A representative sample of habitat features from rivers in the UK and Isle of Man has been generated by River Habitat Survey (RHS) during 1994(RHS) during -1997. . This baseline reference provides a sound basis for describing the physical character and assessing the habitat quality of 500 m lengths of river shown on 1:250000 scale maps and classified for water quality purposes.
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The use of a standard field method, with associated accreditation controls, stratified random sampling strategy and computer database all provide a robust foundation for habitat quality assessment. The outputs have a sound statistical basis and satisfy the practical needs of river management as well as providing policy-makers with relevant information.
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Within the UK, sites of national, regional, or local importance for wildlife habitat quality can be determined, using criteria based on the presence of features of known conservation interest. The occurrence, individually, of rare features, or rare combinations of representative features, can also be used to identify sites of particular regional or local importance for their river habitat quality.
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A habitat quality assessment (HQA) scoring system, based on features considered to be of wildlife importance can be used to compare sites surveyed by the RHS method. However, for meaningful results this comparison must involve the same river type.
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For completeness, the HQA scores for a given river type can be calibrated using known top quality sites. For individual sites, HQA scores should be used in conjunction with a measure of artificial modification to the channel. A simple Habitat Modification Score (HMS) system can be applied to RHS data for this purpose.
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RHS can be further developed to define and predict the likely distribution of sites which satisfy the known habitat requirements of certain aquatic and riparian species. It can also provide the basis for better understanding of the spatial relationships between geomorphological processes and habitat type.