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We propose a conceptual model of vegetation–hydrogeomorphology interactions and feedbacks within river corridors (i.e. river channels and their floodplains) that builds on previous similar hydrogeomorphologically centred models by: i. incorporating hydrogeomorphological constraints on river corridor vegetation from region to reach scales; ii. defining five dynamic river corridor zones within which different hydrogeomorphological processes are dominant so that plants and physical processes interact in different ways, and considering the potential distribution of these zones longitudinally from river headwaters to mouth, laterally across the river corridor, and in relation to different river planform styles; iii. considering the way in which vegetation-related landforms within each zone may reflect processes of self-organization and the role of particular plant species as physical ecosystem engineers within the context of the dominant hydrogeomorphological processes; iv. focussing, in particular, upon a ‘critical zone’ at the leading edge of plant–hydrogeomorphological process interactions that is located somewhere within the area of the river corridor perennially inundated by flowing water (zone 1) and the area that is frequently inundated and subject to both sediment erosion and deposition processes (zone 2). Within the critical zone some plant species strongly influence the position and character of the margin between the river channel and floodplain, affecting channel width, channel margin form and dynamics, and the transition from one river planform type to another; and v. considering the vegetated pioneer landforms that develop within the critical zone and how their morphological impact needs to be scaled to the river size. The model is illustrated using three example reaches from rivers within different biogeographical zones of Europe, and its potential application in the context of river management and restoration/rehabilitation is discussed.

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 est

This report assembles evidence from published sources and available data sets to demonstrate how vegetation interacts with hydromorphology to constrain numerous aspects of river morphology and dynamics, so providing a vital component of any river management and restoration efforts.

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.