Memorandum submitted by the British Ecological
Society (FL 66)
INTRODUCTION
1. The British Ecological Society is the
learned society for ecology in the UK. Founded in 1913 its mission
is to promote the science of ecology worldwide. This response
was produced with input from Professor Alan Hildrew, the BES's
Climate Change Advisory Group and its Public and Policy Committee.
2. The BES response focuses on the potential
for land-use management to help mitigate flooding. The BES supports
an integrated approach to flood risk, in which land-use practices
maximize a range of ecosystem services, such as flood control.
THE ROLE
OF ECOLOGY
IN MITIGATING
FLOODING
3. Flooding is the episodic flow of rivers
over their channel banks and is a natural occurrence and a key
aspect of landscape ecology. While there are many important beneficial
ecological effects of flooding, for instance on fish and other
wildlife, the ecology of river catchments could be managed to
minimise the costs of flooding. Natural ecosystem processes in
catchments can ameliorate the intensity of run-off generated by
any particular rainfall event, and thus reduce the extent of flooding
downstream, where it causes most nuisance and economic damage.
4. The careful management of land-use in
river catchments can help to mitigate, at reasonable economic
costs, the increased occurrence and severity of rainfall that
is expected to result from climate change. The uplands receive
much of the rainfall and generate much of the runoff to flood-prone
rivers—such as the Severn and Wye. The restoration of upland
land-use to native deciduous woodland, would help to:
— increase the interception of rainfall
by vegetation;
— increase water infiltration into
the soil and groundwater;
— increase transpiration to the atmosphere;
— reduce peak flow due to surface runoff.
5. The economic cost of managing land-use
in this way would be modest in the uplands. In addition, this
would have additional benefits for conservation objectives and
increased carbon storage. Increasing natural flood mitigation
measures in the uplands will still require both natural and conventional
flood mitigation measures in the lowlands, since once upland ecosystems
are saturated their ability to reduce flooding events is limited.
6. Giving streams and headwaters more space
next to their channels would encourage the development of lateral
vegetation and wetlands and increase the retention of flood flows
in the upper reaches of rivers. Water would be released more slowly
to downstream areas, where most economic damage from flooding
occurs. River flow would also help to be sustained during dry
periods. Again, there would be some economic cost due to restrictions
on agriculture near streams, which would need to be set against
reductions in flooding downstream and in benefits to water supply
and conservation.
7. The intensification of farming practices
has tended to reduce the infiltration capacity of soil and decrease
water storage in agricultural areas. This can cause higher peak
flows in watercourses. Soil with a good natural structure can,
depending on soil type, can retain large amounts of water. Certain
arable land management practices can lead to soil compaction,
puddling, capping and plough pans, all of which reduce infiltration
and increase surface runoff. Cultivation techniques including
soil management, surface crop cover and headwater management can
all be used to increase water storage capacity. The Soil Framework
Directive and the Water Framework Directive provide the opportunity
to improve the structural health of our soils and could contribute
to reducing flood risk.
8. The best way to manage water flow through
catchments will be to base risk estimates on they dynamics of
land use and hydrology in the catchment. Of course lowland flooding
results on some occasions from combination of events in more than
one catchment.
9. Other land management practices which
could be used to mitigate flooding include, restoring upland bogs,
putting meanders back in rivers and creating new "washlands."
Sustainable urban drainage systems would also help by enabling
rainfall to infiltrate the ground rather than run-off to urban
drains. Such ecological responses would obviously not ameliorate
the risk of flooding, but are part of the solution for reducing
flooding. Projects to reduce flood events should look at both
the effectiveness of the conventional flood management and the
opportunities provided by emerging techniques of restoring natural
functionality in the landscape. There is evidence that such approaches
deliver effective flood management together with social and economic
benefits.
10. The majority of the experimental information
on the effects of forests on runoff in the UK has focused on uplands.
Only a few studies have been carried out on lowland broad-leaved
woodland. More research on how to best to manage ecosystems to
reduce flood events is needed.
IMPACTS OF
FLOODING ON
ECOLOGICAL FACTORS
11. Biological, physical and chemical water
quality are impacted by flooding events. Flooding also has localized
direct impacts on many species. For example, the nests of many
waterbirds are known to have been swept away during this years
floods and ground nesting species in areas that flooded are also
likely to have failed in their nesting attempts this year. However,
assuming the frequency of flooding remains low this is unlikely
to have any long term impact on species abundance and distribution.
12. Summer flooding is not a typical feature
of flood-plain systems in the UK and the long-term impacts of
more frequent summer flooding are almost unknown and more research
is needed in this area. Species living in wet meadows and washes
are typically adapted to winter flooding. In one recent paper
detailing the impacts of summer flooding on the Ouse Washes the
authors conclude that declines in a population of Black-tailed
Godwit are related to the rate of flooding. The generality of
such findings are often unknown.
The British Ecological Society
August 2007
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