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the impact of modifications. Unlike RHS, this
assessment is made during the survey, using
pre-determined criteria for the departure from
near-natural conditions, predicated by a pre-
determined river typology (e.g. LAWA, 2000).
This approach has the advantage of producing
continuous classification maps of entire rivers, but
disadvantages include inter-surveyor error (i.e.
inconsistent observation or interpretation, which
reduces confidence in the precision of results)
and the potential mis-classification of river type
and hence erroneous interpretation of observed
conditions compared with type-specific reference
condition criteria.
These 24 000 sites also provide an invaluable
ground-truth facility for remote-sensing surveys,
particularly where trees obscure channel features
on aerial photographs - and this could be about
40% of total river length (extensive shading;
Table 3.3). A combination of several sources of
information, including RHS, could be used to
diagnose 'hot-spot' problems in river catchments
such as localized erosion (Newson, 2010). The RHS
database therefore provides an important source of
information for Rivers Trusts as they become more
prominent in river management locally (Newson,
this volume). As remote sensing technology
advances (Large, this volume), a combination of
RHS data, validated aerial photograph information
and possibly a reduced version of the RHS
field survey could provide the basis for a rapid
assessment protocol for assessing the physical
state and associated management needs of rivers
(Barquin
et al
., this volume) and scenario-planning
for climate change effects (Ormerod, 2009).
Using the results for river
management
Despite the size of the RHS baseline surveys,
sample sizes are modest when the data are
viewed at individual catchment level; this limits
the conclusions that can be made at smaller
geographical scales. In several river catchments
in England and Wales additional RHS sites
have been surveyed using a stratified random
strategy - to increase the sample size in order
to allow statistically meaningful characterization
at the smaller scale. In other cases, rivers have
been surveyed using a 25% sampling density -
one 500 m site every 2 km of watercourse. As
a result of all these surveys carried out since
1994, there are now over 24 000 sites on the
RHS database, including more than 9000 sites
from the two baseline surveys. This information
has been used for various reasons, including
environmental impact assessment (Raven
et al
.,
2000), river conservation evaluation (Boon
et al
., 2002) and appraisal of riparian restoration
work (Clews
et al
., 2010). For WFD purposes,
RHS information has been used for river basin
characterization, identifying hydromorphological
pressures and helping to determine which water
bodies could be classified as 'reference condition'
and 'heavily modified' (www.environment-
agency.gov.uk/research/planning/33106.aspx).
A good example of making links with biological
water quality metrics so as to determine catchment
character and pressures is given in Vaughan and
Ormerod (this volume).
Acknowledgements
The Environment Agency is thanked for permission
to reproduce the illustrations for Figures 3.1-3.5
from '
Our river habitats - a snapshot'
and '
Our river
habitats - England and Wales summary
'. We are very
grateful to the following for encouragement, advice
and support: Professors Mike Clark, Malcolm
Newson, Steve Ormerod, Colin Thorne, Phil
Boon; the late Professor Ron Edwards; Drs Mark
Diamond, Nigel Holmes, Hugh Dawson, Mark
Everard, Mervyn Bramley, Anne Powell. Special
thanks also to Lucy Taylor, Joanne Barlow, Simon
Hewitt, Alison Ingleby, Laura Price, Peter Livings
and Steven Darling who were closely involved in
the preparation for the 2007-2008 baseline survey,
training of surveyors, data input, validation and
analysis of results.
References
Bates AJ, Sadler JP, Fowles AP, Butcher CR (2005)
Spatial dynamics of beetles living on exposed
riverine sediments in the upper River Severn:
method development and preliminary results.
Aquatic
