CLM20-2 full issue-1 - Flipbook - Page 36
VIEWPOINT: Dams without beavers: could beaver dam analogues yield benefits in the UK?
more seriously. Two widely
advocated remedies are tree
planting to delay runoff from the
uplands and leaky dams to slow
the flow of streams in spate.
Leaky dams have now been
included in the Countryside
Stewardship Scheme, and
indicative designs for these are
presented in a manual published
in February 2022 (Rural
Payments Agency 2022).
Bundles of logs are arranged in
such a way that the stream can
run unhindered through the gap
beneath the dam during normal
flow. The dam will, however,
restrict the flow somewhat in
Leaky dams are popular in river-restoration projects in the UK, but,
times of high rainfall, although
unlike BDAs, they only pool water temporarily, during periods of
there is a risk of the water
high flow. Eden Rivers Trust
scouring the streambed under
Unfortunately, the authorities have been slow to
the dam. Leaky dams constructed as part of
acknowledge this, although there is hope that a
nature conservation projects often tend to be less
new ‘beaver strategy’, announced in 2021, could
tidy than the Countryside Stewardship designs,
see fewer restrictions on reintroductions and
comprising a few logs and branches, although
allow the animals to be released more widely into
they function in a similar way. While they
the wild. The return of beavers to their historic
possibly reduce flooding, both these types of leaky
range will inevitably take time, but in the interim
dam only temporarily ‘pool’ water, and so have
the construction of BDAs could offer a rapid
little beneficial effect on the wider environment or
and widely applicable means of imitating some
wildlife, whether that be fish, invertebrates, birds,
of the positive impacts of beavers in degraded
mammals or vegetation.
landscapes. Furthermore, it is to be hoped that
BDAs are not a suitable choice if pooling of
BDAs in the UK might in future be taken over
water will be a problem, although they can be
by wild-living beavers, as they often are in the
planned carefully so as to avoid the potential
USA, while in the meantime acting as the next
conflicts caused by flooding. In other situations,
best thing to natural dams and thereby aiding
however, a BDA can be constructed with a
ecosystem restoration by creating wetland habitat similar amount of effort to that involved in the
in places where it is lacking.
various types of leaky-dam design, but it produces
benefits similar to those of an actual beaver dam.
By creating permanent or semi-permanent ponds,
Opportunities for BDAs
BDAs provide habitat for a wide range of species
BDAs in the USA originated in the relatively arid
that will receive no benefit from leaky dams. The
western states where degradation of creeks is
acute, but in the UK damage to watercourses may widespread use of leaky dams therefore represents a
serious missed opportunity to increase biodiversity
be less glaringly obvious, particularly because
during river restoration and flood mitigation works.
dredging and the straightening of channels have
The use of beavers as ecosystem engineers in
proceeded over many centuries. We have grown
the UK is likely to be localised, at least in the
used to rivers and streams in this condition and
short term, but there are many places where BDAs
it is only recently, when flood events caused by
could helpfully act as surrogates. Our uplands,
extreme weather have become a problem, that we
for instance, are often devoid of tree cover, which
have begun to take the state of our watercourses
34 Conservation Land Management Summer 2022 | Vol. 20 No. 2
