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Conference papers

Sediment Supply and Channel Morphology Feedbacks in Bedrock and Gravel-Bed Rivers

Abstract : The role of variable sediment supply is often overlooked in modelling studies of landscape evolution, despite sediment playing a key role in the physical processes that drive erosion and sedimentation in river channels. Under a changing climate, or in active tectonic settings, landscapes face pressures from variable sediment supply in the future, with the resulting impact on channel dynamics currently uncertain. Here, we present a combined field and physical modelling study that demonstrates the importance of feedbacks between sediment supply and channel/valley geometry in bedrock, gravel, and mixed gravel-bedrock river systems. In the Rangitikei river catchment, New Zealand, bedrock channels receiving a supply of coarse, hard, sediment are systematically wider than channels with no sediment input for a given discharge. Box flume experiments (0.8 x 0.3 m) exploring this dependency further demonstrate that multiple configurations of bedrock and mixed bedrock-gravel channel geometry can exist for a given discharge, solely due to input sediment supply. Larger flume experiments (12 x 2.4 m) examine the dynamics of analogue gravel-bed river systems, including a setup where the channel was forced through a narrow constriction relative to its unconstrained width, replicating the bedrock valley geometry common to many gravel-bed river systems that transport large volumes of sediment in New Zealand. Experiments were run with a constant sediment supply until they reached dynamic equilibrium, before the sediment supply was increased at the channel inlet, representing scenarios of heightened sediment availability from upland areas driven by a shift to a more extreme climate. The impact of a valley constriction on the channel dynamics was identified through the comparison of the response to increased sediment supply for channels with and without the constriction. These results will help to develop the process-based understanding of channel dynamics under variable forcing regimes, which can be used to aid the development of numerical models and a host of applications including landscape evolution or flood risk.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-02402501
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, December 10, 2019 - 2:47:04 PM
Last modification on : Monday, June 22, 2020 - 7:54:04 AM

Identifiers

  • HAL Id : insu-02402501, version 1

Citation

Edwin Baynes, Heide Friedrich, Dimitri Lague, Philippe Steer, Stéphane Bonnet. Sediment Supply and Channel Morphology Feedbacks in Bedrock and Gravel-Bed Rivers. American Geophysical Union Fall Meeting 2019, American Geophysical Union, Dec 2019, San Francisco, United States. pp.EP31B-07. ⟨insu-02402501⟩

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