In the aftermath of the recent severe flooding in parts of lowland Britain, with adverse impacts upon the lives and businesses of thousands of people, The Mammal Society has urged the government to consider a"bold and cost-effective" wildlife solution as part of its overall flood defence response: bring back the beaver and allow it to apply its benign engineering skills to our river systems.

For many decades Britain’s rivers and streams have been straightened, engineered and cleared of natural debris so as to deliver rainfall as swiftly as possible to the sea; our waterways are fed by man-made ditches and field drains that reduce the land’s natural ability to hold water. Excessive flooding of towns, villages and farmland in the lowlands is the inevitable consequence of this unnaturally rapid transfer of water from the hills. 

Now, in response to the latest winter flooding, conventional engineering solutions, such as paying farmers in the uplands to change how they manage their land to retain more water and reduce flooding further downstream, could cost millions of pounds per year to produce any significant beneficial effects, with future taxpayers facing an ongoing funding commitment.  The European beaver, the master river engineer, could achieve the same effects for free and forever if we are bold enough to re-establish and tolerate it as a natural component of our river systems (as explained by George Monbiot in his book Feral published in 2013).

The European beaver is native to Britain. It was hunted for its fur, meat and castoreum and was extinct in most of Britain by the 16th century.  Beavers are large, semi-aquatic herbivores, eating vegetation such as leaves shoots, twigs and bark, and are well known for their ability to build dams across shallow river channels. This leads to beaver ‘impoundments’ which provide the animals with improved security and greater access to food resources. Collectively these serve to hold large quantities of water in tributaries and side-streams and release it slowly into the main river further downstream.

All over its European range beavers have been successfully reintroduced to many countries.  In Britain, a trial reintroduction is under way in Knapdale, Scotland, and an ‘unofficial’ population has become widely established on the Tay catchment.  Plans for a reintroduction of beavers in Wales are at an advanced stage.  The outcome of the official Scottish Beaver Trial is due to be reviewed by the Scottish Government in 2015.

In England, a study commissioned by Natural England and the People’s Trust for Endangered Species, published in 2009, found that reintroduction of beavers into England was both feasible and desirable, and would lead to significant benefits to riverine, riparian and floodplain ecosystems; since then, several interested groups have developed plans and proposals for experimental release of beavers into England but these projects are currently on hold pending an assessment of the findings of the Scottish Beaver Trial.

The Mammal Society supports the reintroduction of beavers to Britain as part of our obligation to restore a long-lost native species, and because beavers bring many environmental benefits to wetland ecosystems.  The Society urges governing bodies in Britain to re-establish the European beaver on the headwaters and tributaries of a flood-prone lowland river such as the Severn as part of a package of measures to alleviate future flooding.

Reintroductions to non-riverine sites (such as Knapdale) and short rivers (such as the Rheidol in Wales), while relatively non-controversial and less likely to provoke adverse reactions among land managers, will teach us little about the role that beavers could play in the management of water flows and lowland flooding in major river systems.  So there is no justification for waiting until the end of the Scottish Beaver Trial before making such a decision.

Marina Pacheco is The Mammal Society’s chief executive. She said:

“These are desperate times for householders and farmers affected by flooding rivers yet again. We have to acknowledge that our river systems are in poor shape and we need some special help to get flooding back under control in ways that we can afford. The beaver is not the only solution, but we believe it could make a valuable, cost-effective contribution to a package of flood alleviation measures if we allowed it to re-establish on flood prone river systems.”

“In addition to biodiversity benefits, restoring the beaver to Britain’s rivers would bring huge benefits in terms of flood alleviation; these unpaid river engineers would quickly re-establish more natural systems that retain water behind multiple small dams across tributaries and side-streams; as a consequence the severity of flooding further downstream would be greatly reduced, at no cost to the tax payer”.

“Reintegrating beavers into Britain’s rivers and wetlands will not happen without some challenges for land managers; but people coexist with beavers in most other European countries so we can too; and the long-term advantages of tolerating these hard-working flood-managers are clear.”

Beaver activities have multiple physical and chemical repercussions for streams and rivers and the benefits of beaver dams can be considerable, vastly outweighing any minor, localised negative impacts.  Water velocity and associated erosive forces are greatly reduced while large quantities of water are retained within surface, soil and groundwater compartments; this leads to attenuation of ‘flash flood’ phenomena as the stored water takes longer to travel through the catchment.  ‘Beaver rivers’ do not exhibit such high and low extremes of discharge, which is regulated more evenly throughout the year, alleviating both floods and droughts. 

Beaver dam building also improves water quality, through retention of sediments, organic carbon and pollutants; this could significantly reduce the cost of water purification for water companies. 

Lastly, beaver rivers exhibit increased hydrological and morphological complexity and connectivity, and provide greatly enhanced opportunities for many different plants and animals, including invertebrates, fish, amphibians, birds and semi-aquatic mammals; biodiversity is significantly improved and, as a consequence, is likely to be more resilient to the effects of climate change.  Recent studies in the United States have indicated that the economic benefits of beaver reintroduction into a river catchment, in terms of water storage, regulation of water flows, sediment retention and water purification is likely to run into many millions of dollars annually, and many projects are underway to re-establish the similar North American beaver into degraded river catchments throughout the country”

Beavers exert many positive effects on ecosystem functioning including:
•    Regulation of stream flows
•    Flood alleviation
•    Increased water storage and raised water table
•    Sediment retention and sorting
•    Reduction in erosion and decreased turbidity
•    Improved hydrological connectivity within and between surface and groundwaters
•    Increased hydrological & morphological diversity
•    Improved lateral connectivity between channel & floodplain
•    Increased nutrient cycling
•    Improved acid-neutralising capacity
•    Carbon retention, pollutant retention and water purification

And on biological diversity:
•    Increase in habitat heterogeneity
•    Increase in species richness and diversity
•    Increase in aquatic, transition and  deadwood habitats
•    Increase in open canopy riparian habitats and improved riparian understorey
•    Increased in-stream woody debris
•    Improved habitat for invertebrates, fish, amphibians, birds and semi-aquatic mammals
•    Improved connectivity and resilience