The Geomorphic Units survey and classification System (GUS)

The Geomorphic Units survey and classification System (GUS) has been developed for the survey and classification of geomorphic units in streams and rivers, suitable to integrate the hydromorphological assessment at the reach scale (e.g. the Morphological Quality Index, MQI), and therefore to better establish links between hydromorphological conditions at the reach scale, characteristic geomorphic units and related biological conditions. The system includes 3 different spatial scales (i.e. Macro-units, Units, Sub-units) organized in 3 spatial contexts (i.e. Instream, Marginal, Floodplain) and is structured in 3 levels of description (i.e. Broad, Base, Detailed). At each level, different specific information is collected: from the simple census of units and their number, to the measurement of units size and the survey of specific unit characteristics (e.g. sediment, hydrology, vegetation). The method is applied by combining remote sensing analysis and field survey, according to the spatial scale and the level of description. It is applicable to most of fluvial conditions (e.g. from small streams to large rivers), and has been designed to be flexible and adaptable (i.e. including mandatory and/or optional sections) on the basis of specific objectives (e.g. reach characterization, assessment, monitoring) and available data (e.g. image resolution).