Where catchment conditions are likely to contribute a large amount of litter or gravel in stormwater runoff, a gross pollutant trap (trash rack or debris screen) may be appropriate.
Gross pollutant traps perform an important function at the inlet of bioretention practices and wetlands to reduce large contaminants (particles >5 mm) that may clog the system and reduce performance.
Gross pollutant traps provide ease of maintenance to capture large contaminants, but at the same time require a regular maintenance regime to clear these systems. Wet wells in particular should be cleaned
so that materials do not decompose, increasing biological (biochemical) oxygen demand (BOD) and available nutrients. Gross pollutant traps have traditionally been constructed as cages, filters or wells,
but there are opportunities to investigate ‘natural’ alternatives to these practices.
For more information on the maintenance of gross pollutant traps, refer to the Auckland Regional Council Technical Report
TR2010/053 Operation and Maintenance of Stormwater Treatment Devices in the Auckland Region.