Air ventilation impacts of the “wall effect” resulting from the alignment of high-rise buildings

The objective of this study is to investigate the air ventilation impacts of the so called “wall effect” caused by the alignment of high-rise buildings in complex building clusters. The research method employs the numerical algorithm of computational fluid dynamics (CFD – FLUENT) to simulate the steady-state wind field in a typical Hong Kong urban setting and investigate pollutant dispersion inside the street canyon utilizing a pollutant transport model. The model settings of validation study were accomplished by comparing the simulation wind field around a single building block to wind tunnel data. The results revealed that our model simulation is fairly close to the wind tunnel measurements. In this paper, a typical dense building distribution in Hong Kong with 2 incident wind directions (0° and 22.5°) is studied. Two performance indicators are used to quantify the air ventilation impacts, namely the velocity ratio (VR) and the retention time (T_r) of pollutants at the street level. The results indicated that the velocity ratio at 2 m above ground was reduced 40% and retention time of pollutants increased 80% inside the street canyon when high-rise buildings with 4 times height of the street canyon were aligned as a “wall” upstream. While this reduction of air ventilation was anticipated, the magnitude is significant and this result clearly has important implications for building and urban planning.     

Participatory diagnosis in urban planning: proposal for a learning process based on geographical information

Urban planning involves compromise between the diverse and often contradictory issues supported by the different stakeholders. The literature generally agrees on the need to broaden the participation base to overcome this difficulty. However, participation should not be limited to problem solving, but should also take place in the problem setting phase. This paper proposes a participatory diagnosis process for structuring the problem setting phase. We describe an experiment in a participatory diagnosis conducted with the residents of a Geneva neighborhood. The experiment began by identifying the residents' concerns, which were then reformulated under broader issues. Some 20 spatial indicators were built using GIS tools, and were then applied in a second phase of resident consultations to assess the relative importance of each issue. The ensuing priority issues formed the core of the diagnosis. The approach emphasized comparison between the daily experiences of residents and so-called official information (i.e. census tract, traffic measurement, and so on). The residents were therefore involved in a learning process that allowed them to consolidate or modify their opinions. The process led to the emergence of a clearly defined collective awareness that supplanted individual aspirations.     

Rapid Assessment of Urban Wetlands: Do Hydrogeomorphic Classification and Reference Criteria Work?

The Hydrogeomorphic (HGM) functional assessment method is predicated on the ability of hydrogeomorphic wetland classification and visual assessment of alteration to provide reference standards against which functions in individual wetlands can be evaluated. The effectiveness of this approach was tested by measuring nitrogen cycling functions in forested wetlands in an urbanized region in New Jersey, USA. Fourteen sites represented three HGM classes and were characterized as “least disturbed reference” or “non-reference” based on initial visual assessment. Water table levels and in situ rates of net nitrogen mineralization, net nitrification, and denitrification were measured over one year in each site. Hydrological alterations, resulting in consistently low or flashy water table levels, were not correlated with a priori designations as reference and non-reference. Although the flat-riverine wetland class had lower net nitrification and higher denitrification rates than riverine or mineral flat wetland classes, this difference was attributable to the lack of hydrologically-altered wetlands in the flat-riverine class, and thus more consistently wet conditions. Within all HGM classes, a classification based on the long-term hydrological record that separated sites with “normal,” saturated hydrology from those with “altered,” drier hydrology, clearly distinguished sites with different nitrogen cycling function. Based on these findings, current practices for designating reference standard sites to judge wetland functions, at least in urbanized regions, are ineffective and potentially misleading. At least one year of hydrological monitoring data is suggested to classify wetlands into groups that have different nutrient cycling functions, particularly in urban landscapes.     

Spatio-temporal variations in water quality of Nullah Aik-tributary of the river Chenab, Pakistan

This study reports the spatio-temporal changes in water quality of Nullah Aik, tributary of the Chenab River, Pakistan. Stream water samples were collected at seven sampling sites on seasonal basis from September 2004 to April 2006 and were analyzed for 24 water quality parameters. Most significant parameters which contributed in spatio-temporal variations were assessed by statistical techniques such as Hierarchical Agglomerative Cluster Analysis (HACA), Factor Analysis/Principal Components Analysis (FA/PCA), and Discriminant Function Analysis (DFA). HACA identified three different classes of sites: Relatively Unimpaired, Impaired and Less Impaired Regions on the basis of similarity among different physicochemical characteristics and pollutant level between the sampling sites. DFA produced the best results for identification of main variables for temporal and spatial analysis and separated eight parameters (DO, hardness, sulphides, K, Fe, Pb, Cr and Zn) that accounted 89.7% of total variations of spatial analysis. Temporal analysis using DFA separated six parameters (E.C., TDS, salinity, hardness, chlorides and Pb) that showed more than 84.6% of total temporal variation. FA/PCA identified six significant factors (sources) which were responsible for major variations in water quality dataset of Nullah Aik. The results signify that parameters identified by statistical analyses were responsible for water quality change and suggest the possibility of industrial, municipal and agricultural runoff, parent rock material contamination. The results suggest dire need for proper management measures to restore the water quality of this tributary for a healthy and promising aquatic ecosystem and also highlights its importance for objective ecological policy and decision making process.     

Computational Fluid Dynamics Modelling of the Pollution Dispersion and Comparison with Measurements in a Street Canyon in Helsinki

A measuring campaign was conducted in a street canyon (Runeberg St.) in Helsinki in 2003–2004. The concentrations of NO _x , NO₂, PM₁₀ and PM_2.5 were measured at street level and at roof level at an urban background location. This study utilises the data measured from 1 Jan to 30 April, 2004, when wind speed and direction measurements were also conducted on-site at the roof level. The computational fluid dynamics model ADREA-HF was used to compute the street concentrations, and the results were compared with the measurements. The predictions for the selected cases agreed fairly well (within < 25 % for 15 min average values) with the measured data, except for two cases: a windward flow in case of a low wind speed, and a moderate southerly flow parallel to the street canyon. The main reasons for the differences of predictions and measurements are the negligence of traffic-induced turbulence in the modelling and an under-prediction of ventilation of urban background air from a crossing street. Numerical results are presented for various example cases; these illustrate the formation of the vortices in the canyon in terms of the wind direction and speed and the influence of the characteristics of the flow fields on the concentration distributions.     

Three-Dimensional Modeling of an Urban Park and Trees by Combined Airborne and Portable On-Ground Scanning LIDAR Remote Sensing

In this study, we confirmed the utility of airborne and portable on-ground scanning light detection and ranging (LIDARs) for three-dimensional visualization of an urban park and quantification of biophysical variables of trees in the park. The digital canopy height model (DCHM) and digital terrain model generated from airborne scanning LIDAR data provided precise images of the ground surface and individual tree canopies. The heights of 166 coniferous and broadleaf trees of 11 species in the park were estimated from the DCHM images with slight underestimation (mean error = −0.14 m, RMSE = 0.30 m). Portable on-ground scanning LIDAR provided images of individual trees with detailed features. Tree height and trunk diameter were estimated to be within 0.31 m and 1 cm, respectively, from the on-ground LIDAR images. We combined airborne and on-ground LIDAR images to overcome blind regions and created a complete three-dimensional model of three standing trees. The model allowed not only visual assessment from all viewpoints but also quantitative estimation of canopy volume, trunk volume, and canopy cross-sectional area.     

Assessment of a turfgrass sod best management practice on water quality in a suburban watershed

The disposal of manure on agricultural land has caused water quality concerns in many rural watersheds, sometimes requiring state environmental agencies to conduct total maximum daily load (TMDL) assessments of stream nutrients, such as nitrogen (N) and phosphorus (P). A best management practice (BMP) has been developed in response to a TMDL that mandates a 50% reduction of annual P load to the North Bosque River (NBR) in central Texas. This BMP exports composted dairy manure P through turfgrass sod from the NBR watershed to urban watersheds. The manure-grown sod releases P slowly and would not require additional P fertilizer for up to 20 years in the receiving watershed. This would eliminate P application to the sod and improve the water quality of urban streams. The soil and water assessment tool (SWAT) was used to model a typical suburban watershed that would receive the sod grown with composted dairy manure to assess water quality changes due to this BMP. The SWAT model was calibrated to simulate historical flow and estimated sediment and nutrient loading to Mary's Creek near Fort Worth, Texas. The total P stream loading to Mary's Creek was lower when manure-grown sod was transplanted instead of sod grown with inorganic fertilizers. Flow, sediment and total N yield were the same for both cases at the watershed outlet. The SWAT simulations indicated that the turfgrass BMP can be used effectively to import manure P into an urban watershed and reduce in-stream P levels when compared to sod grown with inorganic fertilizers.     

山东半岛城市群城市就业结构变动特征分析

通过对山东半岛城市群就业结构的分析,揭示出山东省城市就业结构的一般规律。从对城市群各城市的分析来看,第一产业的就业人员占据较大比重,城市化水平较低。第二产业的从业人员比重较稳定,第三产业的就业比重总体上升,但其中的传统性行业的就业比重趋于下降而新兴行业比重提高。     

Spatial concentration distributions of sulfur dioxide and nitrogen oxides in Patras, Greece, in a winter period

An economic and quick methodology for performing a preliminary spatial assessment of a city air quality with the purpose to identify locations and zones susceptible to high pollution levels is proposed. A Patras case-study is selected, regarding the air pollutants of sulfur dioxide (SO₂) and oxides of nitrogen (NO_x). A total number of 451 samples of short duration, of which 225 were randomly picked in morning rush hours and 226 within evening rush hours, were collected from 50 locations of the major Patras area during a year period, when peaks of primary air pollutants usually occur. Concentration measurements at prescribed locations used to statistically calculate spatial average concentrations approximating 1-h mean values with mean probable errors less than 25.9% for SO₂, NO and NO_x and less than 15.5% for NO₂. Then iso-concentration contour diagrams plotted indicate high pollution zones and possibly appropriate locations for continuous or random monitoring according to the European Community (EC) Directives. The 1-h mean concentrations were in good correlation to the corresponding traffic rates and useful relationships are given (0.54 ≤ r ≤ 0.63). In addition, comparisons with data available for other cities, as well as with the limit and guide values provided by the EC and the World Health Organization (WHO) were given. The present data could be useful for the design and optimization of a city network of stations for monitoring air quality, for environmental impact assessments, future reference and comparisons due to city development needs, as well as for validating dispersion models.     

Characteristic Air Temperature Distributions Observed in Summer and Winter in Urban Area in Japan

The air temperature distributions in August (summer) and December (winter) were measured in an approximately 15 × 15-km urban area in Hyogo Prefecture, Japan, in order to study the spatial distribution of the air temperature and to propose effective measures against the heat island phenomenon. The air temperature was measured mainly by using thermometer shelters installed in an elementary school and a junior high school. The characteristic air temperature distribution depended on the season. The air temperature was higher inland than in the coastal region in August but was higher in the coastal region in December. The air temperature index indicated that the area where higher air temperatures would most likely appear was 5 to 10 km inland from the coast in August and around the coast in December. The seasonal air temperature distribution was presumably due to the strength of solar radiation and anthropogenic exhaust heat.