Three dimensional hydrodynamic modeling over bed forms in open channels

Three dimensional numerical modeling of idealized sand dunes was used to assess the capability of various modeling formulations to capture the flow structure and resistance introduced by bed forms which are similar to those in the Lower Mississippi River. The selected models were: ECOMSED (HydroQual), MIKE 3 [Danish Hydraulic Institute (DHI)] and H3D (Hayco). The study revealed that the hydrostatic versions of models did not capture the flow separation at the crest of the dunes; however, they did respond to the presence of bed forms and gave a total resistance similar to the non-hydrostatic models.     

Simulation of subcritical flow at open-channel junction

The spectrum of this survey turns on the evaluation of various existing theoretical combining models, when invoked within the internal boundary condition management at a junction. Based on the assumption that: when the Froude number is low (i.e. the flow is subcritical), the energy equation at the junction can be approximated by the stages heads equality. Actual literature and many commercial packages rather use this concept for the treatment of the junction’s internal boundary handling because it is easy to implement and it avoids the solving of nonlinear equations. In the last decade, many nonlinear combining models, based on the momentum conservation through the junction, have been reported. However, using them to operate within the internal boundary condition treatment of an open-channel confluence has not yet been investigated. Hence, this research focuses on studying the practical aspect of several combining models, once applied within the junction’s internal boundary management. Therefore, the recent nonlinear models of Gurram, Hsu and Shabayek have been briefly detailed together with the traditional concept of assuming water stages equality at the junction. Subsequently, an experimental examination was performed according to available experiments as mean to pre-evaluate (separately at the junction) the four junction models in the steady state. Moreover, according to the latter inspection the attention was constrained to study the effect of high/low subcritical Froude number at the junction. Finally, two hypothetical hydraulic problems were defined and computed in order to exhibit the performance of these junction models when used to contend the junction’s internal boundary handling. The problems involved: (a) steady and transient flows; (b) high and low (subcritical) Froude number at the junction. Supported by the experimental and numerical investigations, it can be concluded that even while the Froude number spectrum is subcritical, precautions have to be taken when dealing with the concept of energy heads equality, notably for a Froude higher than 0.35 at the junction.     

AERIAL RADIOMETRY OF EL ALAMEIN OILFIELD,EGYPT, U.A.R.*

Total gamma airborne radiometric survey of El Alamein area in the Western Desert has been carried out by the Atomic Energy Establishment. The flight lines are directed north-south with 500 m spacing, while the ground clearance is about 50 m. Superimposition of the radioactivity profiles over El Alamein Oilfield shows a general decrease of gamma radiation in the central part of the structure framed by zones of relatively higher values. The aerial radioactivity of El Alamein Oilfield is described and it is correlated with some reported radiometric characteristics of other oil bearing structures. The distribution of aeroradiometric measurements over El Alamein Oilfield and its environment has been found to be lognormal.     

Conservative identification of nodal transmissivities: theory,computational experiments and application to the Rharb coastal aquifer (Morocco)

Abstract

In order to calculate the transmissivity from the inverse problem corresponding to the groundwater flow in an isotropic horizontal aquifer, a numerical conservative approach is tested. The method deals with triangulation of the domain and applies the conservation of mass to elements of the mesh using the harmonic mean for internodal transmissivities. An optimal sweeping algorithm is used to evaluate nodal transmissivities from one element to another with a minimal relative error accumulation. The practical importance of the method is demonstrated through two synthetic examples representing those experienced in the field, then through application to a Moroccan aquifer. The computed hydraulic head is well fitted to the reference one, which confirms the validity of the identified transmissivity model.     

Mineralogy, Geochemistry, and Age Constraints on the Beni Bou Ifrour Skarn Type Magnetite Deposit, Northeastern Morocco

Abstract: The Beni Bou Ifrour deposit of northeastern Morocco is a skarn type magnetite deposit. K-Ar age determination suggests that the mineralization occurred at 7.040.47 Ma. The spatial relationship between skarn and dikes of microgran-odiorite derived from the batholith of Wiksane Granodiorite, and the similarity of age (8.020.22 Ma), confirms that the Wiksane Granodiorite is the igneous rock most probably related to mineralization. The skarn is distributed asymmetrically in the limestone, and magnetite ore was developed just below the calc-silicate skarn as two parallel beds separated by 100 m of barren limestone and schist.
The mineralization can be divided into three stages. The early stage is characterized by the formation of calc-silicate minerals, mainly clinopyroxene (80–70 % diopside) and garnet (early almost pure andradite to the late 60 % andradite). The main stage is characterized by the formation of a large amount of magnetite. Epidote and quartz formed simultaneously with magnetite. Fluid temperatures exceeded 500 C during the early to main stages. Fluid with very high salinity (50–75 wt% NaCl equiv.) was responsible for the formation of the magnetite ore. The oxygen isotope composition, together with the fluid inclusion data, suggests that magmatic fluid was significant for the formation of calc-silicate skarn minerals and magnetite. Low temperature (-230C) and low salinity (-10 % NaCl equiv.) hydrothermal fluids dominated by meteoric water were responsible for the late stage quartz and calcite formation.     

Effets de la vitesse d'écoulement sur le transport et la cinétique de dépôt de particules en suspension en milieu poreux saturé

We study in this paper the transport and deposition of suspended particles in saturated porous media. Some chromatographic short-pulse tests were performed in a laboratory column with a tracer and two types of suspended particles. A mathematical model was used to determine the hydrodispersive parameters and deposition rates from the breakthrough curves. The results show that the fitted parameters obtained vary with the flow rate and the characteristics of the suspended particles. We also observe, at high flow rates, that particles have a migration velocity higher than that of the conservative tracer. To cite this article: A. Benamar et al., C. R. Geoscience 337 (2005).     

Multi-hydro hydrological modelling of a complex peri-urban catchment with storage basins comparing C-band and X-band radar rainfall data

ABSTRACT

The spread of impervious surfaces in urban areas combined with the rise in the intensity of rainfall events as a result of climate change has led to dangerous increases in storm water flows. This paper discusses a new implementation of the fully distributed hydrological model Multi-Hydro (developed at École des Ponts ParisTech), when operating storage basins, and its ability to deal with high-resolution radar rainfall data. The peri-urban area of Massy (south of Paris, France) was selected as a case study for having six of these drainage facilities, used extensively in flood control. Two radar rainfall datasets with different spatiotemporal resolutions were used: Météo-France’s PANTHER rainfall product (C-band) and ENPC’s X-band DPSRI. The rainfall spatiotemporal variability was analysed statistically using Universal Multifractals (UM). Finally, to validate the application, the water level simulations were compared with local measurements in the Cora storage basin located next to the catchment’s single outlet.