Characterisation and settling of solids in an open, grassed, stormwater sewer network detention basin

The objective of the study is to develop new operational management practices for detention tanks during rainfall events in order to limit flooding risk and, at the same time, to reduce pollutant discharges by optimising the settling process. This paper presents the results of the characterisation of settled particles in an open stormwaler detention basin with grassed banks and bottom, installed on a separate stormwater network. Solids sampled in the bottom of the basin where the settling process is frequent and solids collected in sediment traps have a fine grain-size distribution close to those of suspended solids in stormwater. The distribution is related to the number and the duration of the flooding events. The pollutant loads are significant but the hydrocarbons and heavy metals concentrations are lower than concentrations measured in solids sampled in detention tanks situated on a combined sewer system.