Suspended particle characteristics in storm runoff from urban impervious surfaces in Toowoomba, Australia

Abstract

Total Suspended Solids as a measure of suspended particles in urban stormwater has limitations and the alternative Suspended Sediment Concentration method was adapted to determine Non-Coarse Particle (NCP) concentration, defined as particles smaller than 500 μm. NCP was partitioned into the following classes: Very Fine Particles (<8 µm, VFP), Fine Particles (8-63 µm, FP) and Medium Particles (63-500 µm, MP). A Site Mean Concentration approach was adopted to differentiate the suspended particle characteristics between three impervious surfaces (roof, road and carpark) using runoff data collected for 35 storms. Runoff particle size distribution (PSD) of all surfaces was dominated by particles less than 63 μm. A weak trend of relatively constant VFP concentration was present in the road runoff data. Roof runoff PSD became finer as NCP concentration increased and, overall, the PSD of carpark runoff was coarser compared to road and roof runoff. These findings have runoff treatment implications as settling processes are influenced by particle size.