Barriers to open green space

The following sub-sections highlight typical barriers associated with previously developed land (PDL) and creating open space and suggests ways of dealing with issues, where appropriate.

Demand and need for open space

There will often be competing demands for the redevelopment of PDL.  This is especially true if the site is located in a high value market area, such as a city centre.  However, in certain circumstances other development types may benefit also from open space.  When seeking to develop open space projects, it may be worth considering if open space can be achieved alongside other schemes that could be used to part or fully fund open space provision through a planning consen. The relevant local authority open space audit, if one exists, should provide a useful guide to what need there is in the local area and what type of scheme could be promoted.

Is creating open space the best choice?

It is also worth bearing in mind that in some cases, open space provision may not be the best use of PDL. For example, where there is already an existing supply of open space to service local needs.  Similarly, there may be benefits with considering the value of promoting a range of different types of open space, such as parks, woodland and rough grass areas.

Established ecosystem value – A site that may be of value as an Open Mosaic Habitat might result in constraints on future development potential, including open space creation. This emerging Biodiversity Action Plan classification therefore needs to be considered in relation to the long term management of sites.  In this context, the creation of temporary open spaces may provide a useful way of managing sites to ensure that future environmental constraints to development do not emerge as a consequence of emergence of successional communities of biodiversity value.

The shape of the site – Some of the sites may be awkward to deal with, such as railway land, where options are limited for creating open space that will be accessible enough to have value to the local community it may serve.  However landowners as well as charities such as Sustrans could be engaged to facilitate access.  Sustans is responsible for creating the National Cycle Network.  It works to take leases on disused railways and turn them into cycle routes, for example, the former Midland Railway line between Bristol and Bath is now the Bristol and Bath Railway Path. Where there are ‘ransom strips’ (areas of land held by a third party that restrict access) however, opportunities for improving access could be limited.  Advice from the relevant Local Authority access officer may be useful to help identify potential solutions for improving access such as considering land swaps.

Waste on site – There may be waste left on site which may need to be removed or covered in the interests of safe operation of the site.

Contamination – Sites may be contaminated and can in certain circumstances require considerable investment in time and resources to contain any risk to future land uses and users.  Although, the provision of open space can often be a cost effective and safe way to manage contamination.

 Fact File – Site Remediation

Environmental Risk Assessment (ERA) for any site is based upon the proposed end use.  However investigation requirements will vary depending on the nature of the proposed end use potential receptors at risk and type and extent of contamination present, plus the degree of confidence required to satisfy the appropriate regulators.

Core to any environmental risk assessment is the conceptual site model (see image below), used to identify sources and pathways of contamination and potential receptors (e.g. human health, farm animals, surface waters and groundwater, and ecosystems).  ERA for public open space is complex given the wide variability of ways in which a space can be used.  Site specific detailed quantitative human health assessments will be required for any site as published assessment criteria (Soil Guideline Values) are not available.  These assessments should be undertaken in line with best practice guidance.  Use of an experienced environmental risk assessor and early dialogue with the local authority Contaminated Land Officer are recommended.

It is not possible to generalise, and assume that remediation in the temporary state will be less than the permanent state, as it will depend on the nature and extent of contamination and receptors at risk, and will be highly site specific.  However, careful consideration of the type of open space, and its use, may be able to reduce remediation costs, particularly in the temporary state.

Risks will be higher where soil is exposed, so areas where bare soils are present may require more extensive clean up e.g. cycling tracks.  Similarly, there is an increased risk in areas where people will eat or where small children will be exposed, so simple measures like the provision of appropriate picnic facilities, seating and dedicated play areas may reduce risk.  The key to cost effective remediation will be co-ordinated masterplanning and landscape design informed by an environmental risk assessment.

Remediation requirements to address risks to receptors are likely to be less stringent for open space developments on Category C and D sites (see Appendix B) than for, for example, a residential development.  However, where uses such as vegetable growing are being considered, levels of contamination may preclude this type of activity.

Should an assessment identify the potential for unacceptable levels of risk, then a remediation options appraisal should be carried out to identify feasible remediation options and a remediation strategy.

Soil quality – The soil quality of previously developed sites is likely to be poor and might require improvements to help establish planting.  For example, industrial sites are likely to have highly compacted soils making it difficult for many species to thrive (although, there is a possibility that some species will have established habitats).  Awareness of what species will be suitable will help to ensure that effective solutions are pursued and advice can be sought from the relevant local authority or a landscape specialist.

Nutrient loading – Nutrient loading of a site can promote the growth of highly competitive species (including certain ruderal species) which out-compete less tolerant species.

Invasive species – The biodiversity value of PDL can be limited by the dominance of ‘invasive’ non-native (or in some cases, native) species or, in other words, species that out-compete and dominate habitats to the detriment of native species.  Additionally some species may also pose risks to human and animal health and affect the integrity of building structures.

Fact File – Controlled Species

Examples of  ‘controlled’ species include: Japanese knotweed, Giant hogweed and Himalayan balsam.

Note: Ragwort is another species very common on PDL and other urban sites.  It needs to be controlled where the land is to be used by grazing animals as it is toxic to them and, if consumed by horses it can be fatal.  However, as a native plant ragwort supports and supplements many species of wild life including fungi and insects.  Good pasture management is therefore recommended, although it should not be treated as other controlled species.

If a project will result in the enhancement or creation of certain grassland communities for wildlife, it is a not recommended to include ragwort but instead to provide other nectar sources of value to wildlife.

Note: Under the Wildlife and Countryside Act 1981 it is an offence to plant or cause Japanese knotweed and giant hogweed to grow in the wild.

Note: As of April 2010, other controlled species will be added to the Schedule 9 of the Wildlife and Countryside Act 1981 (Variation of Schedule 9) (Enland and Wales) Order 2010.  This will include include Himalayan balsam, Impatiens glandulifera (this is the most significant addition as is likely to be encountered on brownfield sites), and about 30 other species.

Note: CIRIA has produced guidance on invasive species: Invasive species management for infrastructure managers and the construction industry (C679), (Wade, M, Booy, O, White, V 2008)