Upscaling from grain-scale processes to alluviation in bedrock channels using a cellular automaton model

Hodge, R. and Hoey, T. (2012) Upscaling from grain-scale processes to alluviation in bedrock channels using a cellular automaton model. Journal of Geophysical Research: Earth Surface, 117, (doi: 10.1029/2011JF002145)

Abstract

The presence of sediment cover in bedrock rivers inhibits saltation-driven incision, and so accurate predictions of the relationship between bedrock exposure (Fe) and relative sediment flux (sediment supply rate over capacity sediment transport rate, Qs/Qt) are necessary to model incision and hence landscape evolution. Theoretical predictions of a linear or negative exponential form for this relationship are not consistent with laboratory data that instead demonstrate a range of different relationships. Here we use a cellular automaton (CA) model to establish how the relationship between Fe and Qs/Qt evolves from the dynamics of, and interactions between, individual sediment grains moving through a bedrock channel. The key model parameter is the probability of grain entrainment, which is altered as a function of the number of neighboring grains in order to reproduce the enhanced mobility of isolated grains on bedrock surfaces. For each model run, an equilibrium sediment cover is attained for a specified sediment input, enabling the relationship between Fe and Qs/Qt to be established. As well as both linear and exponential relationships, model runs reproduce other relationships observed in laboratory experiments. These other relationships require isolated grains to be more easily entrained than grains in sediment clusters, which is consistent with field observations of grain mobility. There is therefore a continuum of relationships between Fe and Qs/Qt; the relationship that is most applicable to a particular reach will depend on the role of channel slope, roughness and shear stress in controlling the entrainment of grains from bedrock and alluvial surfaces.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hoey, Professor Trevor and Hodge, Dr Rebecca
• Authors: Hodge, R., and Hoey, T.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
• Journal Name: Journal of Geophysical Research: Earth Surface
• Publisher: American Geophysical Union
• ISSN: 0148–0227
• ISSN (Online): 2156–2202
• Published Online: 01 December 2011