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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 7, issue 1
Earth Surf. Dynam., 7, 17-43, 2019
https://doi.org/10.5194/esurf-7-17-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
Earth Surf. Dynam., 7, 17-43, 2019
https://doi.org/10.5194/esurf-7-17-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Jan 2019

Research article | 10 Jan 2019

Long-profile evolution of transport-limited gravel-bed rivers

Andrew D. Wickert1 and Taylor F. Schildgen2,3 Andrew D. Wickert and Taylor F. Schildgen
  • 1Department of Earth Sciences and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota, USA
  • 2Helmholtz Zentrum Potsdam, GeoForschungsZentrum (GFZ) Potsdam, 14473 Potsdam, Germany
  • 3Institut für Erd- und Umweltwissenschaften, Universität Potsdam, 14476 Potsdam, Germany

Abstract. Alluvial and transport-limited bedrock rivers constitute the majority of fluvial systems on Earth. Their long profiles hold clues to their present state and past evolution. We currently possess first-principles-based governing equations for flow, sediment transport, and channel morphodynamics in these systems, which we lack for detachment-limited bedrock rivers. Here we formally couple these equations for transport-limited gravel-bed river long-profile evolution. The result is a new predictive relationship whose functional form and parameters are grounded in theory and defined through experimental data. From this, we produce a power-law analytical solution and a finite-difference numerical solution to long-profile evolution. Steady-state channel concavity and steepness are diagnostic of external drivers: concavity decreases with increasing uplift rate, and steepness increases with an increasing sediment-to-water supply ratio. Constraining free parameters explains common observations of river form: to match observed channel concavities, gravel-sized sediments must weather and fine – typically rapidly – and valleys typically should widen gradually. To match the empirical square-root width–discharge scaling in equilibrium-width gravel-bed rivers, downstream fining must occur. The ability to assign a cause to such observations is the direct result of a deductive approach to developing equations for landscape evolution.

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Rivers can raise or lower their beds by depositing or eroding sediments. We combine equations for flow, channel/valley geometry, and gravel transport to learn how climate and tectonics shape down-valley profiles of river-bed elevation. Rivers steepen when they receive more sediment (relative to water) and become straighter with tectonic uplift. Weathering and breakdown of gravel is needed to produce gradually widening river channels with concave-up profiles that are often observed in the field.
Rivers can raise or lower their beds by depositing or eroding sediments. We combine equations...
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