Example | George Whittle Reserve: An 11m x 3m x 1m infiltration trench filled with 40mm aggregate was designed to ensure the 1-in-5 year ARI (0.18 AEP) design storm did not result in increased stormwater runoff from a 1500m2 of hard surfaces on the 3750m2 site (40% impervious) from entering City of Prospect’s stormwater network.
Benefit 2 – Protect urban waterways from erosion (reduce total volume of stormwater runoff)
Example | Dorset Avenue, Colonel Light Gardens, City of Mitcham: A 9000 x 750 x 750 mm infiltration trench delivers over 100,000 litres of water to the verge soils to passively irrigate street trees in an average year.
Source: Johnson T, Lawry D and Sapdhare H (2016) The Council verge as the next wetland: TREENET and the Cities of Mitcham and Salisbury investigate. In: Acta Horticularturae 1108: pp 63-70.
Dorset Avenue, Colonel Light Gardens – demonstration of canopy density and shade benefits of infiltration system: Left-hand side tree receives no infiltration, right-hand side tree with infiltration. Source: City of Mitcham.
Example | The Strand, Colonel Light Gardens, City of Mitcham: An infiltration system consisting of 66 m of 525mm slotted drainage pipe buried within a 20mm single sized aggregate filled trench (900mm wide x 965mm deep) diverts a minimum of 1megalitre per annum, in a dry year, from the stormwater network into the verge subsoil to passively irrigate trees.
The Strand, Colonel Light Gardens – trees in Peragini Park. Source: City of Micham
Benefit 4 - Remove pollutants from stormwater runoff
Expected pollutant removal from infiltration systems
Source: City of Auckland (2002) Stormwater management devices: design guidelines manual (revision to Technical Publication 10). Auckland, New Zealand: Auckland Regional Council.
Benefit 5 - Replenish groundwater and therefore dry weather base flows to waterways
Example | Newenham ecological sponges: Small-scale wetlands manage (detain) frequent flow events up to the 1.5-year average ARI from a 6 hectare urban catchment, incorporating gravel filled infiltration wells at 2-3m depth that are integrated into the wetland liner to enable low flow, sub surface releases to the creek to encourage baseflows.
