Characterising physical habitats and fluvial hydromorphology: A new system for the survey and classification of river geomorphic units

This paper presents a system for the survey and classification of geomorphic units (GUS, geomorphic units survey and classification system) aimed at characterising physical habitats and stream morphology. The method is embedded into a multiscale, hierarchical framework for the analysis of river hydromorphological conditions. Three scales of geomorphic units are considered (i.e., macro-units, units, sub-units), organised within two spatial domains (i.e., bankfull channel and floodplain). Different levels of characterisation can be applied, depending on the aims of the survey: broad, basic, and detailed level. At each level, different, complementary information is collected. The method is applied by combining remote sensing analysis and field survey, according to the spatial scale and the level of description required. The method is applicable to most of fluvial conditions, and has been designed to be flexible and adaptable according to the objectives (e.g., reach characterisation, assessment, monitoring) and available data (e.g., image resolution). The method supports integrated hydromorphological assessment at the reach scale (e.g., the Morphological Quality Index, MQI) and therefore contributes to better establishing links between hydromorphological conditions at the reach scale, characteristic geomorphic units, and related biological conditions.