How to make river assessments comparable: A demonstration for hydromorphology

• Multiple ecological assessments can be harmonized and integrated with a multi-criteria decision analysis approach.
• Hydromorphological river assessment methods from Switzerland, Germany and the US are integrated with the proposed approach.
• Harmonized methods facilitate the direct comparison of method-specific attributes, endpoints and aggregation schemes.
• Integrated methods produce comparable results across frontiers, maintaining data continuity with original assessments.
• The gap between river quality assessment and management can be bridged with the proposed procedure.

River monitoring and assessment programs are important tools to quantify the condition of river ecosystems, identify deficits, and provide preliminary indication of how to improve them. But, they are limited in delivering comparable assessment results across national or transnational borders, aggregating site-specific assessments into broader scale assessments, and supporting river management decisions. We present a multi-criteria decision analysis approach for improving the comparability of ecological assessment methods of different origin and for combining these assessments into a joint procedure. The approach consists of seven consecutive steps. The most central ones concern the hierarchical allocation of ecological assessment endpoints, and the harmonization of the scoring procedure of attributes (ecological indicators or assets) to a common scale from 0 to 1. We demonstrate the approach integrating three programs developed to assess the hydromorphological river condition in Switzerland, Germany, and the USA. In our example, the integrated assessment produces comparable results for the whole range from natural to impacted rivers, while data continuity with original assessments was maintained. Our approach provides a common assessment standard due to the definition of the minimum amount of information required, is flexible regarding measurement and assessment endpoints, and bridges the gap between river quality assessment and management.