Incisional cyclic steps of permanent form in mixed bedrock-alluvial rivers

Norihiro Izumi, Miwa Yokokawa, Gary Parker

Research output: Contribution to journalArticle

Abstract

Most bedrock river channels have a relatively thin, discontinuous cover of alluvium and are thus termed mixed bedrock-alluvial channels. Such channels often show a series of steps formed at relatively regular intervals. This bed form is the bedrock equivalent of cyclic steps formed on beds composed of cohesive soil in gullies. In this paper, we perform a full nonlinear analysis for the case of cyclic steps in mixed bedrock-alluvial channels to explain the formation of these steps. We employ the shallow water equations in conjunction with equations describing the process of bedrock incision. As a model of bedrock incision, we employ the recently introduced Macro-Roughness Saltation Abrasion Alluviation model, which allows direct interaction between alluvial and bedrock morphodynamics. The analysis is greatly simplified by making the quasi-steady assumption that alluvial processes occur much faster than bedrock erosional processes. From our analysis, we obtain the conditions for the formation of cyclic steps in bedrock, as well as the longitudinal profiles of bed elevation, water surface elevation, and areal fraction of alluvial cover. It is found from the analysis that when the sediment supply is small relative to the transport capacity, cyclic steps form only on slopes with very high gradients. The analysis indicates that the shape of a step formed on bedrock is characterized by a relatively short upstream portion with an adverse slope and a long, almost planar downstream portion with a constant slope.

Original languageEnglish (US)
Pages (from-to)130-152
Number of pages23
JournalJournal of Geophysical Research: Earth Surface
Volume122
Issue number1
DOIs
StatePublished - Jan 1 2017

Fingerprint

bedrock
rivers
Rivers
Water
Nonlinear analysis
Abrasion
river
Macros
Sediments
Surface roughness
Soils
beds
slopes
alluvium
saltation
cohesive soil
shallow-water equation
abrasion
morphodynamics
bedform

Keywords

  • abrasion
  • alluviation
  • bedrock
  • cyclic step
  • incision
  • macroroughness

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)
  • Palaeontology

Cite this

Incisional cyclic steps of permanent form in mixed bedrock-alluvial rivers. / Izumi, Norihiro; Yokokawa, Miwa; Parker, Gary.

In: Journal of Geophysical Research: Earth Surface, Vol. 122, No. 1, 01.01.2017, p. 130-152.

Research output: Contribution to journalArticle

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