IN SITU OBSERVATION OF THE WATER-SEDIMENT INTERFACE IN COMBINED SEWERS, USING ENDOSCOPY

The erosion of sewer sediment is one of the major sources of pollution for combined sewer overflows (CSO). The contribution of sewer deposits is linked to the erosion of an organic deposit situated at the water interface. A new method for water-sediment interface observation, using a small diameter endoscope, has been designed. The endoscope was used to investigate Le Marais catchment (Paris): an immobile organic layer was observed at the water-sediment interface. This layer appears in pools of gross sediments, at the upstream of collectors, in zones where velocity is slow.