North
Wiltshire Rivers and Streams
Most of Wiltshire's rivers, especially the chalk streams,
have been managed for a variety of reasons for many centuries.
They are intensively used to convey flood waters and discharges,
to provide water for public, agricultural and industrial
use, and are a popular recreational resource, however, most
have retained some wildlife interest and some are of national
and international importance. There is approximately 850
km of 'main river' in Wiltshire with a further extent of
'ordinary water course' .
The geology and topography (the physical appearance of the
natural features of an area of land, especially the shape
of its surface) through which a river flows determines the
features of the river including channel character and the
chemical composition of the water; this in turn affects the
species of plants and animals that these watercourses support.
Not only are the rivers important habitats in themselves,
they also provide important wildlife corridors linking fragments
different habitats in farmed and built up areas helping wildlife
move from one area to another.
A number of Wiltshire’s river are of national and
European importance and the rest of the main rivers are recognised
County Wildlife Sites. The Salisbury Avon has been designated
an Special Area of Conservation (SAC) due to it’s rich
wildlife including Water Crowfoot, Salmon, Bullhead, and
Sea Lamprey to name a few; much of it has also been designated
a Site of Special Scientific Interest (SSSI) due to the habitat
and species it supports, much of the River Kennet was designated
a SSSI for the same reason.
There are also areas of swamp
habitat alongside the River Kennet at Chilton Foliat that
have been designated a SAC for the population of Desmoulin’s
Whorl Snail it supports. The Bristol Avon and the By Brook
are also important rivers; the Bristol Avon for dragonflies
and damselflies, and the By Brook for Water Crowfoot and
it’s populations of the native White-clawed Crayfish
and Dipper.
The historical management of rivers through the creation,
and subsequent abandonment of water meadow systems along
with more recent management including drainage for agriculture,
channel modification abstraction, pollution and the impact
of development has had a large impact on the on Wiltshire’s
rivers causing its biodiversity to fluctuate.
Chalk streams
Chalk streams have characteristics which set them apart
from watercourses associated with other rock types. Chalk
rock is porous and rain falling onto chalk hills like the
tops at Marlborough Downs and ridge peak of Clyffe Pypard,
soaks directly into the ground, where the chalk acts as an
aquifer. The water is filtered through the chalk, re-emerging
lower down the slope in springs, like a couple that emerge
at Bradenstoke Abbey.
Under ground water is readily stored
beneath the Lyneham plateau and as a result the high
water table was
beneficial
years ago to ensure the moat that was built around the
former Lyneham Court property was always well stocked.
Lyneham had quite a few village ponds and these were
favourable during freezing winter days when they provided
ample
skating arena for the children.
The under surface chalk acts as
a reservoir,
regulating the amount of water
supplied
to
the
springs,
so that its
flow varies little day-to-day. The temperature of the water
scarcely varies either, because the spring rarely deviates
from 10 ºC. On cold winter mornings, it can look as
though steam is rising above the relatively warm river. Chalk is soluble in rainwater because rainwater is naturally
slightly acidic. Because the products of chalk weathering
are dissolved in rainwater, chalk streams transport little
suspended material (unlike most rivers) but are instead mineral
rich. The water runs clear and the river bed is covered by
angular flinty gravel, derived from flints found within the
chalk itself. All these characteristics of chalk streams — consistent
temperature, consistent flow, clarity of water, lack of sandy
debris — contribute to their very particular ecology.
Chalk stream is a term generally applied to all watercourses originating from chalk hills including winterbournes, streams
and rivers. The River Wylye (pronounced 'Why-lee') is a
classic southern England chalk stream; champagne clear
water flowing
over gravel. Consequently, it is popular with anglers keen
on fly-fishing.
Flood Plains
The biggest worry when buying a house is whether the property lies on a flood
plain. Many have witnessed the major floods of Tewesbury, Gloucestershire 2007,
and the tragedies of Boscastle and Carlisle in the early 21st century and it
comes as a relief that Lyneham does not suffer from river overspills.  More..
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