Urban Catchment Research Articles

Macroinvertebrates functional feeding groups (FFGs) of forested streams draining urban catchments in the Niger Delta: identifying and classifying vulnerable and tolerant FFGs

ABSTRACT This study aims to assess the vulnerability and tolerance levels of macroinvertebrate functional feeding groups (FFGs) in forested streams draining urban areas in the Niger Delta. It contributes to our understanding of how human activities affect freshwater ecosystems. Between 2008 and 2012, we conducted monthly measurements of physicochemical variables and collected macroinvertebrates. We categorised sampling sites into three groups based on disturbance levels: least impacted sites (LIS), moderately impacted sites (MIS), and heavily impacted sites (HIS). Multivariate (RLQ) analysis was used to visualise associations among physicochemical variables across the sampled sites, revealing distinct relationships between certain FFGs and different sites. The RLQ model we constructed showed that grazers and collector-filterers were predominantly observed in LIS, suggesting their vulnerability to environmental stressors. Conversely, predators and shredders were more prevalent in impacted sites (MIS and HIS), indicating their tolerance to disturbances such as elevated nitrate levels and higher water temperatures. The fourth corner graph highlighted differing responses of FFGs to physicochemical variables, with predators showing positive correlations with several factors but no significant association with phosphate levels. Overall, these findings showed the importance of considering the responses of different FFGs to environmental variables in assessing the health and integrity of aquatic ecosystems.

A SWMM-based evaluation of the impacts of LID and detention basin retrofits on urban flooding

ABSTRACT Different stormwater management practices have been used to mitigate the impacts of urbanization and attenuate urban flooding risk. However, there is a lack of studies on the comparison between conventional stormwater control measures such as detention basins, their retrofits, and low impact development (LID) practices, especially from the perspective of their impacts on erosive flow attenuation and flood control. The aim of this study is to compare the effects of two detention basins and their outlet retrofits with LID, in an urbanized catchment under designed storm events with different return periods, using a Storm Water Management Model (SWMM) modeling approach. The results show that detention basins are effective in decreasing peak flow and delaying peak time. Detention basin retrofits could significantly reduce the frequency and duration of erosive flows in Sub A detention basin compared with LID, especially in smaller rainfall events. LID outperforms the detention basin retrofits in reducing peak flow from larger storms.

Predicting Suspended Sediment Transport in Urbanised Streams: A Case Study of Dry Creek, South Australia

Sediment transport in urban streams is a critical environmental issue, with significant implications for water quality, ecosystem health, and infrastructure management. Accurately estimating suspended sediment concentration (SSC) is essential for effective long-term environmental management. This study investigates the relationships between streamflow, turbidity, and SSC in Dry Creek, South Australia, to understand sediment transport dynamics in urbanised catchments. We collected grab samples from the field and analysed them in the laboratory. We employed statistical modelling to develop a sediment rating curve (SRC) that provides insights into the sediment transport dynamics in the urban stream. The grab sample measurements showed variations in SSC between 3.2 and 431.8 mg/L, with a median value of 77.3 mg/L. The analysis revealed a strong linear relationship between streamflow and SSC, while turbidity exhibited a two-regime linear relationship, in which the low-turbidity regime demonstrated a stronger linear relationship compared to the high-turbidity regime. This is attributed to the urbanised nature of the catchment, which contributes to a first-flush effect in turbidity. This contributes to sediment hysteresis, resulting in non-proportional turbidity and SSC responses to streamflow changes. The findings demonstrate the effectiveness of a streamflow-based SRC for accurately predicting sediment discharge, explaining 97% of the variability in sediment discharge. The sediment discharge predicted using the SRC indicated a sediment load of 341.8 tonnes per year along the creek. The developed sediment rating curve provides a valuable tool for long-term sediment management in Dry Creek, enabling the assessment of downstream environmental risks. By addressing data limitations, this study contributes to a deeper understanding of sediment transport dynamics in urbanized environments, offering insights for informed decision-making and effective sediment management strategies.

Land-Use Impacts on Soil Erosion: Geochemical Insights from an Urban Drinking Catchment, South-Central Chile

We investigate the influence of land use and land cover (LU/LC) changes on soil erosion and chemical weathering processes within the Nonguén watershed in the Coastal Cordillera of south-central Chile. The watershed is divided into three sub-basins, each characterized by distinct LU/LC patterns: native forest and exotic plantations. A comprehensive geochemical analysis, including trace elements and lithium (Li) isotopes, was conducted on river water and suspended sediment samples collected from streams within these sub-basins to assess how land management practices, particularly plantation activities, influence the geochemical composition of river systems. Our results show that sub-basins dominated by exotic plantations exhibit significantly higher concentrations of major and trace elements in suspended sediments compared to sub-basins dominated by native forests. The elevated trace element concentrations are primarily attributed to increased physical erosion due to forestry activities such as clear-cutting and soil disturbance, which enhance sediment mobilization. Notably, concentrations of elements such as Fe, Al, and As in plantation-dominated sub-basins are raised to ten times higher than in native-dominated sub-basins. In contrast, sub-basins with native forest cover exhibit lower levels of sediment transport and trace element mobilization, suggesting that native vegetation exerts a stabilizing effect that mitigates soil erosion. Despite the substantial differences in sediment transport and element concentrations, Li isotopic data (δ7Li) show minimal fractionation across the different LU/LC types. This indicates that land use changes impact the chemical weathering processes less compared to physical erosion. The isotopic signatures suggest that physical erosion, rather than chemical weathering, is the dominant process influencing trace element distribution in plantation-dominated areas. The study provides critical insights into how forestry practices, specifically the expansion of exotic plantations, accelerate soil degradation and affect the geochemical composition of river systems. The increased sediment loads, and trace element concentrations observed in plantation-dominated sub-basins, raise concerns about the long-term sustainability of forest management practices, particularly regarding their impacts on water quality in urban catchment areas. These results are of significant relevance for environmental management and policy, as they underscore the need for more investigation and sustainable land use strategies to minimize soil erosion and preserve water resources in regions undergoing rapid LU/LC changes.

Unraveling lead sources in a tropical urban Swamp Forest: Insights and challenges

We investigate the contributions of natural (geogenic) and anthropogenic sources of lead (Pb) to the Nee Soon Swamp Forest, a relatively undisturbed catchment in Singapore. Using a Bayesian statistical source tracking approach with Pb isotopes preserved in sediment sections, our findings reveal a predominance of geogenic Pb in contemporary sediments, despite the significant presence of anthropogenic Pb in aerosols from local and distant sources. However, the geogenic Pb isotope signatures of the two main soil types in the catchment overlap with those of anthropogenic sources, introducing considerable uncertainty in using Pb isotopes as tracers within this catchment and potentially across larger areas. This uncertainty raises concerns about past interpretations of Pb contamination in both terrestrial and aquatic environments in Singapore and the broader region. To address these challenges, we emphasize the importance of accurately determining the signatures of all natural sources before using Pb isotopes as tracers in future studies. We also suggest that incorporating additional Pb isotope ratios or other stable isotope ratios (e.g., Ba, Cu, Sr, Zn) could enhance our ability to distinguish between natural and anthropogenic Pb sources. Ultimately, our study highlights the complexity of Pb sources in the environment and underscores the need for more comprehensive approaches to assessing their impacts. SynopsisThis paper highlights insights and challenges in lead (Pb) source tracing studies conducted in urban catchments. These challenges primarily stem from the inadequate identification of all Pb isotope sources. We address these challenges by employing a Bayesian statistical approach to effectively identify, discriminate, and quantify Pb sources within a wetland ecosystem in Singapore.

River invertebrate biodiversity benefits from upstream urban woodland

In urban environments, invertebrate communities are subjected to a broad mixture of impacts, including diffuse pollution. Pollutant mixtures and habitat degradation can combine to apply stress on community diversity. Water quality is influenced by the assemblage and mosaic of catchment land cover. Amongst a wider suite of Nature-Based Solutions, the value of urban woodland is increasingly recognized as having potential to support a range of ecosystem services. Despite an increasing focus on establishing urban woodland for aquatic conservation, its actual influence is yet to be manifested. Therefore, we explored trees’ location in riparian and upstream catchment, within and outside of the urban area. We conducted a combination of systematic literature review and statistical analysis to better understand the woodland influence. Despite the wide range of bioindicators studied and broad worldwide spectrum of geo-climatic regimes covered, literature evidence for benefits were found in at least half the cases. With a focus on the overall family richness and the sensitive orders Ephemeroptera, Plecoptera and Trichoptera family richness as bioindicators, the statistical analysis comprised a national study in England covering 143 sites with substantial urban cover, totaling 4226 invertebrate community observations over 30 years. Two satellite-derived land cover maps were used to enable discrimination between urban and extra-urban woodland. The analysis supported the literature evidence that impervious land had negative effects and woodland positive effects. In the urban and upstream catchment, woodland was more important than pasture or cropland. There was some evidence of those woodland effects being more advantageous when trees are located within the urban area itself. Benefits attributable to woodland were distinctly apparent against a backdrop of improving macroinvertebrate diversity found to be synchronous with long-term reductions in urban pollution signatures. The presence of sparse land, even in small amounts, was detrimental to macroinvertebrate diversity. These areas of low vegetative cover might be detrimental due to high sediment input and legacy industrial contamination. Given the increasing accessibility of land cover data, the approach adopted in this case study is applicable elsewhere wherever macroinvertebrate community data are also available.

Urban drainage network simulation using EPA SWMM for SuDS measures planning: a case study in Brazil

This paper investigates the implementation of sustainable drainage systems (SuDS) measures in a small urban catchment as runoff peak flow and total runoff volume control. The study area was calibrated for the pre-occupation scenario and, subsequently, a post-occupation scenario was proposed. Three structural measures were then tested: infiltration trench, rainwater harvesting, and a detention basin. The modelling was performed using the EPA SWMM. The simulation results showed that there was an increase of more than 115% of the total runoff volume in the post-occupation scenario. The results confirm that these structural measures can contribute to the reduction of peak flows in developing areas. Combinations of measures were more efficient in controlling runoff than isolated measures. To avoid using end-of-pipe solutions, a combination of infiltration trenches and lot scale rainwater tanks measures should be considered. The methodology can be used to test various combinations of structural measures.

Operational sensitivity analysis of flooding volume in urban areas

We focus on a probability-based approach to analyze the flooding volume during extreme rainfall events in urban areas. Our approach considers uncertainty in both non-operational and operational variables. The former are quantities that are tied to the characterization of rainfall events and key catchment features, whose uncertainties stem from incomplete characterization. The latter comprise elements of the system on which actions can be taken within a range of design values. As the non-deterministic nature of these two types of quantities differs at a fundamental level, we rely on an operational Global Sensitivity Analysis theoretical framework that explicitly recognizes this distinction. As a test bed to showcase our approach, we consider an urban catchment in Northern Italy. We assess the sensitivity of the flooding volume to a set of operational variables, such as diameter and roughness of a set of conduits of the sewer network as well as potential improvement of the infiltration capacity of the urban catchment. We show that our approach can identify the operational configuration with the highest effectiveness in mitigating instances of flooding, taking into account the uncertainties in the non-operational quantities that drive the system behavior.

Assessment of socio-economic strategies for managing regional flood risk in an urban coastal catchment

With the cascading flooding events over the past decades, several structural and non-structural measures have been effectively implemented for improved flood management. However, the uneven impacts of the flooding events have highlighted that socio-economic inequality amongst the community needs to be addressed along with hazards to devise long term and sustainable flood management strategies. This study aims to evaluate the impact of socio-economic adaptive scenarios over an urban coastal catchment for reduction in flood risk. Flood risk is estimated utilizing socio-economic aspects (vulnerability) and flood inundation (hazard), for the highly flood-prone coastal city of Mumbai, India. A multivariate approach is used for assessing socio-economic vulnerability, starting with Principal Component Analysis followed by Data Envelopment Analysis, for various socio-economic scenarios, i.e., by reducing percentage of certain feasible socio-economic sensitivity indicators, to identify the key indicators, which contribute to significant change in vulnerability. The flood hazard is assessed through a comprehensive hydrodynamic flood modelling approach to quantify the flood inundation depth and extent. The flood risk is, thereafter, evaluated by combining socio-economic vulnerability and flood hazard using bivariate risk mapping approach. The results indicate that, with the decrease in alteration percentage of certain feasible socio-economic sensitivity indicators, the overall vulnerability and flood risk may be reduced. The areas under very high and high vulnerability classes reduce gradually for all scenarios as the percentage reduction for various indicators is varied from 5 % to 15 %, total illiteracy being the most significant indicator. This study marks the first effort to discern socio-economic vulnerability indicators that have the potential to significantly diminish flood risk, thereby constituting a viable long-term flood risk mitigation strategy. This novel framework is generic and applicable to any flood prone catchments, to devise appropriate long-term flood management measures.

Inferring sediment deposition trend in data scared wetland impacted by degraded urban catchment

The reduction in water retention capacity due to sedimentation in wetlands poses a serious threat to the ecology of this imperative freshwater resource. This also increases the risk of flooding in the river catchment areas that feed these wetlands. Sediments are mostly produced by unplanned development and hillcutting in upstream catchments. Henceforth, it is crucial to understand the trend in sediment deposition to determine management measures. However, measuring sediment deposition in wetlands is challenging. This study investigates a novel and cost-effective approach to discover trends in sediment deposition within wetlands via geospatial techniques and compares their water extents in the Deepor Beel Wetland, a Ramsar site in Assam, India. The water spread areas were assessed via supervised classified Landsat images and the band rationing technique, i.e., the normalized difference pond index (NDPI). This study establishes that sedimentation causes the water level in wetlands to rise, resulting in an increase in the area of water spread. This often suggests that the lean period water volume is increasing, indicating better health of the stream-wetland ecosystem. However, this apparent increase in water volume is actually due to the displacement of water by the sediment that has been deposited on the bed over time. This approach has identified a reduction in the water holding capacity of the wetland to 9.19 million m3 in 18 years by utilizing geospatially derived water spread and elevation data from two years (2003 and 2021) with comparable rainfall. In the absence of recent and past years with comparable precipitation, the proposed method can still be applied by adjusting the apparent increase in volume by considering the difference in the net inflow volume between the two years of interest. The results of sediment transport toward the wetland, as computed by the Soil and Water Assessment Tool (SWAT) model while accounting for the sediment retention rate of the wetland, strongly agree with the proposed approach. The present approach can be extended to similar stream-wetland ecosystems to examine sediment dynamics and help create better management strategies for wetlands and associated catchment conservation and restoration.

Comparative assessment of pollution control measures for urban water bodies in urban small catchment by SWMM

Under the current increasingly serious water pollution situation in urban, the comprehensive treatment and protecting measures in urban small catchment are the necessary step to the water pollution treatment, not only focus on the water bodies themself. In this paper, the Luojiagang river channel and its catchment in Wuhan, which has been heavily impacted by water pollution, are taken as an example for the comparative assessment of pollution control measures in order to explore the effective and sustainable schemes including the LID (Low Impact Development---LID) by using SWMM model (Storm Water Management Model---SWMM). Through the comparison of pollution treatment measures based on scenarios simulation with the baseline scenarios, it was found that the reduction effects of pollutant peak concentrations at the outlet node of Luojiagang River had the decreasing order of: the combined measures (COS) > LID control > the water diversion from Donghu Lake (WAD) > the sewage treatment (SET) > the sediment dredging (SED), and the reduction effects of total pollutant load had the decreasing order of: LID > COS > SET > SED > WAD. The results show that the control of non-point source pollution is the key for the improvement of water quality in Luojiagang River, and LID plays important role in the reduction of both pollutant peak concentrations and load. This study has the implication for the decision making of the water pollution controlling schemes in urban small catchment.

Comparing the hydrological performance of blue green infrastructure design strategies in urban/semi-urban catchments for stormwater management

ABSTRACT Blue green infrastructure (BGI), in recent decades, have been increasingly recognized as robust stormwater control measures to reduce urban flooding, promote infiltration, and restore a catchment's flow to its pre-development stage. However, studies comparing the hydrological benefits of BGI alternatives at catchment scale are often limited to single catchment or single/few BGI options scaled over a catchment. This study designed a set of BGI alternatives as a combination of different BGI facilities in terms of the following: (a) spatial distribution scale (end-of-pipe vs. decentralized) and (b) naturalness scale (less engineered vs. more engineered), in three different urban catchments representing an inner city, a residential suburb, and a new urban housing. In addition, their hydrological performances were compared. A 10-year return period design rain and a continuous rain series of 11 years were modelled for each BGI alternative using the computer model stormwater management model (SWMM). It was observed that in most catchments, decentralized alternatives (both engineered and natural) showed better potential to reduce the magnitude and frequency of flooding than centralized measures. Similarly, the tested decentralized natural, less engineered alternatives showed higher potential to increase infiltration than the decentralized engineered alternatives in all three catchments. Meanwhile, infiltration-based BGI alternatives showed similar potential to mimic pre-development flow as other decentralized BGI alternatives.

SWMMLIDopt: a tool for optimization of low-impact development (LID) measures using the SWMM model

ABSTRACT The present study introduces the SWMMLIDopt tool that aims to optimize the implementation of low-impact development (LID) measures for stormwater management. The developed tool utilizes the capabilities of the stormwater management model (SWMM) and provides a user-friendly interface for conducting multi-objective optimization of the selection and placement of LID measures in urban catchments. The features and capabilities of the developed optimization tool are demonstrated on two urban catchments in Northern Europe, Norway and Finland. The catchments exhibit different catchment sizes and characteristics, complexities and constraints demonstrating the flexibility of the tool. The selection and placement of LID measures within the study catchments were optimized according to two criteria: (1) minimizing the peak flow and (2) minimizing the cost. The generated Pareto-fronts for the study catchments allow for the evaluation of optimal scenarios based on the trade-offs between the two selected criteria. The results obtained using SWMMLIDopt demonstrate its efficacy in optimizing LID measures in urban stormwater management that will aid practitioners in designing cost-effective and climate resilient infrastructure.

Investigation of Flood Inundation under Climate Change and Landuse Change for the Small Urban Catchment

Investigation of Flood Inundation under Climate Change and Landuse Change for the Small Urban Catchment

Litter in French urban areas-part 1: composition, sources, and spatio-temporal variations on urban surfaces.

Urban areas concentrate on human activities that generate large amounts of waste. A small fraction is mismanaged and ends up on urban surfaces and eventually in waterways. The fraction reaching waterways is usually estimated using poorly constrained data, while litter density on urban surfaces and its subsequent transfer dynamics are also poorly documented. This study provides new insights into litter composition, sources, and spatio-temporal variations in the urban catchments of Pin Sec and Jules Verne (Nantes, France), which are dominated by industrial/commercial, collective, and individual housing areas. Regular litter collection on selected street sections was combined with visual counting of street litter (> 1 cm). In total, 50.8 kg (dry weight) of litter were collected and 232,217 items were counted, mainly smoking and food consumption-related items. Litter densities ranged between 40,000 and 452,000 items/km2 depending on local activities, item mobility, and land use as a driver of road and foot traffic. A median litter accumulation rate of 7 g/inhabitant/day was estimated, suggesting that 0.6% of the total amount of waste generated in public places is mismanaged. Results over space show that litter is strongly correlated with land use and that litter accumulation is promoted in green spaces. Results over time show that litter stock is quickly renewed and that items may have long residence time on urban surfaces.

Comparative analysis of event runoff coefficients and curve numbers in contrasting urban environments based on observed rainfall-runoff data

Recently, there has been a growing recognition that the generic values of runoff coefficient (C) and curve number (CN) from standard lookup tables in the literature may not accurately capture the specific characteristics of a given catchment. This study aims to estimate and compare the event C and CN of two contrasting urban catchments in Ljubljana, Slovenia using observed rainfall-runoff data. Estimated parameter values were compared to the tabulated values from the literature (i.e., ASCE, 1992; USDA-NRCS, 2004). Seasonal changes of C and CN, along with diurnal streamflow patterns, were also analyzed to understand the eco-hydrological processes in the urban forest. The results demonstrated that the urban mixed forest exhibited high variability of Cs across all rainfall events with a mean and median of 0.11 and 0.062, respectively. Most of the C values observed in the urban area are clustered around the central tendency with a mean and median of 0.60. These mean C values in both catchments were lower than the tabulated values in the ASCE (1992) design manual. Mean and median CN values in the urban area were 95.45 and 96.81, respectively, lower than the urban mixed forest’s CN values of 82.69 and 83.95. An asymptotic CN∞ of 90.69 was found for the urban area and 71.71 for the urban mixed forest. Central tendency-derived CN values tend to be slightly higher than the tabulated values from USDA-NRCS (2004) and gridded values from GCN250 (Jaafar et al., 2019), while asymptotic CN∞ values were lower. Using central tendency measures as the single lumped value of C and CN may provide a reasonable representation of the runoff behavior in the studied urban area. However, this may present certain challenges in the urban forest catchment. Additionally, pre-event soil moisture conditions and specific storm characteristics contributed to the observed variations in C and CN. Bi-monthly analysis showed that C and CN were high during the autumn and winter months. Diurnal streamflow pattern is most prevalent during low-flow and precipitation-free periods while exhibiting seasonal structures in terms of the shape and timing of maxima and minima. Local estimation of C and CN allows for a more tailored representation of the catchment’s hydrological behavior.

Influence of construction works on urban streamflow water quality variations

Construction activities can have long-lasting impacts on receiving water bodies, especially when they receive polluted urban runoff. Therefore, it is essential to minimize these impacts on water quality and consider the long-term environmental effects of development activities. This study aims to provide insights into the assessment, temporal variations, and key variables associated with the impact of construction works on streamflow water quality. However, current assessment methods relating to construction works and streamflow water quality may lead to spurious correlations. A spurious correlation refers to a connection between two variables that appears to be causal but is not. This study proposes a novel approach to avoid spurious correlations between construction work signatures and water quality, ensuring causality and correlation between water quality parameters. The approach was applied to a developing urban catchment in Hong Kong. Compared to existing assessment models, the proposed approach advances in ensuring true correlations between construction works and streamflow water quality. It is also the first to develop a new indicator to represent the key variable of construction works. In this study, salinity, turbidity, and suspended solids were used as substitutes for construction activity parameters, such as the number of construction works, to correlate with water quality parameters. Additionally, principal component analysis and the construction work signature index were both adopted to calculate the key variables of water quality on behalf of construction works. Results demonstrate that the new approach has significantly improved causality by 45 % compared to previous assessment methods. However, the method has limitations as it does not consider the impact of rainfall on construction works.

Fingerprinting to trace sources of suspended solids in the transport of heavy metals in urban stormwater runoff

Suspended solids are an important pollutant in urban stormwater runoff. Past studies have mainly focused on a single transport stage of pollutants, constraining source identification of suspended solids at the catchment scale. Therefore, identifying the sources of suspended solids in stormwater runoff for the formulation of effective pollution mitigation measures is an effective way to manage suspended solids pollution in receiving waters. Sediment source fingerprinting is a widely used technique to trace the sources of river sediments, which can accurately identify the source of sediment through widely used tracers. This study used six heavy metals including Cd, Cr, Ni, Cu, Zn and Pb as tracers to quantify the sources of suspended solids in stormwater runoff from urban catchments. The spatial and temporal distribution characteristics of suspended solids during stormwater transport were investigated. The study results showed that the concentration of suspended solids was the highest in road runoff and sewer flow, especially particles <44 μm. In addition, relatively large rainfall depth, high rainfall intensity and long antecedent dry periods can lead to higher concentrations of suspended solids in roof and road runoff whereas longer rainfall duration can result in more suspended solids in sewer runoff. Sediment source fingerprinting and principal component analysis confirmed that coarse (>105 μm) particles primarily originate from road deposited sediments (63.80%), while fine (<105 μm) particles primarily originate from stormwater grate sediments and soil. The outcomes derived can help to comprehensively understand the sources of suspended solids and provide guidance for the management of urban stormwater particulate pollution, as well as being a technical reference for pollutant source traceability in urban stormwater runoff.

Drone remote sensing to define heat exchange between urban surfaces and stormwater runoff

ABSTRACT Urban water bodies are often subject to high runoff temperatures from heat exchange between rainfall and urban surfaces; however, this process can be difficult to define due to the complexity of spatially heterogeneous urban areas. This research seeks to improve our understanding of heat exchange in urban stormwater runoff by integrating in situ measurements of runoff temperature with land surface temperature data captured in high spatial resolutions by a drone. To do so, this study monitored four urban catchments in Milwaukee, WI that are dominated by different land surfaces (concrete parking lot, asphalt road, black bitumen roof, and grass). Results indicate that land surface temperature was variable among common land surface types (1.34–2.24 °C), with higher variations in surfaces subject to foot and vehicular traffic. In addition, the temperature of runoff from impervious surfaces responded differently between buildings and those with a ground subsurface, with higher event mean temperatures from concrete (21.4 °C) and asphalt (21.9 °C) ground surfaces as compared with the bitumen roof (19.8 °C), despite similar initial surface temperatures. Ultimately, these outcomes demonstrate how drone remote sensing of land surface temperature and in situ monitoring can be integrated to understand heat exchange processes in urban stormwater runoff.

The Impact of Green Infrastructure on the Quality of Stormwater and Environmental Risk

Increasing urbanization and the associated sealing of areas and the use of storm sewer systems for drainage not only increase the risk of flooding but also reduce water quality in streams into which stormwater is discharged. Green infrastructure (GI) measures are applied with the aim of managing this stormwater sustainably and reducing the associated risks. To this end, a quantitative–qualitative approach was developed to simulate GI—namely, rain gardens, bioretention cells, and vegetative bioswales—at the urban catchment scale. The findings highlight the potential of applying GI measures to managing stormwater more effectively in urban environments and mitigating its negative pollution-related impacts. For the housing estate analyzed, a simulated implementation of GI resulted in a reduction in pollution, measured as total nitrogen (N; 9–52%), nitrate-N (5–30%), total phosphorus (11–59%), chemical oxygen demand (8–46%), total suspended solids (13–73%), copper (12–64%), zinc (Zn; 16–87%), polycyclic aromatic hydrocarbons (16–91%), and the hydrocarbon oil index (HOI; 15–85%). Reducing the concentrations of pollutants minimizes the risk to human health determined via the HOI from a low-risk level to zero risk and reduces the ecological risk in terms of Zn pollution from a significant risk to a low risk of adverse effects. The modeling conducted clearly shows that the GI solutions implemented facilitated a quantitative reduction and a qualitative improvement in stormwater, which is crucial from an environmental perspective and ensures a sustainable approach to stormwater management. Lowering the levels of stormwater pollution through the implementation of GI will consequently lower the environmental burden of pollutants in urban areas.