Stratigraphic controls on seawater intrusion and implications for groundwater management, Dominguez Gap area of Los Angeles, California, USA   总被引：1，自引：0，他引：1  

Tracy Nishikawa  A. J. Siade  E. G. Reichard  D. J. Ponti  A. G. Canales  T. A. Johnson 《Hydrogeology Journal》2009,17(7):1699-1725

Groundwater pumping has led to extensive water-level declines and seawater intrusion in coastal Los Angeles, California (USA). A SUTRA-based solute-transport model was developed to test the hydraulic implications of a sequence-stratigraphic model of the Dominguez Gap area and to assess the effects of water-management scenarios. The model is two-dimensional, vertical and follows an approximate flow line extending from the Pacific Ocean through the Dominguez Gap area. Results indicate that a newly identified fault system can provide a pathway for transport of seawater and that a stratigraphic boundary located between the Bent Spring and Upper Wilmington sequences may control the vertical movement of seawater. Three 50-year water-management scenarios were considered: (1) no change in water-management practices; (2) installation of a slurry wall; and (3) raising inland water levels to 7.6 m above sea level. Scenario 3 was the most effective by reversing seawater intrusion. The effects of an instantaneous 1-m sea-level rise were also tested using water-management scenarios 1 and 3. Results from two 100-year simulations indicate that a 1-m sea-level rise may accelerate seawater intrusion for scenario 1; however, scenario 3 remains effective for controlling seawater intrusion.  相似文献   

Square Kilometre Array: The radio telescope of the XXI century     

K. Grainge  B. Alachkar  Shaun Amy  D. Barbosa  M. Bommineni  P. Boven  R. Braddock  J. Davis  P. Diwakar  V. Francis  R. Gabrielczyk  R. Gamatham  S. Garrington  T. Gibbon  D. Gozzard  S. Gregory  Y. Guo  Y. Gupta  J. Hammond  D. Hindley  U. Horn  R. Hughes-Jones  M. Hussey  S. Lloyd  S. Mammen  S. Miteff  V. Mohile  J. Muller  S. Natarajan  J. Nicholls  R. Oberland  M. Pearson  T. Rayner  S. Schediwy  R. Schilizzi  S. Sharma  S. Stobie  M. Tearle  B. Wang  B. Wallace  L. Wang  R. Warange  R. Whitaker  A. Wilkinson  N. Wingfield 《Astronomy Reports》2017,61(4):288-296

The Square Kilometre Array (SKA) will be the world’s largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the Big Bang, how dark energy is accelerating the expansion of theUniverse, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. This project envisages the construction of 133 15-m antennas in South Africa and 131072 log-periodic antennas in Australia, together with the associated infrastructure in the two desert sites. In addition, the SKA is an exemplar Big Data project, with data rates of over 10 Tbps being transported from the telescope to HPC/HTC facilities.  相似文献   

Lava lakes on Io: New perspectives from modeling     

Tracy K.P. Gregg  Rosaly M. Lopes 《Icarus》2008,194(1):166-172

Loki Patera (310° W, 12° N) is Io's largest patera at ∼180 km in diameter. Its morphology and distinct thermal behavior have led researchers to hypothesize that Loki Patera may either be an active lava lake that experiences periodic overturn, or a shallow depression whose floor is episodically resurfaced with thin flows. Using results from mathematical models, we suggest that a better model for Loki's behavior is the terrestrial superfast spreading East Pacific Rise (EPR), near 17°^30′ south. We propose that, like at the southern EPR, Loki Patera is underlain by a thin, persistent magma “lens” that feeds thin, temporary lava lakes within the patera. Also like the southern EPR, overspilling of the volcanic depression is rare, with most of the lava volume being emplaced via a subsurface network of lava tubes.  相似文献   

Results of Two Pumping Tests in Wisconsin Age Weathered Till in Iowa   总被引：2，自引：0，他引：2  

LaDon Jones  Tracy Lemar  Chin-Ta Tsai 《Ground water》1992,30(4):529-538

  相似文献   

Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis   总被引：2，自引：0，他引：2  

P.N. Froelich  G.P. Klinkhammer  M.L. Bender  N.A. Luedtke  G.R. Heath  Doug Cullen  Paul Dauphin  Doug Hammond  Blayne Hartman  Val Maynard 《Geochimica et cosmochimica acta》1979,43(7):1075-1090

Pore water profiles of total-CO₂, pH, PO^3?₄, NO^?₃ plus NO^?₂, SO^2?₄, S^2?, Fe²⁺ and Mn²⁺ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O₂ > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO₂ concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions.  相似文献   

Letter from the editors     

Alan GillespiePat Anderson  Tracy FurutaniEric Steig 《Quaternary Research》2003,59(1):1

  相似文献   

Asymmetric mantle dynamics in the MELT region of the East Pacific Rise     

D. R. Toomey  W. S. D. Wilcock  J. A. Conder  D. W. Forsyth  J. D. Blundy  E. M. Parmentier  W. C. Hammond 《Earth and Planetary Science Letters》2002,200(3-4):287-295

The mantle electromagnetic and tomography (MELT) experiment found a surprising degree of asymmetry in the mantle beneath the fast-spreading, southern East Pacific Rise (MELT Seismic Team, Science 280 (1998) 1215–1218; Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Wolfe and Solomon, Science 280 (1998) 1230–1232; Scheirer et al., Science 280 (1998) 1221–1224; Evans et al., Science 286 (1999) 752–756). Pressure-release melting of the upwelling mantle produces magma that migrates to the surface to form a layer of new crust at the spreading center about 6 km thick (Canales et al., Science 280 (1998) 1218–1221). Seismic and electromagnetic measurements demonstrated that the distribution of this melt in the mantle is asymmetric (Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Evans et al., Science 286 (1999) 752–756) at depths of several tens of kilometers, melt is more abundant beneath the Pacific plate to the west of the axis than beneath the Nazca plate to the east. MELT investigators attributed the asymmetry in melt and geophysical properties to several possible factors: asymmetric flow passively driven by coupling to the faster moving Pacific plate; interactions between the spreading center and hotspots of the south Pacific; an off-axis center of dynamic upwelling; and/or anomalous melting of an embedded compositional heterogeneity (MELT Seismic Team, Science 280 (1998) 1215–1218; Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Wolfe and Solomon, Science 280 (1998) 1230–1232; Evans et al., Science 286 (1999) 752–756). Here we demonstrate that passive flow driven by asymmetric plate motion alone is not a sufficient explanation of the anomalies. Asthenospheric flow from hotspots in the Pacific superswell region back to the migrating ridge axis in conjunction with the asymmetric plate motion can create many of the observed anomalies.  相似文献   

Authigenic uranium: Relationship to oxygen penetration depth and organic carbon rain   总被引：3，自引：0，他引：3  

James McManus  William M. Berelson  Douglas E. Hammond 《Geochimica et cosmochimica acta》2005,69(1):95-108

We have measured U in benthic incubation chambers, sediment pore waters, and in sediments along the California continental margin. Sedimentary U uptake rates, based on a combination of sediment pore water profiles and benthic incubation chambers, generally agree with those predicted from sediment accumulation rate data. This agreement supports the view that most of the continental margin sedimentary U is delivered by diffusion across the seawater-sediment boundary. The average rate of authigenic U accumulation for all the sites examined here is ∼−0.2 nmol cm^-2 y^-1, which is consistent with published global estimates of sedimentary U uptake. In addition, the accumulation rate of U in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate. These relationships highlight the potential utility for the U accumulation rate as a proxy for these processes.  相似文献   

1-D, 2-D, and 3-D analytical solutions of unsaturated flow in groundwater     

Fred T. Tracy 《Journal of Hydrology》1995,170(1-4):199-214

An excellent tool for checking numerical models of unsaturated flow in groundwater is analytical solutions. However, because of the highly nonlinear nature of the governing partial differential equation, only a limited number of analytical solutions are available. This paper first gives some simple 1-D solutions. Next, by use of a transformation, the nonlinear partial differential equation is converted to a linear one for a specific form of the moisture content vs. pressure head and relative hydraulic conductivity vs. pressure head curves. This allows both 2-D and 3-D solutions to be derived, which is done in this paper. Finally, computations from a finite element computer program are compared with results from one of the analytical solutions to illustrate the use of the derived equations.  相似文献   

Recession curve estimation for storm event separations     

M. Hammond  D. Han   《Journal of Hydrology》2006,330(3-4):573-585

An accurate recession curve model is important for separating individual flow events, which is especially difficult over catchments in regions with a maritime climate where frequent rainfall events cause the flows to rise before they reach the baseflow level. The traditional recession curve equations are based on static linear and nonlinear reservoir models. These models work quite well for ground water dominated recession curves, but not so well when the direct runoff is significant in the recession part. In this study, a new modelling methodology is explored based on self-adaptive parameters in the linear and nonlinear reservoir models. It has been found that the adaptive forms performed better than the static ones, especially when a window for the adaptive parameter estimation is properly selected. While the nonlinear adaptive model had better accuracy over the linear one, it could become unstable if its window is too narrow, indicating that more research work is needed to find an useful pattern for the window size. A comparison between the recession curve models and PDM model (a rainfall-runoff model) has shown that they agreed quite well in most winter events, but less so in the summer.  相似文献