Newtonian nudging for a Richards equation-based distributed model

This report describes a series of simulations conducted with a hydrological model, CATHY, to test a recently implemented data assimilation technique, Newtonian nudging

Assessment and formulation of data assimilation techniques for a 3D Richards equation-based hydrological model

The main objectives of de DAUFIN project are: to develop a unifying modeling framework applicable at the catchment scale and based on rigorous conservation equations for the study of hydrological processes in the stream channel, land surface, soil, and groundwater components of a river basin; to implement data assimilation methodologies within this modeling framework and for other control models to enable the optimal use of remote sensing, ground-based, and simulation data; to test and apply the models and the data assimilation methods at various catchment scales, including hillslopes and subcatchment of the Ourthe water shed in Belgium and the entire Meuse river basin, one of the major basins in Europe with a drainage area of 33000 km² that comprises the Ourthe

Literature review on NAPL contamination and remediation

Remediation of polluted soils and groundwater is of major concern due to the increasing number of contaminated aquifers. Subsurface aquifers constitute one of the most important sources of drinkable water. In recent years, water needs have been increasing due to increases in development and human population. Several sorts of contaminants can be found in groundwater: metal ions, pesticides, aliphatic and aromatic hydrocarbons, polycyclic hydrocarbons, chlorinated hydrocarbons, etc. The toxicity of these compounds varies and so do guidelines that establish allowable concentration levels in drinking water. Among the aforementioned types of compounds, a particular importance is assumed by those which exist as a separate phase when their concentrations in water exceed a certain limit. The transport behavior and dynamics of multiphase contaminants are very different from their dissolved counterparts, and are very difficult both to describe and to model. Several phenomena can take place, such as organic phase trapping, formation of ganglia and pools of contaminant, sorption, hysteresis in both soil imbibition and drainage, capillarity, fingering, and mass-transfer. In such cases, our ability to describe and predict the fate of a contaminant plume in which a separate organic phase occurs is limited, and research within this field is quite open. Much effort has been devoted in trying to describe the characteristics of the phenomena occuring in multiphase systems, and several models and formulations have been proposed for predicting the fate of contaminants when present in such systems (see Miller et al. 1997) for a review on multiphase modeling in porous media). Work has also been done for modeling human intervention techniques for containing and/or reducing soil contaminantion (NRC, 1994), such as pumping, clean water-air-steam injection, soil heating, surfactants, biological methods, etc. Finally, much work has also been done on the numerical solution of mathematical models whose complexity does not allow for an analytical solution. Among the dozens of remediation methods which have been proposed and which are strongly dependent on site environmental conditions, biological methods are achieving increasing importance, due to their “naturalness" and their low costs (NRC, 1993) . It has been noticed that soil microorganisms are able to degrade several classes of compounds, in particular those which partition between an aqueous and an organic phase, or sometimes also gaseous phase, for e.g., hydrocarbons, chlorinated compounds, pesticides. These compounds, or better said, their fractions dissolved in water, are liable to be metabolized by subsurface microrganisms which have the capability to degrade the compounds and to transform them into carbon dioxide and/or other compounds, which are less toxic or unnoxious. Several laboratory and field studies have been conducted for assessing and evaluating the capability and the limits of soil microorganisms to degrade several classes of contaminants (Mayer et al., 1994, 1995, 1996, 1997) . Much work has also been devoted to modeling biodegration of groundwater contaminants. The outline of this report is as follows: section 2 gives a brief description of the characteristics and properties of NAPLs, including a review of the literature with regards to formulations and modeling; section 3 discusses biodegradation of contaminants and past efforts at modeling biodegradation; section 4 surveys specific remediation technologies and experiences; and section 5 discusses open issues for further research. In the final section possible lines of research for the second phase of the PhD program are indicated

Examination of the seepage face boundary condition in subsurface and coupled surface/subsurface hydrological models

A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper, we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

Implementation of a catchment hydrologic model for the Brisy subcatchment of the Ourthe watershed, and generation of a dataset for a 240-day storm-interstorm sequence

This report describes the generation of a synthetic dataset needed for testing and verification of more simplified modeling approaches which aim to develop models applicable at large catchment and river basin scales. The work is carried out within the framework of a European project (DAUFIN) on developing data assimilation methodologies and a unified framework for hydrological modeling of catchment and river basin flow processes

Rapporto di ricerca bibliografica (Stato dell'arte dei modelli di flusso e trasporto in mezzi porosi)

In questo primo rapporto vengono presentate le equazioni fondamentali che reggono i fenomeni di flusso e trasporto in mezzi porosi insieme ai metodi numerici che verranno utilizzati per la soluzione di tali equazioni. I modelli matematici in questione sono basati su equazioni differenziali a derivate parziali che impongono il bilancio di massa sia per il fluido che per il soluto (inquinante disciolto in acqua). Queste equazioni vengono scritte in forma generale per un mezzo poroso tridimensionale; in dipendenza dal tipo di applicazione è possibile adottare modelli mono o bidimensionali che portano a semplificazioni notevoli. L'equazione di flusso è sviluppata per il caso di mezzi porosi a saturazione variabile e può essere quindi utilizzata contemporaneamente nella zona insatura (suoli superficiali) e satura (falde freatiche e artesiane). Nell'equazione di trasporto si considerano i processi di dispersione, diffusione e avvezione, insieme ad alcune fenomenologie di interazione chimico-fisica tra il soluto e la matrice porosa. Accanto a queste equazione, si descrive anche un modello, a scala di bacino, di afflussi-deflussi superficiali accoppiato con un modello di infiltrazione. Questo approccio viene tiene conto di fenomeni importanti qualora vi sia una stretta correlazione tra il moto dell'acqua in superficie e il moto dell'acqua nella zona insatura

Description of a hydrologic dataset for the Brisy subcatchment

This report describes the dataset for the Brisy subcatchment in south eastern Belgium, which is a subcatchment of the Ourthe catchment, itself a subcatchment of the Meuse river basin. The data preparation, organization, and processing steps undertaken for both the Meuse basin and the Brisy subcatchment will be detailed

Simulazione numerica del flusso e trasporto di contaminanti in mezzi porosi a saturazione e densità variabile

La legislazione riguardante la salvaguardia e la tutela delle risorse idriche, e tra queste le acque sotterranee, è in continua crescita in tutti i paesi industrializzati. La protezione delle acque di falda dal sovrasfruttamento e dalla contaminazione di origine diversa (rifiuti urbani e industriali, pesticidi e fertilizzanti, scorie nucleari, ecc...) richiede la previsione degli effetti indotti dalle attività umane sulla quantità e qualità delle risorse sotterranee, previsione che si può conseguire solo attraverso l'impiego di idonei modelli matematico-numerici. Un problema di stringente attualità in tutti i paesi che si affacciano sul Mediterraneo è l'inquinamento degli acquiferi costieri per intrusione di acqua di mare. La simulazione della penetrazione del cuneo salino comporta lo sviluppo di modelli accoppiati di flusso e trasporto che possono essere accuratamente ed efficientemente risolti col metodo degli elementi finiti (FEM) che viene qui implementato in un mezzo poroso tridimensionale a saturazione variabile, e che è quindi in grado di simulare sia la zona insatura (suoli superficiali) che quella satura (falde in pressione). Le non linearità che scaturiscono dall'accoppiamento e dalle leggi costitutive della permeabilità e del coefficiente di immagazzinamento nella zona insatura sono risolte con le tecniche di Picard e di Newton parziale. I modelli discreti finali linearizzati sono trattati col metodo dei gradienti coniugati opportunamente precondizionati per le matrici simmetriche di flusso (PGC) e quelle non simmetriche di trasporto (GMRES, Bi-CGSTAB, TFQMR). Le procedure descritte sono implementate nel codice FEM CODESA-3D (COupled variable DEnsity and SAturation) di cui è offerto un esempio applicativo.In the industrialized countries subsurface water resources are increasingly subject to regulations for protection from over-exploitation and from contamination arising from urban, industrial, nuclear, military, and agricultural activities. Prediction of the effects of anthropogenic impacts on water quantity and quality is an important part of proper aquifer management, and can be achieved through the use of mathematical models. As an example, seawater intrusion in coastal aquifers represents a serious environmental problem, especially in the countries of the Mediterranean basin, and can be simulated using coupled models of water flow and solute transport. Sophisticated groundwater models such as these can be accurately and effciently solved numerically via finite element discretizations of the three-dimensional porous medium. Both saturated (groundwater) and unsaturated (soil water) zones can be represented, and nonlinearities arising from storage-pressure head and conductivity-pressure head dependencies in the unsaturated zone and from coupling of the two equations can be resolved using Picard, Newton, or partial Newton methods. The resulting linearized systems of equations can be solved using a variety of preconditioned conjugate gradient-like methods applicable to symmetric and non-symmetric systems. The mathematical formulation and numerical procedures to be described form the basis of the CODESA-3D (COupled variable DEnsity and SAturation) model