Hydrological performance of extensive green roofs in response to different rain events in a subtropical monsoon climate

Rapid urbanization transforms permeable land into developed areas with predominantly impervious surfaces, significantly increasing stormwater runoff and exacerbating the risk of pluvial flooding. Green roofs provide an attractive strategy for increasing surface permeability by mimicking pre-development hydrologic functions and mitigating flood risks in compact cities. However, the potential of this strategy has not been rigorously assessed, despite advances in global stormwater management. This is mainly due to insufficient scientific knowledge of hydrologic performance and a lack of experimental studies of rainwater-harvesting capacity under specific climatic conditions. This study evaluated the hydrologic performance of a real-scale extensive green roof (EGR) constructed in a subtropical monsoon climate in Nanjing, China. Overall, the EGR showed considerable ability to retain rainfall (mean retention ~?60%, accumulated retention ~?30%), although retention performance varied from 11% to 100% depending on the rainfall event considered, and decreased with increasing rainfall. Event-based rainfall–runoff comparisons demonstrated that the EGR retained rainwater efficiently during the early stages of a rainfall event and significantly attenuated peak runoff flows compared to bare roofs. Statistical analysis showed that total rainfall depth, rainfall duration, and substrate layer moisture influenced the overall retention most strongly, but also the percentage retention and runoff depth, highlighting the impact of substrate properties in addition to rainfall characteristics on EGR hydrologic performance. These findings provide new knowledge of and important insights into the hydrological performance of green roofs in subtropical monsoon climates, which could be used to guide EGR construction to increase landscape permeability, mitigate the risk of pluvial flooding, and enhance the climatic resilience of urban regions.

     

Urban Stormwater Runoff: A New Class of Environmental Flow Problem

Environmental flow assessment frameworks have begun to consider changes to flow regimes resulting from land-use change. Urban stormwater runoff, which degrades streams through altered volume, pattern and quality of flow, presents a problem that challenges dominant approaches to stormwater and water resource management, and to environmental flow assessment. We used evidence of ecological response to different stormwater drainage systems to develop methods for input to environmental flow assessment. We identified the nature of hydrologic change resulting from conventional urban stormwater runoff, and the mechanisms by which such hydrologic change is prevented in streams where ecological condition has been protected. We also quantified the increase in total volume resulting from urban stormwater runoff, by comparing annual streamflow volumes from undeveloped catchments with the volumes that would run off impervious surfaces under the same rainfall regimes. In catchments with as little as 5–10% total imperviousness, conventional stormwater drainage, associated with poor in-stream ecological condition, reduces contributions to baseflows and increases the frequency and magnitude of storm flows, but in similarly impervious catchments in which streams retain good ecological condition, informal drainage to forested hillslopes, without a direct piped discharge to the stream, results in little such hydrologic change. In urbanized catchments, dispersed urban stormwater retention measures can potentially protect urban stream ecosystems by mimicking the hydrologic effects of informal drainage, if sufficient water is harvested and kept out of the stream, and if discharged water is treated to a suitable quality. Urban stormwater is a new class of environmental flow problem: one that requires reduction of a large excess volume of water to maintain riverine ecological integrity. It is the best type of problem, because solving it provides an opportunity to solve other problems such as the provision of water for human use.     

Bioavailable metal uptake rate in urban stormwater determined by dialysis with receiving resins

Bioavailable metal uptake rates have been determined in urban stormwater by dialysis with receiving resins. Values at outfalls reflect the sporadic and variable nature of discharges of bioavailable metals with stormwater. Variations in the uptake rates may be explained in terms of hydrochemical processes affecting bioavailable metal mobilisation and transport in the stormwater system, including rainfall volume, rainfall acidity and gullypot interstitial water mobilisation.     

雨水回收利用生态工程及其应用——以中国科学院研究生院怀柔新校区为例

为了节约北京市的水资源,减少雨水中所携带的污染物排放对环境造成的污染,结合中国科学院研究生院怀柔新校区即将建设的实际工程,对怀柔区的自然环境特征进行了调查,并根据现有校园规划设计方案,对园区内水量平衡进行计算,在最大化收集雨水和剩余中水的基础上,得出为保持园区内水量平衡,每月所需补充或外排的水量。同时,基于水量平衡表所得出的园区内水量较为丰富的结果,采用了自然回收净化、部分间接利用的雨水回收利用生态工程,并提出雨水回收利用流程的方案:针对校园内不同汇水面上的雨水质量不同的特点,分别对它们设计了不同的回收方法,使之最终汇入园区内的景观水系。景观水体中的水通过景观水处理装置进行循环处理,保证水的质量。灌溉绿化及清洗道路可直接抽取景观水使用。应用雨水回收生态工程取得了很好的生态效益与社会效益,既节约了水资源,又可以补充地下水源,防洪减排,还能减少雨水所携带的污染物对环境的破坏。     

Evaluation Approaches for Advancing Urban Water Goals

Urban areas (especially cities) are challenged in meeting their direct water needs from local sources. They also exert strain on global water resources through their indirect (virtual) water use. Agencies concerned with urban water management have visions and goals for managing direct water use, but indirect use is only inferred in more global visions for sustainable consumption. There is limited quantification of “urban water performance” at the macro urban scale (whole of city) to monitor progress toward these goals. It is constrained by a lack of clarity about the evaluation approaches that best serve them. We ask, How can the evaluation approaches described in literature advance urban water management goals? We reviewed the utility of eight evaluation approaches, including urban water system modeling, urban metabolism (territorial and mass balance), consumption (life cycle assessment, water footprinting, and input‐output analysis), and complex systems (ecological network analysis and systems dynamics) approaches. We found that urban metabolism based on water mass balance is a core method for generating information to inform current goals for direct urban water use, with potential for being “coupled” with the other approaches. Consumption approaches inform the management of indirect water use. We describe this in a framework for urban water evaluation to give greater clarity to this field and flag the further research that would be needed to progress this. It includes the recommendation to differentiate the evaluation of direct and indirect urban water, but to also interpret them together.     

Source apportionment of non-storm water entries into storm drains using marker species: Modeling approach and verification

Inappropriate non-storm water entries into the storm drains and the resulting direct discharge into the natural environment on dry-weather days, is a challenging environmental issue in the cities worldwide. To make a preliminary evaluation of non-storm water entry situations, this study presented an approach for source apportionment of non-storm water entries into storm drains based on marker species and a chemical mass balance (CMB) model using a Monte Carlo statistical simulation. Compared with deterministic approaches, this method is capable of accounting for the measurement errors and the impact of variability of the source marker profiles resulting from heterogeneities and therefore presents the most likely range of estimated source contributions. This method was verified using measured data in a catchment in Shanghai, China, covering 374 ha. Here, inappropriate entries of sanitary wastewater, semiconductor wastewater, and groundwater into storm drains can be identified using acesulfame and citric acid, chloride, fluoride and sulfate, and total hardness, respectively, as markers. Using the measured marker profiles, the apportioned source flows were estimated with high precision in comparison to the investigated data, with a relative error less than 11%. Apportioned data revealed strong sanitary source connections to storm drains (i.e., 45.8% of the total sewage output), which were mainly from old residential communities with direct sewer connections to the storm pipes. Additionally, it revealed illicit semiconductor wastewater discharge contributed to 75% of the fluoride load, 52% of the sulfate load, and 32% of the chloride load, despite its low flow component of 9.2%. Therefore, a primary correction strategy of applying end-of-storm pipe control treatment, as well as reconnecting industrial source to the sewer network, was presented. Moreover, the marker library data associated with a variety of source types is expected to provide clear evidence for various non-storm water entry situations in future studies.     

Ecological risk assessment of urban stormwater ponds: Literature review and proposal of a new conceptual approach providing ecological quality goals and the associated bioassessment tools

Stormwater ponds are a common feature of the urban landscape in many countries with advanced stormwater management. Built to control the impacts of urbanization in the form of increased runoff flows, volumes and pollution loads, stormwater ponds are exposed to strong anthropogenic pressures. Meanwhile, as open water systems, they represent new aquatic habitats potentially enhancing the biodiversity of urban areas and balancing the transformation of original ecosystems existing prior to urbanization. In the current context of sustainable development, assessing the ecological risks of stormwater ponds serving as aquatic habitats is therefore crucial for ensuring both the preservation and rehabilitation of biodiversity in urban areas. During the last decade, ecological risk assessments applied to stormwater ponds lacked adoption of integrated interdisciplinary approaches. This prevented advances in developing adaptive methodologies for assessing the ecological quality of stormwater ponds and for providing quality objectives for the management of these facilities. Also, the application of established integrated assessment methodologies, such as the Sediment Quality Triad widely used in North America, based on comparisons with reference sites, is challenged by the man-made features of urban stormwater ponds. The search for a more specific and effective methodology led to the proposal of supplementing the Sediment Quality Triad with the Oligochaete methodology, which was developed and standardized in France for determining the biological status of sediments in stagnant water ecosystems. The benefits of this approach are discussed in a conceptual framework providing ecological quality goals for urban stormwater ponds.     

Surveying the Environmental Footprint of Urban Food Consumption

Assessments of urban metabolism (UM) are well situated to identify the scale, components, and direction of urban and energy flows in cities and have been instrumental in benchmarking and monitoring the key levers of urban environmental pressure, such as transport, space conditioning, and electricity. Hitherto, urban food consumption has garnered scant attention both in UM accounting (typically lumped with “biomass”) and on the urban policy agenda, despite its relevance to local and global environmental pressures. With future growth expected in urban population and wealth, an accounting of the environmental footprint from urban food demand (“foodprint”) is necessary. This article reviews 43 UM assessments including 100 cities, and a total of 132 foodprints in terms of mass, carbon footprint, and ecological footprint and situates it relative to other significant environmental drivers (transport, energy, and so on) The foodprint was typically the third largest source of mass flows (average is 0.8 tonnes per capita per annum) and carbon footprint (average is 2.1 tonnes carbon dioxide equivalents per capita per annum) in the reviewed cities, whereas it was generally the largest driver of urban ecological footprints (average is 1.2 global hectares per capita per annum), with large deviations based on wealth, culture, and urban form. Meat and dairy are the primary drivers of both global warming and ecological footprint impacts, with little relationship between their consumption and city wealth. The foodprint is primarily linear in form, producing significant organic exhaust from the urban system that has a strong, positive correlation to wealth. Though much of the foodprint is embodied within imported foodstuffs, cities can still implement design and policy interventions, such as improved nutrient recycling and food waste avoidance, to redress the foodprint.     

土地利用格局对SWMM模型汇流模式选择及相应产流特征的影响

城市下垫面土地利用格局与地形的复杂性将导致地表汇流模式的多变性。在城市雨洪管理模型中,不同汇流模式的选取对雨洪模拟结果产生重要影响,而这一影响往往被忽视。基于设定与巴中城市社区尺度相近的实验区以及巴中市的真实降水数据,并根据实验区土地利用格局特征,在SWMM雨洪管理模型汇水模块中设置Outlet、Impervious、Pervious 3种汇流演算模式及其演算面积比,分析了不同土地利用格局响应下的不同汇流模式选择对城市雨洪模拟结果的影响。结果表明:(1)Outlet、Impervious两种汇流演算模式下汇水区地表径流的模拟结果相同,但与Pervious演算模式下的模拟结果差异显著。在Pervious模式下地表径流相对另外两种汇流模式最大降低了52%,降雨下渗量提高了近1倍。(2)在Pervious模式下,演算面积比对汇水区地表径流模拟结果具有重要影响。在总不透水面(IA)面积一定的情况下,有效不透水面(DCIA)的减少引起非有效不透水面(UIA)的比率增加。这种土地利用格局的变化致使汇水区总径流量、径流系数显著下降,降雨下渗量逐渐增加,洪峰流量则呈先增后减的趋势,且在非有效不透水面(UIA)比率为30%和40%时(此时非有效不透水面与渗透面面积相接近),洪峰流量最小。对结果的分析表明了雨洪管理模型在小尺度汇水区上应用时,应根据土地利用格局特征选择相应的地表汇流模式。正确的评价和分析不同土地利用格局方案对地表径流的影响,从而更为科学地指导城市雨洪管理和海绵城市的规划与建设。     

Urban stormwater runoff limits distribution of platypus

The platypus (Ornithorhynchus anatinus), like many other stream‐dependent species, is reportedly sensitive to catchment urbanization. However, the primary mechanism limiting its distribution in urban environments has not been identified. We created species distribution models for three platypus demographic classes: adult females (which are exclusively responsible for raising young), adult males (which are more mobile than females), and first‐year juveniles. Using live‐trapping data collected in Melbourne, Australia, we tested whether distributions of the three demographic classes were better predicted by catchment urban density (total imperviousness), by urban stormwater runoff (catchment attenuated imperviousness), or by stream size (catchment area). Two variants of each predictor variable were developed, one that accounted for platypus mobility, and one that did not. Female distribution was most plausibly predicted by stormwater runoff (accounting for mobility), with a steep decline in reporting rate from 0 to 10% attenuated imperviousness. Male distribution was equally plausibly predicted by stormwater runoff and urban density (both accounting for mobility), with a less steep and more uncertain decline with imperviousness than females. Juvenile distribution was most plausibly predicted by stream size (accounting for mobility), but both stormwater runoff and urban density (accounting for mobility) were nearly equally plausible predictors. The superior performance of models that accounted for mobility underscores the importance of accounting for this in species distribution models of highly mobile species. Platypus populations in urban areas are likely to be affected adversely by urban stormwater runoff conveyed by conventional drainage systems, with adult females more limited by runoff‐related impacts than adult males or juveniles. Urban platypus conservation efforts have generally focused on restoring riparian and in‐stream habitats on a local scale. This is unlikely to protect platypus from adverse impacts of urban stormwater runoff, which is most effectively managed at the catchment scale.     

A Database to Facilitate a Process‐Oriented Approach to Urban Metabolism

In view of urbanization trends coupled with climate‐change challenges, it is increasingly important to establish less‐harmful means of urban living. To date, urban metabolism (UM) studies have quantified the aggregate material and energy flows into and out of cities and, further, have identified how consumer activity causes these flows. However, little attention has been paid to the networks of conversion processes that link consumer end‐use demands to aggregate metabolic flows. Here, we conduct a systematic literature search to assemble a database of 202 urban energy, water, and waste management processes. We show how the database can help planners and policy makers choose the preferred process to meet a specific resource management need; identify synergies between energy, water, and waste management processes; and compute optimal networks of processes to meet an area's consumer demand at minimum environmental cost. We make our database publicly available under an open‐source license and discuss the possibilities for how it might be used alongside other industrial ecology data sets to enhance research opportunities. This will encourage more holistic UM analyses, which appreciate how both consumer activity and the engineered urban system work together to influence aggregate metabolic flows and thus support efforts to make cities more sustainable.     

Modeling nitrate-nitrogen removal process in first-flush reactor for stormwater treatment

Stormwater runoff is one of the most common non-point sources of water pollution to rivers, lakes, estuaries, and coastal beaches. While most pollutants and nutrients, including nitrate-nitrogen, in stormwater are discharged into receiving waters during the first-flush period, no existing best management practices (BMPs) are specifically designed to capture and treat the first-flush portion of urban stormwater runoff. This paper presents a novel BMP device for highway and urban stormwater treatment with emphasis on numerical modeling of the new BMP, called first-flush reactor (FFR). A new model, called VART-DN model, for simulation of denitrification process in the designed first-flush reactor was developed using the variable residence time (VART) model. The VART-DN model is capable of simulating various processes and mechanisms responsible for denitrification in the FFR. Based on sensitivity analysis results of model parameters, the denitrification process is sensitive to the temperature correction factor (b), maximum nitrate-nitrogen decay rate (K (max)), actual varying residence time (T (v)), the constant decay rate of denitrifiying bacteria (v (dec)), temperature (T), biomass inhibition constant (K (b)), maximum growth rate of denitrifiying bacteria (v (max)), denitrifying bacteria concentration (X), longitudinal dispersion coefficient (K (s)), and half-saturation constant of dissolved carbon for biomass (K (Car-X)); a 10% increase in the model parameter values causes a change in model root mean square error (RMSE) of -28.02, -16.16, -12.35, 11.44, -9.68, 10.61, -16.30, -9.27, 6.58 and 3.89%, respectively. The VART-DN model was tested using the data from laboratory experiments conducted using highway stormwater and secondary wastewater. Model results for the denitrification process of highway stormwater showed a good agreement with observed data and the simulation error was less than 9.0%. The RMSE and the coefficient of determination for simulating denitrification process of wastewater were 0.5167 and 0.6912, respectively, demonstrating the efficacy of the VART-DN model.     

Inner city stormwater control using a combination of best management practices

Structural best management practices (BMPs) are now commonplace for stormwater management in new suburban developments; however, their installation in older central areas is limited. Here, the effect of disconnecting impervious areas from a combined sewer in favour of a new open stormwater system is investigated. The site, an inner city suburb of Malmö, Sweden, consists of council offices and apartment blocks separated by courtyards, roads and parking places. The BMPs range from green-roofs and open channels to detention ponds and their choice, size and location was dictated by cost, available land, safety and public expectations. The system was assessed by comparing synthetic hydrographs for the 1/2, 2, 5 and 10-year design-storms assuming wet and dry initial conditions. Direct runoff was simulated using the time–area method; and routing through the BMPs using PondPack. As the BMPs are in series, the outflow of one BMP became part of the inflow to the next in the system. Additionally, the water balance for the year 2001–2002 was investigated. It was found that the green-roofs are effective at lowering the total runoff from Augustenborg and that the ponds should successfully attenuate storm peak flows for even the 10-year rainfall.     

Towards a Dynamic Approach to Urban Metabolism: Tracing the Temporal Evolution of Brussels’ Urban Metabolism from 1970 to 2010

Urban metabolism (UM) is a way of characterizing the flows of materials and energy through and within cities. It is based on a comparison of cities to living organisms, which, like cities, require energy and matter flows to function and which generate waste during the mobilization of matter. Over the last 40 years, this approach has been applied in numerous case studies. Because of the data‐intensive nature of a UM study, however, this methodology still faces some challenges. One such challenge is that most UM studies only present macroscopic results on either energy, water, or material flows at a particular point in time. This snapshot of a particular flow does not allow the tracing back of the flow's evolution caused by a city's temporal dynamics. To better understand the temporal dynamics of a UM, this article first presents the UM for Brussels Capital Region for 2010, including energy, water, material, and pollution flows. A temporal evaluation of these metabolic flows, as well as some urban characteristics starting from the seminal study of Duvigneaud and Denayer‐De Smet in the early 1970s to 2010, is then carried out. This evolution shows that Brussels electricity, natural gas, and water use increased by 160%, 400%, and 15%, respectively, over a period of 40 years, whereas population only increased by 1%. The effect of some urban characteristics on the UM is then briefly explored. Finally, this article succinctly compares the evolution of Brussels’ UM with those of Paris, Vienna, Barcelona, and Hong Kong and concludes by describing further research pathways that enable a better understanding of the complex functioniong of UM over time.     

Using spatially explicit commodity flow and truck activity data to map urban material flows

To analyze and promote resource efficiency in urban areas, it is important to characterize urban metabolism and particularly, material flows. Material flow analysis (MFA) offers a means to capture the dynamism of cities and their activities. Urban‐scale MFAs have been conducted in many cities, usually employing variants of the Eurostat methodology. However, current methodologies generally reduce the study area into a “black box,” masking details of the complex processes within the city's metabolism. Therefore, besides the aggregated stocks and flows of materials, the movement of materials—often embedded in goods or commodities—should also be highlighted. Understanding the movement and dispersion of goods and commodities can allow for more detailed analysis of material flows. We highlight the potential benefits of using high‐resolution urban commodity flows in the context of understanding material resource use and opportunities for conservation. Through the use of geographic information systems and visualizations, we analyze two spatially explicit datasets: (1) commodity flow data in the United States, and (2) Global Positioning System‐based commercial vehicle (truck) driver activity data in Singapore. In the age of “big data,” we bring advancements in freight data collection to the field of urban metabolism, uncovering the secondary sourcing of materials that would otherwise have been masked in typical MFA studies. This brings us closer to a consumption‐based, finer‐resolution approach to MFA, which more effectively captures human activities and its impact on urban environments.     

The Changing Metabolism of Cities

Data from urban metabolism studies from eight metropolitan regions across five continents, conducted in various years since 1965, are assembled in consistent units and compared. Together with studies of water, materials, energy, and nutrient flows from additional cities, the comparison provides insights into the changing metabolism of cities. Most cities studied exhibit increasing per capita metabolism with respect to water, wastewater, energy, and materials, although one city showed increasing efficiency for energy and water over the 1990s. Changes in solid waste streams and air pollutant emissions are mixed.
The review also identifies metabolic processes that threaten the sustainability of cities. These include altered ground water levels, exhaustion of local materials, accumulation of toxic materials, summer heat islands, and irregular accumulation of nutrients. Beyond concerns over the sheer magnitudes of resource flows into cities, an understanding of these accumulation or storage processes in the urban metabolism is critical. Growth , which is inherently part of metabolism, causes changes in water stored in urban aquifers, materials in the building stock, heat stored in the urban canopy layer, and potentially useful nutrients in urban waste dumps.
Practical reasons exist for understanding urban metabolism. The vitality of cities depends on spatial relationships with surrounding hinterlands and global resource webs. Increasing metabolism implies greater loss of farmland, forests, and species diversity; plus more traffic and more pollution. Urban policy makers should consider to what extent their nearest resources are close to exhaustion and, if necessary, appropriate strategies to slow exploitation. It is apparent from this review that metabolism data have been established for only a few cities worldwide, and interpretation issues exist due to lack of common conventions. Further urban metabolism studies are required.     

基于韧性理念的中国城市雨洪管理研究热点与趋势

在中国洪涝灾害频发的背景下,海绵城市等雨洪管理实践有助于灾害的缓解,提高城市应对雨洪的“韧性”。韧性城市作为应对灾害风险的城市规划理念,已被应用于一些国家的雨洪风险管理中。本文基于韧性理念,运用科学计量分析工具CiteSpace梳理中国雨洪研究现状,从生态、工程、社会雨洪韧性3方面分析了雨洪管理热点与相关技术,发现在跨领域的雨洪系统管理、区域到街区间不同空间尺度用地调蓄管理方面存在不足,提出未来应构建以“生态-工程-社会”为核心,涵盖“区域-城市-街区”尺度,多技术集成为支撑的自适应韧性雨洪管理体系。     

Measuring Progress towards a Circular Economy: A Monitoring Framework for Economy‐wide Material Loop Closing in the EU28

The concept of a circular economy (CE) is gaining increasing attention from policy makers, industry, and academia. There is a rapidly evolving debate on definitions, limitations, the contribution to a wider sustainability agenda, and a need for indicators to assess the effectiveness of circular economy measures at larger scales. Herein, we present a framework for a comprehensive and economy‐wide biophysical assessment of a CE, utilizing and systematically linking official statistics on resource extraction and use and waste flows in a mass‐balanced approach. This framework builds on the widely applied framework of economy‐wide material flow accounting and expands it by integrating waste flows, recycling, and downcycled materials. We propose a comprehensive set of indicators that measure the scale and circularity of total material and waste flows and their socioeconomic and ecological loop closing. We applied this framework in the context of monitoring efforts for a CE in the European Union (EU28) for the year 2014. We found that 7.4 gigatons (Gt) of materials were processed in the EU and only 0.71 Gt of them were secondary materials. The derived input socioeconomic cycling rate of materials was therefore 9.6%. Further, of the 4.8 Gt of interim output flows, 14.8% were recycled or downcycled. Based on these findings and our first efforts in assessing sensitivity of the framework, a number of improvements are deemed necessary: improved reporting of wastes, explicit modeling of societal in‐use stocks, introduction of criteria for ecological cycling, and disaggregated mass‐based indicators to evaluate environmental impacts of different materials and circularity initiatives. This article met the requirements for a gold – gold JIE data openness badge described at http://jie.click/badges .     

Effects of urbanization on streams of the Melbourne region, Victoria, Australia. I. Benthic macroinvertebrate communities

1. Macroinvertebrate community composition was assessed in small streams of the Melbourne region to test the effects of (a) urban density (catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).
2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high-EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.
3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.
4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams.     

Stormwater Runoff Pollutant Loading Distributions and Their Correlation with Rainfall and Catchment Characteristics in a Rapidly Industrialized City

Fast urbanization and industrialization in developing countries result in significant stormwater runoff pollution, due to drastic changes in land-use, from rural to urban. A three-year study on the stormwater runoff pollutant loading distributions of industrial, parking lot and mixed commercial and residential catchments was conducted in the Tongsha reservoir watershed of Dongguan city, a typical, rapidly industrialized urban area in China. This study presents the changes in concentration during rainfall events, event mean concentrations (EMCs) and event pollution loads per unit area (EPLs). The first flush criterion, namely the mass first flush ratio (MFFn), was used to identify the first flush effects. The impacts of rainfall and catchment characterization on EMCs and pollutant loads percentage transported by the first 40% of runoff volume (FF₄₀) were evaluated. The results indicated that the pollutant wash-off process of runoff during the rainfall events has significant temporal and spatial variations. The mean rainfall intensity (I), the impervious rate (IMR) and max 5-min intensity (I_max5) are the critical parameters of EMCs, while I_max5, antecedent dry days (ADD) and rainfall depth (R_D) are the critical parameters of FF₄₀. Intercepting the first 40% of runoff volume can remove 55% of TSS load, 53% of COD load, 58% of TN load, and 61% of TP load, respectively, according to all the storm events. These results may be helpful in mitigating stormwater runoff pollution for many other urban areas in developing countries.