Effects of Aquifer Bed Slope and Sea Level on Saltwater Intrusion in Coastal Aquifers

The quality of groundwater resources in coastal aquifers is affected by saltwater intrusion. Over-abstraction of groundwater and seawater level rise due to climate change accelerate the intrusion process. This paper investigates the effects of aquifer bed slope and seaside slope on saltwater intrusion. The possible impacts of increasing seawater head due to sea level rise and decreasing groundwater level due to over-pumping and reduction in recharge are also investigated. A numerical model (SEAWAT) is applied to well-known Henry problem to assess the movement of the dispersion zone under different settings of bed and seaside slopes. The results showed that increasing seaside slope increased the intrusion of saltwater by 53.2% and 117% for slopes of 1:1 and 2:1, respectively. Increasing the bed slope toward the land decreased the intrusion length by 2% and 4.8%, respectively. On the other hand, increasing the bed slope toward the seaside increased the intrusion length by 3.6% and 6.4% for bed slopes of 20:1 and 10:1, respectively. The impacts of reducing the groundwater level at the land side and increasing the seawater level at the shoreline by 5% and 10% considering different slopes are studied. The intrusion length increased under both conditions. Unlike Henry problem, the current investigation considers inclined beds and sea boundaries and, hence, provides a better representation of the field conditions.

Fluid Interfaces during Viscous-Dominated Primary Drainage in 2D Micromodels Using Pore-Scale SPH Simulations

We perform pore-scale resolved direct numerical simulations of immiscible two-phase flow in porous media to study the evolution of fluid interfaces. Using a Smoothed-Particle Hydrodynamics approach, we simulate saturation-controlled primary drainage in heterogeneous, partially wettable 2D porous microstructures. While imaging the evolution of fluid interfaces near capillary equilibrium becomes more feasible as fast X-ray tomography techniques mature, imaging methods with suitable temporal resolution for viscous-dominated flow have only recently emerged. In this work, we study viscous fingering and stable displacement processes. During viscous fingering, pore-scale flow fields are reminiscent of Bretherton annular flow, that is, the less viscous phase percolates through the core of a pore-throat forming a hydrodynamic wetting film. Even in simple microstructures wetting films have major impact on the evolution of fluid interfacial area and are observed to give rise to nonnegligible interfacial viscous coupling. Although macroscopically appearing flat, saturation fronts during stable displacement extend over the length of the capillary dispersion zone. While far from the dispersion zone fluid permeation obeys Darcy’s law, the interplay of viscous and capillary forces is found to render fluid flow within complex. Here we show that the characteristic length scale of the capillary dispersion zone increases with the heterogeneity of the microstructure.

Regional differences in concentration of population in Serbia

For understanding the demographic, economic and social development of the researched area, studying the distribution and concentration of population has a great importance. Spatial concentration of population of Serbia is a result of the rapid economic transformation after the Second World War. The intensive migration flows from villages to cities in the 1960s, on the first place, accompanied by a negative trend of natural population change, on the second, led to the redistribution and creation of regional and interregional differences in spatial distribution of population. By applying the chosen measure, concentration index, on the smallest level of the territorial structure of Serbia (settlements), the degree of population concentration is precisely determined and presented. Based on these results, the regional differences in concentration of population in Serbia are explained, which was the aim of this paper. Analyzing the results in the study area, four zones were distinguished: deconcentration i.e. the zone of dispersion, the zone of moderate, the zone of high and of extremely high concentration. A comparative study of a chosen indicator pointed to a certain territorial changes in the distribution of population for the observed period (from 1961 to 2011). At the interregional level, the most intensive spread of dispersion zone is noticed in the regions of South and East Serbia, Sumadija and Western Serbia and Vojvodina, while the highest average value of a given indicator, which records a constant increase as well, is established in the Belgrade region. Micro-level data showed concentration trend in 11.3% of settlements, but population dispersion in 88.7% of settlements. The dispersion zone covers the largest part of Serbia (84.2% of all rural settlements) and the directions of dispersion are clearly noticeable moving from the state border to the interior of the territory, and then from larger regional and municipal centres to the periphery. However, the zone of moderate concentration has decreased in spatial and demographic terms almost three times. Intensified processes of concentration led to the creation of the zone with extremely high concentration of population (41.4% of the total population of Serbia), but it includes only 1.7% of settlements. Areas with a high population concentration are limited to the industrialized and urbanized settlements with favourable traffic-geographical position on the axes of the state development (corridors). The application of concentration index to the settlement level of the Republic of Serbia outlined the differentiation of space, with a significant spatial-demographic imbalance, resulting in uneven distribution and territorial and demographic polarization.

On the Load Dependence of Micro-Hardness Measurements: Analysis of Data by Different Models and Evaluation of Measurement Errors

The influence of applied loads between 0.09807 N and 0.9807 N on measured values of micro-hardness was evaluated by Meyer’s index n, proportional specimen resistance model (PSR) and Hays – Kendall methods, Total Dispersion Zone and Analysis of Variance (ANOVA). The measurement was repeated 6 times using the same hardness reference block with standard hardness Hc= 327 HV0.05 as a sample. The influence of the load on the measured value of micro-hardness is statistically significant, and the relationship between applied load and micro-hardness manifests reverse indentation size effect (ISE) for most of “measurements”. The high value of the uncertainty of results can affect the existence and nature of ISE, especially at low loads.

THE AUTOMATIC TESTERS IN MICROHARDNESS MEASUREMENT AND ISE EFFECT

<p>The measurement of micro-hardness with applied loads 0.09807 N, 0.24518 N, 0.49035 N and 0.9807 N has been carried out by three automatic and one manually-operated micro-hardness testers. The certified reference material (CRM) was the tested sample. Each operator obtained readings of the tester which she/he normally operates. The measurement was repeated after thirty months. The influence of the testers and their stability, as well as applied load on the measured values of the micro-hardness and the indentation size phenomenon (ISE), were evaluated. The parametric and non-parametric tests, Analysis of Variance (ANOVA), Z-score and Total Dispersion Zone were used for the evaluation of the statistical significance of obtained factors. The ISE was evaluated using Meyer’s and Proportional Specimen Resistance model and also by Hays – Kendall approach. The variability of measured values of the micro-hardness values and parameters ISE is high despite the use of automatic hardness testers with practically excluding the impact of the operator. The results are affected by testers and by used testers and by applied loads. The measurement system can not be considered to be stable.</p>

The dispersion zone between fluids with different density and viscosity in a heterogeneous porous medium

A shock front in the concentration between two miscible fluids flowing through a porous medium becomes dispersed owing to the heterogeneous structure of the porous medium. If the fluids have equal viscosity and density and the heterogeneity of the porous medium is statistically homogeneous, the length of the dispersion zone between the fluids is known to increase as (βX)½, where β is the dispersivity and X is the average displacement distance. At present the dispersivity is considered to be a property of only the porous medium. For the case where the fluids differ in density and/or in viscosity we have investigated the effect of the dynamics of the fluid flow on the magnitude of the dispersivity β and on the validity of the X½ dependence of the dispersion zone's length. First, we measured the dispersivity in a 1.8 m long sandstone core with brine displacing water and with gas displacing oil. The measurements demonstrate that the dispersivity does indeed depend on the displacement velocity. Second, we monitored the expansion of the dispersion zone using detailed numerical simulations of the flow in a porous medium with statistically homogeneous heterogeneity. We found that the dispersion zone does grow as X½ in the presence of a density contrast and a viscosity contrast, in spite of the nonlinearity of the governing equations. Third, we quantified the magnitude of the dispersivity by means of a random-walk model and tested the model against the experiments and the numerical simulations. Experiments, simulations and the model show that the dispersivity is strongly dependent on the displacement velocity in the conditionally stable flow regime. They also show that a nearly non-dispersive development of the shock front between the fluids occurs when gravity segregation dominates the dispersive effect of the porous medium. Even a very small difference in density, such as that between water and brine, can suppress the dispersivity significantly.