Characterization of complex pebble movement patterns in channel flow – a laboratory study
Keywords:pebble movement forms, pebble movement patterns, cross-section shape, channel flow, laboratory channel study.
For a long time, studies concerning erosion caused by concentrated overland flow mainly dealt with the erosion and the transport of fine material. More recent studies have shown that rock fragments reduce the intensity of soil erosion processes on the one hand, but on the other hand rock fragment movements also have been observed both in the rill- and interrill erosion processes. However, there is little knowledge about the movement process of rock fragments in shallow channel flow. Are certain movement patterns typical for different shapes? Are there relationships between movement patterns and slope and flow velocity? Are all these patterns and relationships reproducible? To answer these questions, we performed laboratory channel experiments. With these experiments, we could obtain information about movement patterns of pebbles, by varying the following parameters: shape (flat, ellipsoidal, nearly spherical), size (diameter between 1.97 and 4.0 cm) and channel slope (5°, 10°). During the experiments, a high-speed camera was used to capture the motion of eight specially painted pebbles. The resulting image sequences were processed using both automatic image processing and manual visual inspection. Besides the movement patterns, the pebbles velocity, the water velocity and the water depth were estimated. We could show that there were different movement patterns depending on the shape and the slope. For the 5° experiments, the big, flat pebbles lie at the beginning of the tests. After the following yawing, the pebbles mainly showed the movement form rolling around the longest axis. For the 10° experiments the big, flat pebbles showed the same movement pattern firstly, but later in the sequence, they started to roll around their shortest axis and in the end this movement form was combined with saltation. These patterns are described using a simple symbolic language: sequences of pictograms describe the consecutive movement forms. Furthermore, we detected five different velocity groups of the pebbles for each slope: different cross-section shapes of the pebbles result in different acceleration behavior.
The methodology is limited to clear water in laboratory use. Even a larger water depth restricts the image processing. Thus, in the future the experiments will be combined with a small sensor that is implanted in the pebbles and measures forces (acceleration), compass (magnetic flux density) and rotations (gyroscope).
Bunte, K., Ergenzinger, P. 1989. New tracer techniques for particles in gravel bed rivers. Bulletin de la Société Géographique de Liege 25, 85-90.
Bunte, K., Poesen, J. 1993a. Effects of horseshoe vortex erosion on sediment yield from soils covered by rock fragments. Zeitschrift für Geomorphologie 37, 327-335.
Bunte, K., Poesen, J. 1993b. Effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow. Water resources research 29, 1415-1424.
Cameron, C. 2012. A wireless sensor node for monitoring the effects of fluid flow on riverbed sediment. University of Glasgow. School of Computing Science Level 4 Project, 70 pp.
Canny, J. 1986. A Computational Approach to Edge Detection. IEEE Transactions on Pattern Analysis and Machine Intelligence PAMI-8, 679-698.
Chatanantavet, P.,Whipple, K.X., Adams, M.A., Lamb, M.P. 2013. Experimental study on coarse grain saltation dynamics in bedrock channels. Journal of Geophysical Research: Earth Surface 118, 1161-1176.
Einstein, H. A. 1950. The bed-load function for sediment transportation in open channel flows. 1026. US Department of Agriculture.
Ergenzinger, P., De Jong, C. 2003. Perspectives on bed load measurement. IAHS Publication, 113-125.
Euler, T., Herget, J. 2012. Controls on local scour and deposition induced by obstacles in fluvial environments. Catena 91, 35-46.
Francis, J. 1973. Experiments on the motion of solitary grains along the bed of a water-stream. Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences 332, 443-471.
Leser, H. 1977. Feld- und Labormethoden der Geomorphologie. Walter de Gruyter, Berlin New York, 464 pp.
Meselhe, E., Peeva, T., Muste, M. 2004. Large Scale Particle Image Velocimetry for Low Velocity and Shallow Water Flows. Journal of Hydraulic Engineering, 130, 937-940.
Poesen, J., Torri, D., Bunte, K. 1994. Effects of rock fragments on soil erosion by water at different spatial scales: a review. Catena 23, 141-166.
Poesen, J. 1987. Transport of rock fragments by rill flow - a field study. Catena Supplement 8, 35-54.
Poesen, J., Ingelmo-Sanchez, F. 1992. Runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position. Catena 19, 451-474.
Poesen, J. 1990. Conditions for the evacuation of rock fragments from cultivated upland areas during rainstorms. Erosion, Transport and Deposition Processes (Proceedings of the Jerusalem Workshop, March-April 1987). IAHS Publication 189, 145-160.
Rieke-Zapp, D., Poesen, J., Nearing, M.A. 2007. Effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion. Earth Surface Processes and Landforms 32, 1063-1076.
Rieke-Zapp, D., Beer, A., Turowski, J.M., Campana, L. 2012. In situ measurement of bedrock erosion. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences Volume XXXIX-B5, 429-433.
Sklar, L.S., Dietrich, W.E. 2001. Sediment and rock strength controls on river incision into bedrock. Geology 29, 1087-1090.
Sklar, L.S., Dietrich, W.E. 2004. A mechanistic model for river incision into bedrock by saltating bed load. Water Resources Research 40, W06301, doi:10.1029/2003WR002496.
Steidle, G. 2009. Luftfahrtgeschichte - Flugsteuerung: http://www.luftfahrtarchiv.eu/index.php?option=com_content&view=article&id=190:flugsteuerung&catid=39:grundkenntnisse&Itemid=59.
Summerfield, M. A. 1991. Global geomorphology. An introduction to the study of landforms, 537 pp.
Wilson, A., Hovius, N., Turowski, J.M. 2013. Upstream-facing convex surfaces: Bedrock bedforms produced by fluvial bedload abrasion. Geomorphology 180, 187-204.
How to Cite
The authors retain copyright of articles and authorize Cuadernos de Investigación Geográfica / Geographical Research Letters the first publication. They are free to share and redistribute the article without obtaining permission from the publisher as long as they give appropriate credit to the editor and the journal.
Self-archiving is allowed too. In fact, it is recommendable to deposit a PDF version of the paper in academic and/or institutional repositories.
It is recommended to include the DOI number.This journal is licensed under a Creative Commons Attribution 4.0 International License