A numerical study on the influence of geometry on the formation of sandbanks     

Noel Carbajal  Stephanie Piney  Jorge Gómez Rivera 《Ocean Dynamics》2005,55(5-6):559-568

Applying a two-dimensional, non-linear hydrodynamic numerical model in combination with a semiempirical equation for bedload sediment transport, the influence of geometry on the formation of sandbanks is investigated. In the first experiment, the formation of sandbanks in an ideal rectangular basin, resembling the Taylor’s problem, was calculated. Sandbanks occur in a small area at the closed boundary. Similar experiments were carried out for a range of wavelengths of the incident Kelvin wave. The results reveal that large wavelengths favor the generation of sandbanks. In subsequent calculations, the basin was modified by introducing new geographical features like bays and peninsulas. The numerical experiments show that geometry is a fundamental factor to determine the position where groups of sandbanks appear. The results suggest that in regions where the Kelvin wave is diffracted, the formation of sandbanks occurs. An experiment, in which we applied an ideal geometric configuration representing that of the Southern Bight of the North Sea, generated sandbank patterns resembling those observed in the region.  相似文献   

Feeding ecology of flatfish juveniles (pleuronectiformes) in Mar Chiquita coastal lagoon (Buenos Aires, Argentina)     

Ariadna Rivera Prisco  Susana B. García De La Rosa  Juan M. Díaz De Astrarloa 《Estuaries and Coasts》2001,24(6):917-925

During a two-year period in Mar Chiquita coastal lagoon (Buenos Aires, Argentina), the diet of juvenileParalichthys orbignyanus andOncopterus darwinii sorted according to size, area, and season was analyzed. Sampling was carried out using a beach seine net in three zones of different salinity. The small size of the individuals collected and the high percentage of full stomachs, corresponding with high food availability in the lagoon, indicated that Mar Chiquita is used as a nursery ground. The diet ofP. orbignyanus consisted of crustaceans and polychaetes, whereasO. darwinii fed predominantly on small crustaceans (gammarid amphipods, harpacticoid copepods, mysids, and ostracods); polychaetes were less important. Diet of both flatfish species varied with length. Smaller individuals were microphagous, while bigger specimens included larger prey in their diet. Prey taxa number increased for both species, seawards to the mouth of the lagoon, probably related to the salinity gradient. Prey diversity forP. orbignyanus was highest in autumn and spring, and the lowest percentage of stomachs with food occurred in winter. Prey diversity was lowest forO. darwinii in spring and the highest percentage of empty stomachs was found in autumn.  相似文献   

On the resolution of the isotropic component in moment tensor inversion   总被引：1，自引：0，他引：1  

H. Dufumier  L. Rivera 《Geophysical Journal International》1997,131(3):595-606

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A unified hydrogeological conceptual model of the Milk River transboundary aquifer,traversing Alberta (Canada) and Montana (USA)     

Marie-Amélie Pétré  Alfonso Rivera  René Lefebvre  M. Jim Hendry  Attila J. B. Folnagy 《Hydrogeology Journal》2016,24(7):1847-1871

A conceptual model of the transboundary Milk River Aquifer (MRA), extending across the Canada–USA border, was developed based on literature, focused fieldwork and a three-dimensional geological model. The MRA corresponds to the Virgelle Member of the Milk River Formation (Eagle Formation in Montana, USA) and it is an important groundwater resource over a large area (25,000 km²). The Virgelle outcrops near the international border and along the Sweet Grass Arch in Montana. The down-gradient limit of the MRA is the unconformity separating the Virgelle from the gas-bearing sandy shale of the Alderson Member. The MRA is confined above by the Pakowki/Claggett Formations aquitards and below by the Colorado Group aquitard. The MRA contains higher transmissivity areas resulting in preferential flowpaths, confirmed by natural geochemical tracers. Tritium and ¹⁴C delineate restricted recharge areas along the outcrops on both sides of the international border. Drastic decreases in horizontal hydraulic gradients indicate that the Milk River intercepts a large proportion of groundwater flowing to the north from the recharge area. Downgradient of the Milk River, groundwater movement is slow, as shown by ³⁶Cl residence times exceeding 1 Ma. These slow velocities imply that groundwater discharge downgradient of the Milk River is via vertical leakage through the Colorado Group and upward along buried valleys, which act as drains and correspond to artesian areas. When confined, the MRA contains a fossil groundwater resource, not significantly renewed by modern recharge. Groundwater exploitation thus far exceeds recharge, a situation requiring properly managed MRA groundwater depletion.  相似文献   

Mapping groundwater storage variations with GRACE: a case study in Alberta,Canada     

Jianliang Huang  Goran Pavlic  Alfonso Rivera  Dan Palombi  Brian Smerdon 《Hydrogeology Journal》2016,24(7):1663-1680

The applicability of the Gravity Recovery and Climate Experiment (GRACE) to adequately represent broad-scale patterns of groundwater storage (GWS) variations and observed trends in groundwater-monitoring well levels (GWWL) is examined in the Canadian province of Alberta. GWS variations are derived over Alberta for the period 2002–2014 using the Release 05 (RL05) monthly GRACE gravity models and the Global Land Data Assimilation System (GLDAS) land-surface models. Twelve mean monthly GWS variation maps are generated from the 139 monthly GWS variation grids to characterize the annual GWS variation pattern. These maps show that, overall, GWS increases from February to June, and decreases from July to October, and slightly increases from November to December. For 2002–2014, the GWS showed a positive trend which increases from west to east with a mean value of 12 mm/year over the province. The resulting GWS variations are validated using GWWLs in the province. For the purpose of validation, a GRACE total water storage (TWS)-based correlation criterion is introduced to identify groundwater wells which adequately represent the regional GWS variations. GWWLs at 36 wells were found to correlate with both the GRACE TWS and GWS variations. A factor f is defined to up-scale the GWWL variations at the identified wells to the GRACE-scale GWS variations. It is concluded that the GWS variations can be mapped by GRACE and the GLDAS models in some situations, thus demonstrating the conditions where GWS variations can be detected by GRACE in Alberta.  相似文献   

A Compatible Single-Phase/Two-Phase Numerical Model: 1. Modeling the Transient Salt-Water/Fresh-Water Interface Motion   总被引：1，自引：0，他引：1  

Emmanuel Ledoux  Serge Sauvagnac  Alfonso Rivera 《Ground water》1990,28(1):79-87

Abstract A numerical model (NEWVAR) to simulate the transient movement of a discrete interface between salt water and fresh water has been developed. NEWVAR is designed to allow the analysis of a regional two-dimensional ground-water flow in coastal aquifers. The numerical solution permits the prediction of both regional fresh-water levels and two-dimensional fresh-water/salt-water interface by using nested square meshes.
The numerical solution is based on the finite-difference method; the Gauss-Jordan direct method is used for solving steady- and unsteady-state linear equations. Different procedures are used to avoid numerical difficulties in the transient position of the interface toe for two-dimensional areal flow.
The numerical solution was tested against the analytical ones for the cases of an advancing interface and of a floating fresh-water lens over sea water. These tests showed good agreement, thus verifying the finite-difference approximation. The results of an application of this model to a real aquifer are discussed in a companion paper entitled: "A Compatible Single-Phase/Two-Phase Numerical Model 2. Application to a Coastal Aquifer in Mexico."  相似文献   

A Compatible Single-Phase/Two-Phase Numerical Model: 2. Application to a Coastal Aquifer in Mexico   总被引：5，自引：0，他引：5  

Alfonso Rivera  Emmanuel Ledoux  Serge Sauvagnac 《Ground water》1990,28(2):215-223

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Preliminary geochemical and thermodynamic assessment of the geothermal resources, Sulphur Springs area, St Lucia, W.I.     

F. D'Amore  J.R. Rivera  D. Giusti  R. Rossi 《Applied Geochemistry》1990,5(5-6)

A high-temperature geothermal resource has been located on the island of St Lucia (W.I.), which was tapped by means of a well drilled in 1988 to a total depth of 1410 m, in the Sulphur Springs area. The well encountered mainly dacitic agglomerates and lava flows and a permeable zone below ≈1340 m, with a maximum temperature of ≈290°C.Well productivity decreased from an initial value close to 62 t/h to about 33 t/h under well-head pressures of 1.5 MPa (15 bar a) after 255 h of production. Initial reservoir static pressure was 7.5 MPa (75 bar a). A decline in reservoir pressure of about 15% was observed at the end of the production test. During the first two days of exploitation the well initially produced a two-phase fluid with high steam fraction, which then developed into superheated steam with a high content of non-condensable gas exceeding 100 1/kg at standard conditions and a computed P(CO₂) of 1 MPa (10 bar).The average steam fraction at reservoir conditions, computed from gas composition after 120 h of production is 0.3.High HCl concentrations of about 300 ppm are present in the condensate steam indicating the presence of a high concentrated boiling brine to the point of halite saturation. All data support the hypthesis of a hydrothermal hot-water system prior to drilling, that underwent a very rapid drawdown with production.  相似文献   

Saprobic evaluation of Euglena viridis,E. agilis and E. proxima     

G. Vilaclara  E. Robles  F. Rivera  V. Slde ek 《洁净——土壤、空气、水》1988,16(2):187-188

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Comparison of Different Gold Recovery Methods with Regard to Pollution Control and Efficiency     

Lars D. Hylander  David Plath  Conrado R. Miranda  Sofie Lücke  Jenny Öhlander  Ana T. F. Rivera 《洁净——土壤、空气、水》2007,35(1):52-61

This case study performed at the largest gold mining village in the Philippines compares four methods for gold recovery: amalgamation, cyanide leaching, a shaking sluice, and Cleangold® sluices. The results show that a combination of manual panning or Cleangold® sluices followed by cyanidation is the best solution under present conditions, followed by cyanidation alone. Based on the knowledge obtained, remarks on suitable policy actions, which may be applied also in other gold fields, are made.  相似文献