Towards a harmonized approach for hydromorphological assessment of rivers in Europe: a qualitative comparison of three survey methods

1. Characterizing the physical structure and assessing the habitat quality of rivers is becoming more important in the context of environmental planning, appraisal and impact assessment. In Europe the EC Water Framework Directive requires assessment of hydromorphological quality in establishing the ecological status of rivers. 2. Hydromorphological quality assessment plays a crucial role in the Directive because it is used to determine ‘undisturbed’ and ‘heavily modified’ conditions of rivers. A common approach is needed to ensure comparability of classification outputs between EU Member States. 3. Three hydromorphological and river habitat assessment methods, developed in Germany, France and the UK, were used for qualitative cross-comparison in 2001. Each was tested on river stretches in North-East France and in the French Pyrénées. 4. The type of features recorded by all three methods was broadly similar, but differences in survey strategy, data collection, and analysis resulted in variations in quality assessment. Different interpretation of what constitutes ‘undisturbed conditions’ has a major impact on outputs. There are also scale-related problems in comparing the different methods. 5. Despite these differences, there is sufficient common ground to allow refinement of the methods and achieve better harmonization. This will require technical agreement on the terminology and definition of features, and a reach-based hierarchical framework for survey and reporting. 6. An impact-based assessment centred on deviation from undisturbed hydromorphological conditions could be the best option for a simple, practicable classification scheme, but agreement is needed on the criteria used to define and calibrate such a system. 7. Habitat quality assessment using the presence and diversity of features as a basis for classification needs to be improved. Assumptions used for diagnostic interpretation need to be tested and existing databases linked more closely with biological and geomorphological survey information. Copyright © 2002 John Wiley & Sons, Ltd.