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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esurf-2018-84
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2018-84
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Dec 2018

Research article | 13 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Alluvial channel response to environmental perturbations: Fill-terrace formation and sediment-signal disruption

Stefanie Tofelde1, Sara Savi1, Andrew D. Wickert2, Aaron Bufe3, and Taylor F. Schildgen1,3 Stefanie Tofelde et al.
  • 1Institut für Erd- und Umweltwissenschaften, Universität Potsdam, 14476 Potsdam, Germany
  • 2Department of Earth Sciences and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55455, USA
  • 3Helmholtz Zentrum Potsdam, GeoForschungsZentrum (GFZ) Potsdam, 14473 Potsdam, Germany

Abstract. The sensitivity of fluvial fill terraces to tectonic and climatic boundary conditions make them potentially useful archives of past climatic and tectonic conditions. However, we currently lack a systematic understanding of the impacts of base-level, water discharge, and sediment discharge changes on terrace formation and associated sediment storage and release. This knowledge gap precludes a quantitative inversion of past environmental changes from terraces. Here we use a set of seven physical experiments to explore terrace formation and sediment export from a braided channel system that is perturbed by changes in upstream water discharge and sediment supply, or downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace formation, and (3) the transient response of sediment discharge. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, preservation of the initial channel profile on terrace surfaces, and a transient increase in sediment export from the system that eventually returns to its pre-perturbation rate. In contrast, changes in the upstream sediment supply rate may result in longer lag-times before terrace cutting, leading to a less well-preserved pre-perturbation channel profile, and may also produce a gradual change in sediment output towards a new steady-state value. Finally, downstream base-level fall triggers the upstream migration of a knickzone, forming terraces with upstream-decreasing ages. The gradient of terraces triggered by base-level fall mimicks that of the newly-adjusted active channel, whereas gradients of terraces triggered by variability in upstream sediment or water discharge are steeper compared to the new equilibrium channel. Our findings provide guidelines for distinguishing between different types of perturbations when interpreting fill terraces and sediment export from fluvial systems.

Stefanie Tofelde et al.
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Stefanie Tofelde et al.
Stefanie Tofelde et al.
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Short summary
We performed seven physical experiments to explore terrace formation and sediment export from a braided alluvial river system that is perturbed by changes in water discharge, sediment supply or base-level. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace formation, and (3) the transient response of sediment discharge. Our findings provide guidelines for interpreting fill terraces and sediment export from fluvial systems.
We performed seven physical experiments to explore terrace formation and sediment export from a...
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