Sediment Regime and River Morphodynamics

by

Jon Tunnicliffe, Gary Brierly

• LAST REVIEWED: 27 October 2016
• LAST MODIFIED: 27 October 2016
• DOI: 10.1093/obo/9780199363445-0061

Introduction

Morphodynamics is the study of the feedbacks between the geomorphic processes that transfer sediment and the resultant sediment-transferring landform, over some characteristic timescale. Perhaps the quintessential example of morphodynamics is that of a dune, where sand grains borne by wind or water accumulate in rhythmic waves. As the grains are swept up the back of a wave and avalanche over the front, the dune form migrates. The resultant shape and progradation rate of the dune is a function of the strength and turbulence of the flow, the nature of the sediment supply, and the imposed bed slope. Experimental work on dunes carried out by Felix Exner in the 1920s inspired a thread of research the now underpins the broad and diverse field of morphodynamics. The field of study has moved from mainly descriptive to highly quantitative analyses. It encompasses a range of geomorphic environments, from hillslopes and rivers to estuaries to deep marine channels. This review links the notion of a river functioning under a relative surplus or deficit of sediment supply, to the resulting regime of river process and form. In a paper entitled “Coastal Depositional Landforms: A Morphodynamic Approach,” L. Donelson Wright and Bruce G. Thom defined morphodynamics, in the coastal geomorphology context, as “the mutual adjustment of topography and fluid dynamics involving sediment transport” (Progress in Physical Geography 1.3: 412–459, September 1977). The paradigm has been adopted in fluvial geomorphology as a framework for describing the equilibria that evolve under different governing conditions, such as climate (variation in magnitude and frequency of river discharge), vegetation, and the nature and available quantities of the sediment substrate. Detailed process insights into river morphodynamics have come from laboratory flume work, field studies, as well as numerical simulations of sediment transport processes. Our understanding of the relationships between river form, historic conditioning of the landscape, and variables such as valley gradient, the relative concentration of water and sediment supply, and sediment characteristics has evolved considerably as a result of this work. An important application of river morphodynamic theory has been the assessment and prediction of channel change with a step change in governing variables. For instance, the nature of river response following dam removal, heightened sediment supply following placer mining, or changing runoff characteristics after land clearing can be most clearly understood using a morphodynamics framework. Rivers will have a characteristic response in planform character (e.g., sinuosity, channel bifurcation, floodplain extent), bed median grain size, channel cross-section geometry, and local slope in response to this disturbance. There may be a multiplicity of system configurations that satisfy the requirements for stability. There is also a characteristic timescale of response and relaxation. This review first considers the problem of classifying river types, based on essential morphodynamic feedbacks that shape the channel morphology. The next sections review literature that deals with boundaries and bedforms, as they relate to initiation and maintenance of those morphodynamic feedbacks. The following three sections consider the cases of rivers where erosion tends to exceed the supply of sediment, rivers that are close to some kind of an equilibrium, and rivers that are typically overloaded with sediment, resulting in lateral instability, aggradation, and sediment storage. The final sections consider intermittent or ephemeral streams, highlighting some instances where human activities have impacted upon the morphodynamic functioning of river systems.

General Overviews

There are a number of notable works that provide a broad perspective on river morphodynamics, as they pertain to river sediment regime. Schumm, et al. 1987, a notable work in experimental geomorphology, provoked much interest in morphodynamics, and many of the ideas raised in this book have been pursued in more detail in the years since its publication. Publications from two conferences, Gravel Bed Rivers and the IAHR Symposium on Coastal and Estuarine Morphodynamics that occur every five years and two years, respectively, such as Hey, et al. 1982 and Seminara and Blondeaux 2001, have consistently provided benchmark papers on key theoretical and applied questions relating to river morphodynamics from a range of perspectives, such as engineering, ecology, and natural resources management. More recent reviews of the trajectory of morphodynamic research include Wohl 2013, a comprehensive set of papers; Garcia 2008, an ASCE manual; and Church and Ferguson 2015, a concise summary of river morphodynamics. Broad introductions to the topic can be found in Knighton 1998 and Fryirs and Brierley 2013. Parker 2004 is strongly recommended as a practical guide for hands-on simulation and analyses.

• Church, M., and R. I. Ferguson. 2015. Morphodynamics: Rivers beyond steady state. Water Resources Research 51.4: 1883–1897.

  DOI: 10.1002/2014WR016862

  Church and Ferguson provide an authoritative summary of the last fifty years of research into river morphodynamics and sediment transport, emphasizing research reported in Water Resources Research, a journal that has played a central role throughout the development of many important advances in the field. The authors do an excellent job of tracing the trajectory of scientific thinking on problems such as river equilibrium, frequency and magnitude, river classification, and applied management issues.

• Fryirs, K. A., and G. J. Brierley. 2013. Geomorphic analysis of river systems: An approach to reading the landscape. Chichester, UK: Wiley.

  This general overview of river processes and landforms, written at undergraduate level, draws on new research on the topic of morphodynamics and the feedbacks that sustain river sediment regime. Field-based procedures used to analyze any given reach of river are appraised alongside conceptual and theoretical principles.

• Garcia, M., ed. 2008. Sedimentation engineering: Processes, measurements, modeling, and practice. Reston, VA: American Society of Civil Engineers.

  This provides a practical overview of many applied aspects of sediment transport and morphodynamics. Offers good summaries of fluvial geomorphology principles as they apply to engineering and management of river systems. Research progress over the last the last fifty years is summarized, with useful perspectives on the state of the practice.

• Hey, R. D., J. C. Bathurst, and C. R. Thorne, eds. 1982. Gravel-bed rivers: Fluvial processes, engineering, and management. Chichester, UK: Wiley.

  This benchmark collection of papers came from the first Gravel Bed Rivers Workshop, which brought together international scientists and engineers to discuss the state of the art in river science. The workshops have continued, and the seven books (so far) in this series provide definitive references on a broad range of topics related to river process geomorphology, engineering, and management.

• Knighton, D. 1998. Fluvial forms and processes a new perspective. 2d ed. Hoboken, NJ: Taylor and Francis.

  This readily accessible text presents an overview of controls upon fluvial forms and processes. Empirical and theoretical approaches are combined to provide a summary of differing approaches to assessment of channel adjustment.

• Parker, G. 2004. 1D Sediment transport morphodynamics with applications to rivers and turbidity currents.

  This immensely practical resource consists of a set of Powerpoint slides and Excel spreadsheets that outline an engineering approach to morphodynamics. Numerous examples provide application and clear exposition of the essential principles of sediment transport as they relate to rivers and turbidity currents. Parker’s influence on the field has been exceptional, and these slides provide good insight into his (and his collaborators’) techniques for simulation and analysis.

• Rowiński, P., and A. Radecki-Pawlik, eds. 2015. Rivers: Physical, fluvial and environmental processes. GeoPlanet: Earth and Planetary Sciences. Cham, Switzerland: Springer International.

  This text relates sediment transport principles to process-form interactions in river systems, with chapters written by experts in various sub-disciplines in river geomorphology.

• Schumm, S. A., M. P. Mosley, and W. E. Weaver. 1987. Experimental fluvial geomorphology. New York: Wiley.

  This important text demonstrates how laboratory and modeling applications can be used alongside field investigations of process relationships in river systems. Particular emphasis is placed upon drainage basin evolution, hydrology, river-channel morphology, and sedimentology. Insights into controls upon the behavior of incised rivers (gullies) are especially noteworthy.

• Seminara, G., and P. Blondeaux, eds. 2001. River, coastal, and estuarine morphodynamics. Berlin and New York: Springer.

  This collection of nine papers by a number of highly regarded researchers in the field is an outcome of the first IAHR Symposium on River, Coastal and Estuarine Morphodynamics in 1999. The papers span a range of morphodynamic domains, ranging from dunes to debris flows, as well as nearshore to deep marine settings. The IAHR RCEM symposia are excellent sources of information on current research.

• Wohl, E. 2013. Fluvial geomorphology. Treatise on Geomorphology 9. San Diego, CA: Academic Press.

  This collection of forty-one review papers written by top researchers in the field spans a range of research topics in fluvial geomorphology. A number of the papers speak to theoretical and applied elements of fluvial geomorphology, and notably links to river morphodynamics, bedforms, and channel patterns. This is a comprehensive summary of recent advances in river morphodynamics.