Revegetation and Landscaping

Document No:  D14#67391
 
Revision:  1C
 
Date amended:  7-May-2015

Image: orange line.RCN-D13^23151823.GIF 

The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Joseph Filia by e-mail or on (08) 9323 4151.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

 

Revision Register

Ed/Version Number Clause Number Description of Revision Date
1 All Guideline Developed. 17-Feb-2014
1A C. Design requirements Guideline "Vegetation placement within the road reserve" updated. 13-May-2014
​1B​C. Design Requirements​Guidelines "Vegetation placement within the road reserve", "Revegatation Planning and Techniques", "Revegetation Topsoil management" and "Visual Screens within the Road Reserve" updated.​31-Mar-2015
​1C​C. Design Requirements​Links to documents updated​7-May-2015
 

 


Table of Content


A. General

 
Main Roads undertakes revegetation and landscaping, as a routine part of road works following the clearing of vegetation and or soil disturbance. Community expectations are for roads that are attractive as well as safe and efficient.
 
Revegetation and landscaping refers to the materials and treatments used to stabilise soil surfaces, re-establish vegetation cover suited to the location, and to enhance visual amenity and environmental values of the road reserve.  Figure 1 below illustrates how revegetation and landscaping is used to blend the road infrastructure into the surrounding environment. 
 
 
 
 
 Image: Figure 1 - Typical cross section across road reserve.RCN-D14^2378801.JPG
 
Figure 1 Typical cross section across the road reserve
 
 
Main Roads has responsibility for (typically high speed, high volume) roads across the state. The width of road reserves and roadsides vary across the state network.  In rural areas an open channel (table drain) designed to receive road storm water runoff, is usually present adjoining the roadway.  Beyond the table drain, the roadside (from a few meters to over 100 meters wide) extends to the edge of the road reserve and typically contains some local remnant native vegetation. In urban areas the roadway may be edged with a concrete kerb and road storm water runoff is collected into an underground drainage system. Medians may be present between roadways. The roadside may contain signs and other road furniture, footpaths and other facilities.  In the Perth metropolitan region the road network includes designated roads and highways (with driveways and intersections) and controlled access highways and freeways (via interchanges and intersections).
 
 

B. Design Objectives  

 
Revegetation and landscaping must support the safe functioning of the road infrastructure, enhance the road environment for road users and blend the road reserve into the surrounding landscape. 
 
Appropriate design treatments must be determined on a site by site basis to meet local conditions and project requirements. All design treatments should be visually simple to reinforce the road infrastructure and assist driver guidance. The safety of landscape maintenance staff should be a key design consideration near high speed roads. A key environmental design objective for Main Roads is to maximise the absorption of rainfall and surface water flows on site, so ground surfaces should not be more impervious than is necessary. All design treatments must be cost effective within the limited funds available to cover the total project area (typically measured in hectares). As a minimum the treatments should be designed, installed and established to achieve the project objectives and to provide a neat, cared for, appearance while minimising the future maintenance requirements and costs. 
 
In some locations (feature points) a higher standard of revegetation and landscaping may be established and maintained as a priority maintenance zone (PMZ’s) or in association with the local government authority. PMZ’s are designated locations, as determined by the Asset Manager, where special or more frequent maintenance activities occur as part of the road maintenance program.
 
Typical examples include reticulated landscape areas, road sections that are low speed at peak periods and significant environmental areas (SEA’s).
 

C. Design requirements

Design and documentation requirements are based on Main Roads standard drawings, guidelines, specifications and technical criteria as defined via the project design brief to address the specifics of the project scope, commitments and location.

For guidance on the typical project processes including design review and list of codes, design guides and reference materials refer to Typical Project Processes.

 

Design and Drawing Presentation
For design and drawing presentation standards refer to Design and Drawing Presentation.

 

Standard drawings (contract, guideline and presentation)
For examples of the drawing presentation standard accepted by Main Roads refer to Main Roads Presentation Drawings.

For segmental (brick) paving details refer to Main Roads standard drawings 200331-154, 200331-155 and 200331-156, and Main Roads standard Specification 505, Segmental paving.

For guideline drawings on typical landscaping treatments within the maintenance and road edge zone refer to Main Roads Guidelines Drawings under Landscaping Treatments.

For guideline drawings on revegetation refer to Main Roads Guidelines Drawings under Revegetation.

 

Guidelines
All vegetation is placed in accordance with the Main Roads guideline Vegetation placement within the road reserve to ensure clear sightlines and lateral setbacks from the roadway.

The Main Roads guideline Visual Screens within the Road Reserve  provides guidance on visual screens within road reserves managed by Main Roads Western Australia (Main Roads).

The Main Roads guideline Revegetation Planning and Techniques  provides general information, and guidance on project planning and detail on techniques. 

The Main Roads guideline on Topsoil Management provides guidance on best practice in the management of site vegetation and topsoil to help achieve the best outcomes for project revegetation works.

 

 

Specifications
Relevant technical specifications 300 series are available on the Main Roads website Specifications 300 series

 

Design briefs

Specific requirements for a project location are defined using Main Roads design briefs as templates. 

For a typical road project the Standard Design Brief is customised to define the requirements including revegetation and landscaping.

For major projects the standard Scope of Works & Technical Criteria (SWTC) document is customised to define the specific requirements, given the project scope, commitments and location.

The Landscape Design brief  defines the landscape design and documentation requirements for standard projects.

The Visual Impact Assessment brief  defines the requirements to assess and report on visual impacts associated with road work projects.

The Project Revegetation Plan brief defines the requirements to prepare a revegetation plan report, for standard projects, using a Project Revegetation Plan template.

 
 

D. Design Considerations

 
Revegetation and landscaping treatments must support the safety and function of the road infrastructure. Restrictions apply on treatments permitted close to road infrastructure to assist in road safety, to help protect the integrity of the infrastructure assets and minimise the need for on-going maintenance and to achieve a suitable level of amenity.
 
Typical Design Treatment Zones
Typical design treatment zones for revegetation and landscaping across the road verge and median are illustrated below in figure 2.

 

 Image: Figure 2 - Typical treatment zones across the verge and median.RCN-D14^2380016.GIF
 
Figure 2 Typical treatment zones across the verge and median
 
 
 
Restrictions apply within the safety clear zone (refer figure 2), nominated for the road location, on the placement of non-frangible objects (trees and large shrubs with a trunk diameter >100mm). 
 
Standard landscaping treatments should be used within the roadway maintenance zone (refer figure 2) and restrictions apply on the height of vegetation to retain sightlines and minimise maintenance needs.
 
The road edge zone (minimum 500mm) along the roadway (back of kerb and edge of shoulder) requires standard landscaping treatments to stabilise the soil surface and minimise on-going maintenance.
 
Typical treatments zones for revegetation and landscaping are summarised below in table 1.
 
ZONE  DESCRIPTION DESIGN NOTES MANAGEMENT OBJECTIVE
​Roadway (the portion of road reserve for use of vehicles) ​Width as necessary to meet operational needs. ​The roadway is kept clear of all revegetation and landscaping.
 
Maintain and enhance visual quality of pavement and structures.
​Pavement stability. Off road surface drainage.
Road structures. 
Road safety and driver visibility.
Maintain surfaces free of debris and rubbish.
Road edge ​Minimum width of 500mm along the back of kerb or edge of shoulder. Along all roadside verges and medians (where these exist). Surface treatments to provide stable edge and be simple, decorative and low maintenance.
Vehicle recovery area.
Provide stable edge to pavements
Prevent erosion of roadsides.
​Maintenance zone Zone of variable width from marked edge line of outer traffic lane, includes road edge zone. Width varies by location and ​Road safety barriers occur in some locations.
Treatments height generally < 200mm to limit the potential for screening of hidden objects that may reduce the capacity of drains and cause damage to the underside of vehicles leaving the roadway. For example road intersections or entry to roundabouts are paved (in part), maintained clear of vegetation, or planted with grass or low ground covers.
​Vehicle recovery area.
Maintain clear sight distances and setbacks.
Height of vegetation is controlled to meet operational needs.
Ensure effective surface drainage.
Maintained free of debris and rubbish.
Prevent erosion.
Control weeds.
Control fires.
Maintain clearances to utilities.
Maintain and enhance visual quality
Clear zone ​A ‘recovery zone’ or safety ‘clear zone’ variable width from marked edge line of outer traffic lane, includes road edge and maintenance zone. Applies on both sides of the roadway and medians (where these exist). ​Setbacks apply to the placement of tree trunks and other fixed objects to avoid obstacles in the path of vehicles that may run off the road and to reduce the severity of accidents. Generally no restrictions on vegetation height. ​Vehicle recovery area.
Maintain clear of non-frangible objects.
Vegetation is controlled to meet operational needs, e.g. to remove hazards (overhanging branches).
Maintain clearances to utilities.
Prevent erosion.
Control fires.
Control weeds.
Conserve and enhance biodiversity.
Preserve heritage values.
Maintain and enhance visual quality.
Vegetation zone ​Zone of variable width beyond the clear zone. varies by location No restrictions apply for trees and other fixed objects.

Remnant vegetation type and condition varies by location.

No control of vegetation growth with exceptions in some locations.
​Maintain clearances to utilities.
Control fires.
Control weeds.
Prevent erosion.
Vegetation is managed as necessary to:
Remove hazards (overhanging branches).
Maintain and enhance visual quality.
Conserve and enhance biodiversity.
Preserve heritage values.
Boundary zone ​Zone of variable width adjacent to road reserve boundary. varies by location Setbacks apply to the placement of vegetation near fences to avoid overhanging branches into adjoining residential land and to maintain vehicle access along boundary. ​Vegetation is managed as necessary to remove hazards (overhanging branches).
Control fires.
Control weeds.
Prevent erosion.
 
 
    Table 1  Design objectives by treatment zones
 
 
 
Design treatments
A range of standard design treatments are applied across the typical road reserve profile (of verge and median) to suit the location and situation (e.g. intersections and interchanges, drainage basins and roadside stopping places) along urban roads, freeways and rural roads. 
 
Planting species selection and layout should be visually simple to reinforce the road infrastructure and assist driver guidance.  Planting areas should add some visual interest without adding to the current level of visual distractions for drivers. 
 
The use of public art items, special features (materials, colours and finishes) and irrigated planting areas) are limited to specific feature locations for example a feature median in a commercial/civic area.  Broad decorative abstract patterns using hard landscaping and defined planting areas are acceptable, but detailed visual elements that may be a distraction to drivers should be avoided. 
 
Avoid design treatments that may result in unsafe conditions for maintenance staff.  Known issues relate to steep slopes, need for frequent maintenance under busy traffic conditions, frequent weed control and pesticide use, maintenance around roadside items/furniture.
 
 
Soil surface treatments
The recommended standard treatment for paved islands, narrow medians and narrow interchange ramps is segmental paving with limited in-situ concrete at the nibs. For wider medians and interchange ramps hard landscaping is provided from the median nose to a minimum median width of 5 metres. All segmental unit paving adjoining planting or grass areas should include concrete edge restraints. In some locations segmental paving will need to be trafficable.
 
A maintenance safety strip is required along the back of kerbs and edge of shoulders (nominal 500mm) using only approved low maintenance surface treatments such as clean (organic or inorganic) mulch, or unit paving. Except in special areas the recommended practice is not to include planting or grassing for narrow medians and islands or where the available width of soil is less than 1 metre. Low maintenance decorative and porous surface treatments should be used for narrow strips (< 1 metre width) between paths and roadways and around roadside furniture, footings and structures.
 
The reshaping of landform, finished soil levels and the use of permeable soil surfaces treatments should be used to maximise on site infiltration of rainfall and surface water flows, where practical. For example finished soil levels should be shaped to fall away from the back of kerb or path for a nominal 500mm, if practical, or unless specified otherwise in the design documents. 
 
For new road works the finished soil levels after earthworks should be set below the top of back of kerbs, shoulders, paths and footings to allow for the nominated landscaping treatments for the location. Nominal soil level depths after earthworks should be:
    • Grass (with imported topsoil and grass) ~70 mm
    • Planting (with imported topsoil and mulch) ~135 mm
    • Coarse organic mulch materials ~85 mm
    • Clean ‘washed’ backfill (eg basecourse, gravel, aggregate) ~85 mm
 
The finished surface level of soft landscaping treatments (e.g. mulch, grass and topsoil) should be set a nominal 25mm below the top of back of kerb.  Along existing roads the soil should be box out to allow for the placement of the nominated landscaping treatment for the location.
 
Only clean, weed free backfill materials should be used for a nominal distance of 0.5 m around footings of guard rails, wire rope safety barriers, noise walls, retaining walls and other roadside furniture and fixtures such as lighting and signs. Special treatments apply along high speed roads with no clearance to back of kerb areas (no paved shoulder or travel lane line markings) to resist movement caused by the slipstream from large vehicles.  Safety and potential vandalism concerns need to be considered in the specification and placement of inorganic granular materials e.g. potential for loose stones to be used as missiles; gravel moving onto footpaths and posing a risk of pedestrians slipping.
 
Specifications for organic mulch varies with the intended use, e.g. batter stabilisation, surface protection, soil amendment, decorative surface. In the back of kerb zone (and edge of shoulder) the specification for organic mulch (chipped vegetation) should be coarse particle size only, graded to exclude fibrous or fine particles. Anecdotal evidence indicates the cost effective use of large particle mulch in the back of kerb zone for fire resistance and resistance to movement from wind action or slipstream from vehicles. Both are important for Main Roads purposes.  Shredded green waste and fibrous or fine particle much is not acceptable. 
 
Suitable organic mulch materials should retain a decorative appearance and last for nominal 5 years before a top up may be required. Mulch (if organic) is to meet the following product criteria.
    • 98% organic matter.
    • Clean of all soil, weeds, grass stolons, seeds and other extraneous materials.
    • Totally devoid of plastics.
    • Screened to exclude all fibrous and fine particles.
    • Particle size
    • Nominal % between 15mm to 80mm range (screened on a dry weight basis)
    • 90% passing 80mm
    • 20% passing 40mm
    • 1% passing 15mm
    • max particle size of 150mm.
 
 
Vegetation
All vegetation shall be placed in accordance with the Main Roads guideline Vegetation placement within the road reserve (Doc. No. 6707/022) to ensure clear sightlines and lateral setbacks from the roadway.
 
In general a vegetation clearance zone applies from the back of kerb, shoulder, path and footings to minimise the need for ongoing trimming of vegetation growth over kerbs, paved surfaces, under guard rails, wire rope safety barriers, and other roadside furniture and fixtures. All trees should be considered non-frangible objects and only placed outside the nominated clear zone or beyond the deflection limit of safety barriers. 
 
All new planting must be setback from the back of kerbs, in medians and islands to minimise the need for ongoing trimming of vegetation growth over kerbs and onto roadways. Plantings must also be setback from roadside items/furniture and from property boundary fences to retain a workable clearance of the mature foliage/canopy. The setback distance for planting holes is set as equal to the required vegetation clearance plus half the estimated mature canopy (spread) of the selected plant species. 
 
Vegetation is known to be difficult to establish and maintain in narrow medians and in narrow strips and gaps between footpaths and kerbs.  As a general guide vegetation, suitable for the location, may be planted where the available soil width for planting is greater than 3 metres. If vegetation is to be placed in narrow urban medians the mature height of plantings in the centre should be a nominal maximum of 1 metre, with a nominal maximum height of 0.5 metre adjacent to the median maintenance strip. Plantings in narrow medians will need appropriate soil preparation (refer specifications) and a permanent irrigation source to survive over time. This should be limited to nominated feature points and priority maintenance zones. 
 
Species selection is decided on a site by site basis to meet the local conditions, project requirements and commitments. Maximum use shall be made of native flora species indigenous to the work area. Alternatives to or departures from this requirement must be justified.  Revegetation is generally limited to the use of local native plant species that do not require on-going watering once established.  Completion targets need to be set on a project by project basis for species diversity, planting density, composition and other relevant criteria. Within the clear zone the species list should be mainly based on proven, long lived, hardy plants that will survive in the harsh conditions, require low ongoing maintenance and still retain a neat decorative appearance. 
 
The density of planting depends on the expected mature spread of the plant species, with a nominal recommended overall density of 1 plant per two square metres for understory species. The growth form of many local native plants is variable within the species. Only proven form varieties should be selected for use in medians, e.g. prostrate forms of Grevillea thelemanniana and Grevillea obtusifolia, to minimise the need for ongoing plant trimming.  Density and spacing of tree species will vary with the specific project location. For street tree plantings to establish and be effective over the long term it is critical to consider tree root management (e.g. soil quality and volume). 
 
Accepted practice is for most seeding and planting works to rely on the seasonal rainfall only. For most areas no on-going irrigation is specified to minimise ongoing maintenance costs. Temporary watering systems may be appropriate during the construction and establishment period to help establish the required vegetation cover.