide support for the decision making process, i.e., for drawing policies and proposing remediation measures to restore and maintain water resources

Acute Cholangitis following Biliary Obstruction after Duodenal OTSC Placement in a Case of Large Chronic Duodenocutaneous Fistula

Over-the-Scope Clip system, also called “Bear Claw,” is a novel endoscopic modality used for closure of gastrointestinal defect with high efficacy and safety. We present a patient with history of eosinophilic gastroenteritis and multiple abdominal surgeries including Billroth II gastrectomy complicated by a large chronic duodenocutaneous fistula from a Billroth II afferent limb to the abdominal wall. Bear Claw clip was used for closure of this fistula. The patient developed acute cholangitis one day after placement of the Bear Claw clip. Acute cholangitis due to papillary obstruction is a potential complication of Bear Claw placement at the dome of the duodenal stump (afferent limb) in patient with Billroth II surgery due to its close proximity to the major papilla