Locating green infrastructure and maintenance

Content:

Suitable locations

While green infrastructure enhances the street scene, care must be taken when selecting and positioning trees and shrubs to make sure that building frontages and parking areas can still enjoy good natural observation from areas of potential activity such as roads and footways. The effects of soil heave and shrinking on adjacent buildings and walls should not be underestimated; there are guidelines on tree planting in relation to buildings and foundation design in the National House Building Council standards.

Areas of open space, highway verges, traffic islands and gardens are all potential sites for suitable planting. Large open spaces are ideal for planting groups of trees and larger species (either single species or mixed), whilst grass verges that are a minimum of 2m wide provide an opportunity for planting an avenue of trees or for creating semi-natural grasslands that benefit wildlife. 

Less formal areas of open space such as screening bunds provide an opportunity to establish more closely spaced plantations which can develop into effective screens and, eventually, mature woodland edge habitat.

Green infrastructure and highway visibility

Any soft landscaping within visibility splays should not normally be expected to grow to more than 600mm in height above the adjacent carriageway level where the carriageway gradient is level. The council will assess planting in locations where the carriageway is on a slope or there are crests or sags in its vertical alignment, on a site-by-site basis.

Maintenance and inspections

More complex proposals relating to green or blue infrastructure (for example rain gardens or other sustainable drainage system infrastructure) may be considered on a trial basis. It is vital to speak to the council at an early stage regarding design proposals, which should meet asset management principles regarding maintenance affordability and durability. 

Maintenance

The design of green infrastructure must ensure ease of maintenance. Depending on the type of areas being proposed, suitable gated access and hard standing may be required. Design proposals must be shared with the environmental maintenance operations team. The council requires a detailed, costed maintenance plan for all green infrastructure proposals before they can be considered for adoption. 

Inspections

Green infrastructure will be subject to the same inspection process as any other part of the adopted highway. The council must approve the landscaping proposals within adopted highway whether or not they form part of a landscaping scheme submitted to the planning authority for approval. 

Adoptable design

In addition to meeting the above principles, areas the council is prepared to adopt as highway should be concentrated into larger areas, to provide economies of scale and to avoid small or remote areas which are difficult to maintain. Small and remote areas can result in the very opposite of what is intended from creating an attractive and well-cared-for environment. To avoid this the council stipulates the following:

  • Grassed service strips must be a minimum width of 1m to allow for efficient maintenance; 
  • Verges that include tree and/or shrub planting should be at least 2m wide to provide adequate space for appropriate planting to grow and thrive, improve security and minimise impacts on adjacent highway;
  • The minimum areas created for green infrastructure should be 10m2 for standard grass verges and 6m2 for shrub and groundcover planting;
  • Trees must be provided with suitable growing medium and soils that can support both establishment and long-term development. A minimum of 6 to 10 cubic metres of useable soil around each newly planted tree should be achieved. Developers must accommodate requests by the council to inspect trees pits prior to planting.

In more restricted spaces, planting small ornamental trees or shrubs should be considered. The design of this type of planting, with assistance of appropriate guidance, should ensure that long-term maintenance costs are kept to a minimum. However, the following design considerations should be considered:

  • Classification of roads - dual carriageway, main road, estate road, country lane etc.;
  • Visibility - on the inside of bends, from junctions and house driveways;
  • Location of existing service runs - overhead cables, streetlights, underground cables and pipes, drains etc;
  • Location of service runs required to facilitate the development;
  • Aerial space - how close the trees and shrubs are, above ground, to roads, accesses, neighbouring houses etc;
  • Risk of damage to footways, boundary walls, kerbs etc.;
  • The impact on light levels of nearby properties;
  • Screening of undesirable views;
  • Provision of seasonal change that can complement artificial environments;
  • Defining of routes and views;
  • The impact of salt spray on species selection;
  • Species suitability when planting adjacent to footpaths and cycleways.

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