12 May 2022
12 May 2022

Episodic sediment supply to alluvial fans: implications for fan incision and morphometry

Anya Sophia Leenman1,2 and Brett Curtis Eaton1 Anya Sophia Leenman and Brett Curtis Eaton
  • 1Department of Geography, University of British Columbia, Vancouver, Canada
  • 2School of Geography and the Environment, University of Oxford, Oxford, U.K.

Abstract. Sediment supply is widely believed to be a key control on alluvial fan morphology and channel dynamics. Although the sediment supply to natural fans is rather episodic, experimental studies of alluvial fans often use constant sediment supply rates, making it difficult to relate fan dynamics to the magnitude and frequency of sediment supply in the field. This paper presents a series of experiments designed to test the impact of episodic sediment supply on fan evolution and dynamics. We compare four experiments, each with the same mean sediment supply but different durations of high- and low-supply periods. The experiments show that fan morphology and channel dynamics respond systematically to the temporal elongation of sediment supply oscillations: longer supply cycles generate flatter fans with more trenched channels. These results highlight how different basin conditions might generate different fan morphologies: supply limited basins with intermittent sediment supply might generate fans that are flatter than expected. Our results raise the question of whether a constant sediment supply in experimental models can adequately characterise the dynamics of natural fans in the field.

Anya Sophia Leenman and Brett Curtis Eaton

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-267', Lucy Clarke, 14 Jun 2022
  • RC2: 'Comment on egusphere-2022-267', Anastasia Piliouras, 01 Jul 2022

Anya Sophia Leenman and Brett Curtis Eaton

Data sets

Episodic sediment supply to alluvial fans: implications for fan incision and morphometry: experimental dataset Leenman, A. and Eaton, B

Model code and software

Code for basic data processing / analysis steps Leenman, Anya

Code to generate manuscript figures Leenman, Anya

Anya Sophia Leenman and Brett Curtis Eaton


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Short summary
The supply of sediment (sand and gravel) carried by a stream out of a steep mountain valley is widely thought to control the gradient of the fan-shaped landforms that streams often build where they leave their valley. We tested this idea in a set of "sandbox" experiments with oscillating high and low sediment supply. Even though the average sediment supply never changed, longer oscillations built flatter fans, indicating how wetter climates might affect these mountain landforms.