The ‘Nature’
of Chalk Rivers
"A river seems a magic thing. A magic, moving,
living part of the very earth itself." Laura Gilpin, photographer
Chalk rivers are an invaluable resource for wildlife and
are an intrinsic part of our cultural heritage. Our ancestors found
something magical in the crystal waters that issue from the very earth
itself, and they recognised the life-sustaining resources these streams
and rivers provide. As a nation, we have drunk their waters, fed on their
fish and harnessed their power. But more than that, one rarely passes a
healthy chalk stream without stopping to enjoy its rippling surface and
scan for the secrets that inhabit its depths.
The southern and eastern counties
of England are Europe's primary region for chalk rivers. Kent’s chalk
rivers arise in the North Downs. Examples include the Nailbourne,
flowing from Lyminge to Littlebourne, stretches of the Great Stour,
Little Stour and the North Stream near Eastry. All such rivers in Kent are
a priority for conservation in the Kent Biodiversity Action Plan.
All chalk rivers are fed from groundwater, producing
clear waters and a generally stable flow and temperature. These conditions
support a rich diversity of invertebrate life and important fisheries,
notably for brown trout and salmon. Several chalk rivers in England are
world-famous for their fly-fishing. Brook lamprey, white-clawed crayfish
and otter are among the internationally important wildlife species which
chalk rivers support. Other, nationally threatened species such as the
water vole are also characteristic.
Chalk rivers have distinctive plant communities, often
dominated in mid-channel by river water crowfoot, and along the edges by
watercress and water-parsnip. Those rivers that have kept their natural
shape also have low, marshy banks that support a range of water-loving
plants.
Most chalk rivers have 'winterbourne' stretches in their
headwaters. This means they often naturally run dry in late summer because
of a lower water table. A range of invertebrates and plants are adapted to
these conditions.
In common with most lowland rivers, chalk rivers often
suffer from a variety of human impacts. Excessive abstraction from the
water table, mainly for public water supply, has contributed to low flows
on a number of chalk rivers. This has led not only to drying out of upper
sections and river margins, but also to slower flowing water, build up of
silt, and changes in the aquatic vegetation. This trend is likely to be
accelerated by climate change and urban development.
Through history, chalk rivers have had their channels
re-shaped by people, for a variety of reasons: flood defence, land
drainage, navigation, water-milling, and urban development. These changes
often lead to loss of habitat, and have reduced the ability of wildlife to
migrate along rivers. Chalk rivers can also be affected by sewage
discharges, and indirect pollution from agricultural chemicals.
The Environment Agency, in partnership with water
companies, drainage bodies, and local authorities, have a duty to combat
these impacts. On-going work includes trying to prevent low flows and
ensuring that flood defences and development are sympathetic to chalk
river habitats.
Patterns of abstraction for public water supply are
being changed to help reduce low-flows in dry summers. However, given the
demand for water, these efforts can only have a limited affect on river
ecosystems unless physical restoration of the channel also takes place.
One way of helping river wildlife to recover is to allow
vegetation along margins to naturally develop where this will not lead to
flood risk. These margins provide wildlife habitat in their own right, but
also increase the speed of flow, which helps to clear the gravels of silt
(and weed), and provide the loose gravel bed which is so important for
fish-spawning and invertebrates. Creating stone, log or brushwood
structures in the river can also allow the river to ‘heal’ faster. The
Kentish Stour Countryside Project has taken part in such hand's on
projects in the past.
We should continue to cherish our chalk rivers. They
have given us so much over the centuries, and deserve our care and respect
in the future.
Richard Andrews,
Biodiversity Specialist - Environment Agency
