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.