This study has the following principle aims.

  • Identifying the contextual elements of sediment deposits which appear as the most important, or, in a way, as required conditions for clogging. It emerges that a weak slope is not a sufficient condition. We show that the main vulnerable sections are:

    • downstream abrupt changes of geometry (the upper ramifications of man-entry sewers, the slope breakdowns, …)

    • downstream flow losses (diffluence, overflows)

    • under downstream influences (confluence, pumping stations, …).

  • Clearing the general characteristics of these sediment deposits in French man-entry combined sewers. The mean D50 varies from 1mm (Paris) to more than 2mm. The finest deposits are rather specifically located (upstream of local obstacles, or under downstream influences during dry weather - for instance near a pumping station, in very flat sewers -, or downstream from overflows).

  • Evaluating the representativeness of the results from more accurate studies carried out in particular places, for instance the Marseille No 13 trunk.

  • Drawing inferences about knowledge improvements and technical means.

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