Search

Published version made available following 6 months embargo from date of publication (13 May 2016) in accordance with publisher copyright., Rivers in arid and semiarid regions often traverse saline aquifers, creating buoyant freshwater lenses in the adjoining riparian and floodplain zones. The occurrence of freshwater lenses where the river is otherwise gaining saline groundwater appears counterintuitive, given that both hydraulic and density forces act toward the river. In this paper, an analytical solution is presented that defines the extent of a stable, sharp-interface terrestrial freshwater lens (in cross section) in a riverine environment that otherwise contains saline groundwater moving toward the river. The method is analogous to the situation of an island freshwater lens, except in the riverine setting, the saltwater is mobile and the lens is assumed to be stagnant. The solution characterizes the primary controlling factors of riverine freshwater lenses, which are larger for situations involving lower hydraulic conductivities and rates of saltwater discharge to the river. Deeper aquifers, more transmissive riverbeds, and larger freshwater-saltwater density differences produce more extensive lenses. The analytical solution predicts the parameter combinations that preclude the occurrence of freshwater lenses. The utility of the solution as a screening method to predict the occurrence of terrestrial freshwater lenses is demonstrated by application to parameter ranges typical of the South Australian portion of the River Murray, where freshwater lenses occur in only a portion of the neighboring floodplains. Despite assumptions of equilibrium conditions and a sharp freshwater-saltwater interface, the solution for predicting the occurrence of riverine freshwater lenses presented in this study has immediate relevance to the management of floodplains in which freshwater lenses are integral to biophysical conditions.

Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater. This study presents the development of a conceptual and numerical model for the coastal aquifer of Karareis region (Karaburun Peninsula) in the western part of Turkey. The study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers. The SEAWAT model is used in this study to solve the density-dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months. The model was calibrated using the average values of a 1-year dataset and further verified by the average values of another year. Five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years. The result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under “increased pumping” scenario, while a slight change in water level and TDS concentrations was observed in “climate change” scenario. Results also revealed that a reduction in the pumping rate from Karareis wells will be necessary to protect fresh groundwater from contamination by seawater., Scientific and Technological Research Council of Turkey (TUBITAK 113Y042)

In this paper, semi-analytical expressions of the effective hydraulic conductivity (\(K^{E})\) and macrodispersivity (\(\alpha ^{E})\) for 3D steady-state density-dependent groundwater flow are derived using a stationary spectral method. Based on the derived expressions, we present the dependence of \(K^{E}\) and \(\alpha ^{E}\) on the density of fluid under different dispersivity and spatial correlation scale of hydraulic conductivity. The results show that the horizontal \(K^{E}\) and \(\alpha ^{E}\) are not affected by density-induced flow. However, due to gravitational instability of the fluid induced by density contrasts, both vertical \(K^{E}\) and \(\alpha ^{E}\) are found to be reduced slightly when the density factor (\(\gamma \)) is less than 0.01, whereas significant decreases occur when \(\gamma \) exceeds 0.01. Of note, the variation of \(K^{E}\) and \(\alpha ^{E}\) is more significant when local dispersivity is small and the correlation scale of hydraulic conductivity is large.

Recent studies of marsh hydraulics have focused on tide-induced pore-water circulation as the main drive for solute transport in the marsh soil and exchange with coastal water. Our study revealed another important mechanism provided by unstable fingering flow, which largely modified solute transport paths. In the marsh interior, downward penetration of salt fingers forced ambient pore-water and solute plumes to move upward and exit the marsh soil through marsh platform at relatively high concentrations, up to two orders of magnitude higher than exit solute concentrations at the tidal creek bed. The mixing of solute with ambient pore water in the marsh interior was intensified greatly by fingering flow. A critical distance to the creek was determined based on a field-scale model simulation to distinguish tidal circulation-dominated and fingering flow-dominated solute transport zones. The new transport mechanism has implications for understanding the fate of solutes in particularly salt marshes of low creek densities.

Seawater intrusion is identified as a critical issue that needs to be addressed in coastal hydrology, due its irreversible effect on the water quality of coastal freshwater aquifers. Due to the density differences in seawater and freshwater, the density dependent flow phenomenon is dominant seawater intrusion. Three dimensional numerical model is necessary to address the complex hydro-geological formations. Therefore, it is important to develop a three dimensional simulation model to understand the density dependent solute transport process taking place in the seawater intrusion problem. The model developed in this study is based on the transition zone approach which couples the groundwater flow and mass transport equation to solve the density dependent flow. The finite difference method is used as the numerical method to solve the partial difference equations of groundwater flow and solute transport. The method of characteristic is applied to solve the advection term of mass transport equation. Therefore, in this paper, a valued attempt has been taken to simulate the seawater intrusion in the three dimensional point of view under the density dependent flow effect. Motooka area of Fukuoka Prefecture Japan which is a coastal area is selected as an application area for the developed model to emphasize seawater intrusion and justify the model. This area is affected by seawater intrusion and so far numerical study of seawater intrusion under the density dependent flow concept has not performed.

Thesis (Master)--Izmir Institute of Technology, Environmental Engineering, Izmir, 2016, Includes bibliographical references (leaves: 85-88), Text in English; Abstract: Turkish and English, xv, 88 leaves, Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could easily be influenced by seawater. This study presents the development of conceptual and numerical model for the coastal aquifer of Karareis region in the western part of Turkey. The study also presents the interpretation and the analysis of the groundwater levels recorded by groundwater data loggers. Groundwater pumping from Karareis aquifer has increased significantly during the summer period to meet the agriculture and domestic water demands. Levels of groundwater were measured at nine locations in Karareis region; also water samples were collected and analyzed for some parameters. For this study SEAWAT code is used to solve the numerical model for the coupled density dependent flow system. The model was calibrated using the average of one-year dataset of collected groundwater levels. Model validation was handled using the average of groundwater levels measured over more one year. Five scenarios were tested to understand the effects of pumping and climate change on groundwater levels and seawater intrusion in the next ten years. The result of analysis demonstrated a high concentration of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion will extent about 420 m towards the land in the next ten years of increased pumping scenario, while a little change in water level and TDS concentration was recognized in climate change scenario. Results also showed that reducing the pumping from Karareis wells will be necessary to protect the freshwater from contamination by seawater., Deniz suyu girişimi, özellikle deniz tarafından çevrelenen kıyı akiferlerde, tatlı su kaynaklarını tehdit eden en önemli problemlerden biridir. Bu çalışma kapsamında, Türkiye’nin batısında bulunan Karareis bölgesindeki kıyı akiferi için kavramsal ve numerik modelleme çalışmaları yapılmış olup ayrıca spesifik olarak deniz suyu girişimini dikkate alan değişken yoğunluklu yeraltı suyu akım modelleme çalışması sunulmuştur. Bununla beraber akiferdeki yeraltı suyu seviyelerinin ölçümü ve tahminine yönelik çalışmalar da bu tez kapsamında değerlendirilmiştir. Yapılan çalışmada, Karareis kıyı akiferinde yazın tarım ve günlük kullanıma bağlı olarak yeraltı suyu çekimi belirgin olarak artmakta olduğu saptanmıştır. Bölgenin hidrolojik ve hidrojeolojik parametrelerinin tayini için bölgede dokuz farklı lokasyonda yer alan sondaj kuyularında yeraltı suyu seviyesi ölçülmüştür. Kıyı akiferlerindeki deniz suyu girişimi etkisi altındaki yeraltı suyu akımları SEAWAT isimli matematiksel model sürümü ile belirlenmiştir. Model kalibrasyonu ve test için iki yıl boyunca kuyulardan düzenli ölçülen yeraltı suyu seviye verilerinden yararlanılmıştır. Gelecek on yıl için pompaj kuyularından su çekiminin, iklim değişiminin ve deniz suyu girişiminin yeraltı suyu seviyesine etkisini anlamak için beş senaryo test edilmiştir. Yapılan incelemelerde, çalışma alanının özellikle kıyı kesimlerinde, yüksek klorür konsantrasyonu ve elektriksel iletkenlik değerlerinin gözlendiği, deniz suyu girişiminin gelecek on yıllık artan su çekimi senaryosu kapsamında değerlendirilip modellenmesi sonucunda, bölgenin iç kesimlerine doğru 420 metreye kadar tuzlu su girişiminin ilerleyebileceği görülmüştür. Senaryo kapsamında yeraltı suyu seviyesinin veya TDS miktarının minimal düzeyde değişeceği ayrıca ortaya konulmuştur. Son olarak, Karareis bölgesi akiferinde yeraltı suyu çekiminin planlanması ile deniz suyu girişiminin tatlı suyu kaynaklarına etkisi azaltılmış olacak, bölgenin yeraltı suyu kaynaklarının niteliği ve niceliği korunmuş olacaktır., TUBITAK

Closed-form solutions are derived for steady state density-dependent fluid flow and solute transport problems in a one-dimensional vertical soil column. Transport mechanisms considered are advection, molecular diffusion, and velocity-dependent dispersion. Solutions can be obtained for a wide variety of cases. Characteristics of density-dependent solutions, including effects of variations in density and the thickness of transition zones, are investigated for a simple case. Unique features not found in density-independent solutions are observed. Nonuniform concentration profiles with vanishing density effects are also identified.

CO2 injection and storage in deep saline aquifers involves many coupled processes, including multiphase flow, heat and mass transport, rock deformation and mineral precipitation and dissolution. Coupling is especially critical in carbonate aquifers, where minerals will tend to dissolve in response to the dissolution of CO2 into the brine. The resulting neutralization will drive further dissolution of both CO2 and calcite. This suggests that large cavities may be formed and that proper simulation may require full coupling of reactive transport and multiphase flow. We show that solving the latter may suffice whenever two requirements are met: (1) all reactions can be assumed to occur in equilibrium and (2) the chemical system can be calculated as a function of the state variables of the multiphase flow model (i.e., liquid and gas pressure, and temperature). We redefine the components of multiphase flow codes (traditionally, water and CO2), so that they are conservative for all reactions of the chemical system. This requires modifying the traditional constitutive relationships of the multiphase flow codes, but yields the concentrations of all species and all reaction rates by simply performing speciation and mass balance calculations at the end of each time step. We applied this method to the H2O-CO2-Na-Cl-CaCO3 system, so as to model CO2 injection into a carbonate aquifer containing brine. Results were very similar to those obtained with traditional formulations, which implies that full coupling of reactive transport and multi-phase flow is not really needed for this kind of systems, but the resulting simplifications may make it advisable even for cases where the above requirements are not met. Regarding the behavior of carbonate rocks, we find that porosity development near the injection well is small because of the low solubility of calcite. Moreover, dissolution concentrates at the front of the advancing CO2 plume because the brine below the plume tends to reach high CO2 concentrations quite rapidly. We conclude that carbonate dissolution needs not to be feared. © 2013 Elsevier Ltd., This work was supported by the European Commission through the MUSTANG and the PANACEA projects (Seventh Framework Programme FP7/2007-2013 under Grant agreements nos. 227286 and 282900, respectively). We also want to acknowledge the financial support received from Instituto para la Diversificación y Ahorro de la Energía (IDAE, Spanish Government) and by the European Union through the “European Energy Programme for Recovery” and the Compostilla OXYCFB300 project.

In this study, a management model is presented for planning groundwater development in costal deltas with paleo channels. It is demonstrated that paleo channels are the best locations for locating the wells for large-scale pumping. Groundwater flow in these aquifers is simulated using a three-dimensional (3-D) density-dependent flow and transport model SEAWAT, which is suitable for a coastal and deltaic environment. A simulation-optimization model is used to determine the optimal locations and pumpages for groundwater development for a group of production wells, while limiting the salinity below desired levels. The mixed integer problem is solved using the Simulated Annealing algorithm and the SEAWAT simulation model. A trained Artificial Neural Network (ANN) is used as the virtual SEAWAT model to perform the simulations, in order to reduce the computational burden for application of the model on desktop computers. The applicability of the model is demonstrated on a hypothetical, but near-real, delta system. ? Springer Science + Business Media, Inc. 2005.

The concepts of homogenization theory are employed to derive a macro-scale brine transport equation for micro-heterogeneous porous medium of layered structure under assumptions of validity of classical Darcy's law and Fick's law at the local scale. Derived macro-scale model is analogous to the so-called phase field equations. The obtained results are verified with direct numerical experiment. © 2004 Elsevier Ltd. All rights reserved.

A numerical modelling approach, used for the analysis of stable brine displacement results, is described. The purpose of the analysis is to evaluate recent theoretical advances in modelling of density-dependent flow and transport. The data analysis involved two stages. A model based on the classical density-dependent transport theory was developed for the first stage of the analysis. Transport parameters were obtained using a sequential fitting method. The numerical model was then modified to incorporate a non-linear dispersion theory that had been recently proposed for high concentration displacements. This modified model was used to reanalyse the results obtained from the brine displacement experiments. Overall, the results of the analysis indicated that a modified transport model was required to adequately describe stable brine displacements.