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Fluid flow and sediment transport processes in geomorphology: innovations, insights, and advances in measurement
Geomorphology 68 (2005) 1 – 2 www.elsevier.com/locate/geomorph
Preface
Fluid flow and sediment transport processes in geomorphology: innovations, insights, and advances in measurement We live in an era of rapid and innovative technological development. Advances in instrumentation have allowed researchers to strive for a deeper understanding of fundamental geomorphic processes. Recent progress in the measurement and characterization of fluid flow and sediment transport has provided new insight into sedimentary processes and landform responses. For instance, instruments that measure flow turbulence have allowed for the development of new and improved models of both sediment transport processes and bedform dynamics. This research relies on the ability to measure at a high temporal resolution with increased precision and to characterize the three-dimensional components of the flow over a wide range of spatial scales. For example, ultrasonic anemometers are able to measure highfrequency, three-dimensional variations in airflow while acoustic Doppler profilers can characterize flow turbulence in rivers over an extensive and continuous spatial field. Geomorphologists now require such instruments to improve understanding of these processes and, increasingly, are involved in designing and testing new instruments. Despite the promise that these advances hold, it remains to be seen if such an improvement in the spatial and temporal resolution of measurement will lead to anything more than the collection of extensive site- or event-specific empirical datasets. Perhaps due to our relative inexperience with these technologies and the complexities and limitations of their designs, we continue to learn about what these measurements contribute to our understanding of geomorphic processes. There is also a concern that these small-scale 0169-555X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2004.09.029
measurements may be difficult to incorporate into models of landform- or landscape-scale dynamics at longer time scales. This special issue addresses some of these questions and is based on papers presented in three special sessions held at the 53rd Annual Meeting of the Canadian Association of Geographers (CAG). The meeting was hosted from 27 to 31 May 2003 by the Department of Geography, University of Victoria, British Columbia, Canada, and was cosponsored by the Canadian Geomorphology Research Group (CGRG). The purpose of these special sessions and an associated instrumentation workshop also held during the conference was to present new developments in instrumentation for the study of geomorphic processes and to highlight some results obtained from these innovative techniques and approaches. The sessions also emphasized the role of flow turbulence in the dynamics of aeolian and fluvial systems, an area that has benefited enormously from recent technological advances. This was a particularly timely endeavour on the 20th anniversary of Leeder’s (1983) influential work, bOn the interactions between turbulent flow, sediment transport and bedform mechanics in channelized flowsQ. Because much recent progress in aeolian bedform research has drawn upon approaches derived in the fluvial environment, it was our intent to bring together researchers from all geomorphic environments, techniques, and scales of study to stimulate discussion and exchange that might further our understanding of fluid flow, sediment transport, and bedform dynamics. Emphasis was placed on a critical appraisal of key innovations,
2
Preface
insights, and advances in measuring and modelling the dynamics of flow and sedimentary processes in geomorphic systems. To this end, the first two papers present new, innovative technologies for measurement of fluid flow and sedimentary processes developed by geomorphologists such as Orwin and Smart’s turbidimeter and Lamoureux’s lacustrine sedimentation sensor. The next five papers provide critical insight on the use of existing instrumentation and/or models to characterize geomorphic processes. Kostaschuk et al. discuss the measurement of flow velocity using an acoustic Doppler profiler and examine the application of this instrument to the measurement of sediment transport. Pearce and Walker analyze frequency and magnitude biases in the widely used dFrybergerT aeolian sediment drift potential model. Walker provides an in-depth discussion of the physical and logistical considerations for using ultrasonic anemometry in aeolian research. Critical insights on temporal and spatial considerations in measuring and characterizing flow behaviour in fluvial channels are offered by Buffin-Be´langer and Roy and by Lamarre and Roy, respectively. The final two papers present new findings from very different scales of investigation resulting from recent advances in measurement technologies used to characterize aeolian systems. This includes Davidson-Arnott et al.’s event-based examination of the effects of wind turbulence, moisture content, and fetch on sand transport over beaches and Hugenholtz and Wolfe’s regional assessment of recent stabilization of Canadian Prairie dunes in response to climate variation using GIS and digital image processing. Not only does each of these contributions document recent advances in characterizing the dynamics of geomorphic systems and identify important research gaps and opportunities,
but they also highlight some of the cutting-edge research in process geomorphology that is ongoing in Canada today. The guest editors managed the review process and we wish to acknowledge the final editing by Richard Marston. We also extend our gratitude for their constructive reviews on the manuscripts to: Alan Arbogast, Peter Ashmore, Pascale Biron, Joanna Bullard, Mike Church, Robin Davidson-Arnott, Dirk deBoer, Joe Desloges, Patrick Hesp, Ray Kostaschuck, Michel Lapointe, David Muhs, Steven Namikas, Ellen Petticrew, Colin Rennie, Andre´ Robert, John van Boxel, Paul Villard, Giles Wiggs, and Steven Wolfe. References Leeder, M.R., 1983. On the interactions between turbulent flow, sediment transport and bedform mechanics in channelized flows. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems, Special Publication of the International Association of Sedimentologists, vol. 6, pp. 5 – 18.
Ian J. Walker Boundary Layer Airflow and Sediment Transport (BLAST) Research Unit, Department of Geography, University of Victoria, P.O. Box 3050, Station CSC, Victoria, BC Canada, V8W 3P5 E-mail address: [email protected]. Corresponding author. Tel.: +1 250 721 7347; fax: +1 250 721 6216. Andre´ G. Roy De´partement de Ge´ographie, Universite´ de Montre´al, C.P. 6128, Succursale Centre-ville, Montre´al, Que´bec, Canada, H3C 3J7 1 September 2004
Preface
Fluid flow and sediment transport processes in geomorphology: innovations, insights, and advances in measurement We live in an era of rapid and innovative technological development. Advances in instrumentation have allowed researchers to strive for a deeper understanding of fundamental geomorphic processes. Recent progress in the measurement and characterization of fluid flow and sediment transport has provided new insight into sedimentary processes and landform responses. For instance, instruments that measure flow turbulence have allowed for the development of new and improved models of both sediment transport processes and bedform dynamics. This research relies on the ability to measure at a high temporal resolution with increased precision and to characterize the three-dimensional components of the flow over a wide range of spatial scales. For example, ultrasonic anemometers are able to measure highfrequency, three-dimensional variations in airflow while acoustic Doppler profilers can characterize flow turbulence in rivers over an extensive and continuous spatial field. Geomorphologists now require such instruments to improve understanding of these processes and, increasingly, are involved in designing and testing new instruments. Despite the promise that these advances hold, it remains to be seen if such an improvement in the spatial and temporal resolution of measurement will lead to anything more than the collection of extensive site- or event-specific empirical datasets. Perhaps due to our relative inexperience with these technologies and the complexities and limitations of their designs, we continue to learn about what these measurements contribute to our understanding of geomorphic processes. There is also a concern that these small-scale 0169-555X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2004.09.029
measurements may be difficult to incorporate into models of landform- or landscape-scale dynamics at longer time scales. This special issue addresses some of these questions and is based on papers presented in three special sessions held at the 53rd Annual Meeting of the Canadian Association of Geographers (CAG). The meeting was hosted from 27 to 31 May 2003 by the Department of Geography, University of Victoria, British Columbia, Canada, and was cosponsored by the Canadian Geomorphology Research Group (CGRG). The purpose of these special sessions and an associated instrumentation workshop also held during the conference was to present new developments in instrumentation for the study of geomorphic processes and to highlight some results obtained from these innovative techniques and approaches. The sessions also emphasized the role of flow turbulence in the dynamics of aeolian and fluvial systems, an area that has benefited enormously from recent technological advances. This was a particularly timely endeavour on the 20th anniversary of Leeder’s (1983) influential work, bOn the interactions between turbulent flow, sediment transport and bedform mechanics in channelized flowsQ. Because much recent progress in aeolian bedform research has drawn upon approaches derived in the fluvial environment, it was our intent to bring together researchers from all geomorphic environments, techniques, and scales of study to stimulate discussion and exchange that might further our understanding of fluid flow, sediment transport, and bedform dynamics. Emphasis was placed on a critical appraisal of key innovations,
2
Preface
insights, and advances in measuring and modelling the dynamics of flow and sedimentary processes in geomorphic systems. To this end, the first two papers present new, innovative technologies for measurement of fluid flow and sedimentary processes developed by geomorphologists such as Orwin and Smart’s turbidimeter and Lamoureux’s lacustrine sedimentation sensor. The next five papers provide critical insight on the use of existing instrumentation and/or models to characterize geomorphic processes. Kostaschuk et al. discuss the measurement of flow velocity using an acoustic Doppler profiler and examine the application of this instrument to the measurement of sediment transport. Pearce and Walker analyze frequency and magnitude biases in the widely used dFrybergerT aeolian sediment drift potential model. Walker provides an in-depth discussion of the physical and logistical considerations for using ultrasonic anemometry in aeolian research. Critical insights on temporal and spatial considerations in measuring and characterizing flow behaviour in fluvial channels are offered by Buffin-Be´langer and Roy and by Lamarre and Roy, respectively. The final two papers present new findings from very different scales of investigation resulting from recent advances in measurement technologies used to characterize aeolian systems. This includes Davidson-Arnott et al.’s event-based examination of the effects of wind turbulence, moisture content, and fetch on sand transport over beaches and Hugenholtz and Wolfe’s regional assessment of recent stabilization of Canadian Prairie dunes in response to climate variation using GIS and digital image processing. Not only does each of these contributions document recent advances in characterizing the dynamics of geomorphic systems and identify important research gaps and opportunities,
but they also highlight some of the cutting-edge research in process geomorphology that is ongoing in Canada today. The guest editors managed the review process and we wish to acknowledge the final editing by Richard Marston. We also extend our gratitude for their constructive reviews on the manuscripts to: Alan Arbogast, Peter Ashmore, Pascale Biron, Joanna Bullard, Mike Church, Robin Davidson-Arnott, Dirk deBoer, Joe Desloges, Patrick Hesp, Ray Kostaschuck, Michel Lapointe, David Muhs, Steven Namikas, Ellen Petticrew, Colin Rennie, Andre´ Robert, John van Boxel, Paul Villard, Giles Wiggs, and Steven Wolfe. References Leeder, M.R., 1983. On the interactions between turbulent flow, sediment transport and bedform mechanics in channelized flows. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems, Special Publication of the International Association of Sedimentologists, vol. 6, pp. 5 – 18.
Ian J. Walker Boundary Layer Airflow and Sediment Transport (BLAST) Research Unit, Department of Geography, University of Victoria, P.O. Box 3050, Station CSC, Victoria, BC Canada, V8W 3P5 E-mail address: [email protected]. Corresponding author. Tel.: +1 250 721 7347; fax: +1 250 721 6216. Andre´ G. Roy De´partement de Ge´ographie, Universite´ de Montre´al, C.P. 6128, Succursale Centre-ville, Montre´al, Que´bec, Canada, H3C 3J7 1 September 2004