Hierarchical Framework and WFD
Links between the Methodology described in Multi-scale, Hierarchical Framework and the WFD River Typology and Water Bodies, and CEN standards
According to Annex II, pr. 1.1.1(ii), EU Member States have differentiated the “relevant surface water bodies” within the river basin district according to systems A or B identified in section 1.2 of the same Annex. These two systems, which require different types of information, are supposed to be equivalent in their results. An analysis carried out by the Commission (with the support of EEA) has shown the discrepancies in number of river typologies and on their type among Member States. An ad hoc task of the working group ECOSTAT of the Common Implementation Strategy (CIS) for the WFD has analysed and grouped all Member State types in macrotypologies to facilitate their comparability in terms of ecological status of European Rivers. The representativeness of this macrotypology system has still to be proved. The river typology that is being developed under the above-mentioned group, mostly following the system A approach, currently defines 14 river types (Table 1.1) based upon the altitude, area and geology of the river’s catchment. This is a simple, high-level classification within which more detailed classifications and assessments devised by member states may fit. Our approach to describing and assessing the hydromorphology of European Rivers is multi-scale and process based, but it maps onto the high level classification presented in Table 1.1 in the following ways:
- At the catchment level of our multi-scale framework, catchments are characterised according to their altitude, area and geology, using threshold values that match those listed in Table 1.1 (see section 5.2). These catchment properties are then used as catchment-scale indicators in the hydromorphological indicators (section 8.2) that feed into the hydromorphological assessments described in chapter 9.
- At the regional scale, the framework differs from the WFD typology in the use of biogeographic regions as opposed to the WFD ecoregions. Biogeographic regions summarise the unique combinations of climate, topography and terrestrial vegetation communities that are present in Europe, which are the primary controls on hydromorphological processes, whereas the ecoregions in the WFD typology are based on aquatic ecological communities rather than reflecting the controls on hydromorphology. As the typologies should be developed on the hydromorphological characteristics per se, our approach seems to be more consistent with the rationale of the WFD than the latter one, which seems to be based on a slightly circular approach.
- At the reach scale, 22 river types are identified (Chapter 7), based on their level of confinement, planform, bed material calibre and typical valley gradient. These characteristics provide a further link with the WFD river types, since level of confinement and valley gradient typically vary with topographic setting (altitude). The 22 river types are also related to 10 floodplain types that once more reflect valley confinement but also typical ranges of bankfull unit stream power (a function of bankfull discharge, gradient and channel width). This provides a further link with topographic setting and also links to river size. These linkages are discussed in section 7.5. The river types are characterized by an assemblage of geomorphic units, which represent a fundamental component of the characterization of the channel and the river corridor. Geomorphic units and lower spatial scales (hydraulic units, river elements) provide a fundamental link between morphological and biological conditions, as they provide information on presence and diversity of physical habitats. Therefore, classification of river types also provides fundamental information on these aspects.
WFD water bodies and CEN standards
The multi-scale framework proposed in this document has relevance to the CEN (2004) guidance on the assessment of hydromorphology and also the definition of WFD water bodies. However, it is important to understand that the REFORM multi-scale framework aims to be process-based with an explicit focus on understanding hydromorphology in a dynamic way that takes account of changes through time and across spatial scales. This is a different aim from the CEN (2004) guidance, which provides a protocol for ‘recording the physical features of rivers’ rather than providing any process-based understanding. It is also different from the WFD water bodies, which are management units that should be homogeneous with respect to the pressures they are affected by and should not contain elements in a different ecological status. Therefore, further considerations than hydromorphological factors influence their identification. In relation to WFD water bodies, application of the REFORM framework to delineate segments will generate boundaries that often correspond to WFD water body boundaries. Furthermore, there is no reason why these segments should not be subdivided using additional boundaries that correspond to those of water bodies. The European Standard ‘Water Quality – Guidance standard for assessing the hydromorphological features of rivers’ (CEN, 2004) sets a ‘survey unit’ assessment into the context of the WFD river typology (types A and B, see section 1.4.1). Each catchment is subdivided into subcatchments or subareas (called ‘river types’), based mainly on area, altitude and geology, reflecting the WFD typology. The river network within these subareas is then subdivided into ‘reaches’ based on similarity of geology,valley form, slope, planform, discharge (specifically input of significant tributary / change in stream order), land use, and sediment transport (lake, reservoir, dam,major weirs). Finally reaches are subdivided into survey units. The REFORM hierarchical framework uses a more standard geomorphological terminology for the spatial units and, although there is some correspondence in delineation criteria, the procedures recommended for the REFORM framework include a more comprehensive and explicitly process-based set of criteria. Thus, the REFORM framework defines catchments and landscape units which are not dissimilar to the WFD river types. It also defines segments and reaches, where the segments have many similarities to to the CEN (2004) reaches but exclude planform as a criterion. This is because planform and other river channel characteristics can vary widely over much shorter river lengths than a segment. These shorter river lengths of similar river channel characteristics are defined as reaches in the REFORM framework. Thus in the REFORM framework, segments describe river lengths subject to a set of broadly consistent external controls on river geomorphology (valley confinement and gradient, land cover, flow amount and regime, etc. ) whereas reaches refer to river lengths with similar local geomorphological controls and river channel characteristics (planform, bed and bank material and structure,assemblage of geomorphic units, etc.). The rules for delineating landscape units, segments and reaches are detailed in section 4 of this report.