M. González del Tánago

A multi-scale hierarchical framework for developing understanding of river behaviour to support river management

This paper introduces this special issue of Aquatic Sciences. It outlines a multi-scale, hierarchical framework for developing process-based understanding of catchment to reach hydromorphology that can aid design and delivery of sustainable river management solutions. The framework was developed within the REFORM (REstoring rivers FOR effective catchment Management) project, funded by the European Union’s FP7 Programme. Specific aspects of this ‘REFORM framework’ and some applications are presented in other papers in this special issue. The REFORM framework is founded on previous hierarchical frameworks, sixteen examples of which are reviewed. However, the REFORM framework has some particular properties that reflect the European context for which it was developed. The framework delineates regional landscapes into nested spatial units at catchment, landscape unit, segment, reach, geomorphic unit and finer scales. Reaches, regardless of their ‘naturalness’, are assigned to a river type based on valley confinement, planform and bed material. Indicators are quantified at each spatial scale to feed three groups of assessments. First, contemporary indicators at reach and geomorphic unit scales investigate present processes, forms and human pressures within each reach. These feed assessments of present reach hydromorphological function/alteration, including whether the reach is functioning appropriately for its type; riparian corridor function and alteration; and hydromorphological adjustment. Second, indicators at catchment to segment scales investigate water and sediment production and delivery to reaches and how these are affected by human pressures now and in the past. These are used to construct an inventory of changes over space and time. Third, historical reach and geomorphic unit scale indicators are used to construct the trajectory of reach-scale changes. Contemporary reach-scale assessments, space–time inventory, and trajectory of changes are then combined to establish how river reaches of different type, subject to different human pressures, and located in different environmental contexts behave in response to changes at all considered spatial scales. These support forecasts of the likely responses of reaches to future scenarios (e.g., changes in climate, land cover, channel interventions).

Classification of river morphology and hydrology to support management and restoration

As part of an hierarchical, multi-scale, hydromorphological framework for European rivers that has been developed within the REFORM project, a procedure for classifying rivers has been devised. The procedure includes components that categorise river channel morphology, floodplain morphology, flow regime, and groundwater—surface water interactions, and is designed for operational use in the context of river management. Channel morphology is classified at a first level by a basic river typology interpreted using remotely sensed images, and at a second level by an extended river typology that integrates information from field observations. Floodplains are classified by adopting the Nanson and Croke typology with specific reference to the types of floodplain that are most likely to be encountered widely across Europe. Nine flow regime types are identified using a series of hydrological indicators. Finally, where groundwater has a significant influence on river flows, a range of potential groundwater—surface water interactions are identified reflecting the morphological river type and its geological and climatic setting. Within the REFORM project, the river typology has been tested using case studies representative of a wide variety of European catchment conditions. Four case studies are used to illustrate the classification procedure and to discuss its main strengths and limitations.

Diagnosing problems produced by flow regulation and other disturbances in Southern European Rivers: the Porma and Curueño Rivers (Duero Basin, NW Spain)

This research presents an analysis of river responses to flow regulation and other disturbances over time. The study was conducted in the Porma and Curueño rivers, using the hierarchical multi-scale process-based framework developed within the European REFORM Project. The characterisation of the rivers at the landscape unit, segment and reach scales under current and past conditions by different hydro-morphological indicators has provided a useful approach to (1) identify where and how main channel adjustments have occurred, (2) establish causal relationships at different scales and (3) discuss potential future scenarios and restoration strategies. Reduction of mean annual flow at the catchment scale has been observed and associated with forest expansion in the uplands. Channel narrowing, braiding reduction and riparian vegetation encroachment have occurred along both rivers, although with variable intensity among the reaches as a result of their landscape setting. Damming and flow regulation of the Porma River have been directly associated with locally accelerated narrowing, vertical bank profiles, the absence of bare gravel bars and no Salicaceae recruitment observed in certain reaches. The vertical bank profiles and the absence of in-channel bare gravel deposition forms are good indicators of sediment starvation downstream from the dam. The findings from this study suggest the importance of multi-scale approaches to assess the impacts of human-induced, short-term changes (e.g., flow regulation by dams and reservoirs) in the context of other disturbances at broader scales (e.g., climate and land cover changes) and their utility in the diagnosing problems and the proposal of restoration measures.

Indicators of river system hydromorphological character and dynamics: understanding current conditions and guiding sustainable river management

A set of multi-scale, process-based hydromorphological indicators of river character and dynamics has been developed to support river management and restoration activities. Indicators are selected to represent key hydromorphological processes at each spatial scale, i.e., catchment, landscape unit, river segment, river reach. Their evaluation allows identification of the cascade of these processes through the spatial units and the historical changes in their propagation as a consequence of natural or human induced hydromorphological changes. The approach is deliberately open-ended so that it can be adapted to local environmental conditions and management, and it can make the most effective use of available data sets. The indicators support assessments of the current condition of the river and its catchment; past changes within the catchment and their impacts on river reaches. Therefore, they represent a sound foundation for assessing the way the catchment to reach scale units and the geomorphic units within reaches may respond to future natural changes or human interventions. The procedure is illustrated using the example of the river Frome (UK).

Development and application of a multi-scale process-based framework for the hydromorphological assessment of European rivers

Many current river assessment methods emphasise the river ‘reach’ scale (a fixed length of river of the order of a few hundred meters) and provide a wealth of useful information that characterises the river corridor at the time of survey. However, they also have several limitations when they are used for understanding physical processes and causes of river alteration. A multi-scale, process-based framework is needed, which incorporates reach scale information into a larger spatial and temporal assessment of the controls on reach dynamics, and a process-based interpretation of the contemporary status of reaches, their historical dynamics and their likely future trajectories of adjustment. This paper reports on the early development and application of a multi-scale framework that is applicable to European rivers and is aimed at improving understanding of hydromorphological and ecological processes and their interactions. This ongoing research is part of the EU-funded project REFORM (REstoring rivers FOR effective catchment Management) which has the overall aim to provide a framework for improving the success of hydromorphological restoration measures in a cost-effective manner, targeting the ecological status or potential of rivers.