How to minimise the impact of unsealed roads
Unsealed roads can have potentially more damaging impacts on the environment than sealed roads, affecting different elements of the environment, including waterways, the air, land, and local biodiversity.
Road managers must consider the following environmental impacts on the planning, design, construction, and maintenance of unsealed roads:
1. Erosion and sedimentation
In nature, vegetation and plantlife contribute greatly to maintaining the integrity of the land by “holding together” the earth and soil. When one considers it an unsealed road is, at its heart, a lengthy patch of unvegetated land that lacks this extra layer of structural integrity.
The result of this is masses of silt and sedimentation that runoff the road during rains. Not only does this block table drains leading to standing water (which is a leading cause of pavement defects), but it also finds its way into natural waterways causing damage to the ecosystem.
Care in how these roads are designed – as well as proper maintenance – can mitigate the impact of this sediment.
2. Airborne effects
For all unsealed roads, whether they are paved or unpaved, dust is rated according to the nuisance it poses to local residents. This includes the propensity of the unsealed road to generate dust clouds, settling characteristics after disturbance. Furthermore, dust emissions from vehicles travelling along unsealed roads can cause added air pollution, impair visibility and safety for motorists, and pose an overall hazard to health.
Additional care should be taken in areas where mining or industry is strong. Contaminants may have found their way into the soil over the last century such as crystalline silica and asbestos that are particularly harmful to humans and other animals. This leads us into our next point…
3. Land degradation
Roads, through their use and maintenance, can damage soils and displace previously intact parts of the land. Soil can become contaminated, compacted, or be eroded because of road construction and use. Unsealed roads can cause:
- Contamination of the soil due to accidents or industry
- Damage to the earth that restricts the ability of plants to draw water and nutrients from the soil
- The spreading of weeds that stifle the growth of local flora caused by seeds picked up and deposited by vehicle tyres.
- Burial of soil surface from deposition of poorly structured materials.
Just like dams or weirs, a road is another example of a man-made object that may have the unintended effect of diverting water away from where it naturally would have flowed. This can have major impacts on wetlands and may compound pre-existing issues caused by irrigation and agriculture (such as rising watertables, causing soil salinity)
4. Biodiversity
Unsealed roads cause a destruction of habitat when a road is introduced. Roads can remove or reduce suitable habitat, act as a barrier to wildlife movement, cause significant road kills of species, and reduce water quality for aquatic species. Road construction and maintenance activities threaten the conservation value of roadside reserves and instream fauna. There are potential threats from gradual clearing or physical damage to vegetation, smothering or compaction of vegetation by heavy machinery, herbicide drift from roadside vegetation management activities, the spread of weed seedlings from construction and maintenance vehicles, and culverts and fords which can restrict or impede essential migration of fish.
Environmental guidelines are becoming part of road workers’ daily routine and their incorporation into unsealed road management. This will help to reduce the impact that these roads have on the environment. It is recommended that road managers and workers follow a Roadside Management Plan in their consideration of the impact of road planning, design, construction, and maintenance activities.
Reference:
WALGA, 2016, ‘Dust Extent’, Walga Road Condition Assessment Manual, version 1, Walga.
New South Wales Department of Planning and Environment, Erosion and Sediment Control On Unsealed Roads Manual, viewed 28 October 2022, <https://www.environment.nsw.gov.au/research-and-publications/publications-search/erosion-and-sediment-control-on-unsealed-roads>
ARRB Transport Research Ltd, 2000, 'Environmental Considerations', Unsealed Roads Manual, 2nd Edn, ARRB Transport Research Ltd, VIC.