Soils in the built environment
Pressures and opportunities
Pressures
There are a number of pressures acting upon soils in the built environment. These include:
- Development - resulting in the sealing of soil
- Construction - resulting in, for example, soil compaction
- Landscaping (demand for good quality soil) - resulting in the importing of soil from other areas
- Topsoil stripping - resulting in soil loss
- Disposal of waste soils rather than re-using and recovering soils - resulting in soil loss
- Disregard for sub-soils and deeper substrates - resulting in loss of function
- Ongoing continual loading of atmospheric pollutants to soil - resulting in loss of function
- Past and continuing industrial activity - resulting in soil contamination and loss of function
- Fill materials for mineral/waste development - resulting in topsoil and subsoil loss.
The impacts of some of these pressures are less well understood than others and require further investigation.
See more on gathering evidence based-research.
Development
Using land for buildings and transport can damage soils irreversibly. At a minimum the soil is covered (sealed) and prevented from functioning.
Defra is working to ensure that consideration is given to sustainable soil use and protection during planning and development.
Soil sealing
Soil sealing is defined as the covering of the soil surface with a layer of impervious material or changing the nature of the soil so that it behaves as an impermeable medium.
Soil sealing prevents the soil from performing other functions such as food and fibre production or the ecological functions of soil.
Construction
The activities carried out during the construction of a new building or transport link affect soil quality. It is not uncommon to find soils in built environment gardens and green spaces containing building rubble or with compacted layers.
The landscaping phase of new construction may also involve the importing of topsoil, with its own set of risks.
Defra is working to ensure the sustainable use and management of soil during construction.
Importing topsoil (and subsoil)
The importing of soil (both topsoil and subsoil) is common practice in the built environment. This practice is associated with a number of risks that need to be assessed and managed.
Many of these risks arise due to a poor understanding of the soil. The practices involving soil movement are often considered as "dirt shifting" instead of "soil handling".
These risks include:
- Importing unsuitable soils for planned use
- Damage to soil structure
- Mixing of topsoil and subsoil
- Loss of soil function in the area exporting the soil
- Potential to import contaminants
- Potential to import plant and animal diseases that use soil as a host
Some of these risks have been considered in relation to mineral site restoration. This knowledge could be transferred to the built environment.
Opportunities
Current national policy initiatives provide an opportunity to improve the sustainable use of soils in the built environment. These include:
- Review of the planning system
- Work on sustainable development, communities and buildings.
New technologies offer the opportunity to return some of the lost soil functions to the built environment. Examples include the use of permeable paving and the installation of green roofs.
Permeable paving
Permeable paving allows the passage of water from the paved surface to the soil below via voids within areas of solid paving or through porous materials.
By allowing the soil to function beneath the paved surface, permeable paving can:
- Decrease downstream flooding
- Decrease the frequency of combined sewer overflow events
- Eliminate problems with standing water
- Provide for groundwater recharge
- Control erosion of streambeds and riverbanks
- Facilitate pollutant removal.
Green roofs
Green roofs are vegetated roofs, or roofs with vegetated spaces. They are also referred to as eco-roofs and roof gardens.
The soil functions provided by green roofs include:
- Improved rainwater management - the volume and rate of rainwater run off from the roof is reduced dramatically
- Improvement of air quality by removal of carbon dioxide, release of oxygen and water vapour, deposition of particulate pollutants, and absorption of organic volatiles
- Reduction of the urban heat island effect (Met Office website).
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Page published: 1 September 2005