Environmental awareness is growing globally and the environmental impacts of both gravel and forest roads are having an increasing weight in roads management policies. For this reason it is sensible that all new knowledge and guidelines as well as experiences of good practices should be shared in this area. The ROADEX project has earlier generated a publication on Environmental Guidelines, and an Environmental Guidelines pocket book, that sets out the main issues that should be kept in mind in the everyday environmental management of low volume roads.
In addition, ROADEX has also published an eLearning package on Environmental Considerations for Low Volume Roads.
This chapter will be mainly based on the ROADEX eLearning package on Environmental considerations with a special focus on gravel roads and forest roads.
11.2 Identification, ignoring, minimization and adaptation of environmental impacts
When managing environmental impacts on gravel and forest road first task is always the identification of all known and potential impacts that can cause harm to the environment including nature, people and local households. This can be done through a special risk analysis for each project, but an easier way is to go through a specific checklist for gravel and forest roads. Once this has been done the next task is to decide if these potential impacts can be ignored or avoided, or to which level they can be minimised. However there are also certain impacts, such as climate change or increasing axle weights, which in a single road management project cannot be avoided. They have to be accepted and the road has to be adapted to meet the impacts.
General environmental issues that can be related to design, construction, maintenance and renovation of gravel or forest roads are listed in the following:
- impact on natural protection areas
- impact on landscape
- impact on prehistoric relics or natural monuments
- impact on waterways
- impact on wildlife
- impact on endangered species
- impact on local people and households
- impact on multipurpose use
- impact on valuable natural destinations close by
- impact on CO2 emissions
At the other end of the scale there are further issues to be considered:
- Socioeconomic impact of the of local livelihoods and households
- Impact on forest economy
- Impact on traffic safety
- Health impact on the people using the road
- Impact on life cycle costs of the road
Once the environmental impact evaluation and risk analysis have been made, the next task is to consider how these impacts can be avoided or downgraded to an accepted minimum risk level or how they can be mitigated. If these measures are not sufficient, a special adaptation plan should be made. A good example is a drainage design plan based on predicted higher precipitation rates, and erosion protection against flooding.
The most important environmental issues related to gravel and forest road management are discussed in the following:
11.3 Traffic and road maintenance impacts
11.3.1 Noise and vibrations
With gravel roads noise and vibration problems can be related mainly to road roughness problems, ie washboarding, potholes and bumps. Heavy or even empty trucks cause both noise and vibration problems to the households close by when driving over them. Noise is a problem throughout the year but vibrations can get substantially worse during the wintertime when the top soil is frozen and it is leading better vibrations waves. For this reason gravel road maintenance standards should be always raised around houses, even a single one. This is mainly a problem with public gravel roads as there are seldom permanently occupied houses beside a forest road.
Another important impact, important also with forest roads and often forgotten, are health issues associated with human body vibrations caused by uneven road surfaces. ROADEX has carried out research on this issue and published several reports about road roughness and health issues.
The latest research results have shown that driving on rough road sections can increase stress in the occupants of vehicles, and also cause negative impacts on the heart as well as major back problems in the long term.
11.3.2 Dust and dust management
Gravel road dust problems can be a severe issue for people with houses close to the road, but it can be also a traffic safety issue. Because of this special attention should be paid to road sections adjacent to houses on gravel roads. Dust in these sections can be managed by using dust suppressants in proximity to the houses but also special attention on the wearing course quality and thickness can be useful. Sometimes surface dressing or surface sealing has been also used adjacent to houses with potential dust problems.
On roads located on groundwater areas the use of dust suppressants can be prohibited because dust binding chlorides can contaminate groundwater aquifers.
11.4 Impact on waterways
Because gravel and forest roads are normally located in rural areas with only few dwellings, the waterways in these areas are often very valuable biotopes for different species. That is why a special focus should be paid on the protection of these waterways. Two main issues that should be kept in mind are: 1) ensuring that culverts do not prevent migration of fish and other species, and 2) ensuring water from the drainage system is clean when entering in the natural waterway system, and especially small streams and creeks.
Poorly installed culverts have been found to be major obstacles for migration of fish and other water species. As only salmon-like fish (salmon, trout, etc) can jump water obstacles, the lower part of a culvert should not be higher than the water surface after the culvert. This can be done two ways, lowering the culvert, or by adding gravel and rocks after the culvert to ensure continuous stream from culvert to the ditch or creek below the culvert.
A further issue with fish and other species migration is the water flow speed in culverts, creeks and ditches. If the water flow speed is higher than 0.4 m/s it can create a barrier effect for fish migrating, and even as low as 0.2 m/s for younger fish. That is why culverts should not be installed to be too steep. If the culvert inclination cannot be changed the other option is to install some obstacles inside the culvert to lower the speed of the water flow speed and provide temporary shelter to the fish where they can rest.
Water quality and erosion protection
The other environmental challenge with some gravel and forest roads that are close to valuable waterways is how to ensure that the water from the road is clear enough before it enters the waterway. This is especially an issue on silty or silty moraine areas where fines particles can be mixed into the drainage water after a drainage improvement or after heavy rains. This however can be prevented by reducing the water flow speeds exiting the road drains by building dams or filter structures in the side ditches and outlet ditches.
Finally, erosion of the wearing course of a gravel or forest road can also cause problems to waterways. Maintenance guidelines against this problem have been discussed in other parts of this eLearning, especially in Chapter 6 “Drainage”. One further good practice solution has been the placing of recycled cold mix asphalt on the top of the road on sections with known erosion problems.