Treatment MeasuresInfiltration Trenches

An infiltration trench is a shallow, excavated trench filled with gravel, rock of porous material, into which run-off collects. Stormwater filtrates from the trench into the surrounding soil, while particulate and some dissolved pollutants are retained in the trench. The trench discharges the treated stormwater into a conventional pipe system.

The trench is lined with a layer of geotextile fabric, to prevent soil migration into the rock or gravel fill. The top surface of the fill is also covered with a layer of fibre fabric, then finished with a shallow layer of topsoil.

Local soil geochemistry and grading determine the infiltration trench's ability to remove particulate and dissolved pollutants. The trenches can increase the soil water levels, groundwater flow rates and can reduce stormwater flow velocities.