Ecological Services in Tunnels, Bridges and Culverts

Bridges and tunnels, though commonly seen today, were a construction marvel during the late 1700s. Alongside the UK rail and canal evolution came the luxury of being able to transport goods 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 contend with, and 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 for 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 population’s desire to get from A to B in way that’s both efficient and effortless has 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 protect both drivers and wildlife. An example of such mitigation is the major reconstruction of Highway 93 in the US, where eight reconstruction projects were put in place over 90.6km of road in Montana in 2010. The mitigation included 2.4m fencing, crossing features and wildlife guards to try to reduce wildlife-vehicle collisions as well as increase human safety. Studies have begun to assess the 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 greater the 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 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 crossings 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 who are currently undertaking surveys of road tunnels that have been constructed to encourage the safe crossing of amphibian species. This monitoring allows ecologists to better understand how effective the crossings are in conserving and preserving local amphibian populations. The crossings also hold the 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 not only amphibians but a wide range of species.

In North America and western Europe, the wildlife crossing is the main focus of mitigation efforts. The upgrade to new roads has become increasingly common even in the poorest areas. The assessment of wildlife crossings is typically surveyed by 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 as 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 and 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 which enables 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 also 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, 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 where the planners were told that it’s 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 off 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 Countrysid Act (1981) and typically reside in rivers and streams with specific conditions such as depth, substrate size and presence of natural refugia such as 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 is 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 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 legislation
  • 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 effects 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.

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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