ESL - Ecological ServicesTo design and build a mitigation area for a complete water vole population, providing a full replacement length of water course in a minimal area to a high specification, providing a fast and cost effective solution.
The proposal was a large scale industrial development on a site with two thriving colonies of water voles in two separate ditches totalling 560m in length. Both ditches would be lost to the development thus the animals would need to be moved and a completely new habitat created on the perimeters of the site. The Natural England minimum requirement of ‘like for like’ replacement for the habitat lost, a tight development schedule and a limited availability of land meant that clever design and a thorough knowledge of the animals ecology was critical.
The solution was to create a convoluted water course with meanders, bends, dead ends and islands maximising the available land, incorporating steep banks for burrowing and shallow berms for plants to ensure an optimal habitat for the animals and to satisfy the requirements of Natural England. To help minimise cost an existing railway ditch of 350m, smothered in bramble and totally unsuitable for water voles, was cleared and re-profiled. This section was designed to maximise the colonisation of common reed both to provide shelter for water voles and inhibit the re-growth of the bramble while also creating a habitat for breeding birds.
With plants potentially taking up to 18 months to colonise naturally, the process had to be accelerated by transplanting locally abundant native species found on the site. Other obstacles to be overcome were the position of power lines and underground pipelines and a need to control the water levels both because of the proximity of the development and for the welfare of the animals.
In total 1100 m of suitable habitat was created and in only four months the re-planting scheme produced a successful substitute for the existing water courses to be lost. The design of the water courses incorporated a 0.2m fall to an installed sluice enabling control and maintenance of water levels guaranteeing the burrows and surrounding land did not flood. The spoil from the excavations was left in situ and profiled which made sound economic and ecological sense.
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