The Morphological Units System (MUS): development of a new method for the classification and survey of fluvial morphological units

The assessment of stream hydromorphological conditions is required for the classification and monitoring of water bodies by the Water Framework Directive 2000/60, and is useful to establish links between physical and ecological conditions. A recent review of hydromorphological assessment methods carried out within the context of the EU project REFORM (Restoring rivers FOR effective catchment Management) has outlined that existing physical habitat assessment methods, widely used across Europe for the WFD, are affected by a series of important limitations, including the fact that there is a notable difference between the terminology used and the present geomorphological state of the art. The aim of this research is to develop a new system for the survey and classification of morphological units in streams and rivers, suitable to integrate the Morphological Quality Index (MQI) recently developed in Italy, and therefore to better establish links between hydromorphological conditions at reach scale, characteristic morphological units and related ecological conditions. The system under development, named MUS (Morphological Units survey and classification System), includes 3 different spatial scales (i.e. Macro-units, Units, Sub-units) which are organized in 3 spatial contexts (i.e. Instream, Marginal, Floodplain) and is structured in 3 levels of description (i.e. Broad, Base, Detail). At each level, different specific information is collected, corresponding to an increasing level of detail: 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 (at wider spatial scales and broader levels of description) and field survey (at the more detailed levels). It is applicable to most of fluvial conditions (e.g. from small streams to large rivers, confined or unconfined valley settings), and has been developed 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). The compilation of a “glossary” has been the first part of the method development, in which all morphological units have been defined based on existing literature. Then, a first version of the survey sheets has been developed and applied to some Italian rivers. Finally, some examples of possible analyses deriving from the application of the method are presented.