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Experimental Investigation of Lateral Incision in Bedrock Rivers

Experimental Investigation of Lateral Incision in Bedrock Rivers. Ted Fuller Dept. of Geology and Geophysics, SAFL, University of Minnesota. Why study bedrock channels?. Landscape evolution Climate -Uplift- Erosion Incision sets pace of evolution (?) Channel- hillslope coupling

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Experimental Investigation of Lateral Incision in Bedrock Rivers

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  1. Experimental Investigation of Lateral Incision in Bedrock Rivers Ted Fuller Dept. of Geology and Geophysics, SAFL, University of Minnesota

  2. Why study bedrock channels? • Landscape evolution • Climate -Uplift- Erosion • Incision sets pace of evolution (?) • Channel-hillslope coupling • Evolution Models www.wsl.ch/personal_homepages/korup/Gorge1

  3. Why study lateral bedrock incision? • Strath Terraces • Chronology • Indicator of external forcing • Decoupling agent • Channel Width • Incision Models • Stark (2006) • Wobuset al (2006) Alluvium Bedrock

  4. Variable Bed Roughness Experiments • Experimental Summary: • Non-erodible channel bed • Homogeneous erodible channel walls • Incision of walls by abrasion only • Primary variable: Size of roughness element

  5. Bedrock Analog & Reality Check

  6. Experimental Goal & Setup

  7. Experimental Goal & Setup • Quantify lateral erosion rates as function of channel bed roughness

  8. Setup • Roughness: Decreasing • Width: 18.5 cm • Depth: 5-8 cm • Slope: 0.025 • Discharge: constant (13 L/s) Qualitative Results Flow Bed Roughness 16 mm 10 mm 2.4 mm 0.095 mm Erosion Channel Top / Flood Plain Channel Wall

  9. Roughness Trends Increasing Roughness Decreasing Roughness Alternating Roughness

  10. Driving mechanisms of lateral erosion associated with increased roughness • Bedload diffusion • Change in transverse bedload distribution such that a greater number of bedload particles are transported along the wall when roughness is increased. • Bedload deflector • Bedload distribution is uniform between different roughnesses but large particles on the bed in rough sections deflect bedload particles into the wall. • Turbulence • Increased turbulence intensity, or turbulent kinetic energy, associated with rough section is able to direct bedload particles into the wall.

  11. Bedload Sampling

  12. Increasing Roughness - Bedload Data

  13. Decreasing Roughness – Bedload Data

  14. Hypotheses • Threshold bed roughness • Bedload Deflector / Particle-Particle Interaction • Lateral erosion rates can be accelerated by adding roughness to the bed

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