SUMMARY 1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio-temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept. 2. At coarse spatial scales, the hierarchical patch dynamics perspective describes each river network as a unique, patchy discontinuum from headwaters to mouth. The discontinuum is comprised of a longitudinal series of alternating stream segments with different geomorphological structures. Each confluence in the steam network further punctuates the discontinuum because the sudden change in stream characteristics can create a ‘gap’ in the expected pattern of downstream transitions. The discontinuum view recognises general trends in habitat characteristics along the longitudinal profile, but creates a framework for studying and understanding the ecological importance of each stream’s individual pattern of habitat transitions along longitudinal, lateral or vertical vectors at any scale. 3. Object-oriented modelling and programming techniques provide a means for developing robust, quantitative simulation models that describe the dynamic structure of patch hierarchies. Such models can simulate how the structure and function of lotic ecosystems are influenced by the landscape context of the system (the ecological conditions within which the system is set) and the metastructure (structural characteristics and juxtaposition) of finer-scale patches comprising the system. 4. A simple object-oriented, multiscale, discontinuum model of solute transformation and biological response along a stream channel illustrates how changing the branching pattern of a stream and the arrangement of its component patches along the downstream profile will result in substantial changes in predicted patterns of solute concentration and biotic community structure. 5. The importance of context, structure, and metastructure in determining lotic ecosystem function serves to underscore Hynes’ (1975) concept that ‘every stream is likely to be individual.’ Advancing the discipline of fluvial landscape ecology provides an excellent opportunity to develop general concepts and tools that address the individual character of each stream network and integrate the concept of ‘uniqueness within the river discontinuum’ into our ecological understanding of rivers and streams.

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Fluvial landscape ecology: addressing uniqueness within the river discontinuum

Preface Acknowledgements Part I. Background: 1. Introduction 2. Types of rivers 3. Non-regime channels Part II. Upstream Controls: 4. History 5. Tectonics and relief 6. Lithology 7. Climate: hydrology 8. Humans Part III. Fixed Local Controls: 9. Bedrock: alluvium 10. Tributaries 11. Active tectonics 12. Valley morphology Part IV. Variable Local Controls: 13. Floods 14. Vegetation 15. Accidents Part V. Downstream Controls: 16. Base-level 17. Length Part VI. Rivers and Humans: 18. Applications 19. Some unintended consequences 20. River impact on ancient civilisations: a hypothesis References Index.

/pdf/river-variability-and-complexity-57gp2c8tll.pdf

River Variability and Complexity

The etymology and historic usage of such terms as anabranch', anastamose' and braided' within river science are reviewed. Despite several decades of modern research to define river channel typologi ...

Multichannel rivers : their definition and classification

Relative influences of the river channel, floodplain surface, and alluvial aquifer on simulated hydrologic residence time in a montane river floodplain

Meaningful iteration between place-based knowledge of rivers and generalised, theoretically-framed understandings is a significant challenge in river science and management. How can we communicate knowledge of the inherent complexity of river systems in light of managerial quests for simple, easy-to-apply frameworks that can be used by a wide range of practitioners, such that we can meaningfully transfer experiences in river science and management from one situation to another? Identification, definition, classification and naming are vital parts of this process. In a sense, a name is like a 'brand', for which a consistency of product is expected. The River Styles Framework is a flexible, open-ended approach to river science and management. The Framework applies a set of hierarchical principles to differentiate reaches, interpret their process-based behaviour and examine interactions between patterns of reaches at the catchment scale. Here we outline an evolution and tightening of the Framework to better communicate how to identify and name types of river at the reach scale. Like the River Styles Framework itself, the naming convention applies hierarchical procedures, starting at the valley setting scale, and incorporating analyses of river planform, channel and floodplain landforms (geomorphic units) and bed material texture. Using a series of examples from around the world, we show how this naming convention can be applied to name river reaches and can be adapted to particular purposes in a consistent, readily communicable manner. We outline various challenges that are faced in managing the use of such a naming convention.

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What's in a name? A naming convention for geomorphic river types using the River Styles Framework.

Bedrock-controlled channel systems exhibit considerable morphological variation. Both bedrock-influenced and alluvial morphological units coexist to form a system of changing channel patterns in response to changes in the relative influence of the controlling process variables. This article investigates the morphological composition of the bedrock-influenced Sabie River, Mpumalanga Province, South Africa, mapping 25 km of river channel at the scale of individual morphological units. Cluster and discriminant analyses define objective reach–scale "channel type" assemblages based on morphological unit composition. A number of robust clusters emerged that could be broadly classified into five channel types, namely, bedrock anastomosed, mixed anastomosed, pool-rapid, braided, and alluvial single-thread. The cluster analysis revealed that these channel types fit on a continuum from bedrock-dominated channels to fully alluvial systems. Each channel type could also be characterized by a certain set of "dominant" morphological units, which changed from bedrock-influenced at one end of the continuum (bedrock anastomosed, pool-rapid) to alluvial deposits at the other (braided, alluvial single-thread). An investigation of the role of controlling process variables in defining these channel types revealed a broad link between the degree of bedrock influence and the amount of available energy within the system as defined by indices such as the flow regime and water-surface slope variation. It is clear that the bedrock-dominated channel types are characterized by energy levels in excess of those accepted for alluvial systems, and an extended river classification is presented for the Sabie River that includes these bedrock channels. The mixed anastomosing channel type on the Sabie River is characterized by higher available energy levels than braided or alluvial single-thread reaches. As such, it appears to be a higher-energy example of an anabranched system, probably formed as a result of sediment accumulation on top of a high-energy bedrock anastomosed channel template.

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S. O'Regan

Papers

Morphological Classification of Fluvial Environments: An Investigation of the Continuum of Channel Types