Background

For my dissertation, I am investigating the effects of riparian vegetation on channel morphodynamics. I conduct experiments in a laboratory channel at the St. Anthony Falls Laboratory. The experiments are aimed at systematically examining the impacts of sustained vegetation forcing on braided morphology and how it might promote other channel planforms (e.g. meandering, anabranching, wandering) and to investigate the dynamic interaction within the vegetation-flow-sediment system under the simplest possible conditions. In typical field situations vegetation expansion is linked to damped flow regimes and sediment supply associated with upstream dams and irrigation withdrawals, making it difficult to isolate the effects of vegetation from concurrent changes in external controls. Laboratory experiments permit isolation of variables and sequential, quantitative study of relationships among them.

Feedback relationships exist between riparian vegetation and river channel hydraulics, sedimentation, and form. Vegetation increases bank stability through root reinforcement of the sediment and increases the threshold shear stress needed to erode the sediment. In addition, vegetation offers resistance to the flow by increasing the drag and reducing the velocity, thus decreasing the stream power available for erosion and transport. Vegetation typically promotes the deposition of fine sediment (silt, clay) carried in the flow which further increases bank stability due to cohesion. Vegetation is ubiquitous and is transported and dispersed readily by wind and water; it will opportunistically colonize those areas of the channel that are abandoned or exposed at low flows. Braided rivers are particularly susceptible to colonization when only a small fraction of the discharge is decreased; this is because braided rivers have high width/depth ratios and low mean topographic relief. A small reduction in discharge leads to a large reduction in total channel width.

Please view the links to learn about the experimental setup and methods and view movies and images from several of the runs. I am happy to receive comments, suggestions, and ideas for collaboration. I would be especially happy if the movies are used as a teaching tool and would enjoy learning about the experiences you have.

I am very grateful to the staff, faculty, and fellow students (past and present) at St. Anthony Falls Lab. None of these experiments would have been possible without their collective experience and expertise.

Related Publications

Hicks, D.M., Duncan, M. J., Lane, S.N., Tal, M., Westaway, R., Morphological change in braided gravel-bed rivers: measurement, causes, relationship with riparian vegetation, and consequences for instream habitat, Gravel Bed Rivers VI, in press

Tal, M., Gran, K., Murray , A.B., Paola, C., Hicks, D.M., 2004, Riparian vegetation as a primary control on channel characteristics in multi-thread rivers, in Riparian Vegetation and Fluvial Geomorphology: Hydraulic, Hydrologic, and Geotechnical Interaction , Eds. Sean J. Bennett and Andrew Simon, American Geophysical Union Monograph. (PDF)

Murray, A.B ., and Paola, C., 2003, Modeling the effect of vegetation on channel pattern in bedload rivers, Earth Surface Processes and Landforms 28, 131-143.

Gran, K., and C. Paola. 2001. Riparian vegetation controls on braided stream dynamics. Water Resources Research 37 :3275-3283.

Experimental set-up and methods

Movies  

Images