Search Results (57)

The objective of this research was to assess the first flush of rainwater harvested from a fibre–cement roof in southern Brazil. Runoff samples were collected for quantifying pH, total suspended solids, turbidity, conductivity, apparent colour, total coliforms, and Escherichia coli. Statistical methods were employed to describe the data, establish correlations between variables, and assess if the antecedent dry weather periods and rainfall intensity affected water quality. The qualitative characterisation of the first flush was performed using principal component analysis and simple regression analyses. The results show that rainwater runoff can be highly contaminated. Hypothesis tests showed that initial rainfall intensity and antecedent dry weather periods affect the quality of the first flush. Principal component analysis suggested that the most significant variables to characterise the first flush were turbidity and apparent colour. Using first-flush diverters in rainwater harvesting systems does not ensure E. coli removal, but it may reduce the risk of users’ contamination. Practical implications include discussions on the suggested first flush and the consequential impact on the quantity and quality of rainwater harvested. Future studies may consider using the method used in this research to develop guidelines based on more samples across the country. As novelty, one includes a statistically robust qualitative study in a region that lacks research on the quantification and quality of first flush. Such assessment helps to build up Brazilian data for a better understanding of first flush management in rainwater harvesting. Full article

Green roofs (GRs) are increasingly implemented for stormwater management, and retrofitting conventional roofs is emerging as a key strategy for climate change resilience. However, their impact on diffuse pollution, particularly regarding total organic carbon (TOC) and pollutant mass transport, remains insufficiently understood, especially in aged substrates. This study evaluated and compared the runoff quality from aged GRs and ceramic roofs (CRs) by analyzing TOC, pH, electrical conductivity (EC), first-flush occurrence and intensity, and pollutant release patterns. Results showed that GR retrofitting could help mitigate acid-rain effects due to its elevated pH. Despite higher TOC and EC concentrations in runoff, GRs remained within acceptable water quality limits and exhibited a more gradual release of organic matter over time compared with CRs. Statistical analysis revealed that pollutant concentrations in CR runoff followed Lognormal and Weibull distributions, while GR runoff was best described by Normal, Lognormal, and Weibull distributions. These findings reinforce GRs as a viable stormwater management strategy but highlight the need for full runoff treatment when used for rainwater harvesting. The results also emphasize the importance of tailored statistical models to enhance runoff predictions and optimize GR performance in urban water management. The results provide valuable insights for urban planners and policymakers by reinforcing the potential of GRs in stormwater quality management and supporting the development of incentives for green infrastructure. Future research should expand to different GR configurations, climates, and maintenance practices to enhance the understanding of long-term hydrological and water quality performance. Full article

Nature-based solutions play an essential role in enhancing urban soil hydrology by improving water retention properties, reducing surface runoff, and improving water infiltration. This bibliometric analysis study reviewed the literature and identified the current trends in research related to nature-based solutions in urban soil hydrology. The study has the potential to highlight current research areas and future hot topics in this specific field. The research used the Scopus database to collect published articles from 1973 to 2023. The keywords (“trees” OR “vegetation” OR “green infrastructure” OR “blue green infrastructure” OR “greenery” OR “nature-based solutions” AND “hydrolog*” AND “urban” OR “city” OR “soil”) were searched in the Scopus database, and 13,276 articles were retrieved. The obtained publications were analyzed for bibliometric analysis by using Bibliometrix (v4.3.0) and VOSviewer (v1.6.20) software. The maximum number of publications (970) related to nature-based solutions and urban soil hydrology was published in 2023. Additionally, countries such as the United States and China published 54.2% of articles of the global research in the field of nature-based solutions and urban soil hydrology, with 36% from the USA and 18.2% of articles from China. The bibliometric analysis depicted that Beijing Normal University led this specific research field with 540 articles. The top country in terms of collaboration was the USA, with 26.17% as compared to the global countries. The most productive researcher identified was Jackson, T.J., as he had the highest number of publications, showing his considerable contribution to the field. Furthermore, the most frequent keywords used in this research area were hydrology, ecosystem services, urban hydrology, remote sensing, nature-based solutions, climate change, runoff, stormwater management, water quality, vegetation, green roof, bioretention, and land use. The early research trending topics in this field from 2015 to 2023 were remote sensing, soil moisture, climate change, drought, green infrastructure, machine learning, and nature-based solutions. The bibliometric analysis identified limited interdisciplinary research integrations, not using well-significant and standardized methodologies for the evaluation of urban soil hydrology, and under-representation of research from developing countries as current research gaps. Future research directions highlight advanced methods such as combining data-driven technologies with traditional hydrological approaches, and increasing international collaboration, specifically in developing nations, to address urban soil hydrological problems properly. Full article

Sustainable Urban Drainage Systems (SUDS) represent a paradigm shift in stormwater management, offering holistic solutions to urban water challenges. This review examines SUDS principles, design strategies, effectiveness and barriers to implementation. SUDS prioritize infiltration and mimic natural hydrological processes to reduce flood risk, improve water quality and support ecosystems in urban environments. Effective SUDS design integrates different components such as permeable pavements, green roofs, and rain gardens, tailored to the local context. Evidence suggests that well-designed SUDS can mitigate peak flows, reduce runoff volumes, and purify water. However, barriers to widespread adoption include lack of awareness, upfront costs, and regulatory complexity. Overcoming these will require collaborative stakeholder action to prioritize education, policy support, and funding opportunities. Future research should focus on optimizing SUDS design, assessing long-term performance, and quantifying socio-economic benefits. By integrating SUDS into urban landscapes, cities can strengthen hydrological resilience, promote sustainability, and enrich urban life. Full article

Intensifying urbanization and climate change have highlighted the growing role of low-impact development (LID) practices in urban rainwater management systems. However, there is still room for improvement to optimally deploy LID practices, especially under different confluence relationships. In this study, 36 scenarios were designed based on different rainfall conditions, LID practices, confluence relationships, and locations, which were analyzed using hybrid hydraulic and water quality modeling. The following key results were obtained: (1) Series II was the main confluence path in the study area. The greenbelt occupied a large share; accordingly, the control of waterlogging and non-point source pollution in series II was better in the designed rainfall scenarios. (2) In the designed rainfall scenarios, series I had the best mitigation effect on waterlogging and non-point source pollution, with 24.5%, 16.4%, and 15.2% lower values than those of the series II and Parallel scenarios. There were no significant differences among the three confluence relationships under extreme rainfall. (3) Among the different LID practices, bioretention cells contributed to the maximum reduction in pollution (29.91%). Green roofs and permeable pavement resulted in the maximum reductions in total runoff (27.99% and 22.94%, respectively), and permeable pavement also reduced pollution by 26.50%. These results suggest that the pavement at some waterlogging points should be replaced with permeable pavement to avoid the negative effects of future extreme rainfall. Full article

Urbanization increases the number of impervious surfaces in watersheds, reducing infiltration and evapotranspiration, which increases runoff volumes and the risks of flooding and the pollution of water resources. Nature-based solutions (NBS) mitigate these effects by managing water volume and quality, restoring the hydrological cycle, and creating sustainable livelihoods that can promote socioeconomic equity by providing green space. In light of the aforementioned information, this study analyzes the hydrological response of NBS in La Guapil, a densely populated and socioeconomically vulnerable area of Costa Rica with approximately 80% impervious surfaces, focusing on their effectiveness in stormwater management and improving hydrological conditions. Field data from the study area’s storm drainage system, as well as hydrological analyses, were collected and processed to evaluate RCP8.5 climate change scenarios using the Clausius–Clapeyron (CC) relationship. Three scenarios were proposed: (1) the “status quo”, reflecting current conditions, (2) green roofs and green improvements, and (3) detention ponds and green improvements, evaluated using the SWMM, with the latter scenario also using the Iber model. Simulations showed that Scenario 2 achieved the greatest reduction in peak flow (53.74%) and runoff volume (57.60%) compared to Scenario 3 (peak: 28.37%; volume: 56.42%). Both scenarios demonstrate resilience to climate change projections. The results of this study provide a foundation for further research into NBS in Costa Rica and other comparable regions. Full article

Green infrastructure (GI) provides considerable benefits, including stormwater runoff management, biodiversity conservation, and urban sustainability promotion, and thus has garnered widespread attention. However, the limited research on residents’ preferences for GI constrains further promotion in China. To address this issue, data were collected from 436 residents in Wuhan, China, through an online survey. This study employed a comprehensive analytical framework that integrates best–worst scaling (BWS) with the contingent valuation method (CVM) to assess the preferences of residents in Wuhan, China, for six types of GI and estimate their willingness to pay (WTP) for GI enhancements. The conditional model and mixed logit model results indicated that residents preferred GI facilities that offer direct benefits, such as street trees and permeable pavements, and showed a lower preference for structures less suited to a Chinese context, such as eco-roofs. Regarding heterogeneity, only permeable pavements showed significant variation in preferences. Furthermore, the average WTP for GI enhancement was 142.28 RMB/household/year. Factors including familiarity with GI, information sources, and air quality improvement perceptions positively influenced the WTP, while low income negatively impacted the WTP. These findings offer insights for urban planners to develop effective policies to enhance public support for GI and promote urban sustainability. Full article

The issue of combined sewer overflow (CSO) triggered by rainfall has become a significant obstacle to the improvement of water environment quality. This study conducted a long-term monitoring of three types of rainwater outlets, i.e., combined sewer overflows (Test-CSO), separated sewer outlets (Test-SSO), and partially separated sewer outlets (Test-PSSO), to reveal the characteristics of overflow pollution and trace its sources by monitoring the pollutants from different underlying surfaces across various urban functional areas. The results showed that the major pollutants in overflow events exhibited the following order: COD ≥ TSS > TN > TAN > TP. Rainwater elevated COD and TSS in the Test-CSO, while reducing nitrogen and phosphorus concentrations by dilution. The Test-PSSO experienced varying degrees of overflow pollution, primarily due to the sewer sediment. A negative relationship between the rainfall and peak time of overflow pollution was observed. The traceability analysis indicated the overall pollution intensity exhibited the following order: residential areas > industrial parks > commercial areas. In addition to commercial areas, the pollution intensity across underlying surfaces generally exhibited the following order: roofs > roads > grasslands. The roof runoff was an important source of pollutants for overflow pollution, and TSS and COD were the major contributors. Notably, grasslands had a buffering effect on pollutants and pH. Full article

Rapid climate change and increasing water use have led to various problems in small- and medium-sized urban streams during dry periods, such as stream drying, water pollution, and ecological degradation, reducing their physical and ecological functions. Ensuring adequate baseflow and improving water quality during these critical periods are essential for maintaining urban stream health. While previous studies have explored the effects of Low Impact Development (LID) techniques (e.g., green roof, rainwater harvesting system, permeable pavement, infiltration trench) on infiltration and groundwater recharge, they have primarily focused on general flow regimes rather than dry and low-flow periods. This study specifically evaluates the effects of LID techniques on securing baseflow and improving water quality during dry periods, utilizing the SWAT-MODFLOW model and the Web-based Hydrograph Analysis Tool (WHAT) system. The results show that LID techniques reduce peak flow by an average of 27% and secure an additional 43% of baseflow during dry periods. Suspended solids (SS) and total phosphorus (T-P) concentrations were reduced by 15% and 41%, respectively. These findings demonstrate the effectiveness of LID techniques not only in managing stormwater runoff during flood events but also in maintaining baseflow and water quality during dry periods, thus providing valuable insights for sustainable urban watershed management. Full article

In this study, to improve the application and performance of conventional green roof systems, a novel multi-purpose green roof system was simulated numerically using computational fluid dynamics (CFD). The innovative multi-purpose green roof contains a soil layer and water filter, meaning the water retention time not only depends on the soil media but also depends on the filter’s pore size, improving the impact on runoff quality and quantity. In this regard, after mesh sensitivity analysis, the developed model was validated using experimental data, and the results show the accuracy of CFD in the simulation of porous media and filters. Comparisons between experimental and numerical results demonstrate the impact of proper porosity values in the simulation of a porous environment and reveal the source of errors in the numerical prediction of capillary flow in soil media, which can be minimized by adaptive consideration of the parameters, such as wall adhesion and appropriate wettability. Full article

Green roofs (GRs) are a widely recognized green infrastructure (GI) strategy that helps reduce runoff volume and runoff pollution caused by the significant increase in impervious urban areas. However, the leaching of several nutrients from GR substrates is a growing concern. Biochar, a carbon-rich material, possesses advantageous properties that can help address such environmental challenges associated with GRs. Therefore, this paper aimed to undertake a field study to investigate the impacts of various biochar application methods, particle sizes, and amendment rates on the quality of runoff from GRs. Observational data of runoff quality were collected over a two-month period from five newly established 1 m × 1 m biochar-amended GR test beds and a control test bed without biochar, with all test beds subjected to artificially simulated rainfall. The results indicated that the addition of biochar did not result in a significant improvement in runoff pH, whereas the electrical conductivity (EC) was higher in runoff from GRs with biochar-amended substrates. When comparing the total nitrogen (TN) concentration in runoff from the non-biochar GR (ranging from 3.7 to 31 mg/L), all biochar test beds exhibited higher TN release (4.8 to 58 mg/L), except for the bed where medium biochar particles were applied at the bottom of the substrate (ranging from 2.2 to 21 mg/L). Additionally, all biochar-amended GRs exhibited higher TP concentrations in runoff (0.81 to 2.41 mg/L) when compared to the control GR (0.35 to 0.67 mg/L). Among the different biochar setups, GR with fine biochar particles applied to the surface of the substrate had the poorest performance in improving runoff water quality. Despite these mixed results, biochar holds significant potential to improve runoff quality by significantly increasing water retention, thereby reducing pollutant loads. Full article

Green roof systems are regarded as a viable solution for mitigating urban environmental challenges and offering a multitude of environmental benefits. Currently, green roofs are increasingly being utilized for the management of rainwater runoff and wastewater. The integration of decentralized rainwater and sewage on-site treatment technology with urban green buildings is being gradually promoted. Green roofs can also be considered as a form of decentralized rainwater and sewage on-site technology, which holds great potential for widespread adoption in the future. Several studies have suggested that green roofs may serve as a potential source of pollutants; however, there are also studies that clearly demonstrate the efficient removal of nutrients and organic pollutants by green roofs. This article critically examines the existing literature on water treatment aspects associated with green roofs and elucidates their classification and operational mechanisms. Through an analysis of previous research cases, it becomes evident that both substrate and vegetation play a significant role in influencing the treatment performance of green roofs. By designing and configuring appropriate substrate and vegetation, green roofs can play a pivotal role in the purification of water quality. Finally, a brief outlook is presented for the future research directions of green roofs, with the anticipation that green roofs will feature more innovative and environmentally friendly designs, as well as expanded prospects for application. Full article

This study evaluates the public benefits associated with different green roof systems to manage stormwater runoff in Milwaukee, Wisconsin. An internet-based stated-preference conjoint choice experiment was administered to residents of Milwaukee to ascertain the public benefits value of different potential green roof infrastructure programs. This study contributes to the literature on the public benefits of green roofs in two ways. First, this study examined the perceived value of dynamic stormwater retention facilitated using “smart” green roofs with access to real-time weather data versus traditional extensive green roofs. Second, a wider range of public benefits associated with green roofs, including improved water quality, air quality, biodiversity, and urban heat island effects, were estimated. Estimation of these public benefits allows for determination of the optimal public policy for supporting green roofs as a component of decentralized stormwater management in municipalities. Full article

Rainwater runoff samples from a range of roofing materials were temporally collected from 19 small-scale roof structures and two commercial buildings through simulated and actual storm events, and the concentrations of polycyclic aromatic hydrocarbons (PAHs), phosphorus flame retardants (PFLs), and pyrethroid insecticides and other water quality parameters were analyzed. In Part I of this research, the concentrations of these contaminants in roof runoff and soils receiving runoff from a range of roofing materials were evaluated. In Part II, recommendations have been developed for a first-flush exclusion to improve the quality of water harvesting for nonpotable uses. Recommendations focus on a first-flush diversion based on mass removals of total suspended solids (TSS) and PAHs linked to conductivity measurements throughout a storm event. Additionally, an upper-confidence limit (UCL) was constructed to determine the minimum diversion required to obtain 50, 75, 90, and 95% mass removal of TSS and PAH contaminants. The majority of TSS were produced during the initial 1.2 mm of runoff. Likewise, the majority of PAHs were removed during the initial 1.2 mm of runoff, except for the asphalt shingle roofs, where high PAHs were observed after 6 mm of runoff. The Texas Water Development Board (TWDB)-recommended first-flush diversion of one gallon for every 100 square feet of rooftop was not always adequate for removing 50% of TSS and PAHs from the roofs. Rainwater runoff conductivity decreased drastically between 1.2 to 2.4 mm of rainwater runoff. Diverting the first flush based on conductivity has the potential to also divert the majority of TSS and PAHs in roof runoff. Full article

Rainfall runoff may be captured and stored for later use, but the quality of this water can be detrimental in some uses without the use of appropriately designed first-flush diverters. The rainfall runoff water quality was measured on nineteen new small-scale and two aged commercial roofs located near high traffic highways. Roof coverings included asphalt shingles, sheet metal, clay tiles, and tar and gravel. Runoff samples were evaluated for polycyclic aromatic hydrocarbons (PAHs), phosphorus flame retardants (PFRs), and pyrethroid insecticides. Eighteen small-scale roofs were subjected to a range of simulated rainfall events, while natural runoff was sampled on the commercial roofs and one small-scale roof. Runoff was analyzed for pH, conductivity, turbidity, total suspended solids, boron, iron, copper, zinc, manganese, sodium adsorption ratio, nitrate-nitrogen, seventeen PAHs, tris(2-chloroethyl) phosphate, tris(1,3-dichloro-2-propyl)phosphate, bifenthrin, cypermethrin, and lambda-cyhalothrin. Samples from four natural storm events were also analyzed for total coliforms and Escherichia coli. In addition, soils below seventeen existing gutter downspouts were sampled to determine long-term pollutant accumulation. Atmospheric deposition was the main contributor of pollutants in the roof runoff. A majority of samples fell within the U.S. EPA guidelines for non-potable urban and agricultural water reuse. Trace levels of PAHs, PFRs, and insecticides were detected, but all detections were three orders of magnitude below the USGS health-based screening level benchmark concentrations. Results indicate that diverting the first flush, based on turbidity, total suspended solids, or conductivity, can improve the overall water quality and reduce the concentrations of PAHs in harvested rainwater. Downspout soil sampling showed potential for the long-term accumulation of PAHs at concentrations exceeding the minimum human-health risk-based screening levels at these high runoff-loading locations. Full article