URBAN DISCHARGES DURING WET WEATHER - WHAT VOLUMES HAVE TO BE TREATED

To treat urban wet weather discharges, storage tanks seem to be effici ent tools. Using 17' French catchments with an average of one year of measurements, we have estimated the volumes requited at the outlet of the catchments and at the inlet of a tank, to intercept the suspended solids load discharged during several months and during the most pollu ted events. The results vary widely from one basin to another, between 30 and 150 m(3)/active ha to intercept 80% of the annual suspended so lids load. This does not allow us to draw conclusions about the volume s required in an average situation because rainfall depths and return periods of the rainfall events are different between the catchments. T hese factors seem to have a big influence on the interception efficien cy of the storage tanks. The results can only be seen as representativ e of the year during which the measurements were taken.