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The preferential flow and transport through unsaturated zones have received considerable attention in the soil and agricultural fields, particularly in increasing discharge rates and amounts and the subsequent transportation of pollutants to groundwater. Over the past century, traditional stormwater control has been replaced by a new low-impact development (LID) approach called " on-site alternative design strategy", which aims to restore or maintain the hydrological functions of urban watersheds by using the capacity of soil and vegetation to retain and filter wastewater pollution, such as bioretention facilities. Therefore, obtaining an accurate estimation of water Infiltration within Bioretention basins is crucial. The Bioretention modeling usually refers to the implicit reservoir base model, which is based on the mass balance and interaction between all the components of the hydrologic cycle (evapotranspiration, overflow, exfiltration to surrounding soils, infiltration through filter media or non-saturated zone, and underdrain discharge) during the time. Among the existing bioretention models, the unsaturated zone or filter medium is considered a homogeneous medium, and the flow is calculated with conceptual infiltration models, such as the Green-Ampt model, the Horton model, etc. Despite our knowledge that the soil reservoir medium is heterogeneous (e.g., coarse materials, plant root systems), it is, therefore, necessary to use a physics-based infiltration model that considers the impact of non-equilibrium and preferential flow on the hydrological and hydrogeochemical performance of bioretention facilities. The INFILTRON-mod, a generic physics-based package, has been proposed for this aim.This package consists of infiltration models, including the Green-Ampt model and three other specific custom-made models, for uniform and non-uniform flows in soils based on the Darcian approach and mass balance. Uniform and non-uniform flows are modeled using the single and double permeability approaches, respectively. The dual permeability concept assumes that the soil consists of two reservoirs, i.e., the general matrix and fast flow regions, each obeying the Darcian approach. We assumed instantaneous exchange between the two regions. Consequently, we assumed that the wetting fronts in the two reservoirs advance at the same rate. Then the different sets combined with the single or double permeability approaches were tested against numerically generated data using HYDRUS and real experimental data obtained with INFILTRON-exp, "a specific large ring infiltrometer" deployed at several experimental sites.The results show that the custom-made models lead to different results, with some being better. In addition, considering the dual permeability models improved the fits of the experimental data acquired with the infiltrometer. Then, the improved model was used to model the observations from the Wicks Reservoir bioretention basin (Melbourne, Australia), including the water head in the filter layer and outflow rates, and this led to satisfactory results. The results obtained from this study will be used to develop the INFILTRON-mod package that can be easily integrated into the LID modeling performance for calculating the infiltration element in the unsaturated filter medium.

Infiltration systems are increasingly used to reduce peak flows and mitigate the impacts of stormwater runoff. Despite the benefits of infiltration systems, there is a risk for associated pollutants, including heavy metals to be introduced to the underlying soil and groundwater. The subsequent movement of metals in the subsurface and their potential to contaminate water resources is uncertain and profoundly depends on the adsorptive behavior of the surrounding soil. We used two soil types, one natural (quartz–kaolinite–muscovite) and one synthetic (quartz and kaolinite only) with different clay mineralogy to test their potential adsorptive capacities through batch systems, with Zn(II) as a representative tracer. Nonlinear isotherms, Freundlich and Langmuir, provided good fits with the experimental sorption data. Kinetic data were well fitted by a pseudo-second-order model, indicating that cation exchange exists between the clay surfaces and Zn(II) in the liquid phase. We found that the natural soil adsorbed far more Zn(II) when compared to the synthetic soil which was attributed to the presence of the muscovite in the natural soil. Comparison of the observed adsorption capacity of the two soils with their predicted adsorption capacities showed that while the adsorption capacities of the single-sized clay minerals are widely reported, these values cannot be linearly extrapolated to estimate the adsorption capacity of a soil that might contain varied fractions of clay. The results suggest that the designers of infiltration systems should first undertake an analysis of clay mineralogy of the subsurface soil to better predict the fate of heavy metals within the surrounding soils.

Stormwater Control Measures (SCMs) are increasingly applied to capture and utilise urban runoff to augment water supply, reduce flood risk, and to restore natural flow regimes in receiving waters. ...

As urban populations expand globally, the associated increase in urban land cover directly impacts the social and environmental amenity of natural assets, including waterways. The primary driver of...

It is increasingly recognised that urban trees can contribute to reducing stormwater runoff by intercepting and retaining a fraction of rainfall received. What is less studied is the translation of this to reduced pollutant loads being transferred to receiving streams, rivers, and water bodies. In this paper, we assess interception of two tree species (Eucalyptus microcorys and Ulmus procera) in an urban park. These data are used in simple water balance modelling to predict the environmental and economic benefit of reducing nitrogen loads to receiving waterways as a function of reduced runoff volume resulting from rainfall interception by urban trees on public land (21% of the catchment area). We use a highly urbanized catchment in Melbourne, Australia to demonstrate the impact of an urban forest dominated by deciduous trees, evergreen trees or a mixed tree canopy cover. We found that doubling the urban canopy cover in the catchment, while keeping the current mix ratio of deciduous and evergreen trees, could reduce annual runoff volume by 30 mm (92 MLyr−1). Using the prescribed values that developers must pay the local water authority for nitrogen treatment as a condition of new development, we calculate that this would deliver a nitrogen load removal benefit of AUD$ 200/tree. If only deciduous trees are planted, the annual runoff reduction would decrease to 24 mm (73 MLyr−1) and increases to 37 mm (112 MLyr−1) if only evergreen trees are planted. This study highlights both the additional benefits of public street trees and the differences in deciduous and evergreen trees which should be accounted for by policy makers.

For streams draining urban catchments, sediment transport capacity is the key driver of physical impacts including bed sediment removal and channel incision. The main unanswered question is the relative role of flow alteration compared to sediment supply in influencing sediment transport capacity. With this objective, we computed sand and gravel bed sediment transport capacity using the Wilcock and Kenworthy two-fraction bedload transport relation for nine streams in catchments covering a gradient of urbanisation. Computations were done for typical natural bed surface material, based on conditions in the least urban study streams. We compared transport capacity distributions and cumulative transport capacity over one-year between the streams. Transport capacity was up to three orders of magnitude higher in urban streams than in forested-catchment streams. This was driven overwhelmingly by the urbanisation-induced alterations to the flow regime, with only minor feedback from channel form changes. Transport capacity was two to three orders of magnitude greater than measured bedload transport in all but the least urban streams. This excess bedload transport capacity mobilises and removes bed sediment, produces channel incision and enlargement and reduces channel complexity. Rebalancing transport capacity with sediment supply therefore requires significant flow mitigation towards pre-urban conditions. Other responses, which may theoretically help to regain this balance – channel widening, grade control, increasing roughness, sediment augmentation – are either inappropriate or only feasible following flow mitigation measures.

Sustainable Urban Drainage Systems (SuDs) have grown in popularity in recent decades as an efficient and effective solution for urban drainage systems, with the aim of reducing flood risk, improving urban amenity and reducing negative impacts on receiving waters. Infiltration is a critical factor in both the management and modelling of SuDs. Predicting infiltration behaviour is rendered difficult by the inherent heterogeneity of substrate characteristics. Much research has been devoted to understanding the physical processes responsible for preferential flows in soils and developing simplified and physically-based infiltration models for predicting preferential flows and water infiltration into heterogeneous soils. In this study, INFILTRON-mod, a generic physically-based package, is proposed. This package involves infiltration models for uniform and non - uniform flows in soils, considering the Darcian approach and mass balance. Uniform and non-uniform flows are modeled using the single and dual permeability approaches, respectively. The dual permeability concept assumes that the soil comprises two regions, i.e., the general matrix and the fast-flow regions, each obeying the Darcian approach. Then, different sets of infiltration models can be considered for the description of water infiltration into the single permeability soils and, by analogy, into each region of the dual-permeability soils. In this study, we investigate different sets of infiltration models, including the Green and Ampt model and other specific custom-made models. The different sets combined with either single or dual permeability approaches were tested against numerically generated data and real experimental data obtained with INFILTRON-exp, a specific large ring infiltrometer deployed on several experimental sites. First, we validated the proposed sets against numerically generated data for six different synthetic soils representing contrasting behaviors (sand, loam, silt, etc.). The synthetic data were generated with HYDRUS. The cumulative infiltrations were then compared, and the performance of the proposed sets of models was assessed. The results confirm that some sets fit well, whereas others are less accurate. The results also depended on the considered initial conditions.Then, INFILTRON-mod was extended to the modeling of bioretention systems with the implementation of all the components of the hydrologic cycle (evapotranspiration, overflow, exfiltration to surrounding soils, water storage in the filter, and underdrain discharge). The different sets of models were then compared to observations from the Wicks Reserve Bioretention Basin (Melbourne, Australia), including the height of water in the filter layer and the outflow fluxes. The sets of models were then calibrated using two rainfall events before being validated over 20 rainfall events. The model performance was assessed for both the single and dual permeability approaches. We obtained very good fits of the experimental data with a median NSE above 0.8 for outflows, particularly for two infiltration models with the dual permeability approach, demonstrating the benefit of including preferential flows in the model. Our findings will help to develop the INFILTRON-mod package for modeling water infiltration into heterogenous soils and modeling bioretention systems.

Traditional approaches to urban drainage degrade receiving waters. Alternative approaches have potential to protect downstream waters and provide other benefits to cities, including greater water security. Their widespread adoption requires robust demonstration of their feasibility and effectiveness. We conducted a catchment-scale, before-after-control-reference-impact experiment to assess the effect of dispersed stormwater control on stream ecosystems. We used a variant of effective imperviousness (EI), integrating catchment-scale stormwater runoff impact and stormwater-control-measure (SCM) performance, as the measure of experimental effect. We assessed the response of water quality variables in 6 sites on 2 streams, following SCM implementation in their catchments. We compared changes in those streams over 7 years, as SCM implementation increased, to the 12 preceding years, and over the 19 years in 3 reference and 2 control streams. SCMs reduced phosphorus and nitrogen concentrations and temperature, and increased electrical conductivity; with effect size negatively correlated with antecedent rain. SCM-induced reductions in phosphorus and temperature were of a similar magnitude to increases from urban development, when assessed as a function of change in EI. Nitrogen reductions were observed, even though concentrations among sites were not correlated with EI, being more influenced by septic tank seepage. SCMs had no effect on suspended solids concentrations, which were lower in urban streams than in reference streams. This experiment strengthens the inference that urban stormwater drainage increases contaminant concentrations in urban streams, and demonstrates that such impacts are reversible and likely preventable. SCMs reduce contaminant concentrations by reducing the frequency and magnitude of uncontrolled drainage flows and augmenting reduced baseflows. Increased EC and reduced temperature are likely a result of increased contribution of groundwater to baseflows. The stormwater control achieved by the experiment did not fully return phosphorus or nitrogen concentrations to reference levels, but their responses indicate such an outcome is possible in dominant conditions (up to ~20 mm of 24-h antecedent rain). This would require nearly all impervious surfaces draining to SCMs with large retention capacity, thus requiring more downslope space and water demand. EI predicts stream water quality responses to SCMs, allowing better catchment prioritization and SCM design standards for stream protection.

Stormwater control measures (SCMs), also frequently referred to as sustainable urban drainage systems (SUDS), are of growing importance in cities, as part of a global move towards mitigating the impacts of stormwater on receiving environments. They need to be monitored as parts of UDSM systems but require specific and sometimes innovative methods and sensors. This is particularly the case for SCMs such as swales, rain-gardens, bioretention filters, infiltration trenches, green roofs, etc., which have complex and varied configurations and hydrologic behaviour. This chapter deals with measuring the water balance in SCMs by accounting for its various components: inflows, outflows, overflows, storage, infiltration, exfiltration, intrusion, evaporation, and evapotranspiration. It presents a range of suitable methods and tools, indicates key points to consider, and discusses possible difficulties in obtaining accurate monitoring data. Routine monitoring of decentralized and diversified SCMs is still an emerging field for both researchers and practitioners. A significant evolution is therefore expected with its generalization in the next years.

International audience; Bioretention systems are increasingly used worldwide to mitigate the impacts of urban stormwater runoff on the water cycle. Being able to accurately model physical processes occurring within these systems is critical to their design and to being able to predict their performance. Most popular urban hydrological models must now integrate a low impact development (LID) toolbox to keep up with current practices. We aimed to develop and test a generic model of bioretention systems that can serve as a targeted compromise between oversimplification without any physical basis, on the one hand, and physical soundness requiring a large number of parameters for calibration, on the other. The model accounts for evapotranspiration, overflow, infiltration into the filter (single permeability behavior), exfiltration to surrounding soils, along with underdrain discharge. The model was tested against field data from a monitored bioretention basin in Melbourne, Australia. Based on 22 rainfall events (two used for calibration and 20 for validation), results showed that the simulated underdrain outflow rates and their temporal dynamic were well replicated (considering the validation phase with 20 rainfall events: median NSE = 0.75, median PBIAS = − 22%, median RMSE = 0.48 l/s). Despite good performance for outflow rates, there was a discrepancy observed in magnitude between simulated and measured water levels within the bioretention basin. The model therefore seems a useful first step towards the design of a user-friendly model for assessing both performance and impact of bioretention basins for catchment-scale flow regime management.

Green infrastructure strategies are often cited as best practice for urban water management; however, limited research has been undertaken to compare intervention effectiveness during moderate to e...

The process of embalming human remains as part of the funeral home industry, entails replacing blood with embalming fluid. Typically the unused/excess fluids are disposed of directly to the sewershed or septic system. The presence of select contaminants in sewer discharges from 8 funeral homes (facilities) in York Region, Ontario during active embalming processes was studied. A wide range of contaminants including embalming fluids (formaldehyde and triclosan); metals, conventional parameters, persistent organic pollutants (polycyclic aromatic hydrocarbons, pesticides, and polychlorinated byphenyls), nonyl phenols and active pharmaceutical ingredients (APIs) were measured in the final embalming effluent and compared to regulatory sewer limits where available. Two main constituents of embalming fluids—formaldehyde and triclosan—were detected at maximum concentrations of 561,000 μg/L and 505 μg/L respectively. Other persistent organic pollutants detected in embalming effluent included banned pesticides lindane (83 ng/L) and metabolites of DDT (DDE; 2,300 ng/L). Elevated APIs found in over-the-counter drugs and products were also frequently detected at elevated concentrations (oxybenzone, hydrocortisone, lidocaine, naproxen, ibuprofen, ciprofloxacin and DEET). Most contaminants did not exceed regulatory sewer limits where available, however others including biochemical oxygen demand (cBOD5) and conventional parameters were consistently above regulatory limits. Large amounts of formaldehyde and triclosan may pose a risk to receiving sewersheds and receiving sewage treatment plants due to their antimicrobial activities.

Sediment in urban stormwater systems creates a significant maintenance burden, while a lack of coarse‐grained bed sediment in streams limits their ecological value and geomorphic resilience. Gravel substrates, for example, provide benthic habitat yet are often scoured from the channel bed only to end up in a detention basin or treatment wetland. This dual problem of both ‘too much’ and ‘too little’ coarse‐grained sediment reflects a watershed sediment budget that is profoundly altered. We developed a conceptual urban coarse‐grained (>0.5 mm) sediment budget across three domains: hillslopes (urban land surfaces), the built stormwater network and stream channels. We then quantified key sources, sinks and storages for a suburban case study, using a combination of hillslope and in‐channel monitoring, and interrogation of local government records. Around 36% of the sediment supplied to the stormwater network reached the catchment outlet, a level of sediment delivery much higher than observed in similar‐sized natural catchments. The remainder was deposited in the sediment cascade and either stored, or extracted and removed from the catchment (e.g. material deposited in sediment ponds and gross pollutant traps). Conventional urban drainage networks are characterized by high hillslope sediment supply and low storage, resulting in efficient sediment delivery. Channel erosion, deposition in (and extraction from) pipes and channels, and floodplain deposition are small compared to sediment transport through the cascade. An understanding of the sediment budget of urban headwater catchments can provide stormwater and waterway managers with the information they need to address specific sediment problems such as sedimentation in stormwater assets and geomorphic recovery of urban streams.

The potential for catchment-scale stormwater control measures (SCMs) to mitigate the impact of stormwater runoff issues and excess stormwater volume is increasingly recognised. There is, however, limited understanding about their potential in reducing in-channel disturbance and improving hydraulic conditions for stream ecosystem benefits. This study investigates the benefits that SCM application in a catchment have on in-stream hydraulics. To do this, a two-dimensional hydraulic model was employed to simulate the stream hydraulic response to scenarios of SCM application applied in an urban catchment to return towards pre-development hydrologic pulses. The hydraulic response analysis considered three hydraulic metrics associated with key components of stream ecosystem functions: benthic mobilization, hydraulic diversity and retentive habitat availability. The results showed that when applied intensively, the developed SCM scenarios could effectively restore the in-stream hydraulics to close to natural levels. Compared to an unmanaged urban case (no SCMs), SCM scenarios yielded channels with reduced bed mobility potential, close to natural hydraulic diversity and improvement of retentive habitat availability. This indicates that mitigating the effect of stormwater driven hydrological change could result in significant improvements in the physical environment to better support ecosystem functioning. We therefore suggest that intensive implementation of SCMs is an important action in an urbanizing catchment to maintain the flow regime and hydraulic conditions that sustain the 'natural' stream habitat functioning. We propose that stormwater management and protection of stream ecosystem processes should incorporate hydraulic metrics to measure the effectiveness of management strategies.

Directing stormwater runoff to irrigate urban trees has the potential to simultaneously: (i) reduce the volume of runoff generated by impervious surfaces and (ii) reduce tree drought stress and increase growth. Many papers promote this concept, but few have quantified both potential benefits. In this study, we quantified both the runoff retention performance of infiltration trenches retrofitted alongside established street trees and tree drought stress and growth. We compared retention for different soil types, tree phenological types and inlet designs over a period of 18 months. Retention was low on average (18.3%) but was highly variable among infiltration trenches (5.2–43.7%), driven by variation in inlet capacity due to blockages, as well as the flow velocity of runoff leading to the inlet. With appropriately designed inlets, street tree stormwater control measures have significant potential to retain runoff. We observed no clear reduction in tree drought stress or increase in tree growth. This suggests that the established trees in our study already had access to adequate soil water within their rooting volumes, supplemented by nearby irrigated private gardens, or leaky water infrastructure. We suggest that i) mature trees surrounded by greater impervious surface area, ii) newly planted trees, or iii) trees growing in hotter, drier climates, may respond more positively to similar passive irrigation systems. The evolving practice of passive irrigation of street trees with stormwater requires innovative design to maximise runoff capture efficiency under typical sediment and debris loads.

Coarse-grained sediments supplied to a stream, in concert with the flow regime, play an important role in channel form and functioning, but are poorly understood in urban catchments. Improved knowledge of coarse-grained (>0.5 mm) sediment sources and supply rates will underpin strategies to mitigate impacts of urbanization on streams. We quantified key hillslope (i.e. non-channel) sources of sediment in urban areas by monitoring coarse-grained sediment yields from nine street-scale stormwater catchments over one year. From our observations, we developed a suburban hillslope sediment budget and a conceptual model of the response of hillslope coarse-grained sediment supply to different levels of urbanization. Coarse-grained sediment supply from the urban land surface was substantial. The highest unit-area yields came from infill construction sites (2800 kg/ha/yr), followed by gravel surfaces (740 kg/ha/yr), grass/mulch surfaces (84 kg/ha/yr), then impervious surfaces (21 kg/ha/yr), with the latter still producing yields far above background conditions. In typical suburban catchments grass and mulch surfaces and construction areas were key sources, with gravel and impervious surfaces making smaller contributions. Small source areas were important, for example construction produced 32% of sediment from 0.5% of the area. Connectivity of sediment sources to impervious surfaces, and hence to drainage systems, was important in driving sediment yields. Our conceptual model indicates that hillslope coarse-grained sediment supply increases with urbanization from natural to suburban conditions as connectivity increases, then declines with higher levels of urbanization as sources become scarcer. Impervious surfaces provide sources and supply pathways of coarse sediment, but also increase sediment transport capacity, causing severely supply-limited conditions and reducing the persistence of bed sediments in streams. When reducing hydrological connectivity to address the urban flow regime, consideration should be given to maintaining coarse-grained sediment supply through bypass or replenishment arrangements, to help reduce stream degradation and maintain form and functioning.

High levels of E. coli and associated faecal microbes in waterways as a result of agricultural and residential land use can pose environmental, human health, and economic risks. This study aims to understand the impacts of land use, climatic variables, and riparian buffers on in-stream E. coli concentrations. Flow, temperature, and E. coli were monitored during three sampling campaigns within eleven independent catchments. These catchments have varying land use and extents of riparian buffer coverage. Results showed that catchments with predominantly agricultural and residential land uses (average = 349.7 MPN/100 mL) had higher E. coli concentrations than predominantly forested catchments (average = 111.8 MPN/100 mL). However, there were no statistically significant differences in E. coli concentrations between the agricultural and residential land uses. Riparian buffers appear to reduce E. coli concentrations in streams, as indicated by significant negative correlations between in-stream E. coli concentrations with the riparian buffer areal coverage (Pearson's r = -0.95, Spearman's ρ = -0.90) and the ratio of buffer length to stream length (Pearson's r = -0.87, Spearman's ρ = -0.90). We find that riparian buffers potentially disrupt transport pathways that govern E. coli movement, which in-turn can affect the concentration-discharge relationship. This reinforces the importance of protecting and restoring riparian buffers along drainage lines in agricultural and rural-residential catchments to improve downstream microbial water quality.

Rainfall in cities can generate large volumes of stormwater runoff which degrades receiving waterways. Irrigating trees with runoff (passive irrigation) has the potential to increase transpiration and contribute to stormwater management by reducing runoff received by downstream waterways, but the stochastic nature of rainfall may expose trees with high transpiration to drought stress. We hypothesized that for success in passive irrigation systems, tree species should exhibit i) high maximum transpiration rates under well-watered conditions, ii) drought avoidance between rainfall events, and iii) high recovery of transpiration with rainfall following a drought. We assessed 13 commonly planted urban species in Melbourne, Australia against three metrics representing these behaviours (crop factor, hydroscape area, and transpiration recovery, respectively) in a glasshouse experiment. To aid species selection, we also investigated the relationships between these three metrics and commonly measured plant traits, including leaf turgor loss point, wood density, and sapwood to leaf area ratio (Huber value). Only one species (Tristaniopsis laurina) exhibited a combination of high crop factor (>1.1 mm mm−1 d−1) indicating high transpiration, small hydroscape area ( 85%) following water deficit. Hence, of the species measured, it had the greatest potential to reduce runoff from passive irrigation systems while avoiding drought stress. Nevertheless, several other species showed moderate transpiration, hydroscape areas and transpiration recovery, indicating a balanced strategy likely suitable for passive irrigation systems. Huber values were negatively related to crop factor and transpiration recovery and may therefore be a useful tool to aid species selection. We propose that selecting tree species with high transpiration rates that can avoid drought and recover well could greatly reduce stormwater runoff, while supporting broader environmental benefits such as urban cooling in cities.

Bioretention systems are increasingly used worldwide to mitigate the impacts of urban stormwater runoff on the water cycle. The proper management of bioretention systems requires accurate modeling of physical processes occurring within these systems. This study developed and tested a generic and physically-based model called Infiltron-mod. This model makes use of the Darcian approach (assuming Mualem-van Genuchten model for the description of the soil hydraulic properties) and mass conservation. The first version of the model considers evapotranspiration, overflow, exfiltration to surrounding soils, along with the filter hydraulic head and underdrain discharge. The proposed model was tested against field data from a monitored bioretention basin in Melbourne, Australia. We used two rainfall events to calibrate the model and 20 rainfall events for its validation. We achieved quite nice fits of experimental data with median NSE values in the order of 0.7-0.75 for the outflow rates. Despite good performance for outflow rates, we noticed the potential for improvement for the simulation of the height of water in the systems. Such discrepancy is probably the result of preferential flows.As a second step, we developed a specific module to implement the dual permeability approach to model preferential flow. Such an approach may simulate the concomitancy of matrix flow in part of the system and rapid preferential infiltration into macropores. The new module Infiltron-mod-pref was implemented and investigated. Prior to its use for field data, we validated the new module against more straightforward water infiltration experiments. Several large ring infiltration tests were performed on a field dedicated to infiltrating stormwater, and the two versions of the proposed model, Infiltron-mod and Infiltron-mod-Pref. We clearly showed the benefit to account for the preferential flow in the model. The next step will be the use of Infiltron-mod_Pref for field data from the monitored bioretention basin in Melbourne.The proposed approach then seems a useful first step to assess both performance and impact of bioretention basins for catchment-scale flow regime management and has real potential for application where user-friendly and simple model calibration and deployment are desired.

Data collection in urban drainage systems comes with many challenges. However, many examples already exist, containing numerous useful lessons learned. This chapter therefore contains several urban drainage and stormwater management metrology case studies, selected to cover a wide range of scopes, scales, objectives, climates, data validation methods, and data storage approaches. The case studies are initiated by academics as well as by institutions from the water industry.

Water infrastructure in cities is complex and requires proactive management to optimise function. The scale and distribution of assets across municipalities requires affordable systems which can trigger alerts. Systems underpinned by low-cost sensors could meet increasing monitoring needs: more assets, more often, and at a better resolution. However, low-cost sensors require appropriate testing to assess their performance and optimise their use. Here, we focus on low-cost water level sensors, often considered as the main monitoring parameters for water-related infrastructures. We developed a platform and testing protocol to assess the suitability of low-cost sensors. We assessed the performance of three widely used low-cost sensors: laser-ranging, ultrasonic-ranging, and pressure. Our main results showed that the ultrasonic sensor offers the best price to accuracy ratio, and the pressure sensor provides the highest accuracy while still at a very low cost. Our platform and protocol provide a standardised testing and calibration method which can be applied to any sensor. The platform can be used to gather and share results, to enhance community knowledge and encourage the use of new (low-cost or not) sensors. The development of low-cost sensors is an important step toward the wider use monitoring systems for water infrastructure.

Vegetated biofiltration systems (biofilters) are now a well-established technology for treatment of urban stormwater, typically showing high nutrient uptake. However, the impact of high temporal variability of rainfall events (further exacerbated by climate change) on nitrogen and phosphorus removal processes, within different biofiltration designs, is still unknown. Hence, a laboratory-based study was conducted to uncover mechanisms behind nutrient removal in biofilters across different drying and wetting regimes. Two sets of experimental columns were based on (1) the standard biofiltration design (unsaturated zone only), and (2) combination of unsaturated and saturated (submerged) zone (SZ) with additional carbon source. Columns were watered with synthetic stormwater according to three drying and wetting schemes, exploring 1, 2, 3, 4 and 7-week drying. Hydraulic performance, soil moisture and pollutant removal were monitored. The results show that hydraulic conductivity of SZ design experiences less change over time compared to standard design, due to slower media drying, crack formation and lower plant die-off. Varied drying lengths challenged both designs differently, with 2-week drying resulting in significant drop of performance across most pollutants in standard design (except ammonia), while SZ design was able to retain high performance for up to four weeks of drying, sustaining microbial and plant uptake. Increased oxygenation of SZ columns during short-term drying was beneficial for ammonia and phosphorus removal. While SZ design showed better performance and quicker recovery for nitrogen removal, in regions with inter-rain event shorter than two weeks, the standard design (no saturated zone, no carbon source) can achieve similar if not better results.

Biofiltration systems can help mitigate the impact of urban runoff as they can treat, retain and attenuate stormwater. It is important to select the optimal design characteristics of biofilters (e.g., vegetation, filter media depth) to ensure high treatment performance. Operational conditions (e.g., infiltration rate) can also lead to significant changes in biofilter treatment performance over time. The impact of specific operational conditions on water quality treatment performance of stormwater biofilters is still not well understood. Furthermore, despite the importance of design characteristics and operational conditions on biofilter treatment performance, there is a lack of models that can be used to determine the optimal design and operation. In this paper, we developed a series of statistical models to predict the Total Phosphorus (TP) and Total Nitrogen (TN) removal performance of stormwater biofilters using various numbers of design characteristics and operational conditions. These statistical models were tested using data collected from four extensive laboratory-scale biofilter column studies. It was found that all models performed relatively well with a Nash-Sutcliffe Efficiency (NSE) of 0.42 - 0.61 for TP and 0.37 - 0.63 for TN. The most important design characteristics were filter media type and depth for TP treatment, and vegetation type and submerged zone depth for TN treatment. In addition, infiltration rate and inflow concentrations were the operational conditions that greatly influence outflow TP and TN concentrations from stormwater biofilters. As such, these variables need to be carefully considered when designing and operating stormwater biofilters. Sensitivity analysis results indicate that the model was quite sensitive to all regression coefficients and intercepts. Additional modelling exercises show that the model could be further simplified by reducing the number of cross-correlated parameters. These models can be used by practitioners for not just optimising the design, but also operating biofilters using real-time monitoring and control to achieve optimum performance.

International audience; To restore streams degraded by urbanisation, bioretention basins ('raingardens') are implemented worldwide to reduce stormwater volumes, peaks flows and pollutant loads entering streams. While they are effective at this, their ability to mimic natural flow regimes has received limited field investigation. We monitored the hydrology and water quality of a bioretention basin during a three-year period. We found that the basin reduced the delivery of polluted water to the stream (55-65% of catchment runoff released as treated outflow), with peak flows and event concentrations of TSS, TP and TN substantially lowered too. A smaller proportion of catchment runoff infiltrated into the surrounding soil, but the flow regime delivered by the basin to the local stream was not similar to nearby forested streams. Such systems can mitigate the impacts of urban runoff on streams and shift the urban water balance towards natural conditions, but complete flow regime restoration requires catchment-scale action.

Use of Real-Time Control (RTC) technology in Rainwater Harvesting Systems (RWH) can improve performance across water supply, flood protection, and environmental flow provision. Such systems make th...

Green roofs can reduce stormwater runoff with deeper substrates providing greater storage for water retention and evapotranspiration (ET) regenerating storage capacity between rainfall events. In green roof models, ET can be estimated using species-specific plant crop factors (Kc), which characterize water use under non-limiting conditions. We manipulated Kc by altering plant density in a glasshouse experiment under well-watered conditions. We determined Kc of green roof plants growing in pots with different substrate depths (150 mm and 300 mm) and plant densities (0, 1, 2 and 4 plants per pot). We then analyzed the influence of storage and Kc on retention and drought stress using a water-balance model, with a 30-year climate scenario for Melbourne, Australia. We hypothesized that greater planting density and substrate depth would result in proportionally greater ET and therefore higher Kc (glasshouse experiment) and that this would improve retention and reduce drought stress (rainfall simulation). Contrary to our hypotheses, cumulative ET increased by only 38–48% with increased substrate depth and by only 28–38% with increased plant density, despite large increases in plant biomass (67–150%) and growth. Kc values ranged from 1.9–2.2 and 2.7–3.8 for shallower and deeper substrates, respectively. Due to these very high crop factors, our water balance model showed very high annual rainfall retention (97.5%). However, higher Kc and storage only increased rainfall retention by 3–5% and resulted greater drought stress. Plants in deeper substrates experienced 14–29 more days of drought stress, as these plants depleted substrate moisture more efficiently (i.e., had a higher Kc) compared with shallow substrates. These findings suggest that improvements in rainfall retention for green roofs with deeper substrates or higher plant densities are small relative to the increased risk of plant drought stress. The lowest planting density was optimal for improving rainfall retention and reducing plant drought stress.

Stormwater control measures, such as raingardens, tanks, or wetlands, are often employed to mitigate the deleterious effects of urban stormwater drainage on stream ecosystems. However, performance metrics for control measures, most commonly pollutant-load reduction, have not permitted prediction of how they will change stream ecosystems downstream. Stream ecosystem responses have more commonly been predicted by catchment-scale measures such as effective imperviousness (percentage of catchment with impervious cover draining to sealed drains). We adapt effective imperviousness, weighting it by a performance metric for stormwater control measures aimed at stream protection, the stream stormwater impact metric. Weighted effective imperviousness can serve as a predictor of stream response to stormwater control. We demonstrate its application in a before-after-control-reference-impact experiment aiming to test if stream health is improved by dispersed stormwater control measures. Trends in weighted effective imperviousness showed wide variation in degree of stormwater control achieved in the six experimental sub-catchments, despite similar effort in implementing control measures across the sub-catchments. Greater reductions in weighted effective imperviousness (on a log-scale, on which stream response is predicted) per unit effort were observed in smaller catchments with lower starting effective imperviousness. While implementation of control measures was sufficient to expect a stream response in at least two of the experimental sub-catchments, we did not achieve the reduction in effective imperviousness that we were aiming for. Primary limitations to success were the lack of available space in these established suburbs, particularly for final control measures near pipe outlets into streams, and a lack of demand for harvested stormwater. The use of the continuous variable, weighted effective imperviousness, to measure impact on streams, and the protracted period of SCM implementation that varied among catchments, required a new approach to modelling “before-after-control-impact” experiments, which has potentially broader application.

The practice of stormwater infiltration is widely used to reduce the amount of urban stormwater runoff delivered to drainage systems and receiving waters. In theory, the practice recharges groundwater, leading to increased urban stream baseflows. However, little is known about the fate of infiltrated stormwater. We tracked the fate of infiltrated stormwater from an infiltration basin using a network of piezometers for three years. We found that groundwater levels downslope of the basin were increased while water levels in an array of reference piezometers lateral to the basin showed no change. In summer, most of the infiltrated stormwater was evapo-transpired by the vegetation downslope of the basin, and thus did not reach the receiving stream. The reverse was true in the colder months, where some infiltrated stormwater did reach the stream as plant water use declined. Particularly during these Summer-Autumn months, anthropogenic disturbances interacted with the plume of infiltrated stormwater: infiltrated stormwater seeped into nearby sewer infrastructure. The study provides evidence that the fate of infiltrated stormwater largely depends on surrounding land use and that urban groundwater pathways are susceptible to disturbance by anthropogenic features. Infiltrated stormwater may not always reach receiving streams as baseflow as often assumed, which has implications for the design and placement of infiltration structures. This experimental data can be used to refine conceptual models of urban catchments and stormwater models.

Short term studies have found that stormwater biofiltration systems, also known as bioretention systems or raingardens, are very effective in reducing heavy metal concentrations. However, their long-term treatment performance, as well as the spatial and temporal accumulation of metals within these systems remain uncertain. This paper reports on a large scale field study that assessed the changes over time of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) levels in biofilters varying in age, design, and catchment characteristics. The survey incorporated 29 biofilters in 2006/7 and 49 biofilters, in 2014/15, located in three major Australian cities (Melbourne, Brisbane, and Sydney). Noting that these results are influenced by having just one industrial site with 25 filters measured at that site Catchment characteristics were significantly correlated with metal accumulation rates. Biofilters in catchments with current or past industrial activities had elevated heavy metal concentrations in the filter media. Zinc concentrations in the surface 0–100 mm exceed both soil quality and ecological guidelines. In contrast, heavy metal concentrations in residential catchments are unlikely to (ever) reach levels that exceed soil quality guidelines for human health, although zinc concentrations approach ecological guideline criteria.

Biofiltration systems are highly valued in urban landscapes as they remove pollutants from stormwater runoff whilst contributing to a reduction in runoff volumes. Integrating trees in biofilters may improve their runoff retention performance, as trees have greater transpiration than commonly used sedge or herb species. High transpiration rates will rapidly deplete retained water, creating storage capacity prior to the next runoff event. However, a tree with high transpiration rates in a biofilter system will likely be frequently exposed to drought stress. Selecting appropriate tree species therefore requires an understanding of how different trees use water and how they respond to substrate drying. We selected 20 tree species and quantified evapotranspiration (ET) and drought stress (leaf water potential; Ψ) in relation to substrate water content. To compare species, we developed metrics which describe: (i) maximum rates of ET under well-watered conditions, (ii) the sensitivity of ET and (iii) the response of Ψ to declining substrate water content. Using these three metrics, we classified species into three groups: risky, balanced or conservative. Risky and balanced species showed high maximum ET, whereas conservative species always had low ET. As substrates dried, the balanced species down-regulated ET to delay the onset of drought stress; whereas risky species did not. Therefore, balanced species with high ET are more likely to improve the retention performance of biofiltration systems without introducing significant drought risk. This classification of tree water use strategies can be easily integrated into water balance models and improve tree species selection for biofiltration systems.

Green infrastructure delivers a range of benefits for urban water management, amenity, human well-being, and ecosystem health. However, the implementation of green urban infrastructure can be chall...

Cities around the world are embracing stormwater control measures (SCMs) to reduce the environmental damage caused by impervious runoff. At the same time, there is a push to increase tree canopy cover to green neighborhoods and mitigate urban heat. Establishing SCMs that include trees may achieve these two objectives, but it is important to understand which design characteristics promote or reduce tree health and growth. We therefore undertook an 18-month streetscape experiment comparing four tree pit SCM designs, along with a control (non-SCM) street tree planting, to identify design characteristics influencing the water balance and growth of newly planted trees (Acer campestre (L.)) in an established urban area dominated by clay soils. Trees in pits with an underdrain showed double the growth of conventionally planted street trees receiving no stormwater. However, the low exfiltration rates of some non-drained tree pits resulted in some tree pits experiencing waterlogging and subsequent poor tree growth or even death. In other non-drained tree pits, the heterogeneity of urban soils resulted in sufficiently high exfiltration rates to avoid waterlogging and promote increased tree growth, even in these heavy clay soils. Our results suggest that establishing tree growth can be substantially increased by directing stormwater into tree pits, however, waterlogging conditions should be avoided via an underdrain or limiting installation to soils with a sufficiently high exfiltration rate.

Tree pits are attractive stormwater control measures (SCMs) for implementation in dense urban areas because of their small footprint, their potentially low cost and the co-benefits they may bring through improved street tree growth. While they provide street trees with passive irrigation, it remains to be determined if tree pits may achieve meaningful reductions in stormwater runoff. We undertook a streetscape experiment to quantify runoff retention of tree pits in a heavy clay soil with low-rates of exfiltration. We calibrated and validated a water balance model using the field experiment data to identify tree pit characteristics driving runoff retention performance. We then applied the model to different implementation scenarios to ascertain how useful these tree pits may be at reducing runoff to return a more natural flow regime in dense urban areas. The main drivers of runoff retention were identified as exfiltration rates from the tree pits and the connected impervious catchment size. Our results show that it is possible, even in dense urban streetscapes with low conductivity (heavy-clay) soils, to achieve a 90% reduction in annual runoff and to reduce days of runoff to just 15 days per year. However, to achieve this, tree pits need to be sized between 2.5% and 8% of the impervious catchment area, depending on pit exfiltration rates. In practice, achieving these tree pit to catchment area ratios for a dense urban streetscape will require consideration in the planning stages of development works and is expected to be most feasible through implementation of tree pits alongside a suite of other complementary SCMs.

Physical degradation of urban rivers negatively impacts the environmental and social values they provide, and imposes significant financial costs on waterway management agencies. While the impact of urban stormwater runoff on streams is well recognised, the influence of altered bed sediment regimes on urban stream geomorphology is poorly understood. This study reports bedload sediment yields and bedload particle size distributions measured with sediment traps in nine small streams in eastern Melbourne, Australia, across a gradient of urbanization. We assessed relationships between the yield and size of bedload sediment and measures of catchment urbanization (including total imperviousness, effective imperviousness, road density and pipe density) and hydrology (measured through flow gauging at each site). Bedload yields were greater and bedload sediments were coarser-grained in more urbanized catchments. Bedload yields were strongly related to drainage connection of the urban land surface to the stream (captured by measures such as effective imperviousness and pipe density). The increase in bedload yield and calibre in urban catchments was driven mainly by the increase in sediment-transporting runoff from connected impervious surfaces. This study found no evidence of urban land cover severely limiting coarse-grained sediment supply. Most of the bedload material appeared to originate from imported sediment sources (e.g. construction and surfacing materials) in upland urban hillslope areas, which were connected to the channel by efficient transport reaches such as pipes and rock-lined channels, rather than from channel-derived erosion. Findings of this study suggest a rethink of the coarse-grained sediment-supplying potential of urban catchments, which has long been assumed to be low due to sealing of the land surface with hard materials.

Plants are essential components of bioretention systems, with bioretention design-guides around the world providing extensive advice on the role of selection of plants to maximize system performance and sustainability. Four principal hypotheses regarding the role of plants have been identified in bioretention design manuals: (i) Planted systems are more effective than unplanted systems, (ii) Plant species differ in their effectiveness, (iii) Native species are more effective than exotic ones, (iv) Diverse systems are more efficient than monocultures. This paper examines the extent to which these hypotheses are supported by the scientific literature. Comparison of planted and unplanted systems show that increased permeability and hydraulic conductivity, as well as removal of nitrogen, are the main benefits of the presence of plants in bioretention. Knowledge on their positive effect on hydrocarbons remains fragmented, although there is evidence from phytoremediation studies in other plant-based technologies. Choosing the right species makes a difference in hydraulic performance and nitrogen removal, with root traits being identified as important predictors of performance. No scientific results can support the hypothesis that native plants or diversely-planted systems offer better performance than systems planted with fewer species or with exotic species. Questions remain regarding the plant-microbe interaction in the bioretention context, the role of biomacropores in pollutant migration or the differential impact of plant choice on performance.

Vegetation cover, specifically emergent macrophyte cover, is critical to the performance of constructed stormwater treatment wetlands which are widely used to protect receiving waterways. Maintenance of vegetation relies on a suitable water level regime, which in turn is governed by the hydraulic loading rate and efficiency of the outlet control structure. Wetland designers need to take these factors into account to avoid excessive depth and duration of inundation. We investigated the relationship between the water level regime and vegetation cover in 19 stormwater wetlands. We found a strong relationship between the median water level and vegetation cover, where vegetation cover was generally high (>80%) at median depths

Urbanization disturbs groundwater flow through the sealing of native soils with impervious surfaces and through modifications to the subsoil by constructed drainage and other infrastructure (trenches and excavations, e.g. water supply). The impact of these disturbances on groundwater contributions to urban streams (i.e. baseflow) is poorly understood. While high flows caused by impervious runoff to streams are a common focus of urban studies, the route taken by groundwater to become streamflow in urban landscapes is not generally considered. To assess the impact of urbanization on groundwater sources to streams, both rainfall and baseflow were sampled weekly for stable isotopes of water in two nearby streams—one draining a peri-urban catchment and the other draining a forested, natural catchment. In addition, to study the rate of groundwater discharge to the stream, monthly baseflow recession behavior was investigated. We found that baseflow in the forested catchment was constant in stable isotope values (δ18O = −5.73‰ ± 0.14‰) throughout the year. Monthly baseflow recession constants were close to 1 and had little variation (ranging 0.951–0.992), indicating a well-mixed groundwater store and long residence times. In contrast, the urban baseflow isotopic composition featured distinct seasonal variations (δ18O = −3.35‰ ± 1.20‰ from October to March and δ18O = −4.54‰ ± 0.43‰ from April to September) and high week-to-week variability in summer, reflecting a contribution of recent rainfall to baseflow. Recession constants were lower (ranging 0.727–0.955) with pronounced seasonal variations, suggesting shorter residence times and the likely presence of a variety of stores and pathways. These results provide evidence that the urban catchment has diversified groundwater pathways, and its groundwater storage is drained faster than that of the forested catchment. It highlights some of the subsurface hydrological consequences of urbanization. Restoring low-flow aspects of the flow regime through nature-mimicking stormwater management requires careful consideration of how the behavior of natural groundwater pathways can be restored or replicated using innovative stormwater control measures.