Willowburn Realignment: Ecological Impact Assessment


Northumberland County Council proposed to construct a new road that would provide access to a new school and a housing development located on the southern edge of Alnwick, Northumberland.  A number of options were considered for the alignment of the new road, all of which were subject to constraints of varying significance.  The preferred option utilised a narrow strip of land between an existing industrial park and a watercourse known as the Willowburn.

To accommodate the road it was necessary to re-align a section of the Willowburn to the east of its current course.  To facilitate this re-alignment it was necessary to fell a number of broadleaved trees that were growing alongside the watercourse and shading the channel.  A new channel was excavated and, following the diversion of the watercourse into this channel, the old channel was backfilled.

BSG Ecology’s Role in the Project

BSG Ecology was appointed by Northumberland County Council to undertake an ecological impact assessment for the proposed road construction scheme.  This included habitat, breeding birds, badger, bats, otter and water vole surveys, and an appraisal of the watercourse’s suitability for white-clawed crayfish.

During the course of the baseline ecological surveys we recorded a small number of bats roosting in a tree that had been identified for felling.  Tree assessments and bat activity surveys identified a mature alder tree that supported a small common pipistrelle bat roost.  A European Protected Species Licence was obtained that permitted the felling of the tree and the lawful destruction of the roost.  To compensate for the loss of the roost a number of bat boxes were erected on retained trees to the south of the realigned section.

BSG Ecology provided advice to the Council about the design of the proposed re-alignment of the section of the watercourse.  This included the inclusion of features to encourage the development of biodiversity interest within the new channel.  The dense woodland cover along the original watercourse corridor had resulted in extensive shading such that no aquatic plants were present and the ground vegetation in the woodland was similarly impoverished.  Furthermore there was a lot of urban debris in the watercourse and evidence of bank erosion in places.  The watercourse was of low suitability for use by water vole and otter, and the habitat and water quality was considered to be too poor to support white-clawed crayfish.  Overall it was concluded that this section of the watercourse was of low ecological importance in the ecological impact assessment.


Following receipt of the European protected species licence, BSG Ecology worked closely with the appointed arboricultural contractor to facilitate the exclusion of bats from the tree where they were roosting prior to it being felled.  A pre-felling bat survey was carried out that indicated that bats were no longer roosting in the tree, but due to the presence of a dense ivy covering, a precautionary approach was adopted just in case bats were present.  This involved careful section felling of the tree.

Once all trees had been removed, including the tree supporting the bat roost, a new channel was excavated.  The original watercourse channel had previously been straightened and so some gentle meanders were introduced to the new layout together with banks of varying profile and a channel bed that was wide enough to allow marshy areas to develop.  The watercourse was then diverted into the new channel section.

It was important to maintain some tree cover to maintain a diverse habitat corridor that could be used by bats, birds and other species.  The excavation of the new channel was designed to enable more light to reach the banksides for the benefit of aquatic and marginal plants as well as the retention of selected shaded areas to provide cover for fauna.  The result is a sparsely wooded stream corridor where the banks slope gently down to a new meandering channel of variable width and profile.  Monitoring will be carried out to see what vegetation has returned and how the habitat is developing.


Northumberland County Council

Infrastructure, North East, Public Sector