Water vole and otter surveys, Great Western Route Modernisation

The brief

As part of Network Rail’s Great Western Route Modernisation project, ABC Electrification is delivering the electrification of the railway between Bristol and Cardiff. ABC Electrification plans to install Overhead Line Equipment (OLE), which will require piling works along the route.

The 80km stretch of railway to be developed crosses, or is adjacent to, seven UK protected sites and 11 locally protected sites. Features along the route have the potential to support a number of protected species including water voles and otters.

Thomson Ecology has been commissioned to advise on ecology constraints affecting the works. Part of this is to carry out surveys for specific species as have been identified in earlier scoping work.

What we did

Thomson Ecology carried out water vole surveys on suitable waterbodies within 25m of the train line and otter surveys on suitable waterbodies within 100m of the train line.

  • This included habitat suitability and sign surveys of 61 waterbodies, surveying a total of over 23km of bankside habitat.
  • Signs of water voles were identified at four waterbodies and signs of otters were also identified.
  • A re-survey of the waterbodies where water vole and otter signs were identified was recommended prior to the piling works. The aim of these surveys was to identify the locations of water vole burrows and to check if any otter holts had been created in the time since the initial survey was undertaken and immediately before works started.
  • A works exclusion zone of 10m was recommended where signs of water voles were identified to ensure that works carried out adhered to relevant legislation so avoiding the need for mitigation works.
  • Where access to a waterbody was not possible, a precautionary method of working (PMW) was recommended to the client to minimise any potential negative impacts on water voles or otters and to avoid costly delays to their programme of works.

Recommendations and outcomes

Thomson Ecology continues to work with ABC Electrification as the scheme develops and to provide ecological advice and consultation in a timely manner. The results of surveys are shared with Network Rail and other contractors working on the scheme.