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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 Over the past century, traditional stormwater control has been replaced by a new low-impact development (LID) approach called " on-site alternative design strategy", which aims to restore or maintain the hydrological functions of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.

Nature-based systems are being employed to allow stormwater to infiltrate directly in the soil, which is supposed to capture pollutants. To better track the evolution of such systems performances, in particular the infiltration and filtration performances, and to be able to optimize their management, these systems need to be better known. Currently, there is a lack of knowledge and methods regarding the characterization of the macropores and matrix contributions in infiltration and filtration of urban soils, whereas the quality of groundwater and the capacities of these systems are at stake. To tackle these limits, a large infiltrometer of 50 cm in diameter with two water-supply reservoirs of approximately 40 L each, was developed to characterize both hydrodynamic and nanotracers transfer parameters. Cumulative water infiltration was carried out at a constant hydraulic pressure head of 10 cm. Superparamagnetic iron oxide nanoparticles (SPIONs), which mimic both colloidal pollutants and bacteria flow behaviors in soils, were designed to be detectable by ground-penetrating radar (GPR). Fifty volumes of SPIONs solution (i.e., 50 x 5 mL at 3.35g/L) were injected into the ring and the GPR was passed along different survey lines around the ring several times during the infiltration experiment. GPR data was treated with ReflexW (Sandmeier Scientific Software, Karlsruhe, Germany) and Rockware (RockWare, Inc, 2015) to define a 3D block diagram of the infiltration bulb. The probability of presence of the nanoparticles was obtained from comparing the radargrams, before and after nanoparticle injection, by using two methods (Allroggen and Tronicke, 2015; Di Prima et al., 2020) on a R software (https://www.R-project.org/).The large infiltrometer device, compared with a smaller one (Di Prima et al., 2015), is proved effective for estimating water and transfer parameters. The dispersion of SPIONs gave an idea of the relative importance of the transfer through the soil macropores as compared to the soil matrix. The probability of SPIONs presence gave information on the filtration function of soils. The whole device application will be illustrated and discussed with regard to its use for the assessment of the infiltration and filtration functions of bio-infiltration systems. Allroggen, N., Tronicke, J., 2015. Attribute-based analysis of time-lapse ground-penetrating radar data. Geophysics 81, H1–H8. https://doi.org/10.1190/geo2015-0171.1Di Prima, S., Lassabatere, L., Bagarello, V., Iovino, M., Angulo-Jaramillo, R., 2015. Testing a new automated single ring infiltrometer for Beerkan infiltration experiments. Geoderma 262, 20–34. https://doi.org/10.1016/j.geoderma.2015.08.006Di Prima, S., Winiarski, T., Angulo-Jaramillo, R., Stewart, R.D., Castellini, M., Abou Najm, M.R., Ventrella, D., Pirastru, M., Giadrossich, F., Capello, G., Biddoccu, M., Lassabatere, L., 2020. Detecting infiltrated water and preferential flow pathways through time-lapse ground-penetrating radar surveys. Sci. Total Environ. 726, 138511. https://doi.org/10.1016/j.scitotenv.2020.1385

International audience; Cities are patchworks of urban catchments divided into functional units according to their commercial, residential and industrial activities, and socio-urbanistic patterns. The hypothesis of city surface microbiomes being structured by socio-urbanistic variables leading to an emergence of synurbic taxa was tested. According to the r/K microbial ecology theory, a gradient of well-adapted synurbic K-strategists and of opportunistic –r-strategists should occur over city surfaces. K-strategists would be core components while r-ones would be transiently detected. To resolve these patterns, sub-catchments (n = 21) of an area of high commercial and industrial activities were investigated over three time periods covering one year. The sub-catchments' land use patterns and associated human behaviors were converted into socio-urbanistic variables and groupings. Bacterial cells mobilized by runoffs per sub-catchment were recovered, and analyzed by classical approaches, microbial source tracking DNA assays and DNA meta-barcoding approaches. Relationships between these datasets, the runoff physico-chemical properties, and descriptors of the socio-urbanistic groupings were investigated. 16S rRNA meta-barcoding analyses showed evidence of the occurrence of K- and r-like strategists. Twenty-eight core genera were identified, and correlation networks revealed large bacterial modules organized around actinobacterial taxa involved in hydrocarbon degradation processes. Other bacterial networks were related to the occurrences of hygienic wastes, and involved bacteria originating from fecal contaminations. Several r-strategists like Sulfurospirillum were recorded and found associated to point source pollutions. The tpm -metabarcoding approach deciphered these r / K strategists at the species level among more than ten genera. Nine core Klike Pseudomomas species were identified. The P. aeruginosa human opportunistic pathogen and P. syringae phytopathogens were part of these K-strategists. Other tpm -harboring bacterial pathogens showed r-like opportunistic distribution patterns. Correlation network analyses indicated a strong incidence of hygienic wastes and hydrocarbon-pollutions on tpm -harboring bacteria. These analyses demonstrated the occurrence of core synurbic bacterial K-strategists over city surfaces.

Stormwater management zones must enable water to infiltrate easily, primarily due to macropores, but little is known about the transport of pollutants through these macropores. Some coupled methods using, for example, dyes, disc, or ring infiltrometers were developed to give insight on the respective contributions of the macropores versus the matrix to the bulk infiltration. However, these methods do not visualize where and how water infiltrates. Besides, no information is given on the solute transfer in soils, whereas this issue is crucial regarding the quality of soils and groundwater. One of the goals of the national program INFILTRON (https://infiltron.org) project granted by the French national research agency is to develop superparamagnetic iron oxide nanoparticles (SPIONs) which mimic both pollutant and bacteria flow behavior in soils (Raimbault et al., 2021) and are detectable by ground-penetrating radar (GPR). Within its framework (Lassabatere et al., 2020), we aim to show how nano-tracers can help detect preferential treatment flows (lithological heterogeneity, root system) and quantify or qualify the pollutant transfer in heterogeneous soils. A specific device was designed and presented for the concomitant monitoring of water infiltration and nano-tracer injection. This specific infiltrometer involves two water supply reservoirs and a ring diameter of 50 centimeters. This device maintains a constant depth of water (10 cm) above the soil and delivers the water infiltration into the soil. Two rules posed on the reservoirs allow monitoring the water drop and computation of the cumulative infiltration. Fifty volumes of SPIONs solutions (5 mL of 3.35g/l SPIONs solution) were injected into the ring to maintain a constant concentration in the ring. GPR monitors the bulb of infiltrated water and SPIONs. GPR data is treated with ReflexW (©Sandmeier geophysical research) and RockWorks (RockWare®) software. Combining this specific prototype with the use of GPR for the detection of water and the SPIONs gives insight into the processes of infiltration and SPIONs transfer and localization in the soil. These data allow us to understand and model pollutant transfer into the vadose zone.Raimbault, J., Peyneau, P.-E., Courtier-Murias, D., Bigot, T., Gil Roca, J., Béchet, B., and Lassabatère, L.: Investigating the impact of exit effects on solute transport in macropored porous media, 2020, 1–20, https://doi.org/10.5194/hess-2020-494, 2020Lassabatere, L., De Giacomoni, A.-C., Angulo-Jaramillo, R., Lipeme Kouyi, G., Martini, M., Louis, C., Peyneau, P.-E., Rodriguez-Nava, V., Cournoyer, B., Aigle, A., and others: INFILTRON package for assessing infiltration & filtration functions of urban soils, in: EGU General Assembly Conference Abstracts, 11269, 2020. https://doi.org/10.5194/egusphere-egu2020-11269

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.

International audience

The numerical prediction of pressure drop within wall-bounded flow domains at high Reynolds numbers ( Re ) using a large-eddy simulation (LES) approach is a challenging task for industrial applications because the fluid domain is usually underresolved. A lattice Boltzmann method (LBM) with Bhatnagar, Gross and Krook (BGK) collision operator coupled with the Smagorinsky–Lilly turbulence model is used to model these wall-bounded turbulent flows. The near wall region is modelled using wall functions to decrease the required mesh resolution for high Re . The influence of different velocity boundary approaches and wall functions is investigated for the benchmark bi-periodic fully developed turbulent channel flow for friction Reynolds numbers ( Re τ ) of 1000, 2000 and 5200. This benchmark case is validated against direct numerical simulation (DNS) results for turbulent statistics of 1st and 2nd order. Based on this validation, the pressure drop of an industrial Coriolis mass flowmeter is compared to experimental data for Re up to 127 800. The error of the pressure drop calculation in underresolved grids is reduced by two orders of magnitude in comparison to a no-slip approach for curved boundaries.

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.

International audience

International audience; One of the most adopted solutions in developed countries to manage stormwater is detention/retention basins which generate large quantities of sediments that have to be removed regularly. In order to manage them properly, accurate data are needed about their physical and chemical characteristics, particularly on micropollutant concentrations and their associated risk. This work consisted in a two-year sampling of dry sediments from a detention-settling basin. Priority substances, including pesticides, polybrominated diphenyl ethers (PBDE), alkylphenols and bisphenol A (BPA), were monitored. Different sites in the basin bottom were sampled in order to investigate spatial distribution of the contamination. Results show that the increase of the sediment thickness in the basin was heterogeneous with a maximum of 15 cm after two years. Pesticides and PBDE were, if detected, mainly found in low concentrations from 2 ng/g to 286 ng/g. Conversely, alkylphenols and bisphenol A were always quantified at concentrations varying from 6 ng/g to 3400 ng/g. These high levels suggest that these sediments should be managed with precautions. Spatial heterogeneity of alkylphenol ethoxylates and BPA concentrations was observed, with higher contamination of alkylphenol ethoxylates in anaerobic zones and BPA levels correlated with total organic carbon and in a lesser extent to fine particles.

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.

Detention and infiltration basin has been increasingly implemented in France in order to provide additional storage of runoff from impervious surfaces due to rapid urbanization. These sustainable urban drainage systems also ensure quality of stormwater infiltrated into groundwater. In urban areas, these devices accumulate suspended particles eroded from city watershed and represent a geochemical signature of these urban watershed. Urban sediments are known to be polluted by high organic and inorganic substance contents, but their geochemical properties and specificities are insufficiently informed. The objective of this work is to study whether geochemical properties of urban sediment accumulated in detention and infiltration basins is distinguished from other natural sediments (from rivers, lake, marine environment). For this purpose, this study focused on relating watershed characteristics and physico-chemical properties of sediment using multivariate analyses based on rank data values. Data were notably collected from the national programs GESSOL (GEStion du patrimoine SOL, i.e. soil environmental functions - soil heritage management) and EC2CO (Ecosphère Continentale et Côtière, i.e. continental and coastal ecosphere) based on 19 infiltration basins around Lyon (France) and from literature (lake, basin, river etc.). Principal Component Analysis (PCA) was used to identify the most important sources of variation between trace metals and organic matters in different sediments. Cluster analysis was performed to group samples of similar sediment characteristics between major variables and trace metals contents. A significant amount of Fe (from 2.52 to 3.92 wt.%) and organic matters (from 18 to 27 wt.%) was found in the urban sediment. The results of PCA showed the influence of grain size on metal variability. Metals are more associated with the aluminosilicates (

Background Total suspended solids (TSS) loads carried by stormwater runoff is a major pollutant source on receiving water bodies. Stormwater ponds are widely used for controlling TSS discharge. However, the trap efficiency is not satisfactory because it is affected by many complex factors, which are not fully understood. Therefore, there is a necessity to gain insight into the sediment process in stormwater ponds for optimization design of stormwater ponds. To address this issue, we propose a novel modeling framework based on discrete phase model (DPM), aiming to fully represent the sediment transport, settling, and resuspension at grain scale under time-dependent conditions. Results In the newly proposed method, heterogeneous characteristics of sediments’ loads, varying flows and sediment loads, settling and resuspension effect at grain scale, time-dependent conditions, and turbulent effect are all well considered. The proposed models have been coded with C language and hooked in computational fluid dynamics software Fluent, and the methods were tested with a case of laboratory experimental setup. Different bed boundary conditions are tested and compared with the observation data for optimization parameters’ identification. The simulation results demonstrated that the physically based DPM with the newly developed method can well reproduce the evolution of sediment transport, settling and resuspension behaviors compared with the scale experiment. Conclusions The newly proposed method can accurately predict the trap efficiency and temporal–spatial sediment distribution. The decomposition of bed load motion at grain scale is a necessary and valid way to represent the sedimentation process in shallow ponds. The developed model could be a tool to help us gain insight into the sediment transport phenomena at grain scale in shallow tanks since it can provide detailed information which the experiment cannot.

One significant effect of urbanization is the modification of environmental conditions, with potential effects on the functioning of urban ecosystems and on their ability to perform functions and to provide service. This is due to both the multiple changes of surfaces and soils, and to an increased human pressure. These changes have indeed major negative impacts on natural resources such as air, water, soil, and biodiversity they host, and may affect locally the human thermal comfort, in addition to the climate change. A better understanding of the physical and biogeochemical processes leading to these changes is then crucial in order to propose and to optimize the mitigation and adaptation strategies. Following the recent efforts in the development of Critical Zones Observatories (CZOs), a new research initiative will regroup well-monitored and well-characterized urban field sites all over the French national territory within a National Observation Service called Observil. This observatory aims to address a multidisciplinary approach of urban environments, through a smart definition of appropriate variables and indicators required to better describe the physical and geochemical processes involved in the quality and the dynamic of the soil-surface-atmosphere compartments in cities. To do that, a common Spatial Information System dedicated to the creation of a structured observation database is under construction, in order to regroup the data from a large network bringing together 9 French cities under very contrasted environmental conditions (urban morphology, geology, climate). The main scientific questions addressed by this observation network project will be presented, along with a description of the the selected variables measured on the different sites.

The extension of urban and peri-urban areas and the related artificialization of soils drastically impacts the water cycle as well as biogeochemical cycles. In particular, the sealing of soils with impervious surfaces such as roads increases runoff and decreases concomitant infiltration. At the catchment scale, more significant amounts of stormwater must be collected and managed to prevent from flooding urban areas and mitigate discharge to the environment. Sustainable Urban Drainage Systems (SUDS) were developed to alleviate these problems. These systems allow the restoration of one of the main functions of urban and peri-urban soils, i.e., infiltrating stormwater. They simultaneously reduce the risk of flooding and increase groundwater recharge. Another essential service must be ensured and optimized: the removal of pollutants from infiltrating water by the soil, to avoid the degradation of the quality of the groundwater.The INFILTRON project aims to design a methodology for the assessment of infiltration and filtration of pollutants by SUDS. The project is a collaboration of many partners, with expertise in soil physics, urban hydrology, nanoparticle engineering, and modeling, to engineer a specific device for the simultaneous monitoring of water infiltration and pollutant filtration. This infiltration device both infiltrates water and injects nanoparticles (NPs) into the soil. It was sized to account for preferential flow, which is known to have a significant impact on infiltration and pollutant transfer. The engineered NPs were designed to be detectable in the ground using ground-penetrating radar (GPR) and to mimic the transfer of nano-pollutants (emerging pollutants, bacteria, etc.) commonly found in real stormwater. An infiltration-filtration model was developed to interpret the experimental data and to quantify two indicators for the assessment of water infiltration and pollutant filtration. INFILTRON will provide a very interesting toolbox for practitioners and stakeholders for the evaluation of the infiltration and filtration functions of not only SUDS within the framework of stormwater management, but also anthropized soils within the management of urban and peri-urban areas.

International audience; In the past ten years, governments from the European Union have been encouraged to collect volume and quality data for all the effluent overflows from separated stormwater and combined sewer systems that result in a significant environmental impact on receiving water bodies. Methods to monitor and control these flows require improvements, particularly for complex Combined Sewer Overflow (CSO) structures. The DSM-flux (Device for Stormwater and combined sewer flows Monitoring and the control of pollutant fluxes) is a new pre-designed and pre-calibrated channel that provides appropriate hydraulic conditions suitable for measurement of overflow rates and volumes by means of one water level gauge. In this paper, a stage-discharge relation for the DSM-flux is obtained experimentally and validated for multiple inflow hydraulic configurations. Uncertainties in CSO discharges and volumes are estimated within the Guide to the expression of Uncertainty in Measurement (GUM) framework. Whatever the upstream hydraulic conditions are, relative uncertainties are lower than 15% and 2% for the investigated discharges and volumes, respectively.

International audience

International audience; Stormwater detention basins are significant components for the sustainable management of urban stormwater, aiming to control stormwater quantity (prevent from flooding) and quality (trap particulate pollutants by settling). The design and management of such facilities need knowledge of the hydrodynamic characteristics and the sedimentation zones for cleaning purposes. Large‐scale particle image velocimetry (LSPIV), mostly applied in riverine environments, has been proven as a low‐cost, highly efficient, and convenient image‐based methodology for surface velocity measurement. In this study, LSPIV technology is employed to investigate free surface velocity in a field stormwater detention basin. The method is first evaluated by comparing its results with those obtained by acoustic Doppler velocimeter at pilot scale. Then, the technique is applied to better understand the main flow field and to explain spatial sediment distribution within an extended stormwater detention basin. Results illustrate two main flow patterns, which are consistent with observations and preliminary simulated results. LSPIV‐based free surface velocity field measurements can be used to evaluate numerical models and as a support to predict sediment deposition zones in stormwater detention basins and to help for their retrofit and management.

International audience; To characterize the spatio-temporal variation of sediment ecotoxicity in a retention/detention basin, a monitoring program using the Heterocypris incongruens bioassay was carried out for 72 months (5 years) on a field basin close to Lyon in France. Results showed that the variation of ecotoxicity is relatively small from one location of the basin to another, apart from sediment sampling collected in an open-air chamber located in basin supposed to collect gross pollutants and hydrocarbons. Regarding the temporal variation of ecotoxicity, the bioassays also showed a slight variation between 6 and 72 months. On the contrary, they highlighted the high ecotoxicity of the “fresh” sediments collected during rain events using sediment traps. Additional investigations are needed to understand the period of inflexion of ecotoxicity, occurring between 24 h and 6 months. These results can be used by practitioners of urban facilities and networks to improve maintenance strategies of retention/detention basins.

International audience; This paper aims at describing two different recirculation structures observed both numerically and experimentally in the lateral branch of a dividingopen channel flow with identical downstream weirs. The flow conditions leading to each identified recirculation structure are also investigated. Thefirst recirculation pattern is a classic two-dimensional closed recirculation, typically described in the literature. The second one is a three-dimensional helix-shaped recirculation that differs from the first one notably regarding the streamline behaviour.We show that the occurrence of each structure of recirculation can be predicted by means of the Froude number and the aspect ratio in the upstream channel of the bifurcation.

Elevated trace metal concentrations in sediments pose a major problem for the management of stormwater detention basins. These basins provide a nature-based solution to remove particulate pollutants through settling, but the resuspension of these contaminated deposits may impact the quality of both surface and groundwater. A better understanding of trace metal distribution will help to improve basin design and sediment management. This study aims to predict the distribution of trace metal contamination in a stormwater detention basin through (i) investigation of the correlation between metal content in sediments and their settling velocity, and (ii) the coupling of such correlation with a Lagrangian Discrete Phase Model (LDPM). The correlation between Fe, Cr, Cu, Ni, Pb contents and the settling velocity is firstly investigated, based on the sediments collected from 6 sites (inlet and 5 traps at the bottom of a detention basin situated in Chassieu, France) during 5 campaigns in 2017. Results show that Fe is strongly correlated to settling velocity and can be considered as a good indicator of trace metal contents. The derived correlation is then combined with a LDPM for the prediction of trace metal distribution, producing results consistent with in situ measurements. The proposed methodology can be applied for other stormwater basins (dry or wet). As described in this article, the interactions between hydrodynamics and sediment physico-chemical characteristics is crucial for the design and management of stormwater detention basins, allowing managers to target the highest contaminated sediments.

Authors thank the iBio platform (UMR Ecologie Microbienne, Universite Lyon 1) for bioinformatics processor resources and support, and Sylvie Barraud for support on chemical data analyses. They also thank OTHU (Field Observatory in Urban Hydrology) of ZABR (Zone Atelier Bassin du Rhone), the Grand Lyon Metropolis and Rhone-Mediterranean-Corsica Water Agency for technical and administrative supports.; International audience; Urban activities generate surface deposits over impervious surfaces that can represent ecological and health hazards. Bacteriome genetic structures of deposits washed off during rainfall events, over an urban industrial watershed, were inferred from 16S rRNA gene (rrs) sequences generated by high throughput sequencing. Deposits were sampled over a 4 year-period from a detention basin (DB). Major shifts, matching key management practices, in the structure of these urban bacteriomes, were recorded. Correlation analyses of rrs similarities between samples and their respective concentrations in chemical pollutants, markers of human fecal contaminations (HF183) and antimicrobial resistances (integrons), were performed. Harsher environmental constraints building up in the older deposits led to an increase number of rrs reads from extremophiles such as Acidibacter and Haliangium. Deposits accumulating in the decantation pit of the DB showed an increase in rrs reads from warm blooded intestinal tract bacteria such as Bacteroides and Prevotella. This enrichment matched higher concentrations of Bacteroides HF183 genotypes normally restricted to humans. Bacteriomes of urban deposits appeared good indicators of human-driven environmental changes. Their composition was found representative of their origin. Soil particles and rain appeared to be major contributors of the inferred bacterial taxa recovered from recent deposits.

International audience; 12 The present paper aims to identify ways to reduce pollution injected by residents in the urban 13 wastewaters network system. Two approaches are considered. The first one uses flow and 14 pollutant calculation to test whether a polluter can easily be identified in a neighborhood. The 15 second approach uses a survey to examine what incentive would be most effective to 16 influence residents' behavior. Hydrodynamic simulation results show that concentration 17 profiles at the network outlet corresponding to all possible polluters are similar and thus do 18 not point out specific resident source of pollution. Household level survey results show that 19 most socioeconomic and public good-related characteristics do not play a significant role in 20 explaining choices to discard in the home wastewaters network. Apart from the nature of the 21 waste itself, by far, the belief that the respondent has about her neighbors' and relatives' 22 discarding behavior is the main driver of the choice. 23 24

The flow characteristics in open channel junctions are of great interest in hydraulic and environmental engineering areas. This study investigates the capacity of artificial neural network (ANN) models for representing and modelling the velocity distributions of combined open channel flows. ANN models are constructed and tested using data derived from computational-fluid-dynamics models. The orthogonal sampling method is used to select representative data. The ANN models trained and validated by representative data generally outperform those by using random data. Sobols' sensitivity analysis is performed to investigate contributions of different uncertainty sources to model performance. Results indicate that the major uncertainty source is from ANN model parameter initialization. Hence an ANN model training strategy is designed in order to reduce the main uncertainty source: models are trained for many runs with random model parameter initializations and the model with the best performance is adopted. ANN models can capture complex flow structures at combined open channels.ANN models should be trained with representative training and validation data.Representative data can be selected using spatial information of data points.Sobols' analysis reveals major uncertainty source in ANN parameter initialization.

H 2 S emission dynamics in sewers is conditioned by the mass transfer coefficient at the interface. This work aimed at measuring the variation of the mass transfer coefficient with the hydraulic characteristics with the objective of estimating H 2 S emission in gravity pipes, and collecting data to establish models independent of the system geometry. The ratio between H 2 S and O 2 mass transfer coefficient was assessed in a 8 L mixed reactor under different experimental conditions. Then, oxygen mass transfer measurements were performed in a 10 m long gravity pipe. The following ranges of experimental conditions were investigated: velocity flow [0–0.61 m.s −1 ], Reynolds number [0–23,333]. The hydrodynamic parameters at the liquid/gas interface were calculated by CFD. In the lab-scale reactor, the O 2 mass transfer coefficient was found to depend on the stirring rate (rph) as follows: K L , O 2 = 0.016 + 0.025 N 3.85 . A K L , H 2 S / K L , O 2 ratio of 0.64 ± 0.24 was found, in accordance with previously published data. CFD results helped for refining this correlation: the mass transfer coefficient depends on the local interface velocity u i (m.h −1 ): K L , O 2 = 0.016 + 1.02 × 10 -5 u j 3.85 . In the gravity pipe device, K L , O 2 also exponentially increased with the mean flow velocity. These trends were found consistent with the increasing level of turbulence.

International audience; Problems related to hydrogen sulfide may be serious for both network stakeholders and the public in terms of health, sustainability of the sewer structure and urban comfort. H2S emission models are generally theoretical and simplified in terms of environmental conditions. Although air transport characteristics in sewers must play a role in the fate of hydrogen sulfide, only a limited number of studies have investigated this issue. The aim of this study was to better understand H2S liquid to gas transfer by highlighting the link between the mass transfer coefficient and the turbulence in the air flow and the water flow. For experimental safety reasons, O2 was taken as a model compound. The oxygen mass transfer coefficients were obtained using a mass balance in plug flow. The mass transfer coefficient was not impacted by the range of the interface air-flow velocity values tested (0.55–2.28 m·s−1) or the water velocity values (0.06–0.55 m·s–1). Using the ratio between kL,O2 to kL,H2S, the H2S mass transfer behavior in a gravity pipe in the same hydraulic conditions can be predicted.

Congrès SHF, Hydrométrie 2017, LYON, FRANCE, 14-/03/2017 - 15/03/2017; Sewer network managers are more and more implementing discharge sensors within sewer networks. When no permanent relation exists between the local water depth and discharge, velocity sensors are usually installed. In such case, the velocity values measured by these sensorS must be extrapolated to reach the averaged velocity across the flow section. This extrapolation implies uncertainties which are difficult to assess. 3D modelling of the velocity field allows to simulate the response of sensors for assessing these uncertainties, and reduce them by numerical calibration. In the following text, the general methodology is first introduced and then applied to two case studies, including a bend flow and a complex section configuration; Les gestionnaires de réseau d'assainissement urbain sont amenés à équiper leurs réseaux à l'aide de débitmètres. Lorsqu'il n'existe pas une relation permanente permettant de relier localement la hauteur d'eau et le débit, on recourt fréquemment à la mise en place de capteurs de vitesse. Le passage depuis la vitesse mesurée par ces capteurs vers la vitesse moyenne dans la section implique des incertitudes difficiles à évaluer. La modélisation 3D des écoulements permet de simuler la réponse des capteurs pour évaluer ces incertitudes, et, le cas échéant, de les réduire par étalonnage numérique. Après une présentation de la démarche générale, nous l'illustrerons par un cas générique d'un site à l'aval d'un coude et par le cas spécifique d'une section complexe

International audience; Sedimentation is a common but complex phenomenon in the urban drainage system. The settling mechanisms involved in detention basins are still not well understood. The lack of knowledge on sediment transport and settling processes in actual detention basins is still an obstacle to the optimization of the design and the management of the stormwater detention basins. In order to well understand the sedimentation processes, in this paper, a new boundary condition as an attempt to represent the sedimentation processes based on particle tracking approach is presented. The proposed boundary condition is based on the assumption that the flow turbulent kinetic energy near the bottom plays an important role on the sedimentation processes. The simulated results show that the proposed boundary condition appears as a potential capability to identify the referential sediment zones and to predict the trapping efficiency of the basin during storm events.

Les bassins de retenue des eaux pluviales peuvent etre utilises pour controler les polluants particulaires des rejets urbains par temps de pluie. Pour ameliorer leur fonctionnement, il est indispensable de maitriser et mieux modeliser les phenomenes lies au transport des particules (decantation, remise en suspension, dispersion). En general, le debit et les rejets polluants varient en fonction du temps au cours des evenements pluvieux. Cependant, la majorite des etudes faisant appel a la CFD pour simuler le transport particulaire dans les bassins de decantation n'a pas accorde suffisamment d'attention a l'effet des variations temporelles sur les mecanismes de transport. Cet article presente une nouvelle demarche de modelisation du transport particulaire a l'aide de l'approche Euler-Lagrange afin de prendre en compte la remise en suspension en conditions transitoires. Pour ce faire, plusieurs conditions limites au fond ont ete developpees et implementees dans un code de calcul afin de representer l'interaction entre les particules et le fond du bassin. La comparaison des resultats des simulations avec les donnees experimentales sur l'efficacite de decantation et les zones de depot montre que les conditions de type BTKE et BSS estimees a partir des caracteristiques des particules sont satisfaisantes.

Avec l’augmentation de la puissance de calcul des ordinateurs, la simulation 3D devient de plus en plus envisagee en tant qu’outil de conception ou d’instrumentation de sites en reseau d’assainissement. De plus, elle permet la comprehension complete de certains ecoulements particulierement complexes et souvent rencontres en reseau d’assainissement, du fait des nombreux ouvrages speciaux presents. Nous proposons d’utiliser l’approche RANS (Reynolds-Averaged Navier-Stokes) implementee dans plusieurs codes de calcul commerciaux pour simuler ces ecoulements. L’un des defauts majeurs de ces codes de calcul est le manque de fiabilite de certains resultats numeriques, due a la non-connaissance des incertitudes liees au choix d’une strategie de modelisation plutot qu’une autre. Le but de cette etude est de pouvoir quantifier ces incertitudes et definir la plage d’erreur associee aux resultats de simulation, pour le plus de conditions hydrauliques et de strategie de modelisation possible. A terme, l’objectif est de pouvoir etendre l’usage de ces codes aux bureaux d’etude en hydraulique dans le but de mieux concevoir ou mieux instrumenter des sites en vue d’ameliorer la qualite des observations. Les cas d’etudes selectionnes comprennent une canalisation circulaire relativement simple a modeliser mais dont l’ecoulement reste complexe et une jonction a 90°. La canalisation a permis l’etude de la sensibilite des resultats de modelisation aux parametres geometriques. Les premiers resultats montrent que la solution est sensible au changement de rugosite meme en regime torrentiel. La jonction sert a evaluer les performances des nombreuses strategies de modelisation qu’il est possible d’adopter, et leurs effets sur les resultats de simulation. Le modele de proche-paroi « Scalable » semble pertinent pour ce type d’ecoulements.

International audience; The problems related to hydrogen sulfide in terms of deterioration of sewer networks, toxicity and odor nuisance have become very clear to the network stakeholders and the public. The hydraulic and (bio)chemical phenomena and parameters controlling sulfide formation, emission and their incidences in sewer networks are very complex. Recent research studies have been developed in gravity and pressure sewers and some transfer models have been published. Nevertheless, the models do not take into account all the physical phenomena influencing the emission process. After summing up the main scientific knowledge concerning the production, oxidation, transfer and emission processes, the present review includes: (i) a synthetic analysis of sulfide and hydrogen sulfide emission models in sewer networks, (ii) an estimation of their limit, (iii) perspectives to improve the modelling approach. It shows that sulfide formation and uptake models still need refinements especially for some phenomena such as liquid to gas mass transfer. Transfer models that have been published so far are purposely simplified and valid for simple systems. More efforts have to be undertaken in order to better understand the mechanisms and the dynamics of hydrogen sulfide production and emission in real conditions.

Une fraction importante des charges polluantes des eaux pluviales est fixee sur les particules solides souvent vehiculees en suspension et qui decantent facilement lorsque les conditions hydrodynamiques le permettent (faible vitesse d’ecoulement en general). C’est pourquoi la connaissance du transport solide et de la decantation est indispensable a la conception et a la gestion d’un bassin. Une nouvelle methode permettant de simuler les processus de decantation est presentee dans cet article. Elle est fondee sur la comparaison de l’energie transportee par la particule lorsqu’elle decante a l’energie cinetique turbulente pres du fond. L’energie liee a la particule qui decante est calculee a partir de sa vitesse de chute. Sur cette base, un programme a ete developpe et integre dans le logiciel Ansys Fluent. Le modele developpe a ensuite ete teste dans le but d’identifier les zones preferentielles de depot dans un bassin pilote. Les resultats obtenus montrent que les zones de depot observees et simulees sont similaires. Cette methode permet de prendre en compte simultanement les caracteristiques de la particule (principalement la vitesse de chute) et celles de l’ecoulement pres du fond (en particulier l’energie cinetique turbulente).

Les systemes d’assainissement sont de plus en plus equipes de debitmetres. Leur utilisation a des fins de gestion ou de recherche devrait etre systematiquement critiquee, testee et validee afin d’eviter de nombreuses erreurs de mesure. Les methodes de debitmetrie par injection ponctuelle ou continue de traceurs existent depuis de nombreuses annees et sont relativement bien connues. Elles peuvent permettre de verifier les valeurs de vitesse d’ecoulement fournies par exemple par un capteur Doppler en reseau d’assainissement. Apres un bref rappel des principes de la debitmetrie par injection ponctuelle d’un traceur fluorescent (Rhodamine WT), la methode mise en place est decrite : i) double etalonnage en laboratoire, etude des dispositifs d’injection et preparation des solutions a injecter, ii) calcul de la masse de traceur a injec-ter et reduction des incertitudes, iii) acquisition en ligne a tres court pas de temps des concentrations en Rhodamine, iv) correction d’etalonnage, v) traitement des donnees, vi) calcul du debit et de son incertitude et vii) verification du debitme-tre in situ . Les calculs systematiques d’incertitude selon les deux normes en vigueur (loi de propagation des incertitudes et methode de Monte Carlo) sont presentes. En realisant plusieurs injections in situ pour un meme debit, les incertitudes types sur le debit sont de l’ordre de 5 % pour cinq injections et un debit voisin de 2 L/s. Cette methode independante et precise permet de verifier les valeurs fournies par un debitmetre en reseau d’assainissement, a l’aide d’un simple test sur les ecarts.

National audience; Dividing flows have been widely studied. These special structures found in sewers are responsible for complex flows. The understanding of these complex flows is the basis to better manage pollutants transport and mixing in sewer systems. This paper describes two flow structures observed experimentally and numerically in the downstream lateral branch of a 90° open channel dividing flow. These structures are recirculation flows: a classical one (2D) and a helix-shaped one (3D). First, the numerical model has been validated, being confronted with experimental measurements of velocities and water depths for two reference cases. Then, a numerical campaign has been led in order to describe in detail these structures. For the two types of recirculation, the flow visualization, notably of the streamlines in 3D, shows quite different characteristics of exchange with the main flow. It should be the same for their influence on the operation in sewers.; Les bifurcations sont des ouvrages spéciaux présents en réseau d'assainissement et qui sont le siège d'écoulements complexes qu'il est important de comprendre et de maîtriser afin de mieux appréhender le transport de polluants particulaires ou dissous. L'étude présentée dans cet article porte sur la description de deux structures différentes observées expérimentalement et numériquement dans la branche aval latérale d'une bifurcation à 90° à surface libre. Ces deux structures sont des recirculations, l'une classique (2D), l'autre en hélicoïde (3D). Après avoir validé le modèle numérique grâce aux données expérimentales de vitesse et hauteur, une campagne de simulations a été menée dans le but de bien décrire ces structures. La visualisation des lignes de courant en 3D montre que leurs caractéristiques d'échange avec l'écoulement principal dans chaque branche sont très différentes, comme devrait l'être ainsi leurs influences sur le fonctionnement du réseau.

International audience; Flow meters are widely used in urban hydrology to assess discharges, volumes and transport of pollutant loads but may deliver wrong or biased results if they are not checked appropriately. In order to help operators to check flow meters and their discharge values, an operational protocol based on Rhodamine WT tracer experiments is proposed, tested and applied to various case studies. It includes a detailed uncertainty assessment, the reduction of the uncertainty in the injected mass of tracer and a complete data processing. Using Rhodamine WT as a tracer offers the following advantages: i) low injection volume and mass, allowing tracer experiments even for high flow conditions, ii) absence of Rhodamine WT in wastewater, which ensures low and stable background signal, iii) on-line data acquisition at short time step with a portable fluorimeter. Tests show that the protocol provides accurate flow measurements when compared to reference values (electromagnetic flow measurements and salt tracer experiments), with repeated tracer injections giving discharge values with relative standard uncertainties of approximately 5%. Field applications confirm it is an efficient approach to improve the quality of flow measurements in sewers. After an in situ flow meter is checked for various values of discharge, a correction function can be established if necessary for each specific measurement site if there is no alternative solution to improve the measurements by changing the location and position of the sensor or by replacing it by a more appropriate technology. In its present state, the protocol can be applied as a routine method. As a complement, CFD modelling is applied to one of the case studies to explain the causes of bias in flow meter measurements.

La reglementation actuelle des rejets de reseaux d’assainissement vers le milieu naturel oblige le plus souvent a la mise en place d’une instrumentation debitmetrique. La connaissance du fonctionnement hydraulique des deversoirs d’orage est donc indispensable. Dans ce contexte, l’objectif de cet article est, dans un premier temps, de presenter le mode d’utilisation de la modelisation 3D (FLUENT®) pour comprendre le fonctionnement hydraulique des deversoirs d’orage. Dans un deuxieme temps, nous avons valide experimentalement les modeles hydrauliques 3D. Dans un troisieme temps, nous avons applique la modelisation 3D au deversoir de Clichy. Les simulations nous ont permis de connaitre les differentes formes de lignes d’eau et l’evolution du debit deverse le long de la crete. L’etude des conditions aux limites et initiales, ainsi que la qualite du maillage et le choix du modele de turbulence, ont fait l’objet d’une attention particuliere. L’exploitation des resultats des simulations nous a fourni des renseignements importants dans le but d’ameliorer l’instrumentation de ce deversoir.

Chemical and microbial contaminations of urban waters including stormwater runoff, wastewaters, and combined sewer overflow waters have been shown for a number of years. It is clearly demonstrated, for example, that metallic ions, polycyclic aromatic hydrocarbons (PAH), pesticides, and microbial pathogens can be conveyed by such waters, and they have been found strongly associated with suspended matters. The “Water Framework Directive” (WFD) led to the launching of several research initiatives toward the “Best Management Practices – BMP,” through novel or improved technologies aiming at reducing the ecotoxicological impacts and health risks associated with these waters. Some of these techniques consist at keeping these waters for a certain amount of time in a confined system in order to favor settling of their suspended particles and lead, in part, to the natural biological degradation of their contaminants. These systems are typically impervious basins that can receive stormwaters, e.g. detention basins, biofilters, artificial wetlands, or combined sewer overflows, e.g. stabilization ponds of wastewater treatment lagoons. Several key mechanisms occur in these systems (Fig. 1). The deposits formed constitute areas of high levels of contamination. These structures (basins) are ecosystems with an important biological diversity. They can represent a high risk of contamination of the connected surfaces, streams, or groundwater environments into which they are discharged. Investigations regarding their efficiency at retaining and transforming pollutants and killing undesirable microbes are thus required. When landscaped, these structures may lead to the development of urban public spaces. In this context, they are subjected to social practices generally associated with public gardens, practices which accidentally or regularly expose the public to their contaminants. In addition, these structures require maintenance and specific management, exposing workers to their contaminants. It is therefore essential that the chemical and microbiological contaminants present in these systems are accurately characterized and measured (i.e. which chemical forms and microbial species and genotypes, and how much?), and their health hazards and risks be inferred or estimated. In this context, several biofilters, detention basins, and stabilization ponds have been monitored and investigated around the world. The CABRRES project (Chemical, microbiological, spatial characteristics and impacts of contaminants from urban stormwater detention basins: Assessment and Management of Environmental and Human Health Risks, http://www.graie. org/cabrres), funded by the French National Research Agency (ANR), is one of these research initiatives. It is an interdisciplinary research project (Fig. 2) aiming at better defining the interactions between chemical pollutants (including toxic Responsible editor: Philippe Garrigues

International audience; Detention basins are valuable facilities for urban storm water management, from both the standpoint of flood control and the trapping of pollutants. Studies performed on storm water have shown that suspended solids often constitute the main vector of pollutants (heavy metals, polycyclic aro- matic hydrocarbon (PAH), etc.). In order to characterise the ecotoxicity of urban sediments from storm water detention basins, the sediments accumulated over a 6-year period were sampled at five different points through the surface of a large detention basin localised in the east of Lyon, France. A spe- cific ecotoxicological test battery was implemented on the solid phase (raw sediment) and the liquid phase (interstitial water of sediments). The results of the study validated the method formulated for the ecotoxicological characterization of urban sediments. They show that the ecotoxicological effect of the sediments over the basin is heterogeneous and greater in areas often flooded. They also show the relationship between, on one hand, the physical and chemical characteris- tics of the sediments and, on the other hand, their ecotoxicity. Lastly, they contribute to a better understanding of the dynam- ics of the pollution close to the bottom of detention basins, which can be useful for improving their design. The results of this research raise particularly the issue of using oil separators on the surface of detention basins.

Contents Communicating environmental risks and the decision making process 1. Environmental and human health risk management: An overview 2. Communicating environmental risks in developing countries 3. Environmental management in Brazil: reducing organizational risks 4. Tsunami hazards: A case study of risk management in the Caribbean Region 5. Cost-benefit analysis to enhance the risk management decision making process 6. Adjusted Genuine Savings and Human Development Index: A two dimensional indicator for sustainability Management of surface and groundwater resources 7. Management, public opinion and research on Costa Rica's surface and groundwater resources 8. Stormwater management practices: The case of Port-au-Prince, Haiti 9. Impact of surface runoff on the aquifers of Port-au-Prince, Haiti Conservation of Land, Air, Water and Cultural Assets 10. Ethnoecological restoration of deforested and agricultural tropical lands for Mesoamerica 11. Atmospheric aerosols: A case study from the Caribbean Region 12. The potential of Thillandsia sp. to monitor PAHs from automobile sources in Puerto Rico 13. Degradation of PCBs and spilled oil by bioenhancing agents 14. Cryptosporidium oocyst transmission in the aquatic environment of Haiti 201 Risk Management and Wastewater Reuse 15. Health-related aspects of wastewater reuse in urban truck farming: A case study of Yaounde, Cameroon 16. Application of low-cost sorbents to remove chromium from industrial wastewater discharges 17. Viability of the upflow anaerobic sludge process for risk management of wastewater treatment

National audience