Sylvie Barraud

SUDS, LID, BMPs, WSUD and more - The evolution and application of terminology surrounding urban drainage

The management of urban stormwater has become increasingly complex over recent decades. Consequently, terminology describing the principles and practices of urban drainage has become increasingly diverse, increasing the potential for confusion and miscommunication. This paper documents the history, scope, application and underlying principles of terms used in urban drainage and provides recommendations for clear communication of these principles. Terminology evolves locally and thus has an important role in establishing awareness and credibility of new approaches and contains nuanced understandings of the principles that are applied locally to address specific problems. Despite the understandable desire to have a ‘uniform set of terminology’, such a concept is flawed, ignoring the fact that terms reflect locally shared understanding. The local development of terminology thus has an important role in advancing the profession, but authors should facilitate communication between disciplines and between regions of the world, by being explicit and accurate in their application.

The influence of design parameters on clogging of stormwater biofilters: A large-scale column study

A large-scale laboratory study was conducted to test the influence of design and operating conditions on the lifespan of stormwater biofilters. The evolution of hydraulic conductivity over time was studied in relation to a number of key design parameters (media type, filter depth, vegetation type, system sizing, etc). The biofilters were observed to clog over time, with average hydraulic conductivity decreasing by a factor of 3.6 over the 72 weeks of testing. The choice of plant species appears to have a significant effect on the rate of decrease in permeability, with plants with thick roots (e.g. Melaleuca) demonstrating an ability to maintain permeability over time. Other species studied, with finer roots, had no such beneficial effects. As expected, small systems relative to their catchment (and thus which are subjected to high loading rates) are more prone to clogging, as increases in hydraulic and sediment loading can lead to extremely low hydraulic conductivities. Sizing and the appropriate choice of vegetation are thus key elements in design because they can limit clogging, and therefore, indirectly increase annual load treated by limiting the volume of water bypassing the system.

Micropollutants in urban stormwater: occurrence, concentrations, and atmospheric contributions for a wide range of contaminants in three French catchments

This study aimed at: (a) providing information on the occurrence and concentration ranges in urban stormwater for a wide array of pollutants (n = 77); (b) assessing whether despite the differences between various catchments (land use, climatic conditions, etc.), the trends in terms of contamination level are similar; and (c) analyzing the contribution of total atmospheric fallout (TAF) with respect to sources endogenous to this contamination. The studied contaminants include conventional stormwater contaminants (polycyclic aromatic hydrocarbons (PAHs), Zn, Cu, Pb, etc.), in addition to poorly or undocumented pollutants such as nonylphenol and octylphenol ethoxylates (NPnEO and OPnEO), bisphenol A (BPA), polybrominated diphenyl ethers (PBDEs), a wide variety of pesticides, and various metals of relevance (As, Ti, Sr, V). Sampling and analysis were performed using homogeneous methods on three urban catchments with different land use patterns located in three distinct French towns. For many of these pollutants, the results do not allow highlighting a significant difference in stormwater quality at the scale of the three urban catchments considered. Significant differences were, however, observed for several metals (As, Cr, Cu, Ni, Sr and Zn), PAHs, and PBDEs, though this assessment would need to be confirmed by further experiments. The pollutant distributions between dissolved and particulate phases were found to be similar across the three experimental sites, thus suggesting no site dependence. Lastly, the contributions of TAF to stormwater contamination for micropollutants were quite low. This finding held true not only for PAHs, as previously demonstrated in the literature, but also for a broader range of molecules such as BPA, NPnEO, OPnEO, and PBDEs, whose high local production is correlated with the leaching of urban surfaces, buildings, and vehicles.

Computational fluid dynamics modelling of flow and particulate contaminants sedimentation in an urban stormwater detention and settling basin

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 preferential sediment zones and to predict the trapping efficiency of the basin during storm events.

Monitoring of clogging evolution in the stormwater infiltration system and determinant factors

Infiltration is widely used to manage stormwater in cities and their suburbs. Despite its advantages, questions remain about its long-term performance, in particular the potential for clogging. To address this problem, a field study was undertaken to assess the evolution of clogging over time by means of hydraulic resistance (R) measurements. The experiment was carried out on an infiltration basin continuously monitored for 7 years from 2004 to 2010. The work shows that clogging takes place progressively and can be slowed down by the growth of vegetation. It also showed that the variation from one event to another presented high variability. The variation of successive R-values per time unit has been statistically explained by the variation per time unit of two groups of factors: one linked to physical aspects (water volume and particle load), and more interestingly one linked to biological clogging (solar energy and air temperature), which is generally not considered for these systems. L’infiltration est aujourd’hui largement utilisée dans la gestion des eaux pluviales en milieu urbain. Malgré ses avantages, son efficacité sur le long terme pose encore problème en particulier leur aptitude au colmatage. Pour traiter ce problème, des observations de terrain ont été menées de manière à évaluer l’évolution du colmatage au cours du temps à l’aide de mesures de résistance hydraulique (R). L’observation a été menée sur un bassin d’infiltration suivi en continu sur 7 ans de 2004 à 2010. Le travail montre que le colmatage est très progressif est peut être ralenti par la croissance de végétation. Il montre également une grande variabilité d’un évènement à l’autre. La variation entre deux valeurs de R par unité de temps a pu être expliquée statistiquement par les variations par unité de temps de deux groupes de facteurs : l’un lié à des aspects physiques (volume d’eau et charge particulaire) et de manière plus intéressante à des facteurs biologiques (énergie solaire et température d’air) non considérés habituellement.

Review on physical and chemical characterizations of contaminated sediments from urban stormwater infiltration basins within the framework of the French observatory for urban hydrology (SOERE URBIS)

Urban stormwater infiltration basins are designed to hold runoff from impervious surfaces and allow the settling of sediments and associated pollutants. However concerns have been expressed about the environmental impacts that may be exerted by the trapped pollutants on groundwater, soils and ecosystems. In this context, sediment characterization represents a key issue for local authorities in terms of management strategies. During the last two decades, several studies were launched including either physical or chemical characterization of stormwater sediments but without real synthesis of data and methods used. Consequently, there is an important need for reviewing the current experimental techniques devoted to the physico-chemical characterization of sediment. The review is based on the outcomes of two experimental sites for which long term monitoring and data collection have been done: the Cheviré basin (near Nantes) and the Django Reinhardt basin (near Lyon). The authors summarize the studies dealing with bulk properties, pollutant contents, their potential mobility and speciation. This paper aims at promoting the significant progresses that were made through a multidisciplinary approach involving multi-scaled and combined experimental techniques.

Long-term stormwater quantity and quality analysis using continuous measurements in a French urban catchment

The assessment of urban stormwater quantity and quality is important for evaluating and controlling the impact of the stormwater to natural water and environment. This study mainly addresses long-term evolution of stormwater quantity and quality in a French urban catchment using continuous measured data from 2004 to 2011. Storm event-based data series are obtained (716 rainfall events and 521 runoff events are available) from measured continuous time series. The Mann-Kendall test is applied to these event-based data series for trend detection. A lack of trend is found in rainfall and an increasing trend in runoff is detected. As a result, an increasing trend is present in the runoff coefficient, likely due to growing imperviousness of the catchment caused by urbanization. The event mean concentration of the total suspended solid (TSS) in stormwater does not present a trend, whereas the event load of TSS has an increasing tendency, which is attributed to the increasing event runoff volume. Uncertainty analysis suggests that the major uncertainty in trend detection results lies in uncertainty due to available data. A lack of events due to missing data leads to dramatically increased uncertainty in trend detection results. In contrast, measurement uncertainty in time series data plays a trivial role. The intra-event distribution of TSS is studied based on both M(V) curves and pollutant concentrations of absolute runoff volumes. The trend detection test reveals no significant change in intra-event distributions of TSS in the studied catchment.

Event-based quantification of emerging pollutant removal for an open stormwater retention basin - loads, efficiency and importance of uncertainties.

Up to now, emerging contaminants have not been further-studied in in-situ stormwater best management practices and especially in detention basins. In this article, the efficiency of a dry stormwater detention basin was investigated regarding the removal of 7 alkylphenols and alkylphenol ethoxylates, 9 polybrominated diphenyl ethers, 45 pesticides and bisphenol A. Concentrations of contaminants were obtained by chemical analysis on dissolved and particulate phase distinctly. The removal efficiency was assessed on total, dissolved and particulate phase accounting for the global chain of uncertainty with a 95% confidence interval. Results showed that pesticides (rather hydrophilic) are not trapped in the detention basin but are released contrarily to B209 which is mostly in particulate phase. Alkylphenols and alkylphenol ethoxylates are present in both phases and the efficiency is storm event-dependent. Uncertainty consideration in efficiency determination revealed efficiency data, usually presented by raw values are not relevant to conclude on the performance of a detention basin. In this case study, efficiency data with a 95% confidence interval indicate that only 35%, 50% and 41% of campaigns showed an impact (in trapping or releasing) of the detention basin on alkylphenols and ethoxylates, polybrominated diphenyl ethers and pesticides respectively.

Stormwater retention basin efficiency regarding micropollutant loads and ecotoxicity.

Retention basin efficiency in micropollutant removal has not been very well studied, in particular for pollutants highlighted by the European Water Framework Directive of 2000 such as pesticides, polybrominated diphenyl ethers (PBDEs) and alkylphenols. This study is based on in situ experiments carried out on a stormwater retention basin with the aim of estimating the basin efficiency in trapping and removing micropollutants from stormwater run-off from an industrial catchment drained by a separate sewer system. Along with stormwater, the basin receives some dry weather effluent flows, which are supposedly non-polluted. Ninety-four substances from five families (metals, polycyclic aromatic hydrocarbons (PAHs), PBDEs, alkylphenols and pesticides) were analyzed during 10 event campaigns in urban wet weather discharges at the inlet and outlet of the basin. The ecotoxicity of the samples was also tested. The results show high inter-event variability in both chemical and ecotoxic characteristics. They indicate good event efficiency concerning heavy metals and most PAHs. The studied pesticides, mainly found in the dissolved fraction, were not trapped. Particulate fraction study highlighted that settling is not the main process explaining micropollutant removal in a retention basin, as was noted for alkylphenols and PBDEs.

Influence of spontaneous vegetation in stormwater infiltration system clogging

The paper presents the role of spontaneous vegetation on the hydraulic performance of an infiltration basin. The objective of the research was more particularly to study this role of different types of spontaneous vegetation found in situ in an infiltration basin near Lyon. The saturated hydraulic conductivity of three areas covered by Phalaris arundinacea, Polygonum mite, Rumex crispus and similar non-vegetated zones was compared. Eight field campaigns were carried out from July 2010 to May 2011 in order to compare the performance of each type of vegetation and its evolution over time. The results suggest a positive impact of vegetation on hydraulic performance in particular in summer during the growth of the plants. The hydraulic conductivity in this period was twice to four times higher than in bare areas or in vegetated zones during the plant rest periods. Some species were also found more appropriate to limit clogging (Phalaris arundinacea) likely due to its specific structure and growth process.