Characterisation, classification, and evaluation of some groundwater samples in the Mostaganem area of northwestern Algeria

Mostaganem City, located in the northwestern part of Algeria, has grown and has been urbanized rapidly. The city and surrounding areas depend heavily on groundwater as a resource for drinking water, as well as domestic, industrial, and agricultural uses. Understanding the groundwater chemistry provides insight into the interactions of water with the environment and contributes to better resource management. In total, 12 groundwater samples from wells in Mostaganem City have been analyzed for major physical–chemical elements and metals. The results show that the waters have pH values ranging between 7.1 and 8.1, salinity between 226 and 1,073 mg/L, and nitrate concentrations between 15 and 47.7 mg/L. The high concentration of nitrates is explained by the utilization of chemical fertilizers in agriculture. Almost all samples are of type Na–SO₄ and Na–HCO₃, and the trace metal concentrations are within the admissible standard ranges. We conclude that the groundwater in Mostaganem may safely be used for drinking, domestic, agricultural, and industrial purposes.     

A Coastal Aquifer Study Using Magnetotelluric and Gravity Methods in Abo Zenema, Egypt

Magnetotelluric (MT) soundings and gravity methods were employed to study the deep freshwater aquifer in the area north of Abo Zenema city on the eastern side of the Gulf of Suez, Egypt. Seven MT sites and 48 gravity stations were surveyed along northeast–southwest profiles as close as possible to a line perpendicular to the coast of the Gulf of Suez. The MT survey was conducted using high and low frequencies to investigate shallow and deep areas, respectively. One-dimensional inversion was conducted using a heuristic inversion scheme of the Bostick algorithm. The MT data were also inverted with a 2-D smooth model inversion routine using the nonlinear conjugate gradient method to infer variation in vertical and lateral resistivity inside the Earth. A 100-Ohm-m homogeneous half-space initial model was used to invert the TE mode data only. Then, the inverted model obtained from the TE mode data was used as an initial model for inversion of the TM mode data. The inverted model thus obtained from the TM mode data inversion was used as an initial model for the inversion of the joint TE and TM responses. Two-dimensional (2-D) forward modeling of the gravity data was conducted using the 2-D polygon method of Talwani’s algorithm for an arbitrarily shaped body and was based on the subsurface information from the MT survey and the available information about the geological structure of the study area. This method enabled us to obtain the basement structure of the coastal aquifer in the study area. The results from the analysis and the interpretation of MT and gravity data were used to detect and delineate the groundwater coastal aquifer in the study area.     

Statistical improvement in detection level of gravitational microlensing events from their light curves

In astronomy,the brightness of a source is typically expressed in terms of magnitude.Conventionally,the magnitude is defined by the logarithm of received flux.This relationship is known as the Pogson formula.For received flux with a small signal to noise ratio(S/N),however,the formula gives a large magnitude error.We investigate whether the use of Inverse Hyperbolic Sine function(hereafter referred to as the Asinh magnitude)in the modified formulae could allow for an alternative calculation of magnitudes for small S/N flux,and whether the new approach is better for representing the brightness of that region.We study the possibility of increasing the detection level of gravitational microlensing using 40 selected microlensing light curves from the 2013 and 2014 seasons and by using the Asinh magnitude.Photometric data of the selected events are obtained from the Optical Gravitational Lensing Experiment(OGLE).We found that utilization of the Asinh magnitude makes the events brighter compared to using the logarithmic magnitude,with an average of about 3.42×10~(-2)magnitude and an average in the difference of error between the logarithmic and the Asinh magnitude of about 2.21×10(-2)magnitude.The microlensing events OB140847 and OB140885 are found to have the largest difference values among the selected events.Using a Gaussian fit to find the peak for OB140847 and OB140885,we conclude statistically that the Asinh magnitude gives better mean squared values of the regression and narrower residual histograms than the Pogson magnitude.Based on these results,we also attempt to propose a limit in magnitude value for which use of the Asinh magnitude is optimal with small S/N data.     

Vulnerability evaluation of the strategic buildings in Algiers (Algeria): a methodology

Algeria is a country with a high seismic activity. During the last decade, many destructive earthquakes occurred, particularly in the northern part, causing enormous losses in human lives, buildings, and equipments. In order to reduce this risk in the capital and avoid serious damages to the strategic existing buildings, the government decided to invest in seismic upgrade, strengthening, and retrofitting of these buildings. To do so, seismic vulnerability study of this category of buildings has been considered. Structural analysis is performed based on a site investigation (inspection of the building, collecting data, materials characteristics, general conditions of the building, etc.) and existing drawings (architectural plans, structural design, etc.). The aim of these seismic vulnerability studies is to develop guidelines and a methodology for rehabilitation of existing buildings. This paper presents the methodology followed in our study and summarizes the vulnerability assessment and strengthening of one of the strategic buildings according to the new Algerian Seismic Design Code RPA 99/version 2003. As a direct application of this methodology, both static equivalent method and nonlinear dynamic analysis are performed and presented in this paper.     

The crustal structure of the Sahel Basin (eastern Tunisia) determined from gravity and geothermal gradients: implications for petroleum exploration

An analysis of Bouguer gravity anomaly data and geothermal gradient data obtained from bottom hole and drill stem tests temperature is used to determine the crustal structure of the Sahel Basin in eastern Tunisia and its role in the maturation and location of the large number of oil and gas fields in the region. The regional Bouguer gravity anomaly field is dominated by gradual increase in values from the northwest to southeast and is may be caused by crustal thinning as revealed by regional seismic studies. In addition, higher geothermal gradients in the same region as the Bouguer gravity anomaly maximum add an additional constraint for the existence of crustal thinning in the region. A detailed analysis of the Bouguer gravity anomaly data was performed by both upward continuation and horizontal gradients. These two techniques were combined to show that the study area consists of two structural regions: (1) the North–South Axis (NOSA)–Zeramedine region which is characterized by northwest-dipping, northeast-striking faults, thicker crust (30–31 km) and low geothermal gradients, and (2) the Mahres–Kerkennah region which is characterized by vertical, northwest-striking faults, thinner crust (28–29 km) and higher geothermal gradients. The correlation of a variety of features includes mapped and geophysically defined faults, volcanic rocks, a thinned crust and high geothermal gradients within the same location as known oil and gas fields indicate that the faults are a major factor in the location of these petroleum accumulations.     

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer,Sfax, southeastern Tunisia

Major element concentrations and stable (δ¹⁸O and δ²H) and radiogenic (³H and ¹⁴C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ¹⁸O and δ²H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO₄ and Ca-Na-Cl-SO₄. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ¹⁸O and δ²H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

     

Impact of permafrost development on groundwater flow patterns: a numerical study considering freezing cycles on a two-dimensional vertical cut through a generic river-plain system

The impact of glaciation cycles on groundwater flow was studied within the framework of nuclear waste storage in underground geological formations. The eastern section of the Paris Basin (a layered aquifer with impervious/pervious alternations) in France was considered for the last 120 ka. Cold periods corresponded with arid climates. The issue of talik development below water bodies was addressed. These unfrozen zones can maintain open pathways for aquifer recharge. Transient thermal evolution was simulated on a small-scale generic unit of the landscape including a “river” and “plain”. Coupled thermo-hydraulic modeling and simplified conductive heat transfer were considered for a broad range of scenarios. The results showed that when considering the current limited river dimensions and purely conductive heat transfer, taliks are expected to close within a few centuries. However, including coupled advection for flows from the river to the plain (probably pertinent for the eastern Paris Basin aquifer recharge zones) strongly delays talik closure (millennium scale). The impact on regional underground flows is expected to vary from a complete stop of recharge to a reduced recharge, corresponding to the talik zones. Consequences for future modeling approaches of the Paris Basin are discussed.     

Coupled atmosphere–ocean data assimilation experiments with a low-order model and CMIP5 model data

Climate Dynamics - Coupled atmosphere–ocean data assimilation (DA) experiments are performed for estimating the Atlantic meridional overturning circulation (AMOC). Recovery of the AMOC with...