How appropriate is the Thiem equation for describing groundwater flow to actual wells?     

Franziska Tügel  Georg J. Houben  Thomas Graf 《Hydrogeology Journal》2016,24(8):2093-2101

The Thiem equation of radial groundwater flow to a well is more than 100 years old and is still commonly used. Here, deviations caused by some of its simplifications are quantified by comparing the analytical to a numerical model that allows the implementation of more complex geometries. The assumption of horizontal flow in the Thiem equation, which necessitates uniform inflow over the entire screen length of the fully penetrating well, was found to cause deviations from actual pumping wells where the pump is placed above the screen, resulting in non-uniform inflow and additional drawdown. The same applies to partially penetrating wells, where inflow peaks and additional drawdown occur, especially when the well is screened in the lower part of the aquifer. The use of the Thiem equation in the near-field of a well should thus be restricted to situations where the screen inflow is relatively uniformly distributed, e.g. when it covers large portions of the aquifer thickness. The presence of a gravel pack and a background gradient, on the other hand, are of limited importance.  相似文献   

New records of cold‐water coral sites and fish fauna characterization of a potential network existing in the Mediterranean Sea          下载免费PDF全文

Gianfranco D'Onghia  Crescenza Calculli  Francesca Capezzuto  Roberto Carlucci  Angela Carluccio  Porzia Maiorano  Alessio Pollice  Pasquale Ricci  Letizia Sion  Angelo Tursi 《Marine Ecology》2016,37(6):1398-1422

New cold‐water coral (CWC) sites were recorded along the Apulian margin (Central Mediterranean). The species composition and depth distribution of CWCs were updated. A distribution of the CWC sites coincident with the course of the dense‐water masses that flow between the Southern Adriatic and Northern Ionian was confirmed. The faunal assemblages of five of these CWC sites were investigated and compared using experimental longlines during the spring–summer and autumn–winter seasons, between 2010 and 2014. Differences in ecological variables amongst the sites in each season were evaluated by means of a set of univariate and multivariate methods (analysis of variance, permutational multivariate analysis of variance, non‐metric multidimensional scaling). Although some differences were detected in relation to the different depths examined during spring–summer, the CWC sites showed similar features in terms of species richness and diversity as well as in the abundance of the same fish species (Galeus melastomus, Conger conger, Helicolenus dactylopterus, Merluccius merluccius, Phycis blennoides and Pagellus bogaraveo) most probably because of the distribution of adult specimens in structurally complex and heterogeneous habitats, which act as a potential ‘refuge network’ with respect to commercial fishing. The presence of maturing and mature individuals as well as post‐reproductive females indicates that these CWC sites also act as spawning areas, representing a potential ‘renewal network’ for the fish populations. The term ‘network’ used here refers to several similar subsystems (CWC sites) that play the same ecological role in a wider system (Apulian margin). These CWC communities need coherent conservation measures and management strategies according to the Ecosystem Approach to Fisheries.  相似文献   

Pivotal principles for digital earth development in the twenty-first century     

Cheryl Desha  Timothy Foresman  Annapurna Vancheswaran  Angela Reeve  John Hayes 《International Journal of Digital Earth》2017,10(4):371-385

ABSTRACT

Reductionist thinking will no longer suffice to address contemporary, complex challenges that defy sectoral, national, or disciplinary boundaries. Furthermore, lessons learned from the past cannot be confidently used to predict outcomes or guide future actions. The authors propose that the confluence of a number of technology and social disruptors presents a pivotal moment in history to enable real time, accelerated, and integrated action that can adequately support a ‘future earth’ through transformational solutions. Building on more than a decade of dialogues hosted by the International Society for Digital Earth (ISDE), and evolving a briefing note presented to delegates of Pivotal 2015, the paper presents an emergent context for collectively addressing spatial information, sustainable development, and good governance through three guiding principles for enabling prosperous living in the twenty-first century. These are: (1) open data, (2) real-world context, and (3) informed visualization for decision support. The paper synthesizes an interdisciplinary dialogue to create a credible and positive future vision of collaborative and transparent action for the betterment of humanity and planet. It is intended that these Pivotal Principles can be used as an elegant framework for action toward the Digital Earth vision, across local, regional, and international communities and organizations.  相似文献   

Assessment of hydrodynamic simulation results for eco‐hydraulic and eco‐hydrological applications: a spatial semivariance approach     

Nicholas J. Clifford  Philip J. Soar  Oliver P. Harmar  Angela M. Gurnell  Geoffrey E. Petts  Joanne C. Emery 《水文研究》2005,19(18):3631-3648

Output from a three‐dimensional numerical flow model (SSIIM) is used in conjunction with high‐resolution topographic and velocity data to assess such models for eco‐hydraulic applications in river channel design and habitat appraisal. A new methodology for the comparison between field measurement and model output is detailed. This involves a comparison between conventional goodness‐of‐fit approaches applied to a spatially structured (riffle and pool) sample of model and field data, and a ‘relaxation’ method based upon the spatial semivariance of model/field departures. Conventional assessment indicates that the model predicts point‐by‐point velocity characteristics on a 0·45 m mesh to within ±0·1 m s⁻¹ over 80% of the channel area at low flow, and 50% of the area at high in‐bank flow. When a relative criterion of model fit is used, however, the model appears to perform less well: 60–70% of channel area has predicted velocities that depart from observed velocities by more than 10%. Regression analysis of observed and predicted velocities gives more cause for optimism, but all of these conventional indicators of goodness of fit neglect important spatial characteristics of model performance. Spatial semivariance is a means of supplementing model appraisal in this respect. In particular, using the relaxation approach, results are greatly improved: at a high in‐bank flow, the model results match field measurements to within 0·1 m s⁻¹ for more than 95% of the total channel area, provided that model and field comparisons are allowed within a radius of approximately 1 m from the original point of measurement. It is suggested that this revised form of model assessment is of particular relevance to eco‐hydraulic applications, where some degree of spatial and temporal dynamism (or uncertainty) is a characteristic. The approach may also be generalized to other environmental science modelling applications where the spatial attributes of model fits are of interest. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

An assessment of the utility of regional diatom‐based tidal‐level transfer functions     

Graham P. Wilson  Angela L. Lamb 《第四纪科学杂志》2012,27(4):360-370

In order to understand natural sea‐level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom‐based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom‐based tidal‐level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site‐specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal‐level transfer functions, may be more appropriate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Erratum to: Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands     

Angela Fontán Bouzas  Javier Alcántara-Carrió  Isabel Montoya Montes  Andrés Barranco Ojeda  Silvia Albarracín  Jaime Rey Díaz de Rada  Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):231-231

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Evaluating the impact of increasing temperatures on changes in Soil Organic Carbon stocks: sensitivity analysis and non-standard discrete approximation     

Diele  Fasma  Luiso  Ilenia  Marangi  Carmela  Martiradonna  Angela  Woźniak  Edyta 《Computational Geosciences》2022,26(5):1345-1366

Computational Geosciences - The SOC change index, defined as the normalized difference between the actual Soil Organic Carbon and the value assumed at an initial reference year, is here tailored to...  相似文献   

Nest building in a Mediterranean wrasse (Symphodus ocellatus): are the algae used randomly chosen or actively selected?          下载免费PDF全文

Mauro Sinopoli  Carlo Cattano  Renato Chemello  Angela Timpanaro  Valeria Timpanaro  Michele Gristina 《Marine Ecology》2015,36(4):942-949

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A Different View of Solar Spectral Irradiance Variations: Modeling Total Energy over Six-Month Intervals     

Thomas N. Woods  Martin Snow  Jerald Harder  Gary Chapman  Angela Cookson 《Solar physics》2015,290(10):2649-2676

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The Bonn Agreement Aerial Surveillance programme: trends in North Sea oil pollution 1986-2004     

Carpenter A 《Marine pollution bulletin》2007,54(2):149-163

This paper examines the use of aerial surveillance activities conducted in the North Sea region of Europe since 1986 to assess trends in levels of oil inputs into the marine environment, both across the whole region and within the waters of the different coastal states. It makes use of data collected under the aegis of the 1969 Bonn Agreement through its Annual Reports on Aerial Surveillance and examines developments in surveillance methods and technology which have led to improvements in the detection of oil spills, even during the hours of darkness. The paper then examines country specific data for the eight North Sea contracting parties to the Agreement to assess trends in oil spills in the region.  相似文献