The Rivers and Streams of England and Wales: An Overview of their Physical Character in 2007–2008 and Changes Since 1995–1996 - River Conservation and Management - page 26

small and medium-sized rivers ( ca ≤ 150 m wide).
It combines the basic principles and terminology
of fluvial geomorphology and freshwater ecology
(Raven et al., 1997). Channel features and
modifications are recorded at 10 equally spaced
'spot-checks' along a 500 m length of river (an
RHS 'site'), together with an overall 'sweep-up'
summary for the whole site, including information
on land use in the river corridor (Environment
Agency, 2003). Information from more than 100
variables, together with site photographs and map-
based data such as altitude, distance from source,
channel slope and geology are entered into a
computer database. This allows the relationship
between physical variables (e.g. channel width,
slope), channel modifications and habitat features
to be analysed at individual spot-check and 500 m
site levels.
The RHS survey method and associated training
of surveyors are designed to ensure that features
are recorded in a consistent, repeatable way,
are ecologically relevant (e.g. Harper et al .,
1995), and represent valid indicators of fluvial
morphological form and function (Newson and
Newson, 2000; Harvey et al ., 2008). Since initial
development, several improvements have been
made to the survey protocol (Fox et al ., 1998),
while accreditation of surveyors and a strict
validation protocol maintain a high standard of
quality control. The RHS was used to develop and
test two European guidance standards for assessing
hydromorphological character and modification of
rivers (British Standards Institution, 2004, 2010;
Boon et al ., 2010). It has also been adapted for
use elsewhere, including Mediterranean areas (e.g.
Buffagni and Kemp, 2002).
A major strength of RHS is the breadth of
information that it records, allowing sites to be
characterized and compared using many different
variables (e.g. Jeffers, 1998a, b; Szoszkiewicz et al .,
2006; Hughes et al ., 2008; Vaughan and Ormerod,
this volume). However, for general reporting
purposes, two simple descriptive indices, based
largely on expert opinion, were developed initially
and remain a well-established, albeit simple, output
from

and the character of adjacent land; the Habitat
Modification Score (HMS) indicates the extent of
artificial modification to the river channel. The
original scoring protocols for HQA and HMS,
together with various options for assessing habitat
quality at different geographical scales and for
species-related purposes are described fully in
Raven et al. (1998a, b). Subsequent improvements
have been made to the HMS protocol so that the
impact of different modifications can be assessed
more specifically. More objective river channel
indices, based on habitat features and modification
have also been developed (Vaughan, 2010). The
HMS score can be expressed as one of five
Habitat Modification Classes (HMC), ranging from
'near-natural' channel form (class 1) to 'severely
modified' (class 5). Broad links between HQA,
HMS and biological communities derived from
multivariate analyses can be useful in targeting
more specific diagnostic investigations (e.g. Hughes
et al ., 2008; Harvey and Wallerstein, 2009), but
there are inherent limitations if the HQA, HMS
or HMC indices alone are used to investigate
relationships between habitat features and biota
(Vaughan and Ormerod, this volume).

Sampling strategy and assessment
of change
The two RHS baseline surveys, carried out in
1994-1996 and 2007-2008, had two main aims:
first, to provide an unbiased picture of the 150 000
km of rivers and streams in England and Wales;
second, to provide comprehensive geographical
coverage of the river network, allowing detailed
mapping of habitat features at a national scale. To
achieve this, both surveys used stratified, random
sampling schemes - three randomly-located 500 m
RHS sample sites were surveyed in each 10 km
square of the Ordnance Survey mapping grid. For
the 1994-1996 survey all of the RHS sites were
selected from those watercourses appearing on
the 1:250 000 scale river network (Raven et al. ,
1998b). After 1994, revisions were made to the
field survey protocol and the data quality was
improved; consequently only the 1995-1996 data
were used for subsequent analysis and comparison

RHS: Habitat Quality Assessment (HQA)

provides a measure of river habitat diversity