Characterisation of river reaches: The influence of rock type

Abstract

Abstract The characterisation of geomorphological, hydrological and ecological properties of river systems represents a popular and important research direction in fluvial studies, particularly with regards to contemporary international environmental legislation. Recent research has also drawn attention to the unique ecological value and high level of environmental threat associated with groundwater-fed catchments, emphasising the importance of underlying rock type in the development of river typologies. A standardised field method for assessing physical river habitat quality known as River Habitat Survey (RHS) has been developed in the UK and provides an extensive data set of surveyed river reaches. This paper uses information from the RHS database to explore the influence of rock type on reach-scale sedimentological and vegetation characteristics. A range of reach-scale indices are derived from the RHS database for analysis, supported by landscape variables which provide detail on the catchment context. River reaches were then classified into broad lithological groups which reveal statistically significant differences along two key gradients in environmental conditions: an energy gradient associated with stream power and sediment calibre which is inversely related to in-channel vegetation roughness, and a riparian vegetation gradient that also reflects the inverse relationship between instream and riparian vegetation cover. The results emphasise the differences in reach-scale geomorphological and ecological structure between groundwater-fed and surface water-fed catchments, supporting the inclusion of underlying reach lithology in the development of river typologies.