Aeromagnetic signature analysis of Gasus area and its surrounding,central eastern desert,Egypt

This study presents analysis and interpretation of aeromagnetic data to construct subsurface structure maps and determine the depths to magnetic basement. Subsequent analysis steps are applied to the total magnetic intensity (TMI) data. These steps include Reduction to the Pole (RTP) map that was derived from the TMI map then subjected to spectral frequency analysis to isolate RTP map into high and low frequencies and determine pseudo-depth for each map from power spectrum in which there were two main average levels (interfaces) at depth 1.3 and 0.7 km for the deep-seated and near-surface magnetic structures, respectively. 3D Euler deconvolution technique is applied to calculate the depth to the magnetic contacts; the results show clustering of solutions, the shallow solutions are related to the outcrops less than 80 m from flight level, and the solutions which are related to sedimentary cover locations (Um al-Huweitat, Wasif, and Mohamed Rabah basins) are ranged between 200 and to more than 1100 m. Moreover, anomaly enhancement techniques such as tilt derivative (TD), horizontal tilt derivative (TDX), and source edge detect (SED) are applied to enhance shallow features, and determining structure element boundary for both shallow- and deep-seated anomalies and revealing possible faults such as 2D forward modeling are applied to selected profiles to adjust the interpreted structures and map the boundaries and basement relief of the three basins (Mohammed Rabah, Wasif, and Um al-Huweitat). The analysis shows that the study area is affected with network of dip–slip faults due to high shearing and compression stress which formed grabens and horsts at different depth levels in the study area. The trends of predominant faults related to deep-seated structures are NW–SE with depths ranged between 1 and 1.4 km and in regard to the shallow-seated structure, the predominant fault trends are NW–SE, NNW–SSE, and NNE–SSW with depths ranged between 0.3 and 0.8 km.     

Impacts of karst phenomena on engineering properties of limestone foundation bed,Ar Riyadh,Saudi Arabia

Evaluation of mechanical and petrophysical properties of the karst limestone became essential to avoid future risks in the construction of new urban cities built on limestones. Therefore, this study aims to evaluate the impact of karsts phenomena on engineering properties of limestone foundation bed at Ar Riyadh in Saudi Arabia. Three hundred core plugs were obtained by rotary drilling at depths ranging from the ground surface to 20 m collected from 24 boreholes in two sites: (1) karst limestone (KL) at Al Aziziyah district and (2) massive hard limestone (HL) at Hittin district in Ar Riyadh city, Saudi Arabia. Petrographic, SEM, EDX, and XRD analyses are used to identify the mineralogical composition and microstructures of limestone samples. The petrophysical properties included the ovendry density, P-wave, and porosity where the mechanical properties covered the uniaxial compressive strength (UCS), point load strength index (PLI), and rock quality designation (RQD) for the karst and hard limestone samples. KL is characterized by 17.11% total porosity, 14.71% water absorption, 32.1 MPa UCS, 1.70 g/cm³ ovendry density (γ dry), 51% weathered RQD, 5.49 MPa medium shear strength, and low modulus of deformation of the plate loading test. HL showed 11.63% total porosity, 9.45% water absorption 43.1 MPa UCS, 2.50 g/cm³ ovendry density (γ dry), 78% hard to fresh rock affinity RQD, and 9.93 MPa high strength and high modulus of deformation of the plate loading test. For the water absorption (%), KL at Al Aziziyah district showed a range of 12.85–17.80% averaged 14.71%. HL at Hittin district varied between 7.04 and 11.29% with an average of 9.45%. KL proved to be dense with ovendry density (γ dry) averaged at 1.70 g/cm³ while HL showed very dense affinity of 2.50 g/cm³. KL clarified a UCS range from 22.5 to 40.1 MPa and an average of 32.1 MPa while HL showed a range from 35.4 t o 48.1 MPa with an average of 43.1 MPa. KL is moderately weathered with RQD average of 51% while HL showed a hard to fresh rock affinity of 78%. Point load test clarified a medium shear strength with 5.49 MPa for KL and high strength of 9.93 MPa for HL. Plate loading tests indicated low and high modulus of deformation for KL and HL, respectively. Results of petrographical analyses and XED of limestone samples showed that the strength parameters of samples mostly composed of micrite (mudstone/wackestone) and dolomite in hard limestone of Hittin district. In Al Aziziyah district (KL), the samples mostly consist of foraminifera and high amount of calcite as in karst limestone (wackestone/packstone). Rock mechanical tests with combination of fabric analyses have shown that strength parameters depend not only on the amount of karst but also on the amount of allochem. Major geomechanical differences between the two types of limestone provide the proper base for prioritizing areas to alleviate future risks and sustainable urban planning for decision makers. The karstic limestone, therefore, is considered as an acceptable foundation bed for light engineering structures. However, for heavy structures and buildings, improving the foundation bed strength by grouting, cement injection, and mat foundations is necessary to avoid future failure risks.     

Late Cretaceous (Cenomanian-Turonian) ammonites from southern Morocco and south western Algeria

On the basis of nine lithostratigraphical profiles, 23 cephalopods taxa (nautilus and ammonites) are described from the Preafrican Trough and the Kem Kem region. Among them, a new species is proposed: Spathites (Jeanrogericeras) asflaensis nov. sp. This fauna is placed in its biostratigraphical framework and correlated with the standard zonation of the late Cenomanian–early Turonian. Moreover, stratigraphic correlations are proposed for the whole Maghreb from the Tarfaya Basin in the west to central Tunisia in the east. Selected taxa reveal the paleogeographical context of the western Tethys; a complex distribution of emerged areas and epicontinental seas impacted by an important marine trangression that constantly modified the costaline.     

Shell concentrations from the Miocene Ar Rajmah Group at Soluq-Al Abyar road cut,southern Al Jabal Al Akhdar,NE Libya

The Miocene Ar Rajmah Group, exposed along the Soluq-Al Abyar road cut in southern Al Jabal Al Akhdar, NE Libya, is very rich in both micro- and macrofossils, especially molluscs and echinoids. Seven shell concentrations were recognized of which four from the Benghazi Formation; pectinids–small oyster concentration (BSC1), Echinolampas sp.–Clypeaster cf. martini concentration (BSC2), molluscan shell concentration (BSC3), and Echinolampas cf. amplus–Clypeaster acclivis concentration (BSC4). Three shell concentrations occur in the Wadi Al Qattarah Formation; large oyster concentration (QSC1), Crassostrea gryphoides–Chlamys zitteli concentration (QSC2), and Cubitostrea digitalina concentration (QSC3). The main factors controlling the formation of the shell concentrations were storm-induced waves and currents, reduced sediment input, settling behavior of benthic macro-invertebrates, and productivity.     

Regionalisation of the “intensity-duration-frequency” curves in Northern Algeria

The flood events observed during last years in the urban areas are subject of main interest for quantification of the hydro-climatic risks and climatic change to the regional scales. The establishment of a statistical relationship between the intensities of intense rains and the recurrence of these events allows us to determine the dimensions of the works according to a previously defined level of risk. They constitute today a leading tool for various users. This work concerns the study of the maximum annual rains, recorded at 49 stations in the northern Algeria. The objectives of this work are to determine the estimators who are the “intensity-duration-frequency” curves and to extract from these whole of information the b Montana climatic parameter to be regionalized for the calculating the river flow and for the dimensioning of the networks of cleansing in the event of insufficiency of data. Different durations going from 15 min to 24 h are studied. We utilised the collocated co-kriging as multivariate estimation method for interpolation in order to yield the space distribution maps of b Montana climatic parameter, with the benefit of using spatially correlated secondary variables, such as the digital elevation model and the distance from the coastline that are known at any localisation. All features led to choose the digital elevation model as covariate for interpolating b Montana values, yielding a better regionalisation of the studied climatic parameter. The geostatistical handling of b Montana values strictly related to auxiliary variables that constitute physical factors overcomes the data shortage in planning, managing and preventing the rain flood risk.     

Storm water injection in Bahrain: pilot studies

Kingdom of Bahrain often suffers from urban flooding problems despite being a desertic country. An attempt has been made in this contribution to study the efficacy of the storm water injection systems not only in tackling urban flooding problems but also in augmenting the depleting ground water resources of the country. Two pilot studies were carried out in a centrally located area, one in a relatively open area and another in a densely populated location. A set of one recharge well and one observation well of about 40 m depth and 30 m apart was drilled in each site. Storm water was injected into the recharge wells after allowing it to pass through a specially designed natural filter system. Ground water levels were monitored at the observation wells on monthly basis and water samples were collected periodically during and after the rainfall events for chemical analysis. Initial results showed that the volume of storm water injected is proportional to the volume of storm water generated in an area. However, in the long run, the injection well having favourable hydrogeological situation and lesser silts in the storm water performed better in terms of total recharge despite having lesser volume of storm water available. Ground water quality for some parameters such as lead and cadmium remained an issue of concern, but could be controlled through construction of stricter filter system. Dilution of the injected storm water with the host ground water too significantly reduced the risks of contamination. The injection well located in the open area performed better than that of the densely populated area despite having lesser volume of storm water available. Site selection of the recharge wells, therefore, plays a vital role in the efficacy of a storm water injection system.     

Combination of GIS and mathematical modeling to predict floods in semiarid areas: case of Rheraya watershed (Western High Atlas,Morocco)

The Tinitine sub-watershed of Rheraya is renowned for its semiarid climate, irregular supply of water flow, and its historical floods; for these reasons, it is classified as vulnerable areas during a rainfall event. We conducted this study to propose flood prediction models adapted to this risky zone. For this, a hydrological method of flood forecasting rainfall-runoff used to determine a model conforms to the semiarid basin. This model is based on the articulation of the series production and transfer function. The goal of the production function is to determine the portion of the rainfall runoff, which is performed by two approaches that differ in their structures: (1) the first approach is based on the mathematical model of Horton; (2) the second approach is based on the determination of the part of the rain contributes to runoff and obtained by a spatial map of runoff coefficient (GIS). The transfer function is based on the two models of Clark and Nash, rainy efficient routes to the catchment outlet from a unit hydrograph. The characteristic parameters of these models are obtained through the application of mathematical optimization methods such as genetic algorithms. Thereby, the coupling function producing Horton (identified by the parameters: initial infiltration?=?15.03, final infiltration?=?0.3, and phi?=?0.45) and Clark transfer function (identified by the parameters C_A?=?0.21 and C_B?=?0.79) was given very satisfying results, mainly the low difference between observed and simulated hydrograph and Nash coefficient which is about 85%. This shows the interest of this coupling model in flood forecasting.     

Integrated multi-parameter approach for delineating groundwater potential zones in a crystalline aquifer of southern India

Groundwater resources in the semi-arid regions of southern India are under immense pressure due to large-scale groundwater abstraction vis-à-vis meager rainfall recharge. Therefore, understanding and evaluating the spatial distribution of groundwater is essential for viable utilization of the resource. Here, we assess groundwater potential at the watershed scale, in a semi-arid environment with crystalline aquifer system without a perennial surface water source using remote sensing, geophysical, and GIS-based integrated multi-parameter approach. GIS-based weighed overlay analysis is performed with input parameters, viz., geology, geomorphology, lineament density, land use, soil, drainage density, slope, and aquifer thickness. The watershed is categorized into four zones, namely, “very good” (GWP4), “good” (GWP3), “moderate” (GWP2), and “low” (GWP1) in terms of groundwater potential. Overall, ~?70% of the study area falls under moderate to low groundwater potential, indicating a serious threat to the future availability of the resource. Therefore, serious measures are required for maintaining aquifer resilience in this over-exploited aquifer (e.g., restricting groundwater withdrawal from GWP1 and GWP2 zones). Further, as the aquifer is under tremendous anthropogenic pressure, rainwater harvesting and artificial recharge during monsoon are advocated for sustainable aquifer management. Due to the direct dependence of crop production vis-à-vis farmer economy on groundwater, this study is an important step towards sustainable groundwater management and can be applied in diverse hydrological terrains.     

Approximate approaches to geometric corrections of high resolution satellite imagery

The exploitation of different non-rigorous mathematical models as opposed to the satellite rigorous models is discussed for geometric corrections and topographic/thematic maps production of high-resolution satellite imagery (HRSI). Furthermore, this paper focuses on the effects of the number of GCPs and the terrain elevation difference within the area covered by the images on the obtained ground points accuracy. From the research, it is obviously found that non-rigorous orientation and triangulation models can be used successfully in most cases for 2D rectification and 3D ground points determination without a camera model or the satellite ephemeris data. In addition, the accuracy up to the sub-pixel level in plane and about one pixel in elevation can be achieved with a modest number of GCPs.     

Strain Analysis and Microstructural Investigation of the Jabal Tays Ophiolite Complex,Eastern Arabian Shield,Saudi Arabia

Geotectonics - The present study deals with the Jabal Tays ophiolite area, which was affected by Al Amar-Idsas fault. It is one of the most important tectonic features in the Eastern Arabian...