Abstract:This paper explores the signi®cance of groundwater dominance in the surface water system through a combination of review and an exposition of the general hydrology, ecology and geomorphology of rivers draining the main UK aquifers. Groundwater dominance is shown to vary according to the nature of the aquifer lithology, the mechanism of groundwater:surface water interaction and the scale at which one examines this interaction. Using data derived from a range of studies including the UK Environment Agency River Habitat Survey and the UK Institute of Freshwater Ecology RIVPACS invertebrate database it is shown that the nature of the aquifer and mode of in¯uent discharge strongly control the hydrological and ecological characteristics of the environment but that a speci®c groundwater ecology or hydrogeomorphology is masked by the overriding controls exerted by aquifer geology and catchment topography. Despite this, it is clear that river systems dominated by groundwater¯ows have speci®c hydrological characteristics and management issues that require holistic, multidisciplinary approaches that recognise the signi®cance of groundwater and the nature of the interaction with the surface water environment. Copyright # 1999 John Wiley & Sons, Ltd.KEY WORDS groundwater dominance; hydrogeomorphology; ecology; water quality GROUNDWATER AND SURFACE WATER RESEARCH The physical characteristics of groundwater and surface water have been considered to be distinctive, although more recent studies have described surface water as a`perched groundwater aquifer ' (Shand et al., 1995) in recognition of the isotopic history of both components. The broad distinctions however, are generally considered to be a stable¯ow and thermal regime and a stable chemical regime that re¯ects the underlying aquifer geology. Groundwater research has until recently been dominated by two areas of scienti®c enquiry, hydrogeology and hydrology, the former concentrating on the quality and quantity of subterranean transmission of water as a resource, the latter concentrating on the maintenance of low ows and the stability of the¯ow regime (Younger, 1995). A similar research model exists in the study of geomorphology and groundwater, which has traditionally been dominated by morphogenetic studies of karst landscapes, that focus attention on the role of chemical degradation of the land surface and the features associated with cavity¯ows within the vadose zone (Brown, 1996). In applied hydrology, the role of groundwater in sustaining low¯ows has provided the focus for much recent research which has identi®ed the clear link between low¯ow regime and the nature of the soils and lithology in the upstream catchment (Gustard et al., 1992). Ecological studies of groundwater rivers have also tended to be dominated by research in carbonate (chalk) groundwater systems (Berrie, 1992).Recently, the aquifer±river`boundary' has begun to blur as the scienti®c community recognises the importance of river±aquifer interactions. This has been driven by recognition of the ...

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ABSTRACT1. Characterizing the physical structure and assessing the habitat quality of rivers is becoming more important in the context of environmental planning, appraisal and impact assessment. In Europe the EC Water Framework Directive requires assessment of hydromorphological quality in establishing the ecological status of rivers.2. Hydromorphological quality assessment plays a crucial role in the Directive because it is used to determine 'undisturbed' and 'heavily modified' conditions of rivers. A common approach is needed to ensure comparability of classification outputs between EU Member States.3. Three hydromorphological and river habitat assessment methods, developed in Germany, France and the UK, were used for qualitative cross-comparison in 2001. Each was tested on river stretches in North-East France and in the French Pyr! e en! e ees.4. The type of features recorded by all three methods was broadly similar, but differences in survey strategy, data collection, and analysis resulted in variations in quality assessment. Different interpretation of what constitutes 'undisturbed conditions' has a major impact on outputs. There are also scale-related problems in comparing the different methods.5. Despite these differences, there is sufficient common ground to allow refinement of the methods and achieve better harmonization. This will require technical agreement on the terminology and definition of features, and a reach-based hierarchical framework for survey and reporting.6. An impact-based assessment centred on deviation from undisturbed hydromorphological conditions could be the best option for a simple, practicable classification scheme, but agreement is needed on the criteria used to define and calibrate such a system.7. Habitat quality assessment using the presence and diversity of features as a basis for classification needs to be improved. Assumptions used for diagnostic interpretation need to be tested

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The reduction of the biomass of three main problem species of submerged aquatic macrophytes was proportional to the light at the stream surface both under artificially shaded sections of stream and in naturally shaded areas when compared to the biomass in adjacent open and unshaded sections of stream. The effect of marginal vegetation in varying the shading effect given to streams of differing width and orientation are described. It is recommended that light should be reduced to about half that presently available in the open, by shading from marginal vegetation but it is warned that too much shade is detrimental to the fish populations of the stream and leads to accentuated local accumulations of leaves. The long term effects are considered but it is expected that partial shading will increase the diversity of submerged plant species. It is suggested that the practice of stream realignment is discontinued and that the natural tendency of streams to create their own meandering channels is allowed but within some defined and generally acceptable framework.

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