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Le Bourget-du-Lac, France

Audru J.-C.,Bureau de Recherches Geologiques et Minieres | Bitri A.,Bureau de Recherches Geologiques et Minieres | Desprats J.-F.,Bureau de Recherches Geologiques et Minieres | Dominique P.,Bureau de Recherches Geologiques et Minieres | And 9 more authors.
Engineering Geology | Year: 2010

Mayotte is a French Overseas Territory of the Comoros archipelago. Since the 1980, Mayotte has developed quickly: its population has multiplied by four in less than 30. years, infrastructure expanded rapidly in lowlands and slums developed in steep areas (through deforestation) or close to riverbeds. This development urgently required steps to ensure the safety of urban areas.From 2002 to 2006, a major programme of natural hazards evaluation and zonation was conducted by the French Geological Survey in the 17 districts of Mayotte. The programme resulted in the publication of the first single-hazard zonation maps for Mayotte, at 1:25. 000-scale in rural areas and at 1:10. 000-scale in urban areas. Hazard maps regarding landslides and rock falls, stream floods, seismic lithological and topographical amplification potential, liquefaction potential and cyclonic marine submersion were produced for mayors and land planners. These atlases also included prevention guidelines to minimize risks associated with land-use or urbanization within hazard-prone areas.This article presents the main achievements of the programme whose main problems were the absence of archives, of previous studies and the original volcanic geology of the island of Mayotte. The atlases highlight areas with numerous landslides, zones susceptible to flash floods, sectors likely to be submerged by storm surges and areas subject to seismic site effects due to thick volcanic weathered formations. This programme emphasizes the fundamental role in such tropical volcanic islands, of a good knowledge of the weathered formations, for the assessment of most natural hazards.This initial hazard mapping represented the first step to achieve specific regulatory Risk Prevention Plans for an efficient land use risk mitigation and reduction policy in Mayotte. © 2010 Elsevier B.V.

The 27th of January 2012 decree aims at reducing water intake for potable uses, at improving drinking water networks efficiency and sustainability, and enhancing financial management of these networks. Moreover, by imposing an objective of yield, this decree indirectly implies an increase of the rhythm of renewal of the drinking water networks.

Metadier M.,SAFEGE | Metadier M.,INSA Lyon | Bertrand-Krajewski J.-L.,INSA Lyon
Water Research | Year: 2012

This paper presents one of the largest databases on the quality of urban wet weather discharges measured since the development of continuous in-sewer water quality sensors in the late 1990s. Five years of continuous turbidity measurements enabled the validation of 263 and 239 rainfall events, respectively on two experimental catchments in Lyon (France), Chassieu (185. ha separate sewer) and Ecully (245. ha combined sewer). Except for high rainfall events of summer and second half of winter, analysis of database representativeness showed that all seasons were relatively well represented. As a first analysis of the database, traditional tools used in the urban drainage field were applied to assess: i) statistics and analysis of distributions of TSS and COD events loads and event mean concentrations (EMCs) and ii) the correlations between these statistics and events characteristics and iii) M(V) curves describing the intra-event mass distribution. Results showed that: i) EMCs and loads were approximately log-normally distributed, with a clear impact from wastewater contribution in Ecully, ii) EMCs are not correlated with storm event characteristics, whereas loads have shown significant correlation with key storm event variables such as total event volume, rainfall depth, maximum rainfall intensity and discharge and iii) M(V) curves dynamic could be classified in three categories, however with no clear correlation with storm event characteristics. The visual analysis of continuous time series of TSS and COD pollutographs, derived from turbidity time series showed that event pollutographs were highly variable, due to complex interacting processes during and between events, and suggests that further progress in knowledge and modelling of urban wet weather pollutant loads and pollutographs should be based on more detailed analyses of continuous time series rather, than on the traditional single event approach. © 2011 Elsevier Ltd.

In 2006, DEFACTO, the public institution for the planning of La Défense district ordered a study to estimate the consequences of a 1910 type flood on the district of La Défense 10 and to define actions to reduce flood vulnerability. The company SAFEGE has been chosen to work on this study. Two main steps have been followed. The first one consisted in doing a diagnosis of buildings vulnerability but also of other elements that could affect the companies work. Visits and meetings have been organised to define which elements would be flooded. This work led to analyse the equipment's vulnerability but also the direct impact of the flood. The second part of the study consisted in proposing actions to reduce flood vulnerability. It was based on an estimation of minimal needs for the company to be able to work. Two scenarios have been studied. The first one proposes no change compared with the initial situation. It is made to determine the length, work and costs that would be necessary to repair the damage. The second one is to propose preventive and curative actions to reduce flood vulnerability.The global aim is to guarantee the continuity of the companies' work. © Société Hydrotechnique de France, 2011.

Metadier M.,SAFEGE | Metadier M.,CNRS Laboratory of Civil and Environmental Engineering | Bertrand-Krajewski J.L.,CNRS Laboratory of Civil and Environmental Engineering
Water Science and Technology | Year: 2011

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling. © IWA Publishing 2011.

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