Hydrogeophysical investigation of groundwater potential in the El Bawiti, Northern Bahariya Oasis, Western Desert, Egypt

The future development of agriculture, industry, and civil activity planned to be in the Western Desert. This strategy need to the groundwater resource. Vertical electrical soundings (VES) and electromagnetic (TEM) measurements conducted in the El Bawiti, northern Bahariya Oasis. The measurements give detailed information about the geometry of the different hydrogeological layers in the aquifer system and depth to them. A total of 22 VES and TEM were carried out within El Bawiti area. Thirty-one sub soil samples were collected from eight sites to determine the chemical characteristics and address the effects of lithogenic source and anthropogenic activity on them. The geoelectrical measurements and borehole information indicate the presence of five geoelectrical units, from top to base; the surface cover, sand and shale, upper aquifer (Nubian sandstone), sand and shale, and lower aquifer (Nubian sandstone). Surface cover was equally distributed in thickness and composed of dry sand, gravel, and clay deposits. The regional resistivity of the upper aquifer increased in the southwestern part and decline in the northern, eastern, southern, and western parts. The decline in the resistivity reflects the high water yields and potentiality, as well as low salinity. The resistivity of the lower aquifer increased due the northwestern part and the southwestern part. The information collected during this research provides valuable data for estimating the fresh- to brackish-water resources and for development of a groundwater management plan. The integrated analyses carried out represent a significant and cost-effective method for delineating the main aquifer in this area. In turn, future well locations can be placed with more confidence than before, in accordance with the evaluation of the potentiality of the groundwater aquifers in the area. The electrical conductivity of the soil ranges from 302 to 8,490 μS/cm, increases in the western and central-northern parts. It is attributed to the location from the salt-affected soils (playa), the relatively lower elevation units (depressions) and the position in landscape in the Oasis. Sodium adsorption ratio ranges from 0.44 to 11 and the exchangeable sodium ratio ranges from 0.11 to 5. The estimated magnesium hazard fluctuated below 50%. The statistical analyses were accomplished in soil chemistry and discussed.     

3D Crustal and Lithospheric Structures in the Southeastern Mediterranean and Northeastern Egypt

Crustal and lithospheric thicknesses of the southeastern Mediterranean Basin region were determined using 3D Bouguer and elevation data analysis. The model is based on the assumption of local isostatic equilibrium. The calculated regional and residual Bouguer anomaly maps were employed for highlighting both deep and shallow structures. Generally, the regional field in the area under study is considered to be mainly influenced by the density contrast between the crust and upper mantle. Use of the gravity and topographic data with earthquake focal depths has improved both the geometry and the density distribution in the 3-D calculated profiles. The oceanic-continental boundary, the basement relief, Moho depth and lithosphere-asthenosphere boundary maps were estimated. The results point to the occurrence of thick continental crust areas with a thickness of approximately 32 km in northern Egypt. Below the coastal regions, the thickness of crust decreases abruptly (transition zone). An inverse correlation between sediment and crustal thicknesses shows up from the study. Furthermore, our density model reveals the existence of a continental crustal zone below the Eratosthenes Seamount block. Nevertheless, the crustal type beneath the Levantine basin is typically oceanic; this is covered by sedimentary sequences more than 14 km thick. The modeled Moho map shows a depth of 28–30 km below Cyprus and a depth of 26–28 km beneath the south Florence Rise in the northern west. However, the Moho lies at a constant shallow depth of 22–24 km below the Levantine Basin, which indicates thinning of the crust beneath this region. The Moho map reveals also a maximum depth of about 33–35 km beneath both the northern Egypt and northern Sinai, both of which are of the continental crust. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thinning beneath south Cyprus (LAB ~90 km depth), followed by thickening beneath the Eratosthenes seamount, Florence Rise, Levantine Basin and reaching to maximum thickness below Cyprian Arc (LAB ~115–120 km depth), and further followed by thinning in the north African margin plate and north Sinai subplate (LAB ~90–95 km depth). According to our density model profiles, we find that almost all earthquakes in the study area occurred along the western and central segments of the Cyprian arc while they almost disappear along the eastern segment. The active subduction zone in the Cyprian Arc is associated with large negative anomalies due to its low velocity upper mantle zone, which might be an indication of a serpentinized mantle. This means that collision between Cyprus and the Eratosthenes Seamount block is marked by seismic activity. Additionally, this block is in the process of dynamically subsiding, breaking-up and being underthrusted beneath Cyprus to the north and thrusted onto the Levantine Basin to the south.     

Surface complexation modeling for predicting solid phase arsenic concentrations in the sediments of the Mississippi River Valley alluvial aquifer, Arkansas, USA

The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21-36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory.     

Flood prediction and mitigation in coastal tourism areas,a case study: Hurghada,Egypt

Flood mitigation involves the management and control of floodwater movement, such as redirecting flood runoff through the use of floodwalls and flood gates, rather than trying to prevent floods altogether. The prevention and mitigation of flooding can be studied on three levels: on individual properties, small communities, and whole towns or cities. The current study area is located in Hurghada on the Red Sea, which is considered an important area for coastal tourism. The study area is located at distance 7.50 km from El Gouna city along the Red Sea and east of Hurghada–Al Ismaileya road. The aim of this research is to derive the runoff flow paths across the study area and their flow magnitudes under different rainfall events of 10, 25, 50, and 100 year return periods in order to design the flood mitigation measures to protect such important areas. Field data (e.g., topographic data and rainfall intensities) were collected for the study area. The results indicated that the site is exposed to high flash flood risk and protection work is required. In order to protect the area from flood risks, locations of number of drainage channels and dams were selected and designed based on flood quantity and direction. The proposed mitigation system is capable of protecting this crucial area from flood risks and increases the national income from tourism. This study can be applied in different areas of Egypt and the world.     

Geology of the Early Devonian oolitic iron ore of the Gara Djebilet Field, Saharan Platform, Algeria

The oolitic iron ore of the Gara Djebilet field occurs within the Early Devonian sediments of the Tindouf Basin (Algerian Sahara), particularly in the Upper Djebilet Formation of Pragian age. Three large lenses form three individual deposits, extending E-W for about 60 km, namely Gara West, Gara Center and Gara East.The mineralization is interbedded with argillaceous to sandy sediments and it can be related to a barrier island palaeoenvironment, bordered by an inner lagoon or shallow embayment and an epicontinental sea. Trapped by Palaeozoic shoals, the oolitic sediments show a mineralogy marked mainly by magnetite, hematite, goethite, maghemite, chamosite (bavalite), siderite, apatite and quartz. Three paragenetic associations present a vertical distribution with a Lower non-magnetitic ore, a magnetitic ore and an Upper non-magnetitic ore.Three petrographical facies types have been defined: a cemented facies (FOC); a detrital facies (FOD); and a non-detrital facies (FOND).Chemical data for the whole field show a difference between the Lower non-magnetitic ore (Fe=54.6%), the Magnetitic ore (Fe=57.8%) and the Upper non-magnetitic ore (Fe=53%). The Magnetitic ore, which corresponds mainly to the workable ore (cutoff grade at 57%), has the following composition: SiO₂=4.9%, Al₂O₃=4.2%, Fe₂O₃=61.43%, FeO=19.2%, and P₂O₅=1.8%. The corresponding calculated economical ore reserves are 985×10⁶t, with 57.8% Fe.Regarding the genesis of the oolitic iron ore, a southern source is suggested for the iron, with deposition taking place in a quiet environment. There, the ooids developed by an intrasedimentary accretion mechanism around detrital grain within an iron-rich mud.The Gara Djebilet field is an important occurrence of the “North African Palaeozoic Ironstone Belt” extending from the Zemmour to Libya which also includes ironstones of Ordovician, Silurian and Devonian age.     

Estimation of dielectric permittivity,water content,and porosity for environmental engineering and hydrogeological studies using ground penetrating radar,a short review

Ground penetrating radar is a noninvasive geophysical technique that can be used to infer subsurface geological, geotechnical, and petrophysical attributes. For water contamination studies, ultimate target, i.e., contaminant flow, is demarcated with the help of dielectric permittivity, water content, and porosity. The dielectric permittivity facilitates to evaluate water content; whereas the dielectric permittivity can be estimated by using the interval velocity, and porosity can be estimated by using the information of water content and dielectric permittivity. All these parameters are interlinked. This paper describes different empirical and mixing relationships to calculate approximately these parameters and their utilization in predicting the hydrogeological model of the area.     

Estimation of frequency dependent coda wave attenuation structure at the vicinity of Cairo Metropolitan Area

Estimation of seismic wave attenuation in the shallow crust in terms of coda wave Q structure previously investigated in the vicinity of Cairo Metropolitan Area was improved using seismograms of local earthquakes recorded by the Egyptian National Seismic Network. The seismic wave attenuation was measured from the time decay of coda wave amplitudes on narrow bandpass filtered seismograms based on the single scattering theory. The frequency bands of interest are from 1.5 to 18 Hz. In general, the values obtained for various events recorded at El-Fayoum and Wadi Hagul stations are very similar for all frequency bands. A regional attenuation law Q _c = 85.66 f ^0.79 was obtained.     

岩芯尺度的宽频介电常数频谱实验室测量设备的误差分析及其在物质测量中的应用(英文)

宽频介电常数频谱测井技术最近被引进石油工业.这种新技术区别于传统介电常数测井技术在于多频率频谱的测定和利用.高频谱端包含介质油水饱和度信息,而低频谱端对介质中孔隙结构和水的分布形态很敏感.这种新技术可以有效地被应用于比如超淡水介质或者超黏度重油等对于常规测井来说是很困难的测量环境,而且受介质水中的含盐度影响很小.随着井下测井仪器的投入使用,相应的实验室岩芯测定设备和方法就变得重要起来.因为实验室环境相对较为稳定和可控,实验室岩芯测量结果是对井下测量的很好地验证和校订.文献中记载了许多非破坏性的实验室介电常数的测量设备,然而这些设备的共同局限性是它们对岩芯尺寸和岩芯样本的要求和限制,一般要求粉末状岩芯或者一厘米左右的小柱状岩芯.在碳酸盐介质中,非均匀性和各项异性非常普遍,小的岩芯样本能否涵盖井下设备测量尺度(1.5英寸)的特性很值得商榷.本文中介绍了一种最新设计的实验室大直径宽频介电常数测量设备.这个设备可以直接测量石油工业传统的1.5英寸岩芯样本,测量是非毁坏性的,也就是测量后的岩芯样本可以直接用于其它实验室测量设备,比如电阻率测量或核磁共振测量等.大量重复性试验测得的介电常数色散频谱的精确度对于低损耗介质在2%以内而对于高损耗介质在对孔隙度和含盐度校正以后精确度在3%.文中详细介绍了测量设备所使用的反演程序的算法模型,以及反演误差的算法.反演最后的误差可以用来做数据质量的评定.该测量装置被用于许多物质的测定.测定物质的数据库中合成石英(fused quartz),Teflon,合成陶瓷以及单晶硅的介电常数值可以在文献中找到.该设备的测量结果与文献参考值相符合,说明了该设备测量结果的可靠性.该设备还测量了矿物晶体碳酸钙,晶体白云石以及晶体硬石膏的介电常数,这是常见的碳酸盐介质的主要成分.这些测量给出了碳酸盐介质的边界成分区域值作为参考.该设备测量的两个单晶硅柱状样本的介电常数频谱特性发现退火会改变晶体的结构提高强度,同时会改变介质介电常数的特性.同时矿物晶体碳酸钙测量值高于粉末状测量结果也说明晶体结构可能会导致介电常数测量的不同.该设备具有1.5英寸的大尺度,因此具有和井下设备相仿的测量范围,因而不受介质水平各项异性的影响.但另一方面,该设备仍可以研究垂直各项异性.垂直各项异性的主要原因可能是化学成分不同,孔隙结构不对称或者温度对水分布的影响等等.在对岩石地面露头采样的研究中,宽频介电常数频谱实验室设备检测出了岩芯垂直各项异性,通过对比核磁共振一维孔隙度剖面结构发现总孔隙度不均衡以及分布不对称为该各项异性的主要来源,并且被CT图像所证实.     

Lithostratigraphy,deformation history,and tectonic evolution of the basement rocks,Republic of Yemen: an overview

Basement rocks of presumed Precambrian age, in Yemen Republic (105,000 km²), are exposed in the northwestern and southeastern parts of the country. The basement rocks of southern Saudi Arabia and northern parts of Yemen are almost continuous and similar in the lithostratigraphic succession. In spite of the presence of such common basic characteristics for each, there are slight differences of local structural framework and major tectonic events. The structural complexity, great variety of rock units and types, multi-intrusive environments, and multiplicity of metamorphic events in the study basement rocks make the main target of lithostratigraphic analyses, in particular, daunting in the southern Arabian Shield. As reported here, accepting that the southern shield consists of five terranes and suture zones requires a limitation of such tectonic modifications. This led to the renaming of certain formations and groups and the revision of the lithostratigraphic successions for some regions. As a result, new lithostratigraphic relationships and names as well as tectonic events are proposed. Based on field and space image data, the basement rocks in Yemen exhibit at least six major phases of deformation (D1 to D6) including intensive brittle and ductile deformations that trend NW–SE and NNE–SSW (in major). Neoarchean rocks are well developed and restricted in the southeastern exposures (Al Bayda, Al Mahfid, and Al Mukalla terranes), whereas the final Pan-African cratonization of several rock units is widespread on all terranes, in which the major tectonic events and deformation history were concentrated during pre-Pan-African and early to late Pan-African orogenies. A correlation and evolution of the Precambrian rocks in Saudi Arabia and Egypt are taken into consideration.