Ecological Services in Tunnels, Bridges and Culverts

Ecological Services in Tunnels, Bridges and Culverts

Bridges and tunnels, although commonly seen today, used to be a construction marvel during the late 1700s. Alongside the rail and canal evolution in the UK came the luxury of goods being transported effectively and cheaply, a key factor which enabled the Industrial Revolution. The UK was not easy country to tame, with mountains, rivers and canals to attend with, bridges and tunnels were a requirement At Acer Ecology we have a wealth of knowledge and experience in providing ecological surveys for tunnel, bridge and culvert repair works. We understand that repair works are essential in maintaining these structures in the long-term and ensuring their future use and/ or conservation. However, these structures can support a range of protected species and therefore these projects need to be managed in such a way to avoid adverse impacts to these species.

Negative Effects of these Structures

The human populations desire to get from A to B in way that’s both efficient and effortless as contributed to the fragmentation of many types of habitat and has lead to multiple wildlife casualties. People are also at risk from wildlife attempting to cross the roads and railways to get to better foraging or breeding grounds. Due to this major factor transportation agencies have begun to put in place mitigation to take into the account of the safety of both drivers and wildlife. An example of such mitigation is in the US. There were eight reconstruction projects underway at highway 93 in Montana, that were over 90.6km, all of which completed in 2010. The mitigation that was put into place included 2.4 m fencing, crossing features and wildlife guards. This aimed to try to reduce wildlife- vehicle collisions as well as increase human safety. Studies have begun so as to access their effectiveness of such mitigation strategies.

Fragmentation of habitats is the greatest problem due to the high rate of death from collisions.  Furthermore, the bigger the animal the more need it has to migrate across these areas to get from one habitat to the next. Solutions to these problems need to be provided to allow both humans and wildlife to coexist safely on our transport systems. To combat this animal crossings or bridges can be provided such as underpasses, overpasses and crossing on road surfaces. However, each needs to appeal to the species characteristics. As a result, designing mitigation strategies to suit specific species of animals can have design errors which highlights the complexity of designing animal crossing constructions.

It’s Not All Doom and Gloom!

Frog life is a charity promoting the protection of amphibians, they are currently undergoing surveys of road tunnels that have been constructed to encourage the safe crossing of amphibian species. This monitoring will allow ecologists to better understand how effective the crossings are in conserving and preserving local amphibian populations. The crossings also hold to potential to be adapted to hedgehogs and to water voles. The information collected will enable the organisation and other ecologists to best understand which animal crossings enable conservation and which may benefit a wide range of species not just amphibians.

In North America and western Europe the wildlife crossing is the main focus of mitigation efforts. The upgrade in new roads has become increasingly common even in the poorest areas. The assessment of wildlife crossings is typically surveyed by the documenting their use by wildlife through photographs, footprints, and land use. Not many studies have documented the type of use, the success of use and the reduction in the risk of extension. These parameters provide an insight into the success of green bridges as well allow a more comprehensive assessment of their effectiveness.

Wildlife Crossings

Wildlife crossings, as mentioned above, have been found to be one of the most effective solutions to transportation infrastructure. Bridges, although used by humans, can also be adapted for the use of wildlife which can be in the form of proper bridges or just the land above a railway tunnel. Green bridges, landscape bridges or wildlife overpasses tend to have a variety of trees and vegetation to allow the movement of birds, mammals and insects where movement was once inhibited. Not only do the crossings allow the free movement of wildlife, allowing them to connect to colonies on either side, they create a crossing point for people and integrates the road and railway system into the surrounding countryside.  

This simple solution to prevent wildlife and human fatalities on our roads and railways has been widespread across Europe and North America but has only been used in a few locations in the UK. This is shocking when considering that the first worldwide study on green bridges found that they have become an important cog in the sustainability of future transport ventures. Furthermore, Natural England is trying to ensure that the natural environment is conserved for the benefit of the UK’s future generations so it is increasingly vital that road and tunnel construction is done so in a way that benefits all that it will affect ensuring its sustainability.

In the UK green bridges and wildlife crossings are few and far between. The A21 at Scotney Castle in Kent is a dual carriageway by-pass for Lamberhurst, the planners were told that its construction would negatively affect the local landscape and its wildlife. In response to this a wildlife crossing was constructed. It now enhances the surrounding habitat and the local population of dormice. In the UK’s capital city, London, green bridges have come into play. One was built in Mile End Park to try and mitigate the effects of habitat fragmentation by roads and railway lines. The bridge itself spans five lanes of the A11 and is 25m wide with landscaped parkland. The rainwater even runs of the bridge into tanks either side of the construction and then is recycled so as to enhance the water content within its soil.

White Clawed Crayfish- Gentle Watercourse Under a Culvert

White Clawed Crayfish are nationally protected under the wildlife and countryside act (1981) and typically reside in rivers and streams with specific conditions such as depth, substrate size and presence of natural refugia, overhanging banks etc. Due to their niche and specific habitat preferences they are rare and vulnerable. Culvert works can result in pollution and sediment to enter the watercourse which white clawed crayfish are extremely vulnerable to.  At Acer Ecology we have the licensed staff that can undertake white clawed crayfish surveys and provide you with the ecological solutions you require to continue with maintenance and repair works.

Bats- The Dark Space Dwellers

Bats are a highly typical species when working with these structures. Stone and brick tunnels, bridges and culverts provide easy access in to a sheltered environment due to their open nature and can provide ample opportunity for roosting bats. Bats essentially adopt one of two roosting strategies. The first are termed ‘crevice-dwellers’ which will take advantage of any spaces between the stone or brickwork. The second strategy belongs to the ‘horseshoe’ species of bat which will freely hang from the ceilings of tunnels or under arches in the side walls of tunnels. Bats can occupy tunnels, bridges and culverts in the active summer months, but they can also provide suitable conditions for hibernation over the winter period.

As these structures can support significant populations of bat as well as a rich variety of species, it is essential that repair works to these structures are undertaken in conjunction with bat surveys and suitable mitigation measures to ensure that that works comply with national and European legislation.

At Acer Ecology our ecologists have received high standard professional training in confined spaces safety and are trained in searching for hibernating bats and in assessing the overall potential of use by bats. The objectives of a bat survey are to:

  • Locate the presence of bats and if they are likely by surveying trees and buildings which may be suitable roosts
  • Identify any bat activities across the site, their favourite communing and foraging routes
  • Recommend and assist when needed with ecological mitigation and enhancement

With the growing human population, the need for wildlife mitigation when dealing with our roads and railways. It is paramount if we wish to be able to preserve our wildlife for generations to come.

How We Can Help!

Acer Ecology can assist you with:

  • Complying with the relevant legislations
  • Securing planning permission for your project
  • Enabling you to achieve your business goals
  • Conducting nesting bird surveys
  • Conducting Phase 1 surveys on vegetation that needs to be cleared around your tunnels and bridges

By considering the effect that your proposal may have on the surrounding wildlife early on in the development process the more likely we are able to ensure your development stays on time, preventing any costly delays. We can provide you with expert ecological advice on your transportation infrastructure such as roads and tunnels, so that your development proceeds efficiently, on time and within your proposed budget.



GOV Green Bridges

Road Ecology Wildlife Crossing Structures Handbook

Beben, D., Crossings Construction as a Method of Animal Conservation

Peoples Way Wildlife Crossings

Author: Ashely Dale