Characterization of wash-off from urban impervious surfaces and SuDS design criteria for source control under semi-arid conditions

Removal and fate of microplastics in permeable pavements: An experimental layer-by-layer analysis

The increasing prevalence of microplastics (MP) in urban environments has raised concerns over their negative effects on ecosystems and human health. Stormwater runoff, and road dust and sediment, act as major vectors of these pollutants into natural water bodies. Sustainable urban drainage systems, such as permeable pavements, are considered as potential tools to retain particulate pollutants. This research evaluates at laboratory scale the efficiency of permeable interlocking concrete pavements (PICP) and porous concrete pavements (PCP) for controlling microplastics, including tire wear particles (TWP) which constitute a large fraction of microplastics in urban environments, simulating surface pollution accumulation and Mediterranean rainfall conditions. Microplastic levels in road dust and sediments and stormwater runoff inputs were 4762 ± 974 MP/kg (dry weight) and 23.90 ± 17.40 MP/L. In infiltrated effluents, microplastic levels ranged from 2.20 ± 0.61 to 5.17 ± 1.05 MP/L; while tire wear particle levels ranged between 0.28 ± 0.28 and 3.30 ± 0.89 TWP/L. Distribution of microplastics within the layers of PICP and PCP were also studied and quantified. Microplastics tend to accumulate on the pavements surface and in geotextile layers, allowing microplastic retention efficiencies from 89 % to 99.6 %. Small sized (< 0.1 mm) fragment shaped microplastics are the most common in effluent samples. The results indicate that permeable pavements are a powerful tool to capture microplastics and tire wear particles, especially by surface and geotextile layers. The study aims to shed light on the complex mobilisation mechanisms of microplastics, providing valuable insights for addressing the growing environmental concern of microplastic pollution in urban areas.

Theoretical analysis of urban runoff pollutographs: identification of characterization variables and impact

This research presents a novel methodology to determine runoff water retention volumes that allow the design of storage tanks for storm sewer overflows. It is based on the use of the Stormwater Management Model (SWMM) to generate hydrographs and runoff pollutographs of a fictional urban basin. Three pollutants (TS, BOD5 and TN) are simulated for a given set of rains and the values taken by a proposed set of characterization variables for the pollutographs obtained are analysed. Correlation and determination coefficients that exist between the different variables are analysed while also performing a multivariate characterization using PCA and cluster analysis. In the case study presented, using IDF curves of the studied city, a probability of occurrence (Tr) is assigned to the values taken by the proposed characterization variables. To assess the impact and identify the most unfavourable pollutographs within the set of selected rains, impact evaluation variables (IEV's) are established, based on the proposed characterization variables and by simulating the discharge to a receiving water body (river with initial concentration and constant flow). Finally, a storm sewer overflow is simulated, deriving a maximum flow for purification, and dimensioning retention tanks for different fractions of the total volume of runoff to control the maximum values of a specific IEV impact evaluation variable. Taking a design return period Trssd ≥ 10 years, the results obtained in the study case were 146.50 m3/ha imp for a 100% retention of the total runoff volume and 117.20 m3/ha imp for an 80% retention.

Performance monitoring of constructed floating wetlands: Treating stormwater runoff during the construction phase of an urban residential development

In the context of climate change and global trend towards greenfield urbanisation, stormwater and transported pollutants are expected to increase, impairing receiving environments. Constructed floating wetlands (CFWs) can improve stormwater retention pond performance. However, performance data are currently largely restricted to mesocosm experiments, limiting design enhancement fit for field implementation. The present 12-month field study aims to fill part of these gaps by identifying limitations and necessary design improvements for CFWs on a large retention pond/lake. Water in a 2.6-ha lake receiving stormwater from a 45-ha urban area under development in subtropical Queensland, Australia, was recirculated during dry weather periods to minimise algal growth and the risks of blooms. Pollutant removal efficiencies of two full-scale CFWs were evaluated during storm events and dry weather periods as a function of inlet and outlet pollutant concentrations, flow and rainfall. Inlet TSS and TN concentrations in runoff during the construction phase of the development exceeded required water quality limits while TP inflow concentrations were low and often below the detection limit. Median pollutant load reduction efficiencies during storm-events were - 20 % TSS, -2 % TN and 22 % TP at CFW1 and 51 % TSS, 3 % TN and 17 % TP at CFW2, respectively. TSS and TN concentration removal efficiencies at CFW1 were low and highly variable, partly due to low inlet concentrations, high flow velocities and short hydraulic retention times (<1 day). However, CFW1 significantly reduced TSS concentrations during dry weather periods. In contrast, CFW2 significantly reduced TSS concentrations during both storm events and during inter-event periods. This study highlights treatment limitations associated to the operational conditions of CFWs at field-scale not identifiable in a mesocosm-scale study. Further research is necessary to investigate treatment performance of CFWs during the operational phase of the development with higher nutrient levels.

A Water Resilience Evaluation Model for Urban Cities

Cities around the world are having to become more resilient to the effects of climate change and ongoing development pressures and consequently are seeking to improve urban water resource management. In order to analyze the key factors affecting a city’s water resilience, this research establishes an urban water resilience evaluation model. The DEMATEL method is used to calculate the intensity of the interaction among the water resilience indicators and to establish their causal relationships. Then, an ANP structured diagram is established and the weighting of the water resilience evaluation index for the city of Wuhan is obtained using the Super Decisions software. The key water resilience factors for Wuhan are shown to have significant mutual influences, with the main factors found to be the utilization of rainwater resources, the utilization of reclaimed water, and the total annual runoff control of the city. This method provides a sound basis for the evaluation of urban water resilience with scope to extend this to other cities. The results provide useful guidance for policy makers and other key stakeholders in supporting more sustainable urban development.

Effects of land use, climate, and imperviousness on urban stormwater quality: A meta-analysis

Many natural and anthropogenic factors cause degradation of urban stormwater quality, resulting in negative consequences to receiving waters. In order to improve water quality models at a variety of scales, accurate estimates of pollutant (nutrients, total suspended solids, and heavy metal) concentrations are needed using potential explanatory variables. To this end, a meta-analysis was performed on aggregated stormwater quality data from the published literature from 360 urban catchments worldwide to understand how urban land use and land cover (LULC), climate (i.e., Kӧppen-Geiger zone), and imperviousness (1) affect runoff quality, and (2) whether they are able to predict stormwater pollutant concentrations. Runoff pollutant concentrations were more influenced by LULC and climate than imperviousness. Differences in LULC significantly affected the generation of metals and some nitrogen species. Road, city center, and commercial LULCs generally produced the most elevated pollutant concentrations. Changes in climate zones resulted in significant differences in concentrations of nutrients and metals. Continental and arid climate zones produced runoff with the highest pollutant concentrations. Rainfall patterns seemed to have a more important role in affecting runoff quality than seasonal temperature. Differences in imperviousness only significantly affected chromium and nickel concentrations, although increased imperviousness led to slightly (not significantly) elevated concentrations of nutrients, suspended solids, and other heavy metals. Multiple linear regression models were created to predict the quality of urban runoff. Predictive equations were significant (p < 0.05) for 67% of the pollutants analyzed (ammonia, total Kjeldahl nitrogen, total nitrogen, total phosphorus, cadmium, nickel, lead, and zinc) suggesting that LULC, climate, and imperviousness are useful predictors of stormwater quality when local field monitoring or modeling is not practical. This study provides useful relationships to better inform urban stormwater quality models and regulations such as total maximum daily loads.

Adaptation Strategies for Flooding Risk from Rainfall Events in Southeast Spain: Case Studies from the Bajo Segura, Alicante

The management of runoff during torrential rainfall events is a significant problem in urban areas of southeast Spain. The increase in soil sealing and the occupation of areas prone to flooding have aggravated this problem. Due to this situation, municipal administrations, in collaboration with the concession holder for the supply of water and sewage services, Hidraqua Gestión Integral de Aguas de Levante SA, are committed a more efficient management of non-conventional water resources. An example of this can be found in the municipalities of Rojales, Daya Nueva, and San Fulgencio. These towns are located in the Bajo Segura region of the province of Alicante, where various initiatives have been implemented that break away from the traditional paradigm of rigid infrastructures. These initiatives include green spaces or areas, and sustainable urban drainage systems (SUDS) or nature-based solutions (NBS). This article presents various case studies. Firstly, in the town of Rojales, where several actions are being undertaken to improve the management of wastewater and rainwater and provide a solution to unauthorised dumping, as well as encouraging the use of reclaimed water with the creation of a recreational green area, El Recorral Park. Secondly, in the case of Daya Nueva, the Europa Park constitutes a recreational green area, Europa Park, facilitates runoff drainage by SUDS and NBS. Finally, the creation of a floodable pond in the municipality of San Fulgencio encourages the use of wastewater, thus avoiding the discharge of this non-conventional water resource into the sea. In addition, the pond facilitates the appropriate management of runoff water. The working method in this article has been twofold: firstly, bibliographical references have been consulted from other national and international areas; and secondly, the technical projects in the case studies have been analysed in detail. Several field trips have been made to the selected municipalities, accompanied by the technical personnel in charge of the execution of the projects, to examine the measures adopted. The results show that the implementation of these systems contributes to adapting to climate change and creates more resilient urban spaces.

N, P, and COD conveyed by urban runoff: a comparative research between a city and a town in the Taihu Basin, China

Stormwater runoff containing various pollutants exerts adverse effects on receiving water bodies and deteriorates the urban aquatic environment. Although numerous studies have been conducted on runoff pollution, research comparing its characteristics in cities with those in towns is rare in the literature. To close this gap, the present study was conducted. The instantaneous concentrations of ammonia-N, TN, TP, and COD during the rainfall events in the town were higher than those in the city in most conditions. The outfall concentrations increased with the increase of rainfall intensity. EMCs (the average value of EMC) and CV (coefficient of variation) of TN and DTN in the town were higher than those in the city, which may lie in the differences of urban environment planning and management, road cleaning methods, garbage disposal methods, industrial enterprise, etc. On the one hand, EMCs and CV of TP in the city's industrial areas were lowest among three functional areas, while on the other hand, in the town it was in the commercial areas rather than the industrial areas that EMCs and CV were the lowest, which may be caused by the low level of economic development of small towns in China. The concentrations of COD in the town were generally higher than that in the city. Compared with the city, the correlation among COD and various forms of N was stronger in the town, which may illustrate a stronger similarity of pollutant sources in the town. According to the results, road runoff in the town contributed more to urban aquatic pollution; thus, further research should concentrate on this particular type of runoff.

Soil Sealing and Hydrological Changes during the Development of the University Campus of Elche (Spain)

The University Miguel Hernández of Elche was created in 1996 and its headquarters is located in the city of Elche. A new campus was developed where new buildings and infrastructures have been established for over 25 years in the north of the city. The university is growing, and the land cover/land use is changing, adapted to the new infrastructures. In fact, the landscape changed from a periurban agricultural area mixed with other activities into an urbanized area integrated into the city. The purpose of this work was to evaluate the progressive sealing of the soil and the consequences on the surface hydrology. The area is close to the Palmeral of Elche, a landscape of date palm groves with an ancient irrigation system, which is a World Heritage Cultural Landscape recognized by UNESCO. The evolution of the land occupation was analyzed based on the Aerial National Orthophotography Plan (PNOA). Soil sealing and the modifications of the hydrological ancient irrigation system were detected. Based on the results, proposals for improvement are made in order to implement green infrastructures and landscape recovery that can alleviate the possible negative effects of the soil sealing in the area occupied by the university.

Sustainable Urban Drainage Systems in Spain: Analysis of the Research on SUDS Based on Climatology

Sustainable urban drainage systems (SUDS), or urban green infrastructure for stormwater control, emerged for more sustainable management of runoff in cities and provide other benefits such as urban mitigation and adaptation to climate change. Research in Spain began a little over twenty years ago, which was later than in other European countries, and it began in a heterogeneous way, both in the SUDS typology and spatially within the peninsular geography. The main objective of this work has been to know through bibliographic review the state of the art of scientific research of these systems and their relationship with the different types of climates in the country. These structures have a complex and sensitive dependence on the climate, which in the Iberian Peninsula is mostly type B and C (according to the Köppen classification). This means little water availability for the vegetation of some SUDS, which can affect the performance of the technique. To date, for this work, research has focused mainly on green roofs, their capabilities as a sustainable construction tool, and the performance of different plant species used in these systems in arid climates. The next technique with the most real cases analyzed is permeable pavements in temperate climates, proving to be effective in reducing flows and runoff volumes. Other specific investigations have focused on the economic feasibility of installing rainwater harvesting systems for the laundry and the hydraulic performance of retention systems located specifically in the northeast of the Iberian Peninsula. On the contrary, few scientific articles have appeared that describe other SUDS with vegetation such as bioretention systems or green ditches, which are characteristic of sustainable cities, on which the weather can be a very limiting factor for their development.

The influence of the correlation-covariance structure of measurement errors over uncertainties propagation in online monitoring: application to environmental indicators in SUDS

This paper presents a methodology to assess the influence of the correlation-covariance structure of measurement errors in online monitoring over the propagation of uncertainties, applied to wet-weather environmental indicators in sustainable urban drainage systems (SUDSs). The effect of auto-correlated and heteroskedastic errors in measured time-series over the estimated probability density function (PDF) of different environmental indicators is analyzed for a wide variety of possible error structures in the data. For this purpose, multiple correlation-covariance structures are randomly generated from exploring the parametric space of a linear exponent autoregressive (LEAR) model, employing a Bayesian-based Markov Chain Monte Carlo sampling technique. Significant differences tests are proposed to identify the most correlated parameters of the correlation-covariance error model with statistics of the environmental indicator PDFs. The method is applied to total suspended solids (TSS) and chemical oxygen demand (COD) time-series recorded during 13 rainfall events at the inlet and outlet of a SUDS train (stormwater settling tank-horizontal constructed wetland). In this case, results showed that the total error in the estimation of the analyzed environmental indicators is mostly explained by standard uncertainties (flattening of the PDFs) rather than bias contributions (displacement of the PDFs). The correlation-covariance model parameters related to the temporal delimitation of hydrographs/pollutographs and the intensity of the autocorrelation showed to have the strongest influence in the propagation of measurement errors (flattening/displacement of the PDFs).

Sustainable Urban Drainage Systems in Spain: A Diagnosis

Sustainable urban drainage systems (SUDS) were almost unknown in Spain two decades ago; today, urban drainage in the country is transitioning towards a more sustainable and regenerative management in a global context where green policies are gaining prominence. This research establishes a diagnosis of SUDS in Spain and examines the extent to which the country is moving towards the new paradigm in three dimensions: (a) the governance and social perception of the community, (b) the regulative background, and (c) the implementation and the technical performance of SUDS. The diagnosis identifies barriers that hinder the change. Then, we define the challenges that Spain has to face to overcome obstacles that delay the transition. Barriers to the governance sphere are related to the lack of involvement, knowledge, and organisational responsibilities. Within the regulative framework, the absence of national standards hinders the general implementation at the national scale, although few regional and local authorities are taking steps in the right direction with their own regulations. From the technical perspective, SUDS performance within the Spanish context was determined, although some shortcomings are still to be investigated. Despite the slowdown caused by the hard recession periods and the more recent political instability, SUDS implementation in Spain is today a fact, and the country is close to reaching the stabilisation stage.

Nature-based solutions as enablers of circularity in water systems: A review on assessment methodologies, tools and indicators

Water has been pushed into a linear model, which is increasingly acknowledged of causing cumulative emissions of pollutants, waste stocks, and impacting on the irreversible deterioration of water and other resources. Moving towards a circular model in the water sector, the configuration of future water infrastructure changes through the integration of grey and green infrastructure, forming Nature-based Solutions (NBS) as an integral component that connects human-managed to nature-managed water systems. In this study, a thorough appraisal of the latest literature is conducted, providing an overview of the existing tools, methodologies and indicators that have been used to assess NBS for water management, as well as complete water systems considering the need of assessing both anthropogenic and natural elements. Furthermore, facilitators and barriers with respect to existing policies and regulations on NBS and circularity have been identified. The study concludes that the co-benefits of NBS for water management are not adequately assessed. A holistic methodology assessing complete water systems from a circularity perspective is still needed integrating existing tools (i.e. hydro-biogeochemical models), methods (i.e. MFA-based and LCA) and incorporating existing and/or newly-developed indicators.

Influence of rainfall intensity and pollution build-up levels on water quality and quantity response of permeable pavements

Permeable pavements are part of stormwater management practices known as sustainable urban drainage systems (SUDS). This study describes the influence of several environmental variables, such as the rainfall regime or the pollution build-up level, on the hydraulic and water quality performance of permeable pavements. Four infiltrometers with different configurations of pavement layers were used to study the influence of two rainfall regimes (Atlantic and Mediterranean) and two rainfall intensities (0.5 and 2.2mm/min). The influence of the progressive pollution build-up level was studied by dry sprinkling of road deposited sediments collected with a mechanical street sweeper with a dose of 5g/m²/d. The results show that permeable pavements retained a significant rainwater volume and improved the infiltrated water quality in terms of suspended solids, organic matter and nutrients when compared to the corresponding surface runoff potentially generated from an impervious pavement. The volume of rainwater retained inside them varied between 16 and 66% depending on the variables studied. The water infiltrated from permeable pavements subjected to a Mediterranean rainfall regime contained, in general, higher concentrations of organic matter (22 to 89mg Chemical Oxygen Demand/l) and nutrients (0.6 to 2.1mg Total Nitrogen/l and 0.05 to 0.45mg Total Phosphorus/l) than those under Atlantic regime. However, the latter infiltrated higher loadings in terms of mass. Nitrogen was the substance that infiltrated the most, reaching a 25% of the total mass of nitrogen deposited on the pavements surface. The concentration and mass loading in infiltrated water increased as the pollution build-up level did. The leachability of nutrients and organic matter was greater for high rainfall intensities. The results suggest that it is essential to carry out an adequate cleaning in dry conditions, especially when high intensity rainfall events are foreseen, because of its greater capacity to mobilize pollutants.

Predicting biochemical oxygen demand in European freshwater bodies

Biochemical Oxygen Demand (BOD) is an indicator of organic pollution in freshwater bodies correlated to microbiological contamination. High BOD concentrations reduce oxygen availability, degrade aquatic habitats and biodiversity, and impair water use. High BOD loadings to freshwater systems are mainly coming from anthropogenic sources, comprising domestic and livestock waste, industrial emissions, and combined sewer overflows. We developed a conceptual model (GREEN+BOD) to assess mean annual current organic pollution (BOD fluxes) across Europe. The model was informed with the latest available European datasets of domestic and industrial emissions, population and livestock densities. Model parameters were calibrated using 2008-2012 mean annual BOD concentrations measured in 2157 European monitoring stations, and validated with other 1134 stations. The most sensitive model parameters were abatement of BOD by secondary treatment and the BOD decay exponent of travel time. The mean BOD concentrations measured in monitored stations was 2.10 mg O2/L and predicted concentrations were 2.54 mg O2/L; the 90th percentile of monitored BOD concentration was 3.51 mg O2/L while the predicted one was 4.76 mg O2/L. The model could correctly classify reaches for BOD concentrations classes, from high to poor quality, in 69% of cases. High overestimations (incorrect classification by 2 or more classes) were 2% and large underestimations were 5% of cases. Across Europe about 12% of freshwater network was estimated to be failing good quality due to excessive BOD concentrations (>5 mg O2/L). Dominant sources of BOD to freshwaters and seas were point sources and emissions from intensive livestock systems. Comparison with previous assessments confirms a decline of BOD pollution since the introduction of EU legislation regulating water pollution.

Hydrological Performance of Green Roofs at Building and City Scales under Mediterranean Conditions

Green roofs are one specific type of sustainable urban drainage system (SUDS); they aim to manage runoff at the source by storing water in its different layers, delaying the hydrological response, and restoring evapotranspiration. Evidence of their performance in the Mediterranean is still scarce. The main objective of this paper is to analyse the hydrological performance of green roofs at building and city scales under Mediterranean conditions. A green roof and a conventional roof were monitored over one year in Benaguasil (Valencia, Spain). Rainfall and flow data were recorded and analysed. Hydrological models were calibrated and validated at the building scale to analyse the hydrological long-term efficiency of the green roof and compare it against that obtained for the conventional roof. Results show that green roofs can provide good hydrological performances, even in dry climates such as the Mediterranean. In addition, their influence at the city scale is also significant, given the average runoff coefficient reduction obtained.