Effects of restricted recharge in an urban karst system     

Laura?ToranEmail author  Kathleen?Gross  Youa?Yang 《Environmental Geology》2009,58(1):131-139

Urban karst systems are typically considered more vulnerable to contamination and excess storm discharge because of potential source areas, increased sediment loading, and focusing of water from impervious surfaces. However, urban hydrology can lead to unexpected patterns, such as pirating of recharge into man-made storm systems. Valley Creek Basin in southeastern Pennsylvania, presents such an urban karst system. Four springs were monitored for suspended sediment, water chemistry, and storm response for an 18-month period. The baseflow suspended sediment concentrations were low, less than 4.0 mg/l. Furthermore, trace metal analysis of baseflow water samples and spring mouth sediment showed only low concentrations. The response to storms within the system was rapid, on the order of 1–3 h. The maximum water stage increases at the urban springs were typically less than 15 cm, with springs from more commercialized areas showing <2 cm increase. A nearby retention basin, in contrast, had water level rises of 100 cm, suggesting that pirating of recharge into stormwater systems occurs. Thus, the concept of an urban karst system as a contaminant conduit is not the only one that applies. In Valley Creek Basin, reduced infiltration due to paving led to smaller storm response and less contaminant input, and the smaller capture area due to diversion of stormwater led to short flow paths and rapid storm response. Although contaminant levels have not increased due to urbanization, the springs may be at risk for future contamination. Short flow paths may reduce flushing, which means that the system will not cleanse itself if contamination occurs.  相似文献   

GRIDA3—a shared resources manager for environmental data analysis and applications     

Fabrizio Murgia  Riccardo Biddau  Alessandro Concas  Roberto Demontis  Luca Fanfani  Zeno Heilmann  Cristian Lai  Giuditta Lecca  Eva Lorrai  Marino Marrocu  Vittorio Alessandro Marrone  Laura Muscas  Elisaveta Peneva  Andrea Piras  Massimo Pisu  Gabriella Pusceddu  Guido Satta  Daniela Theis  Andrea Vacca  Paolo Valera  Ana Melina Vallenilla Ferrara  Ernesto Bonomi 《Earth Science Informatics》2009,2(1-2):5-21

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains.  相似文献   

Overcoming Challenges Associated with the Analysis of Nacre by Atom Probe Tomography     

Katja Eder  Laura M. Otter  Limei Yang  Dorrit E. Jacob  Julie M. Cairney 《Geostandards and Geoanalytical Research》2019,43(3):385-395

In this study atom probe tomography was used to study nacre, an important biocomposite material that is challenging to prepare and analyse by atom probe and, when successful, yields data that is challenging to interpret. It was found that these challenges mainly arise from the insulating and heterogeneous nano‐scale properties of nacre. We outline our current best practice for preparing and running atom probe tips, such as using a low acceleration voltage (< 3 kV) and current (≤ 50 pA) to avoid damage to the microstructure, and using transmission electron microscopy to confirm that the region of interest is located close to the apex of the atom probe tip. Optimisation of the preparation parameters led to several successful atom probe experiments, with one of the data sets containing part of an organic membrane and others showing organic inclusions within the reconstruction.  相似文献   

Improved Monte Carlo inversion of surface wave data   总被引：2，自引：0，他引：2  

Laura Valentina Socco  Daniele Boiero 《Geophysical Prospecting》2008,56(3):357-371

Inversion of surface wave data suffers from solution non‐uniqueness and is hence strongly biased by the initial model. The Monte Carlo approach can handle this non‐uniqueness by evidencing the local minima but it is inefficient for high dimensionality problems and makes use of subjective criteria, such as misfit thresholds, to interpret the results. If a smart sampling of the model parameter space, which exploits scale properties of the modal curves, is introduced the method becomes more efficient and with respect to traditional global search methods it avoids the subjective use of control parameters that are barely related to the physical problem. The results are interpreted drawing inference by means of a statistical test that selects an ensemble of feasible shear wave velocity models according to data quality and model parameterization. Tests on synthetic data demonstrate that the application of scale properties concentrates the sampling of model parameter space in high probability density zones and makes it poorly sensitive to the initial boundary of the model parameters. Tests on synthetic and field data, where boreholes are available, prove that the statistical test selects final results that are consistent with the true model and which are sensitive to data quality. The implemented strategies make the Monte Carlo inversion efficient for practical applications and able to effectively retrieve subsoil models even in complex and challenging situations such as velocity inversions.  相似文献   

Patterns of water, heat, and solute flux through streambeds around small dams   总被引：1，自引：0，他引：1  

Fanelli RM  Lautz LK 《Ground water》2008,46(5):671-687

Hyporheic exchange, enhanced by complex stream channel morphology, can influence biogeochemical processing in the streambed. These processes chemically alter water passing temporarily through the streambed, which eventually returns to the stream channel and can potentially affect surface water quality. To assess the degree of biogeochemical cycling induced by complex streambed morphology, we instrumented two 20-m reaches of Red Canyon Creek, Wyoming, each containing a small log dam, with in-stream minipiezometers and temperature data loggers. We simultaneously observed pore water geochemistry and streambed temperature dynamics in several bedforms located upstream or downstream of the dams. We modeled seepage flux into the streambed using heat transport modeling.
Upstream of the dams, low-permeability sediments have settled out in low-velocity pools, and enhanced anaerobic biogeochemical cycling occurred in the streambed. Rapid flux into the streambed occurred in glides immediately above the dams, where streambed temperature dynamics and geochemistry were nearly identical to the stream. In riffle sequences downstream of the dams, the streambed was oxygen rich, showed evidence of nitrification, and temperature dynamics indicated high connectivity between the streambed and the stream. Further downstream, streambed pore water geochemistry indicated ground water discharge occurring at the pool-riffle transition. Assessing streambed biogeochemical cycling may be facilitated by coupling streambed temperature measurements with pore water geochemistry and can aid in understanding how hyporheic exchange contributes to overall stream biogeochemistry.  相似文献   

Probabilistic evaluation of seismic performance of 3‐story 3D one‐ and two‐way steel moment‐frame structures     

Hiroyuki Tagawa  Gregory MacRae  Laura Lowes 《地震工程与结构动力学》2008,37(5):681-696

This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Unsteady thermoelastic analysis of a circular disk with a hot central core and subjected to adiabatic conditions     

Carlos A. Rossit  Patricio A. A. Laura 《Ocean Engineering》2000,27(4)

The unsteady thermoelastic analysis of a cooling circular disk or cylinder which is originally at uniform temperature is a classical problem of the theory of thermal stresses. More recent studies consider the case of composite structural configurations. The present paper deals with a situation which, apparently, has not been previously considered: unsteady thermal stresses caused by the presence of a hot, central nucleus. The temperature field is obtained in terms of a Fourier–Bessel expansion and then, radial and tangential stresses are evaluated analytically. The problem is of basic interest in mechanical and naval engineering systems.  相似文献   

BET_EF: a probabilistic tool for long- and short-term eruption forecasting   总被引：6，自引：3，他引：3  

Warner Marzocchi  Laura Sandri  Jacopo Selva 《Bulletin of Volcanology》2008,70(5):623-632

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Sensitivity Analysis of Three-Dimensional Steady-State and Transient Spray Irrigation Models     

David Heebner  Laura Toran 《Ground water》2000,38(1):20-28

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CRAFIT: A Computer Program for Calibrating Breakthrough Curves of CRAFLUSH, a One-Dimensional Fracture Flow and Transport Model     

Laura Toran 《Ground water》2000,38(3):430-434

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