The physical component of river channel (instream) habitat is of acknowledged significance, particularly in headwater streams; furthermore, physical habitats have been heavily impacted by human needs for river services: principally flood defence (channel modification) and water resources (flow regulation). Despite the control exercised on physical habitats by fluvial geomorphology (channel shape, bed material size, bedforms and bars) and flow regime (including the varying hydraulics of flow around these forms), their interaction has hitherto lacked a distinctive spatial formulation and biological validation. This article describes the challenges faced by a need (in both theoretical and practical areas) to understand the detail of physical habitat conditions in stream channels. A number of mesoscale approaches are emerging, both from ecology and geomorphology. We outline the field validation of a ‘habitat hydraulics’ approach to the interaction between river discharge and channel form. Qualitative ‘flow types’ are shown to be representative of discrete hydraulic conditions within mesoscale units of the channel bed described as ‘physical biotopes’. The approach is compared with parallel ecological research on ‘mesohabitats’ and ‘functional habitats’. The extent, pattern and discharge-variability of physical biotopes can be surveyed in the field and used as a spatial guide to biological sampling (in this case for benthic invertebrates). Biological patterns (at the scale sampled here) appear to respond first to the river continuum concept’s longitudinal zonation of the channel, but there is a marked secondary signal in statistical analyses from the pattern of biotopes. Given the promise of the physical biotope approach, its logical extension in predictive mode is via the hierarchical concepts shared by freshwater ecologists and geomorphologists; however, there is little agreement on scale terminology, hierarchical principles and, above all, a truly geo-morphological channel classification, based on reaches, into which mesoscale habitat typologies could be fed. Assuming a relationship between biological diversity and that of physical biotopes it should be the aim of river managers, whether intervening in the channel form or its flow regime, to optimize certain parameters of the pattern of biotopes; these parameters should be a focus for future research. Both the rapid survey and proper description of these patterns will benefit from the application of remote-sensing technology, improved instruments for microscale hydraulic studies and a GIS approach based upon the spatial principles of landscape ecology.

Fluvial geomorphology is rapidly becoming centrally involved in practical applications to support the agenda of sustainable river basin management. In the UK its principal contributions to date have primarily been in flood risk management and river restoration. There is a new impetus: the European Union's Water Framework and Habitats Directives require all rivers to be considered in terms of their ecological quality, defined partly in terms of 'hydromorphology'. This paper focuses on the problematic definition of 'natural' hydromorphological quality for rivers, the assessment of departures from it, and the ecologically driven strategies for restoration that must be delivered by regulators under the EU Water Framework Directive (WFD). The Habitats Directive contains similar concepts under different labels. Currently available definitions of 'natural' or 'reference' conditions derive largely from a concept of 'damage', principally to channel morphology. Such definitions may, however, be too static to form sustainable strategies for management and regulation, but attract public support. Interdisciplinary knowledge remains scant; yet such knowledge is needed at a range of scales from catchment to microhabitat. The most important contribution of the interdisciplinary R&D effort needed to supply management tools to regulators of the WFD and Habitats regulations is to interpret the physical habitat contribution to biodiversity conservation, in terms of 'good ecological quality' in rivers, and the 'hydromorphological' component of this quality. Contributions from 'indigenous knowledge', through public participation, are important but often understated in this effort to drive the 'fluvial hydrosystem' back to spontaneous, affordable, sustainable self-regulation.

The occurrence of two ‘rare’ floods (August 1973, August 1977) in the Plynlimon experimental catchments has confirmed the susceptibility of small upland catchments to summer flooding and provided clues to complications in the geomorphological interpretation of floods in terms of their magnitude and frequency. Magnitude may be treated both in terms of work and effectiveness; the emphasis here is on effectiveness, as revealed by simple surveys. The first Plynlimon flood was more effective on slopes and the second in channels, despite peak discharges of similar return periods and almost identical rates of work revealed by bedload trapping. Effectiveness/frequency studies are likely to require a much more detailed approach, subdividing both the characteristics of the flood and the spatial elements of the affected catchments; a simple slope/channel subdivision is found to be suitable for accounts of effectiveness found in the literature on British floods this century. Effectiveness studies also require regular surveys throughout the recovery period following major flooding; in upland catchments these surveys should concentrate on identifying threshold phenomena and illustrating the relationship between effectiveness and work assessments of magnitude.

This paper addresses the role that fluvial geomorphology might play in the management of sediment-related river maintenance in the U.K. Sediment-related river maintenance refers to the operational requirement of river management authorities to remove deposits of sediment or protect river boundaries from erosion, where these compromise the flood defence levels of service. Using data collected as part of a National Rivers Authority (NRA) Research and Development Project it is possible to identify the geomorphic causes of problems, and engineering responses to sediment-related river maintenance (SRRM) in England and Wales. The Project identified the management problem as widespread and often treated in isolation from the causative processes. Geomorphological guidance is shown to be both relevant and complementary to conventional engineering practice through its ability to identify the cause of a SRRM problem. A methodology for conducting a geomorphological survey, or 'fluvial audit', is presented, which synthesizes historical data on the catchment land-use and channel network, with contemporary morphological maps to present a statement of the location and type of sediment supply, transport and storage within the river basin under scrutiny. The application of geomorphology to two contrasting SRRM problems is explored using case studies from two catchments: the River Sence, a fine sediment system, and the Shelf Brook, a coarse sediment system.

ABSTRACT1. Under definitions of 'strong' sustainability, ecosystem protection and the valuation of natural goods and services figure prominently. These priorities also lie at the heart of the EC Water Framework Directive (WFD).2. This paper explores the ability of fluvial geomorphology to describe, monitor and predict river channel conditions and behaviour at the basin and smaller scales. It also examines how geomorphology can help to create management 'tools' and work in interdisciplinary frameworks with freshwater ecology to assess instream physical habitat.3. Systematic views of river basins and predictive techniques based on system drivers have been popular in fluvial geomorphology for 50 years. System states are seen as resulting from the balance between all relevant processes. However, channel dimensions and forms at a site are much harder to predict and their dynamic adjustment can occur rapidly, exhibiting 'threshold' behaviour.4. Direct human impacts have been a focus of research but long-term monitoring of channel states and adjustments has been neglected; River Habitat Survey offers major opportunities in this respect, even though it was not designed specifically for geomorphological interpretation.5. In the UK, local or 'reach'-scale channel adjustment is widespread, justifying a major empirical survey effort in support of management decisions. Channels are supply-limited in sediment terms, polycyclic in profile, confined within glacial and periglacial sediments and extensively manipulated by engineering modifications. Whilst system properties are vital to the choice of management options over long timescales, conditions on a hierarchy of smaller scales can confound the systematic attempts of geomorphologists to classify and predict channel states.6. Freshwater ecologists have long appreciated the need for a scaled approach to river systems. This paper argues for extensions to shared data collection and analysis programmes before immutable policy becomes established around unfinished management tools. Adaptive management creates a more realistic medium for the use of uncertain geomorphological and ecological predictions.

Recent results from the Institute of Hydrology's hydrometeorological and hydrological studies on water use by forest and grassland confirm earlier predictions of a reduction in water yields following afforestation. This reduction is due primarily to the increased interception losses from forests. This paper shows how the water yield from uplands is related to the relative proportions of land under forest and hill farming, and estimates how water yields will change if a greater proportion of hill land is afforested.

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