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Site-specific Data (site-specific + data)
Selected AbstractsLife-Cycle Performance of RC Bridges: Probabilistic ApproachCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2000Dimitri V. Val This article addresses the problem of reliability assessment of reinforced concrete (RC) bridges during their service life. First, a probabilistic model for assessment of time-dependent reliability of RC bridges is presented, with particular emphasis placed on deterioration of bridges due to corrosion of reinforcing steel. The model takes into account uncertainties associated with materials properties, bridge dimensions, loads, and corrosion initiation and propagation. Time-dependent reliabilities are considered for ultimate and serviceability limit states. Examples illustrate the application of the model. Second, updating of predictive probabilistic models using site-specific data is considered. Bayesian statistical theory that provides a mathematical basis for such updating is outlined briefly, and its implementation for the updating of information about bridge properties using inspection data is described in more detail. An example illustrates the effect of this updating on bridge reliability. [source] Characterizing sediment acid volatile sulfide concentrations in European streamsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007G. Allen Burton Abstract Sediment acid volatile sulfide (AVS) concentrations were measured in wadeable streams of a wide variety of ecoregions of western Europe (84 sites in 10 countries and nine ecoregions) to better understand spatial distribution and ecoregion relationships. Acid volatile sulfide has been shown to be a major factor controlling the bioavailability and toxicity of many common trace metals, such as Cd, Cu, Ni, Pb, and Zn. Sediment characteristics varied widely. The ratio of the sum of the simultaneously extracted metals (SEM) to AVS ranged from 0.03 to 486.59. The ,SEM-AVS ranged from ,40.02 to 17.71 ,mol/g. On a regional scale, sediment characteristics such as dominant parent soil material showed significant trends in AVS distribution and variation by ecoregion. Total Fe and Mn were correlated weakly with SEM concentrations. Three AVS model approaches (i.e., the SEMAVS ratio, SEM-AVS difference, and carbon normalization) were compared at threshold exceedance levels of SEM/AVS > 9, SEM-AVS > 2, and SEM-AVS/foc > 150 ,mol/g organic carbon (OC). Only 4.76% of the sediments exceeded all three AVS thresholds; 22.6% of the sediments exceeded two models; and 13% of the sediments exceeded one model only. Using the SEM:AVS, SEM-AVS, and fraction of organic carbon models, and including site-specific data and regional soil characteristics, ecoregions 1 (Portugal), 3 (Italy), 4 (Switzerland), and 9 (Belgium/Germany) had the highest potential metals toxicity; ecoregions 13 and 8 (Belgium/France) showed the lowest potential toxicity. However, because AVS can vary widely spatially and temporally, these data should not be considered as representative of the sampled ecoregions. The general relationship between AVS levels and sediment characteristics provides some predictive capability for wadeable streams in the European ecoregions. [source] Pumping-Induced Drawdown and Stream Depletion in a Leaky Aquifer SystemGROUND WATER, Issue 2 2007James J. Butler Jr The impact of ground water pumping on nearby streams is often estimated using analytic models of the interconnected stream-aquifer system. A common assumption of these models is that the pumped aquifer is underlain by an impermeable formation. A new semianalytic solution for drawdown and stream depletion has been developed that does not require this assumption. This solution shows that pumping-induced flow (leakage) through an underlying aquitard can be an important recharge mechanism in many stream-aquifer systems. The relative importance of this source of recharge increases with the distance between the pumping well and the stream. The distance at which leakage becomes the primary component of the pumping-induced recharge depends on the specific properties of the aquifer, aquitard, and streambed. Even when the aquitard is orders of magnitude less transmissive than the aquifer, leakage can be an important recharge mechanism because of the large surface area over which it occurs. Failure to consider aquitard leakage can lead to large overestimations of both the drawdown produced by pumping and the contribution of stream depletion to the pumping-induced recharge. The ramifications for water resources management and water rights adjudication can be significant. A hypothetical example helps illustrate these points and demonstrates that more attention should be given to estimating the properties of aquitards underlying stream-aquifer systems. The solution presented here should serve as a relatively simple but versatile tool for practical assessments of pumping-induced stream-aquifer interactions. However, this solution should not be used for such assessments without site-specific data that indicate pumping has induced leakage through the aquitard. [source] Characteristics of preferential flow and groundwater discharge to Shingobee Lake, Minnesota, USAHYDROLOGICAL PROCESSES, Issue 10 2002Hans F. Kishel Abstract Small-scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater-lake interaction within underlying organic-rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10,3 m day,1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater,lake interaction. These results suggest that site-specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge-dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Application of an adjusted ,2 statistic to site-specific data in observational dental studiesJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 1 2002Chul Ahn Abstract Background: When a binary response is observed on teeth from each subject belonging to 2 or more exposure groups, application of the usual Pearson ,2 tests is invalid, since such responses within the same subject are not independent. Consequently, special statistical methods are needed to control for the correlation among teeth (sites) within the same subject. A simple adjustment to the Pearson ,2 statistic has been proposed for comparing proportions in site-specific data. However, the required assumptions for this statistic have not yet been thoroughly addressed. These assumptions are guaranteed to hold in experimental comparisons, but may be violated in some observational studies. Method: We investigate the conditions under which the adjusted ,2 statistic is valid and examine the performance of the adjusted ,2 statistic when these conditions are violated. Results: Our simulation study shows that the adjusted ,2 statistic generally produces good empirical type I errors under the assumption of a common intracluster correlation coefficient. Even if the intracluster correlations are different, the adjusted statistic performs well when the groups have equal numbers of clusters (subjects). Conclusion: The discussion is illustrated using an observational study of caries on the roots of teeth. Zusammenfassung Hintergründe: Wenn eine binäre Antwort auf Zähne von jedem Subjekt, das zu 2 oder mehreren experimentellen Gruppen gehört, benutzt wird, ist die Anwendung des gewöhnlich genutzten Pearson ,2 Testes nicht zulässig, da solche Antworten innerhalb des selben Subjektes nicht unabhängig sind. In der Konsequent werden spezielle statistische Methoden gebraucht, um die Korrelation unter den Zähnen (Flächen) innerhalb desgleichen Subjektes zu kontrollieren. Eine simple Adjustierung zu der Pearson ,2 Statistik wurde vorgeschlagen, um die Verhältnisse der flächenspezifischen Daten zu vergleichen. Jedoch wurde sich der notwendigen Anwendung für diese Statistik noch nicht ausführlich gewidmet. Diese Anwendungen sind garantiert bei experimentellen Vergleichen anzuwenden, aber mögen in einigen beobachteten Studien verletzt werden. Methoden: Wir untersuchten die Bedingungen unter welchen der adjustierte ,2 Test richtig ist und prüften die Leistung des adjustierten ,2 Testes, wenn diese Bedingungen verletzt werden. Ergebnisse: Unsere Simulationsstudie zeigt, dass die adjustierte ,2 Statistik im Allgemeinen gute empirische Irrtümer vom Typ I erbringt unter der Anwendung eines gewöhnlichen Intracluster Korrelationskoeffizienten. Auche wenn die Intracluster-Korrelationen unterschiedlich sind, ist die adjustierte Statistik gut zu nutzen, wenn die Gruppen gleiche Nummern von Clustern haben (Subjekte). Schlußfolgerungen: Die Diskussion wird illustriert unter Nutzung einer beobachteten Studie von Wurzelkaries. Résumé Origine: Lorsqu'une réponse binaire est observée sur les dents de chaque sujet appartenant à 2 groupes ou plus, l'application du test habituel ,2 de Pearson n'est pas valable puisque de telles réponses pour le même sujet sont indépendante. En conséquence, des méthodes statistiques spéciales sont nécessaires pour contrôler les corrélation entre les dents (sites) pour le même sujet. Un simple ajustement de la statistique ,2 de Pearson a été proposée pour comparer les proportions pour les données spécifiques de sites. Cependant, les hypothèses requises pour cette statistique n'ont pas encore été consciencieusement émises. Ces hypothèses sont certifiées être valable pour les comparaisons experimentales, mais peuvent ne pas être respectées dans quelques études observationnelles. Méthode: Nous recherchons les conditions pour lesquelles la statistique ,2 ajustée est valable et examinons sa performance lorsque ces conditions ne sont pas respectées. Résultats: Notre étude simulée montre que la statistique ,2 ajustée produit généralement de bonnes érreurs empiriques de type 1 dans l'hypothèse d'un coéfficient de corrélation commun intra-groupe. Même si les corrélations intragroupes sont différentes, la statistique ,2 ajustée s'exécute bien quand les ensembles ont des nombres égaux de groupes (sujets). Conclusion: La discussion est illustrée par une étude observationnelle des caries radiculaires. [source] Modelling the supply of ecosystem services from agriculture: a minimum-data approach,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 1 2006John M. Antle We argue that to support agriculture,environmental policy decision making, stakeholders need ,quantitative back-of-the-envelope' analysis that is timely and sufficiently accurate to make informed decisions. We apply this concept to the analysis of the supply of ecosystem services from agriculture. We present a spatially explicit production model and show how it can be used to derive the supply of ecosystem services in a region. This model shows that the supply of ecosystem services can be derived from the spatial distribution of opportunity cost of providing those services. We then show how this conceptual model can be used to develop a minimum-data (MD) approach to the analysis of the supply of ecosystem services from agriculture that can be implemented with the kinds of secondary data that are available in most parts of the world. We apply the MD approach to simulate the supply of carbon that could be sequestered in agricultural soils in the dryland grain-producing region of Montana. We find that the supply curve derived from the MD approach can approximate the supply curve obtained from a more elaborate model based on site-specific data, and can do so with sufficient accuracy for policy analysis. [source] | ||||||||||