Spatial heterogeneity and inter-event variability of sediment settling distributions in a stormwater retention tank

The Django Reinhardt sedimentation basin (in Chassieu, France) provided the basis for an experimental monitoring campaign to better understand and model sedimentation behaviour in full-scale sedimentation systems. Twelve sediment traps placed at the base of the sediment basin permitted solids settled during storm events to be sampled for both settling velocity (according to the French VICAS laboratory analysis protocol) and heavy metal concentrations. The first three monitoring campaigns demonstrated significant spatial variability in the sediment settling velocity, within a given storm event. Temporal variability between events was also found to be substantial. Uncertainties in the estimated setting velocities were found to be typically less than 7 %. Importantly, the concentration of heavy metals was observed to increase with increasing sediment settling velocity.