Hydrographs' attenuation in sewers. Effects on stormwater source control regulation

International audienceIn this paper we propose an empirical approach to quantify the hydrographs' attenuation in sewers. The purpose is to evaluate attenuation's consequences for the scale-transfer between the parcel and the catchment in urban settings, and in particular for stormwater source control (SC) regulation. In fact, SC regulation practices often consider this scale-transfer by a linear approach. We draw a formulation for the attenuation of peaks in partially full pipes, and we assess, by a sensitivity analysis, the respective weights of the different pipes' and hydrographs' characteristics on attenuation. We found that the driving factors of the peak attenuation vary according to the distance from the outlet, and we draw possible guidelines for SC regulation

Microbial decomposition

International audienceWithin aquatic ecosystems, microbial decomposition of organic matter plays a prominent role in the energy and mass transformation processes (Jorgensen, 1983a). Organic waste water discharge in a river results in dissolved oxygen uptake, either directly by chemical oxidation of the reducing pollutants (see Chap. 10), or by their metabolism by microorganisms, i.e. their biodégradation. Raising the temperature of rivers reduces oxygen solubility and accelerates the kinetics of chemical and microbiological oxygen and polluting load reduction...

A posteriori analysis of the design and the maintenance of retention ponds in the Ile-de- France region

International audienceThis text presents the results of a one-day workshop on retention ponds in the "Villes nouvelles" in the Ile-de-France" region. 25 experts participated to this seminar which took place in March 2001. All the relevant technical and scientific disciplines involved in the design and the maintenance of retention ponds were represented. It appears that these ponds designed in the seventies are the signature of a typical urbanism. They contributed to organise the appropriation of the new urban areas by their inhabitants. Today the main related stakes deal with the development and the evolution of the multiple uses of these retention ponds

Urban stormwater source control policies: why and how?

International audienceStormwater source control is becoming a common strategy for urban stormwater management in many countries. It relies on regulations or other policy instruments compelling or inciting to implement, for each new urban development, small-scale facilities to locally store and manage stormwater. Local authorities that pioneered source control since the 1980s have already observed that small-scale facilities systematically implemented over a catchment are able to influence its hydrological behaviour. This capability is the main strength of source control, as it allows compensation for the negative effects of urbanization. Yet, it also represents its main risk: if initial decision-making is not sufficiently accurate, source control can produce long term negative effects. Because of its current spreading, source control will acquire an increasing role as a driver of hydrological changes in urban catchments, and the directions of these changes depend on current policy-making practices. This paper presents an analysis and a critical discussion of the main objectives that policy-makers attribute to stormwater source control. The investigation is based on a sample of French case studies, completed by a literature review for international comparison. It identifies four main objectives, some typical of urban stormwater management and some more innovative: flood reduction, receiving waters protection, sustainable development, costs reduction. The discussion focuses on how current policy-making practices are able to translate these objectives in concrete policy instruments, and on which knowledge and tools could improve this process. It is shown that for some objectives, basic knowledge is available, but the creation of policy instruments effective at the catchment scale and adapted to local conditions is still problematic. For others, substantial lacks of knowledge exist, casting doubts on long term effectiveness of current policy instruments. Research directions are identified to improve source control policies and thus the future hydrologic behaviour of many urban catchments

Discharges of endocrine disrupting chemicals by combined sewer overflows into receiving water: case-study of the Paris conurbation

8 p.International audienceAlkylphenol ethoxylate (APEOs) and bisphenol A (BPA) are well known as endocrine disrupting compounds. Among sources of these compounds within receiving waters, wastewater treatment plant effluents have been widely studied. However, Although APEOs and BPA are regularly quantified within wastewater and to a lesser extent in runoff, few studies deal with their discharges by combined sewer overflows. In this context, this study was launched to investigate the concentrations and the mass loads discharged per year by CSO in the Seine River. Therefore, discharges occurring at the one of the most important CSOs of Paris conurbation from June to November 2010 were sampled. During this period, eight events were collected by automatic samplers and even mean sample were analyzed in laboratory using liquid chromatography coupled to a tandem mass spectrometry. The first results highlight an important contamination of CSOs by BPA and levels of APEOs close to those reported in wastewaters. At the annually scale and according to our mass load calculation, CSOs do not appear as a relevant source of BPA and APEOs within the Seine River

Relationship between turbidity and total suspended solids concentration within a combined sewer system.

8 pagesInternational audienceThis article confirms the existence of a strong linear relationship between turbidity and total suspended solids (TSS) concentration. However, the slope of this relation varies between dry and wet weather conditions, as well as between sites. The effect of this variability on estimating the instantaneous wet weather TSS concentration is assessed on the basis of the size of the calibration dataset used to establish the turbidity - TSS relationship. Results obtained indicate limited variability both between sites and during dry weather, along with a significant inter-event variability. Moreover, turbidity allows an evaluation of TSS concentrations with an acceptable level of accuracy for a reasonable rainfall event sampling campaign effort

Do stormwater source control policies deliver the right hydrologic outcomes?

International audienceThe number of stormwater source control (SC) regulations adopted by local authorities is rapidly growing in many countries. We can expect that, in the near future, the hydrologic behavior of many urban and periurban catchments will reflect this diffusion. This paper discusses SC regulations through two complementary approaches: starting on three French case-studies, it analyzes how regulations are developed today and identifies a set of shortcuts in policy-making practices. Then, the hydrologic model of a periurban catchment in the Paris region is used to test the impacts that these regulations can produce if widely applied. The main finding is that inertia in policy-making, driving a singular focus on flow-rate based regulations, can produce negative impacts in the long-term. Further efforts on volume-based regulations are advocated, both in terms of research and policy-making. © 2012 Elsevier B.V. All rights reserved

Global warming as a driving factor for cyanobacterial blooms in Lake Karaoun, Lebanon

18 pagesInternational audienceThe Middle East region suffers already from the gradual effects of climate change and will be among the most vulnerable regions in the future. As a result, productivity should undergo losses due to high temperatures, drought, floods and soil degradation which threaten food security of Levantine countries. Since water is the critical factor in the region, even slight changes in air temperature and rainfall patterns will have considerable impact. It has been proven that potential climate change may disrupt, on one hand, most ecosystems through changes in their physicochemical conditions, and on the other hand the species which are living in these ecosystems. Then, the biodiversity can be found challenging. In this study, the effects of climate change on population and phytoplankton communities of Lake Karaoun were investigated since 1992. The climate regime shifts have been shown to alter the lake ecosystem. In the past, Lake Karaoun was characterized by a highly diversified microflora dominated by diatoms and green algae. Recent climatic fluctuations, with culmination in 2008-2011 and temperatures exceeding 40˚C have upset this biodiversity. Blooms of cyanobacteria, specifically Microcystis aeruginosa and Aphanizomenon ovalisporum, have occurred and disturbed both the ecosystem and the functioning of the lake

Eau dans la ville et développement durable : Actes des treizièmes journées du Diplôme d'études approfondies Sciences et techniques de l'environnement, organisées les 15 et 16 mai 2002, à Créteil

International audienceDix ans que le concept de développement durable, a acquis droit de cité et a quitté le petit cercle restreint des militants et des experts. La France dispose même aujourd'hui d'une.ministre et d'une secrétaire d'état au développement durable. Du fait de cette célébrité soudaine, le développement durable et les principes quilui sont attachés, comme le principe de précaution, se retrouvent souvent employés au mieux à mauvais escient, au pire à contresens. Malgré ces inconvénients, la notion de développement durable a eu le mérite, entre autres, de repositionner le débat environnemental dans le cadre du développement de la société à la fois aux plans économique, social et même, s'agissant des expériences de démocratie participative, politique.Dans ce contexte, le secteur de l'eau apparaît particulièrement crucial..

Urban lakes: interaction between phytoplankton dynamics and trace metal speciation

9 p.International audienceUrban lakes have a particular influence on the water cycle in urban catchments. Thermal stratification and a longer residence time of the water within the lake can boost the phytoplankton production. On the other hand, trace metals are naturally found in environment in trace amounts due to erosion and physic-chemical or biological alteration processes. Trace metals are essential to growth and reproduction of organisms. However, they are also well known for their toxic effects on animals and humans. Their ecotoxicity depends on metal properties and chemical speciation (particulate, dissolved: labile or bioavailable and inert fractions). The interaction between phytoplankton production and trace metal speciation is not well understood until present time. The aim of this research is twofold: (1) to analyze the driving processes of the phytoplankton production in an urban lake through physical-chemical and biological field data collection and (2) simultaneously to survey the chemical speciation of trace metals in this lake. To address these issues, a field survey and laboratory analysis, including physical-chemical, biological variables, organic matter and trace metal concentrations, have been designed and implemented in an urban study site: Lake Créteil in France