NUMERICAL STUDIES ON AIRFLOW AND POLLUTANT DISPERSION IN URBAN STREET CANYONS FORMED BY SLANTED ROOF BUILDINGS

Based on the CFD technique, fifteen cases were evaluated for the airflows and pollutant dispersions inside urban street canyons formed by slanted roof buildings. The simulated wind fields and concentration contours show that W/H, W/h and h/H (where W is the street width, and H and h are the heights of buildings at the leeward and windward sides of the street, respectively) are the crucial factors in determining the vortex structure and pollutant distribution within a canyon. It is concluded that (1) in a symmetrical canyon, at W/H =0.5 two vortices (an upper clockwise vortex between the slanted roofs and a lower counter-clockwise one) are developed and pollutants accumulate on the windward side of the street, whereas at W/H=2.0 only one clockwise vortex is generated and thus pollution piles up on the leeward side, (2) in a step-up canyon with W/H =0.5 to 2.0 (at h/H =1.5 to 2.0)and a step-down canyon with W/h=1.0 (at h/H =0.5 to 0.667), the pollution level close to the lower building is higher than that close to the taller building since a clockwise vortex is generated in the step-up canyon and a counter-clockwise one in the step-down canyon, (3) in a narrow step-down canyon with W/h=0.5 (at h/H =0.667) very poor ventilation properties is detected, and inside a wider step-down canyon with W/h=2.0 the vortex structure and consequently pollutant distribution varies greatly with h/H.     

TRAFFIC EMISSION TRANSPORTATION IN STREET CANYONS

Spatial distributions of traffic-related pollutants in street canyons were investigated by field measurements and Computational Fluid Dynamics (CFD). Two typical street canyons were selected for field monitoring, and a three-dimensional numerical model was built based on Reynolds-averaged Navier–Stokes equations equipped with the standard k ? ε turbulence models for CFD simulations. The study shows that the pollutant concentrations of vehicle emission correlate well with the traffic volume variation, wind d...     

优选数值计算方法用于不对称街道峡谷的研究

分别将迎风、混合及调和QUICK格式用于对称街道峡谷的汽车排放污染物浓度预测,并与风洞实验结果相比较,研究表明数值模拟与风洞实验吻合较好,调和QUICK格式的预测效果最佳。将调和QUICK格式用于不对称街道峡谷的研究,发现当迎风面建筑物高于背风面建筑物时,峡谷内的流场和浓度场与对称街道峡谷相似,即峡谷内有一个顺时针方向的强漩涡,使得背风面污染物浓度高于迎风面污染物浓度。同时,随着迎风面建筑物高度的增加,漩涡中心的位置成垂直向上分布,且与迎风面建筑物的高度基本成线性关系;当迎风面建筑物低于背风面建筑物且差别较大时,街道峡谷内出现了两个反时针方向旋转的强漩涡,使得峡谷内的流场与浓度场都发生较大的变化,迎风面污染物浓度会高于背风面污染物浓度。同时表明,峡谷上方的顺时针方向漩涡的中心呈抛物线向右上方向发展,而峡谷下方的逆时针方向旋涡的中心呈抛物线向左E方向发展。     

Impact of roof surface runoff on urban water quality

The pollutant impacts of urban stormwater runoff on receiving waters are well documented in research literature. However, it is road surfaces that are commonly identified as the significant pollutant source. This paper presents the outcomes of an extensive program of research into the role of roof surfaces in urban water quality with particular focus on solids, nutrients and organic carbon. The outcomes confirmed that roof surfaces play an important role in influencing the pollutant characteristics of urban stormwater runoff. Pollutant build-up and wash-off characteristics for roads and roof surfaces were found to be appreciably different. The pollutant wash-off characteristics exhibited by roof surfaces show that it influences the first flush phenomenon more significantly than road surfaces. In most urban catchments, as roof surfaces constitute a higher fraction of impervious area compared with road surfaces, it is important that the pollutant generation role of roof surfaces is specifically taken into consideration in stormwater quality mitigation strategies.     

城市对称街道峡谷气流及污染物扩散特征的研究

与风洞实验的对比表明数值模拟能较好地预测街道峡谷浓度场。研究了宽、窄两种峡谷（高宽比范围为0．17～3．25）的内部流场和浓度场。表明：当高宽比大于1时,随着高宽比的增加,峡谷内旋涡数逐渐增多,污染物浓度也随着旋涡的变化而变化;当高宽比小于1时,峡谷内由一个旋涡演变为两个方向相反的旋涡,随着高度的进一步减小,两个旋涡开始左右分离,其浓度也随着旋涡的变化而变化。当旋涡为顺时针时,使得背风面污染物浓度出现显著上升的趋势,而当旋涡为逆时针时,会使得迎风面的污染物浓度出现显著上升的趋势。总体看来,随着建筑物高度的增加,污染物难以扩散,从而使峡谷近地面处的污染物浓度增大。     

乌东德水电站蓄水对攀枝花河段水环境的影响

攀枝花市区河段位于乌东德水库库尾。水库蓄水后，由于水流流速减缓，污染物迁移、扩散能力减弱，攀枝花市河段水功能区纳污能力将有所减小，有必要对乌东德水电站水库蓄水后攀枝花市区河段的水体纳污能力进行分析，并提出相应的水污染控制措施。从乌东德水库蓄水对攀枝花市区河段的纳污能力、主要取水口水质、钒钛产业园区岸边污染带的影响以及钒钛产业园区事故排污几个方面分析了乌东德水库蓄水对攀枝花市区河段水环境的影响，并提出了相应的保护对策，以实现水资源的持续利用和环境建设的协调发展。     

The Role of Green Roofs as a Source/sink of Pollutants in Storm Water Outflows

Green roofs are increasingly used as sustainable urban drainage systems due to their retention and detention capacity; however, the impact of green roofs in term of water quality is still a debated issue among researchers. A monitoring programme was carried out at the University of Genoa on a full-scale experimental site to assess the quality of storm water outflows. As for rainfall, the bulk deposition (dry and wet fractions) is collected to evaluate the role of the overall atmospheric deposition in altering storm water quality. The pollutant load observed in the green roof outflow is limited; concentration values for solids and metals are lower than those generally observed in storm water runoff from impervious surfaces. Suspended solids and Chemical Oxygen Demand (COD) are below respectively 10 and 20 mg/l, on average; as for heavy metals, copper and zinc are equal to 30 μg/l on average, while iron is equal to 120 μg/l. The Event Mean Concentration (EMC) statistics of the pollutant loads associated with the rainfall and outflow have been compared and discussed. The observed green roof behaviour as a sink/source of pollutants with respect to the atmospheric deposition is also investigated based on both concentration and mass. Results demonstrate that: green roof behaves as a source with respect to solids, COD and potassium while zinc and mainly copper are retained within the green roof stratigraphy. The resulting mass delivery behaviour reveals that no significant first flush occurs for pollutant constituents irrespective of the hydrologic characteristics and pollutant sources.     

邯郸市区不同下垫面降雨径流水质变化特征研究

为缓解邯郸市城区水资源供需矛盾,合理利用雨洪资源,在对生活区屋面、城区道路、公园绿地降雨径流水质进行检测的基础上,分析了雨水径流中主要污染物的变化过程,探讨降雨径流水质受环境条件影响情况。通过研究得出城区初期雨水径流污染最为严重,随降雨历时的延长,污染物浓度逐渐下降并趋于稳定。不同城区下垫面雨水径流污染物含量差异明显,城区主干道路降雨径流水质最差。     

地震波斜入射下深厚覆盖层河谷加速度分布特征分析

我国西部地区普遍具有高山峡谷和深厚河床覆盖层的特点,而对于深厚覆盖层河谷场地的地震动分布特征的研究却很少。本文采用黏弹性人工边界及其相关地震动等效荷载输入的方法,研究了地震动P波和SV波入射角度及入射波峰值对深厚覆盖层河谷场地加速度放大系数分布特征的影响。结果表明：（1） P波和SV波入射角度一定时,入射波峰值对河谷两岸平台及岸坡的加速度放大系数影响很小;（2） P波左侧入射时,随着入射角度的增大,左岸平台及岸坡x分量的加速度放大系数增幅较大,z分量的加速度放大系数增幅较小保持在2倍左右,河谷覆盖层表面x和z分量加速度放大系数逐渐趋于均匀分布;（3） SV波左侧入射时,随着入射角度增大,整个河谷覆盖层表面x分量的加速度放大系数呈现出坡脚附近较小,中间部位和两岸平台较大;z分量放大系数呈现出相反的规律。这些结论可以为具有覆盖层河谷工程场址的地震动参数设计及加速度监测点布置提供一定的参考。     

Area proportion optimization of different LID facilities and effect of runoff pollution controlEI北大核心CSCD

为探究低影响开发（LID）设施对缓解城市洪涝灾害以及削减污染物负荷的效果，以淮南市某老旧小区为研究对象，基于SWMM模型构建了暴雨径流管理模型，分析了单项LID设施不同面积占比时的总成本效益，针对4种LID设施组合方案，模拟了不同设计降雨重现期的地表径流、排放口流量及污染负荷。结果表明：对于单项LID设施，占屋顶总面积45%的绿色屋顶、占不透水道路面积60%的渗透铺装和占绿地总面积10%的生物滞留设施总成本效益最高；不同LID设施组合均有较好的雨洪控制效果及污染物削减效果，但随着降雨量的增大，效果均有所减小。     

Priority organic pollutants in the urban water cycle (Toulouse, France)

Application of the European Water Framework Directive requires Member States to have better understanding of the quality of surface waters in order to improve knowledge of priority pollutants. Xenobiotics in urban receiving waters are an emerging concern. This study proposes a screening campaign of nine molecular species of xenobiotics in a separated sewer system. Five sites were investigated over one year in Toulouse (France) using quantitative monitoring. For each sample, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, nonylphenols, diethelhexylphthalate, linear alkylbenzene sulphonates, methyl tert-butylether, total hydrocarbons, estradiol and ethinylestradiol were analysed. Ground, rain and roof collected water concentrations are similar to treated wastewater levels. Run-off water was the most polluted of the five types investigated, discharged into the aquatic environment. The wastewater treatment plant reduced xenobiotic concentrations by 66% before discharge into the environment. Regarding environmental quality standards, observed concentrations in waters were in compliance with standards. The results show that xenobiotic concentrations are variable over time and space in all urban water compartments.     

初期弃流后板房屋面雨水污染物质量浓度衰减规律

为研究初期雨水弃流后不同降雨重现期条件下屋面雨水的污染物质量浓度变化规律,以板房屋面为例,采用3 mm的初期雨水弃流深度,基于暴雨径流管理模型(SWMM),构建了板房屋面径流模型,在采用雨水收集箱中污染物质量浓度实测值对模型验证后,模拟分析了不同降雨重现期板房屋面雨水的污染物质量浓度衰减规律.结果表明:雨水收集箱中污染...     

NUMERICAL MODELING PURIFICATION PERFORMANCE OF POT TEST

A three-dimensional mathematical model was developed to simulate the pollutant removal efficiency of the soil and plants in the pot test. The advection, dispersion, diffusion, adsorption, biochemical reaction and plant uptake processes were taken into account in the model. The three-dimensional modified Richards equation was used in simulating flow field. The mass balance law was employed in deriving the equation for pollutant transport, where the diffusion and dispersion were described with the Fick-type law, the adsorption was macroscopically expressed as form isotherm, and the bio-chemical degradation process was assumed to follow the Monod kinetics. The mathematical model was descretized by the finite element numerical method. In the pot test, the hydraulic loading was assumed to have the intermittent pattern simulating the rainfall duration and the occurrence of frequency, and the concentrations of pollutants in the influent and effluent were measured. The computed overall removal rates for the COD_Cr and TN in four cases are in the range of 90.62% ? 95.43% and 85.01% ? 96.46%, respectively. The differences between the computed and tested overall removal rates for the COD_Cr and TN are smaller than 5%. The time-varying oscillation pattern of the concentrations of the COD_Cr and TN were rationally simulated, which showed that the model presented in this article could be used to assess the pollutant removal efficiency of the soil and plants in related cases.     

城区雨水管网径流污染特征研究

以新乡市城区屋面作为汇水区域,开展试验对雨水管网中场次降雨径流水文水质过程进行研究,可为有效利用城市雨水、控制非点源污染等提供依据。水质指标包括SS、COD和TN。结果表明:水质指标中SS、COD变化趋势基本一致,随着降雨过程的持续浓度逐渐降低并趋于一个稳定值;TN随着雨量的累积浓度逐渐降低,但在降雨结束前有反弹趋势;指标标准差率呈SS>COD>TN的趋势;径流初期屋面冲刷效应明显,初期径流量可定义为前1³mm的降雨量;径流中SS与COD、TN之间的相关性较好,在控制径流污染时可采取措施同时去除;径流污染物直接通过城区排水管网汇入受纳水体后对其水质影响较大,尤以SS、COD的变化最为明显。     

利用数字图像处理技术测量浓度场的实验研究

利用数字图像处理技术是当前研究环境污染物扩散机理的重要手段。该文通过水槽实验,分析了污染物图像的灰度与污染物的浓度、光源的距离以及排放口所在水深的关系,并建立了污染物浓度与图像灰度关系的方程。利用该方程对射流在横流中测量的图像进行了浓度场计算,得到的结果与实际情况吻合较好,因此,该方法能广泛应用于物质扩散机理的研究。     

城市屋顶降雨径流过程单位线模型研究

城市屋顶按透水性质可分为不透水与绿色(渗透)屋顶.对于绿色屋顶,基于土壤水饱和下渗理论,考虑基质土壤层厚度有限性及表面积水深影响,推导建立了降雨径流过程的单位线模型,再联合不透水屋顶降雨径流过程单位线模型,共同构成城市屋顶降雨径流过程的单位线模型,并建立了统一的数学方程表达形式,参数包括响应速率与径流(产流)起始时间....     

Aerial photographic analysis of channel narrowing and vegetation expansion in Canyon De Chelly National Monument,Arizona, USA, 1935–2004

Aerial photographs from the past 70 years show narrowing of channels in Canyon de Chelly National Monument, which coincided with the establishment and expansion of woody riparian vegetation, primarily non‐native tamarisk (Tamarix ssp.) and Russian olive (Elaeagnus angustifolia) and native cottonwood (Populus spp.). Rectified air photo sets were used to map the extent of woody riparian vegetation cover in the canyon bottom as well as the channel planform geometry for 6 years: 1935, 1964, 1975, 1981, 1989 and 2004. In 1935, vegetation covered less than 1 per cent of the canyon bottom and the channel was braided and 91 m wide on average. By 2004, the channel in the upper 75% of the canyon had narrowed to a single thread an average of 6.5 m wide and was lined by riparian vegetation, with vegetation covering up to 45% of the canyon bottom in some reaches. A relative timing index was developed that incorporates information from both channel and vegetation area expansion or contraction into a single variable. Vegetation establishment lagged channel narrowing in the upper reaches of the canyons, but narrowing and vegetation establishment occurred simultaneously in the middle and lower reaches. Narrowing progressed downstream through time, and the lowermost reaches remained braided and unincised in 2006. We interpret these patterns to suggest that riparian vegetation is responding to and interacting with changes in the channel morphology of Canyon de Chelly rather than driving channel change. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrocarbons and heavy metals fixed to the lift station sediment of the Paris combined sewer network.

This work aims to characterise the pollutant loads fixed to the Lift Station (LS) sediments. Firstly, levels of n-alkanes, PAH and heavy metals (Fe, Zn, Cu, Pb and Cd) of LS sediments were assessed, and were found of the same order of magnitude as those reported for street runoff. In addition, investigations on LS sediment reveal that n-alkane distributions reflect the combination of biologic and petrogenic inputs, while PAH distributions indicate a major pyrolytic origin with traces of petrogenic contaminations. The metallic fingerprints also attest to the important contribution of road traffic emissions. Secondly, a comparison between LS sediment and the Gross Bed Sediment (GBS) pollutant contamination was established in order to optimize the in-sewer deposits management. For hydrocarbons, a similar contamination between both sediments is found. For the heavy metals, this comparison indicates a similar Fe and Zn content, while Pb, Cu and Cd contents differ. Indeed, LS sediment shows a higher Cu content, linked to the occurrence of intensive brake lining abrasion, compared with GBS, which reflects a higher Pb and Cd content, owing to the contribution of roof runoff. This result reveals the impact of specific inputs such as road traffic or roof runoff on the in-sewer sediments contamination, and provides a complete overview of the LS sediment contamination. This database could be used by the municipality to optimize their contaminated in-sewer sediment management.     

围垦工程对沙枉河口污染物输运影响分析

河口两侧实施围垦工程改变了河口形态和动力环境,对河口污染物输运也将产生一定影响。以连云港市赣榆县沙枉河口为例,采用平面二维扩散输运模型对河口两侧高滩围垦工程实施前后沙枉河口污染物输运的影响范围进行了数值计算,分析了河口两侧浅滩围垦工程对河口污染物输运范围的影响。分析结果表明,河口两侧浅滩实施围垦工程使得河口过流通道缩窄,具有排放口向深水迁移的效应,有利于河口受污水体向动力较强的深水区稀释;但围垦工程实施使得通道和前沿区域动力改变,当两侧围垦工程前沿水流减弱时,动力变化不利于污染物输运;相反,围垦工程促使前沿水流增加时,动力变化则有利于污染物输运。