Environmental impacts of Baltim and Ras El Bar shore-parallel breakwater systems on the Nile delta littoral zone,Egypt     

O.?E.?FrihyEmail author  M.?M.?El Banna  A.?I.?El Kolfat 《Environmental Geology》2004,45(3):381-390

This study evaluates the impacts resulting from the construction of two large-scale detached breakwater systems on the Nile delta coast of Egypt at Baltim and Ras El Bar beaches (~18.3 km shoreline length). The two protective systems were installed in a water depth of between 3 and 4 m and consist of 17 units in total (each ~250 m long). A comprehensive monitoring program spanning the years 1990 to 2002 was implemented and included beach-nearshore profiles, grain size distribution of seabed sand and information related to the background coastal processes. Evaluation of these systems concentrates on the physical impacts on coastal morphodynamics, mitigation and their design implications. The beach and nearshore sedimentation (erosion/accretion patterns) and grain texture of seabed sediment in the study areas have been substantially disrupted due to the interruption of longshore transport by the shore-parallel detached breakwaters. Rate of shoreline and seabed changes as well as alongshore sediment volume have been substantially affected, resulting in accretion in the breakwater landward sides (tombolo or salient) followed by downdrift erosion. The preconstruction beach erosion at Baltim (–5 m/year) and at Ras El Bar (–6 m/year) has been replaced, respectively, by the formation of sand tombolo (35 m/year) and salient (9 m/year). On the other hand, beach erosion has been substantially increased in the downdrift sides of these protective systems, being –20 m/year at Baltim and –9 m/year at Ras El Bar. Further seaward, the two protective systems at Baltim and Ras El Bar have accumulated seabed sand at maximum rates of 30 and 20 cm/year and associated with downdrift erosion of –45 and –20 cm/year, respectively. Strong gyres and eddies formed in the breakwater gabs have drastically affected swimmers and subsequently caused a significant number of drownings each summer, averaging 35 and 67 victims/year at Baltim and Ras El Bar beaches, respectively. This study provides baseline information needed to help implement mitigation measures for these breakwater systems.  相似文献   

Exchange of light rare earths for Ca in apatite     

Abderrahmane Iqdari  Bruce Velde  Noureddine Benalioulhaj  Saint-Clair Dujon  Nacer El Yamine 《Comptes Rendus Geoscience》2003,335(4):381-390

Diffusion experiments were carried out on natural apatite crystals that were immersed in molten light rare earth element (REE) chloride salt at temperatures between 900 and 1150 °C for periods up to 35 days. Electron microprobe analysis of the crystals showed that light REEs replaced Ca according to electronic balance, i.e. $\text{2}\text{REE}{}^{\mathrm{3+}}$ for $\text{3}\text{Ca}{}^{\mathrm{2+}}$. These diffusion profiles indicate that a maximum amount of substitution in the structure occurs when two of the ten Ca ions in apatite are replaced by the REE diffusing elements. Anisotropic diffusion is observed between a and c crystallographic directions. Comparison of maximum distance indicates that the larger ions move more easily in the apatite structure. We conclude that the light REEs diffuse within the channel structures of the mineral, and that this diffusion is controlled by the substitution type of elements in the calcium sites. To cite this article: A. Iqdari et al., C. R. Geoscience 335 (2003).  相似文献   

FeO-rich rims and veins in Allende forsterite: Evidence for high temperature condensation at oxidizing conditions     

S. Weinbruch  H. Palme  W. F. Müller  A. El Goresy 《Meteoritics & planetary science》1990,25(2):115-125

Abstract— Forsteritic olivine grains in the Allende meteorite are commonly rimmed by FeO-rich olivine. New evidence is presented in this paper that the fayalitic rims formed by condensation from a gas and not by thermal equilibration of forsterite with FeO-rich metal or FeO-rich olivine in the interior of a parent body. A similar origin is inferred for fayalitic veins within forsterite crystals. A good correlation of FeO with MnO was observed along profiles from forsteritic cores to fayalite-rich rims, excluding oxidation of metal as a source of rim FeO. The fayalite content of the rim is generally lower than that of the adjacent matrix olivines excluding formation of FeO-rich rims by equilibration with present matrix. This is also supported by systematic differences in Cr between rim and matrix olivines. Chromites, associated with FeO-rich olivine, were found at the boundary between forsterite and fayalite-rich rim, within the rim itself and in fayalitic veins. Condensation of chromite from a gas phase is likely for the latter two occurrences since no other suitable source of Cr is available. Chromite at the forsterite-fayalite interface was formed by diffusion of Cr from forsterite. Increasingly oxidizing conditions, apparently enabled formation of chromite. The steep compositional gradient between forsterite and fayalite provides severe constraints on the thermal history of forsterite grains. The width of oxidized zones (halos) around metal inclusions in the interior of forsterite grains are not compatible with this steep gradient. Their development requires longer diffusion times than would be allowed by the rims, indicating that these forsterite grains must have had an independent history of oxidation prior to formation of the rim. Condensation calculations indicate that FeO-rich olivine can be formed by condensation from a gas with enhanced oxygen fugacity. Increasing the oxygen fugacity would provide conditions allowing the thermodynamic stability of chromite. High temperatures and oxidizing conditions must have prevailed for some time in that part of the solar nebula where the Allende meteorite formed.  相似文献   

Wave-induced responses in a fluid-filled poro-elastic solid with a free surface—a boundary layer theory     

Chiang C. Mei  Mostafa A. Foda 《Geophysical Journal International》1981,66(3):597-631

Summary. Wave-induced stress in a porous elastic medium is studied on the basis of Biot's linearized theory which is a special case of the mixture theory. For sufficiently high frequencies which are pertinent to ocean waves and seismic waves, a boundary layer of Stokes' type is shown to exist near the free surface of the solid. Outside the boundary layer, fluid and the solid skeleton move together according to the laws of classical elasticity for a single phase. This division simplifies the analysis of the equations governing the two phases; and several examples of potential interest to geophysics and foundation mechanics are treated analytically.  相似文献   

Circulation and Mixing Processes in the Liverpool Bay Area of the Irish Sea   总被引：1，自引：0，他引：1  

K. F. Bowden  S. H. Sharaf El Din 《Geophysical Journal International》1966,11(3):279-292

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Internal atmospheric hydromagnetic planetary-gravity waves in zonal wind-magnetic shears     

O. M. El Mekki 《Solar physics》1982,75(1-2):351-360

Internal atmospheric hydromagnetic planetary-gravity waves propagating through a latitudinally sheared zonal flow and a zonal magnetic field sheared both latitudinally and vertically are studied.It is shown that the waves possess four critical latitudes. At two of them the waves propagate on one side only with their energy and momentum fluxes differing by an additive factor on the two sides of the critical latitude, whereas at the other two they are capable of propagating on both sides and exhibit the value effect behaviour, with their energy and momentum fluxes attenuated by an exponential factor as they cross the critical latitude.  相似文献   

The energy-dependent radiation transfer in a homogeneous finite sphere     

S. A. El Wakil  H. Machali  M. T. Attia  E. A. Saad 《Astrophysics and Space Science》1987,137(2):239-250

Radiation transfer problem in the slowing-down region is solved for a spherical geometry. Modelled kernels are used to represent the slowing-down kernel. Calculations are performed for the radiation flux at the boundary of the sphere for two cases: (i) in the presence of internal source, (ii) if the radiation is incident on the sphere. Numerical results are obtained by using the Padé approximant technique.  相似文献   

A menagerie of graphite morphologies in the Acapulco meteorite with diverse carbon and nitrogen isotopic signatures: Implications for the evolution history of acapulcoite meteorites     

Ahmed El Goresy  Ernst Zinner  Catherine Caillet 《Geochimica et cosmochimica acta》2005,69(18):4535-4556

Morphologies, petrographic settings and carbon and nitrogen isotopic compositions of graphites in the Acapulco meteorite, the latter determined by secondary ionization mass spectrometry, are reported. Seven different graphite morphologies were recognized, the majority of which occur enclosed exclusively in kamacite. Individual graphite grains also rarely occur in the silicate matrix. Kamacite rims surrounding taenite cores of metal grains are separated from the Ni-rich metal cores by graphite veneers. These graphite veneers impeded or prevented Ni-Fe interdiffusion during cooling. In addition, matrix FeNi metal contains considerable amounts of phosphorous (≈ 700 ppm) and silicon (≈ 300 ppm) (Pack et al., 2005 in preparation) thus indicating that results of laboratory cooling experiments in the Fe-Ni binary system are inapplicable to Acapulco metals. Graphites of different morphologies display a range of carbon and nitrogen isotopic compositions, indicating a diversity of source regions before accretion in the Acapulco parent body. The isotopic compositions point to at least three isotopic reservoirs from which the graphites originated: (1) A reservoir with heavy carbon, represented by graphite in silicates (δ¹³C = 14.3 ± 2.4 ‰ and δ¹⁵N = −103.4 ± 10.9 ‰), (2) A reservoir with isotopically light carbon and nitrogen, characteristic for the metals. Its C- and N-isotopic compositions are probably preserved in the graphite exsolutions that are isotopically light in carbon and lightest in nitrogen (δ¹³C = −17 to −23 ‰ δ¹⁵N = −141 to −159 ‰). (3) A reservoir with an assumed isotopic composition (δ¹³C ∼ −5 ‰; δ¹⁵N ∼ −50 ‰). A detailed three-dimensional tomography in reflected light microscopy of the decorations of metal-troilite spherules in the cores of orthopyroxenes and olivines and metal-troilite veins was conducted to clarify their origin. Metal and troilite veins are present only near the fusion crust. Hence, these veins are not pristine to Acapulco parent body but resulted during passage of Acapulco in Earth’s atmosphere. A thorough search for symplectite-type silicate-troilite liquid quench textures was conducted to determine the extent of closed-system partial silicate melting in Acapulco.Metal-troilite spherules in orthopyroxenes and olivines are not randomly distributed but decorate ferromagnesian silicate restite cores, indicating that the metal-spherule decoration around restite silicates took place in a silicate partial melt. Graphite inclusions in these spherules have C- and N- isotopic compositions (δ¹³C = −2.9 ± 2.5 ‰ and δ¹⁵N = −101.2 ± 32 ‰) close to the average values of graphite in metals and in the silicate matrix, thus strongly suggesting that they originated from a mixture of graphite inclusions in metals and silicate matrix graphite during a closed system crystallization process subsequent to silicate-metal-sulfide partial melting. Troilite-orthopyroxene quench symplectite textures in orthopyroxene rims are clear evidence that silicate-sulfide partial melting took place in Acapulco. Due to petrographic heterogeneity on a centimeter scale, bulk REE abundances of individual samples or of individual minerals provide only limited information and the REE abundances alone are not entirely adequate to unravel the formational processes that prevailed in the acapulcoite-lodranite parent body. The present investigations demonstrate the complexity of the evolutionary stages of acapulcoites from accretion to parent body processes.  相似文献   

Evaluation and validation of landslide-susceptibility maps obtained by a GIS matrix method: examples from the Betic Cordillera (southern Spain)   总被引：3，自引：2，他引：3  

C. Irigaray  T. Fernández  R. El Hamdouni  J. Chacón 《Natural Hazards》2007,41(1):61-79

This work presents the results of applying the matrix method in a Geographic Information System (GIS) to the drawing of maps of susceptibility to slope movements in different sectors of the Betic Cordillera (southern Spain). In addition, the susceptibility models built by the matrix method were compared with a multivariate statistical method, and the first method gave the best results. The susceptibility maps drawn by the GIS matrix method were validated by calculating the coefficients of association with the degree of fit between recent slope movements registered in 1997 and the different levels of susceptibility of previously drawn maps (1995–1996) in different representative zones of the Betic Cordillera (southern Spain). The first sector studied showed excellent degrees of fit, with an error of less than 10% for all the slope failures and 3% when considering only failures of natural origin. In the second sector, the relative errors were less than 5%. In the third sector, the error hardly exceeded 6%. The results are discussed in the different zones and for each type of slope movement. In any case, these results evidence the predictive capacity of susceptibility maps drawn in GIS by the matrix method, for a great number of slope movements.  相似文献   

Les sondages électromagnétiques temporels comme outil de reconnaissance du gisement phosphaté de Sidi Chennane (Maroc) : apport à la résolution d'un problème d'exploitation     

Azzouz Kchikach  Pierre Andrieux  Mohammed Jaffal  Mostafa Amrhar  Mohammed Mchichi  Baadi Boya  Mbarek Amaghzaz  Thierry Veyrieras  Khadija Iqizou 《Comptes Rendus Geoscience》2006,338(5):289-296

Exploitation of the phosphatic layers in Sidi Chennane deposit (Morocco) collides frequently with problems bound to the existence, in the phosphatic series, of sterile bodies qualified as derangements. Our study shows that these bodies, masked by the Quaternary cover can be mapped using the Time-Domain ElectroMagnetic Soundings method (TDEM). It is based on the acquisition and the interpretation of a series of tests carried out above a visible derangement in an old trench of exploitation and on 2500 TDEM soundings carried out in a virgin area of the deposit. The article concerns to the analysis of the results and of the proceeding for a possible large geophysics survey. To cite this article: A. Kchikach et al., C. R. Geoscience 338 (2006).  相似文献