Typology 10 – Permeable Footpath

Permeable footpaths allow direct rainfall and overland flows to infiltrate into underlying soils rather than being discharged into the stormwater drainage system. Permeable footpaths are particularly beneficial where allotment runoff discharges onto the surface of the footpath in the vicinity of a tree.

Capital and operational costs are influenced by site specific factors including proximity to underground services and ease of access for construction and maintenance. The indicative cost estimate below is for a straightforward site (i.e. assuming service relocation not required and access is unconstrained) and the infrastructure dimensions shown in the standard drawings. The standard drawings are based on permeable asphalt footpaths which are more cost effective than permeable bluestone footpaths. Permeable bluestone footpaths can also be used. The indicative cost estimates will be updated as we gain more experience with this typology.

Capital cost – $1,000
Operational cost – $100 per year

City of Melbourne has installed permeable bluestone footpaths in the CBD which includes Collins Street.

Permeable asphalt has been used in parking bays including Eades Place, West Melbourne.

Vegetation – Tree only

Asphalt – The permeable asphalt layer lies above a layer of washed aggregate to create a stable surface and facilitate infiltration. The pavement slopes towards the road so that during peak rainfall events, when the infiltration rate of the pavement is exceeded, stormwater runoff flows into the kerb and channel.

Tree surround – The standard drawing shows a compacted granitic gravel surface surrounding the tree trunk. Alternatively, the area around the tree could be planted with understorey vegetation or covered with permeable pebble mix paving (refer Design Standard 201.06).

Allotment run off – Permeable footpaths are particularly suited to locations where allotment runoff is discharged across the footpath.

Other
Hold points must be noted on construction drawings so construction supervisors can easily ensure that key staff are invited to hold point inspections.

The performance of permeable footpaths can be assessed using MUSIC. The recommended modelling parameters are shown in Table 1. The typical performance of permeable footpaths is shown in Table 2.

Table 1 Recommended MUSIC parameters for Permeable footpaths

Table 2 Typical performance of permeable footpaths (assuming 10 m2 of permeable footpath with no external catchment))

The long-term performance of assets can be strongly influenced by practices and procedures adopted during the construction and establishment phase. It is recommended that hold-points are used to allow City of Melbourne, or the system designer, to check that the design intent is met during critical stages of the construction and establishment period.

Hold points must be noted on construction drawings so construction supervisors can easily ensure that key staff are invited to hold point inspections.

It is the contractor’s responsibility to provide a minimum of 24 hours weekday’s notice (unless agreed to prior) to the superintendent to arrange for an inspection for the hold points.

Recommended construction and establishment phase hold points

It is important to ensure that assets are functioning properly before responsibility for them is transferred to the asset owner (generally at the end of the establishment phase). The following aspects should be checked prior to handover.

Documentation – Construction documentation AND as constructed survey received.
Permeable paving hydraulic conductivity – At least 500 mm/hr
Vegetation growth – Average height of trees > 2000 mm
Vegetation condition – Tree healthy and free from disease

Recommended routine inspection and maintenance activities for permeable footpath

Recommended monitoring activities for permeable footpath