Impacts of Upstream Building Width and Upwind Building Arrangements on Airflow and Pollutant Dispersion in a Street Canyon

A two-dimensional numerical model for evaluating the wind flow and pollutant dispersion within a street canyon was first developed using the FLUENT code, which was then validated against a wind tunnel experiment. Then, the effects of the upstream building width and upwind building arrangement on the airflow and pollutant dispersion inside an isolated street canyon were investigated numerically. The numerical results revealed that: (1) the in-canyon vortex center shifts downwards as the upstream building width increases; (2) the recirculation zone covers the entire upstream building roof for the cases when W/H = 0.5, 1.0, 1.5, and 2.0 (W is the upstream building width and H is the building height), whereas the flow reattaches the upstream building roof for the cases when W/H = 2.5 and 3.0; (3) when the upstream building width is shorter than the critical width W_C (= 2H), an increase in the upstream building width leads to an increase in the pollution level on the leeward wall of the canyon and a decrease in the roof-level concentrations at the upstream building; (4) when the upstream building width is longer than the critical width, the roof-level concentrations at the upstream building are negligibly small and the pollution level on the leeward wall of the canyon is almost unaffected by a further increase in the upstream building width; (5) when the buildings are placed upwind of the canyon, the flow attaches the upstream building roof and, therefore, almost none of the pollutants are distributed on the upstream building roof; and (6) the pollution levels inside the canyon and on the downstream building roof increase significantly with the number of upwind buildings.     

VARIABILITY IN MEASURED BEDLO AD-TRANSPORT RATES1

ABSTRACT: Variability in bedload-transport rates during constant water discharge is an inherent part of the bedload-transport process. Although this variability has been measured extensively in the laboratory, similar information generally is not available from field measurements. During a four-day period of nearly constant water discharge, four sets of consecutively collected bedload samples, ranging from 43 to 120 samples, were obtained at the same cross channel location using a standard 65-pound Helley-Smith bedload sampler. When the measured transport rates are converted to dimensionless rates and plotted as cumulative frequency distributions, they show good agreement with a theoretical probability distribution function of rates derived for the case of ripples on dunes. The distributions show that during constant water discharge individual measured rates at a fixed point vary from near zero to four times the mean rate, and 60 percent of the sampled rates will be less than the mean. Because of the large variation in transport rates that occurs at every location in the cross section, many observations are required to establish an accurate estimate of the mean rate at any given location.     

IDENTIFICATION OF AQUIFER DISPERSIVITIES: METHODS OF ANALYSIS AND PARAMETER UNCERTAINTY1

ABSTRACT: This paper presents a method for estimating aquifer dispersivities in solute transport models. Sensitivity equations are derived for the calculation of sensitivity coefficients. A modified Gauss-Newton algorithm is used to perform the least-squares minimization. A statistical procedure is outlined to assess reliability of the estimated parameters. The solute transport model is solved by the upstream weighted, multiple cell balance method which combines the concepts of local mass balance and finite element approximations. A one-dimensional solute transport problem in a vertical column system is first used to illustrate the inverse technique. A second example considers the parameter identification problem for three-dimensional solute transport with a unidirectional steady and uniform flow field. The third example solves the parameter identification problem in a three-dimensional, stream-aquifer, solute transport system with steady state flow. Numerical experiments are conducted to study data requirements for parameter identification.     

STATISTICAL METHODS AND SAMPLING DESIGN FOR ESTIMATING STEP TRENDS IN SURFACE-WATER QUALITY1

ABSTRACT: This paper addresses two components of the problem of estimating the magnitude of step trends in surface water quality. The first is finding a robust estimator appropriate to the data characteristics expected in water-quality time series. The Hodges-Lehmann class of estimators is found to be robust in comparison to other nonparametric and moment-based estimators. A seasonal Hodges-Lehmann estimator is developed and shown to have desirable properties. Second, the effectiveness of various sampling strategies are examined using Monte Carlo simulation coupled with application of this estimator. The simulation is based on a large set of total phosphorus data from the Potomac River. To assure that the simulated records have realistic properties, the data are modeled in a multiplicative fashion incorporating flow, hysteresis, seasonal, and noise components. The results demonstrate the importance of balancing the length of the two sampling periods and balancing the number of data values between the two periods. The inefficiency of sampling at frequencies much in excess of 12 samples per year is demonstrated. Rotational sampling designs are discussed, and efficient designs, at least for this river and constituent, are shown to involve more than one year of active sampling at frequencies of about 12 per year.     

Evaluating the effects of spatial monitoring policy on groundwater quality portrayal

What size sample is sufficient for spatially sampling ambient groundwater quality? Water quality data are only as spatially accurate as the geographic sampling strategies used to collect them. This research used sequential sampling and regression analysis to evaluate groundwater quality spatial sampling policy changes proposed by California's Department of Water Resources. Iterative or sequential sampling of a hypothetical groundwater basin's water quality produced data sets from sample sizes ranging from 2.8% to 95% coverage of available point sample sites. Contour maps based on these sample data sets were compared to an original (control), mapped hypothetical data set, to determine at which point map information content and pattern portrayal are not improved by increasing sample sizes. Comparing series of contour maps of ground water quality concentration is a common means of evaluating the geographic extent of groundwater quality change. Comparisons included visual inspection of contout maps and statistical tests on digital versions of these map files, including correlation and regression products. This research demonstrated that, down to about 15% sample site coverage, there is no difference between contour maps produced from the different sampling strategies and the contout map of the original data set.     

A FIELD TECHNIQUE FOR WEIGHING BEDLOAD SAMPLES1

ABSTRACT: A technique for weighing bedload samples that was developed for laboratory use has been modified for field application. The technique involves determining the submerged weight of bedload samples as they are collected. The submerged weights are converted to dry weights from a knowledge of the specific gravity of the bedload material. The technique makes bedload transport data available immediately and eliminates costly and time-consuming steps involved with saving samples for laboratory analysis. Only samples designated for particle-size or other lab analyses need to be saved.     

Testing hypotheses about management to enhance habitat for feeding birds in a freshwater wetland

The level of water was manipulated in a freshwater wetland, with the aim of enhancing abundances of benthic animals and, ultimately, improving habitat for feeding birds (Japanese Snipe, Gallinago hardwickii). We tested whether these actions had the predicted and desired effects on benthic animals, by contrasting changes in two managed locations to one control location which was left unmanipulated. The number of taxa and abundances of chironomids decreased strongly and significantly in the manipulated locations, while the abundance of oligochaetes appeared to vary in a seasonal manner. Temporal variability of the structure and composition of assemblages was also increased in manipulated locations. Such effects have previously been suggested to indicate stress in benthic assemblages. Therefore, in contrast to what was predicted, managerial actions made benthic fauna less abundant and thus, less suitable as habitat for feeding birds. Several general lessons can be learned from these results. (1) Effects of managerial actions like these are difficult to predict a priori and can only be reliably evaluated with an experimental framework. (2) Because abundances of animals vary naturally, evaluations of managerial actions must include appropriate spatial replication. (3) Sampling at hierarchical temporal scales is important, because abundances of animals may vary in an unpredictable manner at short temporal scales and because changes in temporal variability may be a symptom of stress. (4) Combined use of uni- and multivariate techniques provides a comprehensive set of tools to assess the effects of restoration and creation of new habitats. Finally, these results emphasise the need for clear predictions about desired outcomes and specific experimental plans about how to test whether the desired results were achieved, before managerial actions are taken. Although this is often very difficult to achieve in real situations, it is necessary for practices of management to evolve on the basis of sound empirical experience.     

Did Child Restraint Laws Globally Converge? Examining 40 Years of Policy Diffusion

Objective: The objective of the current study is to determine what factors have been associated with the global adoption of mandatory child restraint laws (ChRLs) since 1975.

Methods: In order to determine what factors explained the global adoption of mandatory ChRLs, Weibull models were analyzed. To carry out this analysis, 170 countries were considered and the time risk corresponded to 5,146 observations for the period 1957–2013. The dependent variable was first time to adopt a ChRL. Independent variables representing global factors were the World Health Organization (WHO) and World Bank's (WB) road safety global campaign; the Geneva Convention on Road Traffic; and the United Nation's (UN) 1958 Vehicle Agreement. Independent variables representing regional factors were the creation of the European Transport Safety Council and being a Commonwealth country. Independent variables representing national factors were population; gross domestic product (GDP) per capita; political violence; existence of road safety nongovernmental organizations (NGOs); and existence of road safety agencies. Urbanization served as a control variable. To examine regional dynamics, Weibull models for Africa, Asia, Europe, North America, Latin America, the Caribbean, and the Commonwealth were also carried out.

Results: Empirical estimates from full Weibull models suggest that 2 global factors and 2 national factors are significantly associated with the adoption of this measure. The global factors explaining adoption are the WHO and WB's road safety global campaign implemented after 2004 (P <.01), and the UN's 1958 Vehicle Agreement (P <.001). National factors were GDP (P <.01) and existence of road safety agencies (P <.05). The time parameter ρ for the full Weibull model was 1.425 (P <.001), suggesting that the likelihood of ChRL adoption increased over the observed period of time, confirming that the diffusion of this policy was global. Regional analysis showed that the UN's Convention on Road Traffic was significant in Asia, the creation of the European Transport Safety Council was significant in Europe and North America, and the global campaign was in Africa. In Commonwealth and European and North American countries, the existence of road safety agencies was also positively associated with ChRL adoption.

Conclusions: Results of the world models suggest that the WHO and WB's global road safety campaign was effective in disseminating ChRLs after 2004. Furthermore, regions such as Asia and Europe and North America were early adopters since specific regional and national characteristics anticipated the introduction of this policy before 2004. In this particular case, the creation of the European Transport Safety Council was fundamental in promoting ChRLs. Thus, in order to introduce conditions to more rapidly diffuse road safety measures across lagging regions, the maintenance of global efforts and the creation of road safety regional organizations should be encouraged. Lastly, the case of ChRL convergence illustrates how mechanisms of global and regional diffusion need to be analytically differentiated in order better to assess the process of policy diffusion.