M. Parsons, M. Thomas, R. Norris
Cooperative Research Centre for Freshwater Ecology
Monitoring River Health Initiative Technical Report Number 21
Environment Australia, 2002
ISSN 1447 1280
ISBN 0 642 54887 0
The River Habitat Survey (RHS) is a river assessment method used in the United Kingdom. The RHS arose from a need to develop a nationally standardised system to measure, classify and report on the physical structure of rivers (Raven et al., 1997). In designing the RHS, consideration was given to seven basic requirements. Thus, the RHS should:
Information derived from the RHS is designed to assist river management decisions and provide an ability to predict the physical features of a stream that would occur under unmodified conditions (Raven et al., 1997). The RHS was conducted in two phases. The first phase involved the design and testing of survey methods as well as sampling of a reference site data base of more than 3000 stream sites across the U.K. (Fox et al., 1998). The second phase is currently under-way and aims to use the RHS in management applications such as catchment management plans, environmental impact assessments, stream rehabilitation plans and wildlife conservation (Raven et al., 1998b).
The RHS uses the physical structure of streams to assess the character and quality of rivers (Table 2.8.1). Statistical theory was used to aid the survey design and the selection of sampling sites throughout the U.K. (Jeffers, 1998b, Fox et al., 1998). At each randomly selected site, a 500m length of river is surveyed. At 50m intervals along this length of river, 10 spot checks are performed. A range of features is recorded at each spot check (Table 2.8.1). To ensure that features and modifications not occurring at the spot checks are included, a sweep up checklist is also completed (Raven et al., 1998b). In addition, cross sectional measurements of water and bankfull width, bank height and water depth (Table 2.8.1) are made at one representative location within the 500m sampling site (Raven et al., 1998b). When used in conjunction with the survey data, these measurements provide information about the geomorphological processes acting on the site (Raven et al., 1997). Map variables such as altitude, slope, planform and geology (Table 2.8.1) are measured in the laboratory. Data are entered onto an electronic database and photos of each sampling site are also stored electronically (Raven et al., 1998b).
Background and map derived data
Channel data
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Bank data (left and right recorded separately)
Other site data
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The RHS takes the view that 'in rivers, habitat is the result of predictable physical processes and so conveniently sits between the forces which structure rivers and the biota which inhabit them' (Harper and Everard, 1998 p395). Thus, the RHS measures variables that represent the character of stream habitats, with the assumption that these variables reflect the geomorphological processes that are acting to form those habitats (Newson et al., 1998b). While geomorphological theory underlies many of the variables collected, the RHS is not strictly a geomorphological survey and specific measurements of geomorphic processes rates are not considered (Newson et al., 1998b).
In RHS, the basis for assessing habitat quality, using the information collected at individual 500m sampling sites is:
Habitat quality assessment can be achieved using four main approaches (Figure 2.8.1). In the first approach, habitat quality is assessed by identifying sites that have pristine and modification free channel characteristics and which are located in areas with a semi-natural land use. In the second and third approaches, reference site groups that represent similar river types are derived, and rarity of individual features or combinations of features is determined within these reference site groups. In the fourth approach, a habitat quality assessment (HQA) score is calculated from the presence and extent of habitat features recorded in the survey (Raven et al., 1998a). The extent of artificial modification in the channel can also be expressed as a separate habitat modification score (HMS, Raven et al., 1998b).
| QUESTION | BASIS FOR ANSWER |
| 1] Is the site outstanding? | Must have pristine (totally unmodified) channel AND exclusively semi-natural land-use |
| 2] Is the site of high habitat quality based on the occurrence of one or more rare features? | Presence of at least one natural feature which occurs in 5% or less of RHS reference sites within a particular geographical region and/or of the same river type |
| 3] Is the site of high habitat quality based on the occurrence of a rare combination of features? | Presence of a combination of natural features which occurs in 5% or less of RHS reference sites within a particular geographical region and/or of the same river type |
| 4] How does the HQA score for the site compare with other sites of the same river type? | Compare it with all HQA scores from RHS reference sites of the same river type, if possible calibrated using a top quality benchmark site |
Although still under investigation, one promising outcome of the RHS is an ability to predict the features that are likely to occur in a stretch of river, from map based variables (Jeffers, 1998a). This predictive ability will potentially assist in identifying the effects of channel modification, as well as enabling targets against which rehabilitation efforts can be measured.
The focus of the RHS on the measurement of habitat quality reflects the underlying assumption that biotic diversity is directly related to habitat diversity (Harper and Everard, 1998). To bridge these two concepts, the RHS uses both a biotope and a functional habitat approach (Newson et al., 1998a). The biotope approach is top down in that the use of habitat units by biota is inferred from a knowledge physical conditions (Newson et al., 1998a). The functional habitat approach is bottom up, in that each habitat is defined from knowledge of the biota that are found in each habitat (Newson et al., 1998a). Thus, it is assumed that by assessing habitat features within this framework the physical influences on biotic composition and the physical influences on habitat formation will both be included.
As mentioned in the previous section, assessment of habitat quality considers the occurrence of habitat features that are of known value to wildlife. The link between these features and wildlife is treated slightly differently in each of the four main approaches. In the first approach, the focus on naturalness reflects the value of this state to wildlife conservation (Raven et al., 1998a). In the second and third approaches, rarity can include features that are of known value to wildlife (Raven et al., 1998a). In the fourth approach, the HQA score considers the presence or absence of features that are of known wildlife interest (Raven et al., 1998a). While there is an empirical basis for the relationships between physical features and biotic structure and process (Resh and Rosenberg, 1984; Harper and Everard, 1998), there is an implicit assumption that the features included in assessments of habitat quality, and in the RHS in general, reflect those relationships. This has not been specifically tested, however, one promising development that may strengthen knowledge in this area is the proposal to link the RHS with the biological assessment program RIVPACS (Wright et al., 1998).