Groundwater hydrochemistry and origin in the south-eastern part of Wadi El Natrun,Egypt

The demand for water is rapidly increasing in Egypt, because of high population and agriculture production growth rate, which makes research of water resources necessary. The regional multi-aquifer system of the Miocene–Pleistocene age is discharged in Wadi El Natrun area. Intensive aquifer overexploitation and agricultural development in the area are related to groundwater quality deterioration. Hydrochemical and hydrogeological data was evaluated to determine the groundwater origin and quality in the south-eastern part of wadi, which appears to be more significant for water supply owing to lower groundwater salinity. The dominance of the high mineralised Cl groundwater type was found; however, also less mineralised SO₄ and HCO₃ types were identified there. Based on the ion relations, halite and gypsum dissolution and ion exchange are the most important hydrochemical processes forming the groundwater chemical composition. The Cl dominated groundwater matches the discharge part of the regional hydrogeological system. Contrary, the presence of HCO₃ and SO₄ hydrochemical types corresponds to the infiltration and transferring parts of the hydrogeological system indicating the presence of zones conducting low mineralised groundwater. The discharge area of the over-pumped aquifer in Wadi El-Natrun lies 23 m beneath the sea level with the shoreline being at the distance of 100 km, thus there is a real risk of seawater intrusion. Using the hydrochemical facies evolution diagram, four samples in the centre of the discharge area indicate advanced seawater intrusion. The zones of the highest demand for groundwater quality protection were indicated based on a spatial pattern of hydrogeochemical composition.     

Mineralogy and Geochemistry of Uraniferous Sandstones in Fault Zone,Wadi El Sahu Area,Southwestern Sinai,Egypt: Implications for Provenance,Weathering and Tectonic Setting

Paleozoic rocks in the Wadi El Sahu area are affected by many major faults in different directions. A reverse fault trending NE-SW is exposed for about 300 m of its length as it cuts through the Abu Hamata and Adedia formations on the south side of Wadi El Sahu. A secondary ascending hydrothermal solution carrying heavy metals and radioactive minerals passed through the fault plain and the surrounding fractures, forming mineralized and radioactive zone. The mineralized zone thickness ranges from 60 cm to 200 cm along the fault plain. These rocks were analyzed radiometrically using a portable gamma-ray spectrometer, chemically by employing ICP-ES and ICP-MS, as well as mineralogically by both binocular and Environmental Scanning Electron microscope. Gold content was also determined by fire assay. REE and U contents reached up to 2682 and 1216 ppm, respectively. Mineralogical investigations indicated the presence of uraninite, torbernite, autunite, sklodowskite, kasolite as uranium minerals, thorite as a thorium mineral, monazite, allanite and xenotime as REE-bearing minerals, zircon and columbite as accessory minerals, gold and nickel as precious and base metals, in addition to cassiterite, chalcopyrite, chalcocite and chrysocolla. High REE and U contents are attributed to the circulation of epigenetic U and REE-bearing hydrothermal solutions along the fault plain and its surrounding fractures. Hydrothermal alteration processes could then be confirmed by the presence of the M-type tetrad effect in the REE-patterns of the ferruginous sandstone. The non-chondritic ratio of Nb/Ta, Zr/Hf and Y/Ho in the studied sandstone may be attributed to the tetrad effect. The Ce and Eu anomaly with unusual REE-patterns was represented by the presence of conjugated M-W tetrad effects, indicating either the dual effect of hydrothermal solutions or groundwater with seawater. The results clarify that the tetrad-effects could be used as evidence for the environment of deposition and as an indication for gold mineralization.     

Experimental Investigation of Kinetic Energy and Momentum Coefficients in Regular Channels with Stiff and Flexible Elements Simulating Submerged Vegetation

The paper addresses the problem of determination of the energy and momentum coefficients for flows through a partly vegetated channel. These coefficients are applied to express the fluid kinetic energy and momentum equations as functions of a mean velocity. The study is based on laboratory measurements of water velocity distributions in a straight rectangular flume with stiff and flexible stems and plastic imitations of the Canadian waterweed. The coefficients were established for the vegetation layer, surface layer and the whole flow area. The results indicate that the energy and momentum coefficients increase significantly with water depth and the number of stems per unit channel area. New regression relationships for both coefficients are given.     

Improvement of the JRC Calculation Using Different Parameters Obtained Through a New Survey Method Applied to Rock Discontinuities

This paper presents a new, fast and economical method for digitizing a rock surface profile to determine its joint roughness coefficient (JRC) value (Barton and Choubey, Rock Mech Rock Eng 10:1–54, 1977) using a set of existing parameters, the appropriateness of which has been tested. The new procedure was applied to four rock road cuts in the Alpujarra area of Granada province (Andalusia, Spain), supported by 117 digitized profiles. The method avoids any personal subjectivity bias. The usual subjectivity in the visualization and assessment of the JRC value is estimated here by a survey test answered by 90 trained users. The survey test consisted of a set of JRC visual comparisons of 12 roughness profiles, selected from the 117 profiles surveyed during the field research in the Alpujarra region, with the Barton typical profiles. The results of the survey clearly show systematic inaccuracies in the traditional procedure that are reduced if the advice presented in the conclusions of this paper is taken in account when performing the visual estimation.     

Towards a data assimilation system for morphodynamic modeling: bathymetric data assimilation for wave property estimation

Data assimilation is mainly concerned with the proper management of uncertainties. The main objective of the present work is to implement and analyze a data assimilation technique capable of assimilating bathymetric data into a coupled flow, wave, and morphodynamic model. For the case presented here, wave significant height, wave direction of incidence, and wave peak period are being optimized based on bathymetric data taken from a twin experiment. An adjoint-free variational scheme is used. In this approach, a linear reduced order model (ROM) is constructed as an approximation of the full model. The ROM is an autoregressive model of order 1 (AR1) that preserves the parametrization. Since the ROM is linear, the construction of its adjoint is straightforward, making the implementation of 4D variational data assimilation effortless. The scheme is able to update the morphodynamic model satisfactorily despite the fact that the model shows nonlinear behavior even for very small perturbations of all three parameters. The size and direction of the perturbations necessary for constructing the ROM have a significant impact on the performance of the technique.     

Jurassic microbial communities in hydrothermal manganese crust of the Rifian Calcareous Chain,Northern Morocco

The stratigraphic record of the Middle and Upper Jurassic in the Western Tethys is characterized by successive eustatic and tectonic events recorded as stratigraphic unconformities, which are revealed by hardgrounds, palaeokarsts, palaeosoils, and by the deposition of Fe–Mn crusts. The study of a Mn crust from the Middle-Upper Jurassic discontinuity in the Jbel Moussa Group (Rifian Cordillera), from stratigraphic, geomicrobiologic, mineralogical, and geochemical standpoints allows us to establish its hydrothermal origin. The manganese crust is composed by Ca-birnessite, cryptomelane and coronadite. Major- and trace-elements analyses of the whole crust show high contents in MnO (> 70 wt.%), a negative Ce anomaly and a positive Eu anomaly. Analysis of the microstructures under scanning electron microscopy reveals crystalline and microbial laminations, probably owing to fungal mycelium. Mineralogical and geochemical composition, together with microbial structures, suggest that this Mn crust formed as a result of venting hydrothermal fluids through synsedimentary faults. Chemosynthetic microbes were probably involved in the precipitation of Mn.     

Thermochronological data from Sudan in the frame of the denudational history of the Nubian Red Sea margin

Low‐temperature thermochronology provides information on the timing of rifting and denudation of passive margins, and the Red Sea with its well‐exposed, young rift margins is a suitable setting for its application. Here we present new apatite fission‐track (AFT) data from Sudan northern hinterland and Red Sea coastal areas. From the former region we obtained ages between 270 ± 2 Ma ad 253 ± 53 Ma, and from the coastal belt between 83 ± 8 Ma and 39 ± 7 Ma. These data prompted a review and comparison with low‐temperature thermochronological data from the whole Nubian Red Sea Margin, and a discussion on their implication in assessing the margin evolutionary style. AFT data are available for Egypt and Eritrea as well as apatite (U‐Th)/He (AHe) ages for two transects transversal to the margin in Eritrea. Both in Egypt and Eritrea AFT data record a cooling event at about 20–25 Ma (Early Miocene) and an earlier, more local, cooling event in Egypt at about 34 Ma (Early Oligocene). The thermal modeling of the Sudan samples provides an indication of a rapid cooling in Miocene times, but does not support nor rules out an Early Oligocene cooling phase. The re‐assessment of new and existing thermochronological data within the known geological framework of the Nubian and conjugate Arabian margins favours the hypothesis that early rifting stages were affecting the whole Gulf of Suez–Red Sea–Gulf of Aden system since the Oligocene. These precocious, more attenuated, phases were followed by major extension in Miocene times. As to the mode of margin evolution, AFT age patterns both in Egypt and Eritrea are incompatible with a downwarp model. The distribution of AHe ages across the Eritrean coastal plain suggests that there the escarpment was evolving predominantly by plateau degradation. Copyright © 2009 John Wiley & Sons, Ltd.     

Landslide-hazard mapping through multi-technique activity assessment: an example from the Betic Cordillera (southern Spain)

Landslide hazard in a region limited to data from a regional scale about triggering factors is assessed via cross tabulation between determining factors and landslides with recent activity. Firstly, landslide susceptibility was evaluated and validated through a bivariate statistical method between the previously identified stability conditioning factors and the mapped landslides. In this way, the most susceptible areas for assessing landslide hazards were selected. The main problem to solve in this type of research is the landslide activity. For this purpose, several techniques were applied: news reports, differential interferometric synthetic aperture radar, digital photogrammetry, light detection and ranging, photointerpretation, and dendrochronology. Both the strong and weak points of these techniques are also mentioned. The landslide return period was computed via the association between landslide activity and triggering factors, in this case annual rainfall. Finally, landslide hazard was mapped solely based on landslides with recent activity and their computed return period. The relationship between landslide occurrence and triggering factors shows that, according to both the considered assumptions and the observations made, deep-seated landslides are triggered or reactivated together with superficial landslides once every 18 years, while superficial landslides as flows or falls occur once every 5 years. The results show that there is generally a low landslide hazard in the study zone, especially when compared to landslide susceptibility. This means that landslides are mainly dormant from a natural evolution point of view, but could be reactivated as a result of geomorphological, climate, or human changes. In any case, the landslide hazard is successfully assessed, with a prediction of a 6% annual probability of a high hazard in 5% of the area, intersecting with the main infrastructures of the region; thus, control strategies are justified in order to avoid damage in extraordinary rainfall periods.     

Impact of control structures on assimilative capacity of rivers and fish habitat

This research studies the impact of water level control structures on self-assimilative capacity of rivers and on fish habitat. Constructing a water level control structure in a river reach will alter its hydraulics as well as its water quality, thermal regime and fish habitat. A mathematical model is developed to simulate river hydraulics, water quality, temperature and fish habitat. Diurnal dissolved oxygen concentrations are investigated to show their impact on fish. A case of a Nile River reach was studied to investigate the impact of the existence of the Esna barrage on the water quality and fish in its upstream reach. The barrage has negative impacts on the upstream self-assimilative capacity of the rivers. The waste load that the river could absorb was only 54 % (at low flow) and 78 % (at high flow) of the entire load if no barrage was present. Including in the simulation of the effects of photosynthesis and respiration, the above mentioned percentages were raised to 54 % and 91 %, respectively. Although water level control structures have negative impacts on the upstream self-assimilative capacity of the rivers, they have positive effect on downstream dissolved oxygen concentrations due to reaeration that happens across them. Downstream dissolved oxygen concentration increased by 6 % from its upstream concentration value. The barrage has a positive effect on fish habitat in the upstream section. The weighted usable area of Tilapia fish is doubled in case of barrage existence. The barrage causes a slight decrease in water temperature that reaches an average of 0.13 degree in the month of June.