Slow The Flow advocates Nature-based solutions to flood management, because of their multiple benefits. One of these is beautifully described in our new guest blog post from Douglas Fraser at Sheffield Hallam University (SHU), whose BSc (Hons) Environmental Science and MSc Environmental Management students are researching the ways in which Slowing the Flow of floodwater can positively impact on habitats for endangered species, such as the water vole (or ‘Ratty’ from The Wind in the Willows). We look forward to their results, and to following the progress of students on the new BSc (Hons) Climate, Sustainability and Environmental Management course, starting in autumn 2024.
The native water vole (Fig. 1) is, at best, an endangered species in the British Isles (Mathews & Harrower, 2020). Scientifically called Arvicola amphibius, it is a rodent which is similar in size and colour to the brown rat. Due to this appearance and as it lives close to slow-flowing rivers, it used to be commonly known as the water rat – hence Ratty, in The Wind in the Willows (Grahame,1908) – a book written when water voles were a popular, familiar sight on rivers with well-vegetated banks, in rural Britain.
Figure 1: Water vole (Arvicola amphibius). Picture credit: McGuire & Whitfield (2017).
By contrast, the brown rat (Rattus norvegicus) is often in active conflict with humans due to their adaptability to all habitats, their scavenging, fast breeding and historic vectoring of fatal disease. Voles are rarer than rats, because they are more specific in their food and habitat requirements, and because of their vulnerability to human-induced changes to the environment. So, they are also in conflict with humans, but it is less deliberate. Agricultural changes to river courses (straightening and speeding flow) and their banks (overgrazing or herbicide effects) as well as the regrettable introduction of the predatory American mink into the British river systems, has led to the reduction of water voles. Mink (originally escaped / released from fur farms, since 1929) is like a polecat (wild ferret), but more amphibious and a voracious predator of birds, fish and other mammals, including the water vole. Research in the 1990s showed that water voles were being systematically eradicated by mink (Strachan, cited by Tansley, 2024) and the population (in 2015) had declined by over 90% since the 1970s (McGuire and Whitfield, 2017).
Mink spread along river watercourses, but rarely travel far from the surface watercourse (Mammal Soc., nd). This means that where the surface rivers are interrupted by going underground for a section of their flow, the mink usually stay downstream in the surface water. Unmolested, voles may still exist in the upper catchment. In these wet uplands, the presence of water voles can be detected by the angled cut through soft rush (Juncus sp.) stems and leaves, resulting from the herbivorous water voles nibbling (Fig. 2). Even better evidence is the entrances to burrows, just above the waterline (Fig. 3), often with vole droppings nearby (Fig. 4).
Figure 2: Angled cuts on soft rush can be evidence of water vole grazing
Figure 3: Water vole burrow entrances on shallow, vegetated bank.
Figure 4: Water vole burrow entrance and droppings.
Where water voles exist, it is clearly important to protect them from molestation by human activity or mink invasion. Water voles dig burrows in the banks, so prefer relatively stable, slow-flowing water levels. This is an important consideration for those of us who wish to slow the flow off the uplands. Water vole habitats, therefore, must not be further dammed up, as raising water levels will drown the voles in their burrows.
In slowing the flow in other channels, near water vole populations, an increased area of suitable habitat may be created. Slow flow and stable conditions can allow for a broader community of bankside vegetation available for grazing. Water voles exhibit a dietary preference for an extensive range of waterside vegetation (Strachan & Jefferies, 1993).
The following picture-story relates to the creation of new water vole habitat by slowing the flow on a small, open field drain in the wetlands above Sheffield. (But first a word of warning: another consideration when changing the flow of even a small stream in a catchment is to consider alerting the Lead Local Flood Authority (LLFA), which has oversight of the strategic flood risk management. As long as your flow-slowing activities have landowner and water-rights permission and are not going to lead to problematic local flooding, then it should be fine. But it is best to build a good relationship with those with the power to impose fines under Section 23 of the Land Drainage Act (1991) (see Derbyshire, n.d.).)
In partnership with our local Wildlife Trust (Sheffield & Rotherham WT), students of BSc (Hons) Environmental Science and MSc Environmental Management, at Sheffield Hallam University, took a linear field drainage ditch, which held little surface water and created new watery habitat with slower, more consistent flow. This channel was adjacent to a known population of water voles, but the ditch itself did not hold enough water for voles to have bothered moving in. The ditch drained into groundwater of wet land, downhill, so there was a physical break in surface water between the channel and the downstream river population of mink.
Figure 5: The barrier – essentially a drystone wall with a little clay soil ‘mortar’. Height should be slightly lower than the channel depth and left with leaks.
Figure 6: A covering of locally dug bankside turves (mainly Juncus sp.) to grow over the barrier.
Figure 7: Repeat as often as the ditch gradient allows, and within hours find the water levels rising.
Figure 8: Revisit one week later to find stable ponds.
Figure 9: Only six months later and a habitat has developed. We hope the local water vole population will expand into this site.
Monitoring of success is, of course now necessary. Little is currently known about how quickly water vole populations will expand into new habitats, but eDNA techniques are possible in slow flowing rivers. If Kenneth Grahame’s characterisation of ‘Ratty’ (being gentle and very relaxed) is accurate, water voles will need all the help we can give.
This is the kind of project that we are doing with local agencies, to expand our students’ practical experience for outdoor skills as well as for networking with the agencies. It is also important to verify if such actions are effective.
Whilst it is healthy for people to help repair the environmental damage, there is a bigger agenda that is also helping. Beavers (Castor fiber) are expert leaky dam builders. The reintroduction of this native ‘keystone’ species is already providing hope for water voles, who have been observed expanding territories in beaver-engineered wetlands (Puttock, et al., 2023).
SHU starts a new course in autumn, 2024: BSc (Hons) Climate, Sustainability and Environmental Management, into which we have built projects and monitoring.
References
Derbyshire (n.d.). Guidance Notes: Land Drainage Consent Applications. Online: https://www.derbyshire.gov.uk/site-elements/documents/pdf/environment/flooding/consent/guidance-notes-for-land-drainage-consent-applications.pdf. Accessed 21/05/2024.
Grahame, K. (1908). The Wind in the Willows. Pub.: Methuen. Children’s novel reprinted many times, with multiple film adaptations.
McGuire, C. & Whitfield, D. (2017). National water vole database and mapping project. Part, 1, 2006-2015. The Wildlife Trusts. Online: https://www.wildlifetrusts.org/sites/default/files/2018-05/water_vole_report_2006-2015_final.pdf. Accessed: 21/05/2024.
Mammal Society (n.d.). Species – American Mink fact sheet. On-line: www.mammal.org.uk/species-hub/full-species-hub/discover-mammals/species-american-mink. Accessed 21/05/2024
Mathews, F. & Harrower, C. (2020). IUCN – compliant Red List for Britain’s Terrestrial Mammals. Assessment by the Mammal Society under contract to Natural England, Natural Resources Wales and Scottish Natural Heritage. Natural England, Peterborough ISBN 978-1-78354-485-1
Puttock, A., Newman, M., Graham, H., Elliott, M., Chant, J., Auster, R.E., & Brazier, R.E. (2023). Positive coexistence of water voles and beaver: water vole expansion in a beaver engineered wetland. Mammal Communications 9: 7-15, Blandford Forum
Strachan, R. & Jefferies, D.J. (1993). The water vole Arvicola terrestris [A. amphibius] in Britain 1989-1990: its distribution and changing status. Vincent Wildlife Trust.
Tansley, D. (2024). Is Eradication of Invasive Mink Now Possible? Mammal Society. On-line: https://www.mammalsociety.org.uk/blog/is-eradication-of-invasive-mink-now-possible. Accessed 21/05/ 2024.