The active layer in gravel-bed rivers: An empirical appraisal

D. Vázquez-Tarrío, GEMMA PIQUE ALTES, D. Vericat, R. J. Batalla

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

The vertical position of the streambed–water boundary fluctuates during the course of sediment transport episodes, due to particle entrainment/deposition and bedform migration, amongst other hydraulic and bedload mechanisms. These vertical oscillations define a topmost stratum of the streambed (i.e. the ‘active layer or active depth’), which usually represents the main source of particles entrained during long and high-magnitude bedload transport episodes. The vertical extent of this layer is hence a capital parameter for the quantification of bedload volumes and a major driver of stream ecology in gravel-bed rivers. However, knowledge on how the active depth scales to flow strength and the nature of the different controls on the relation between the flow strength and the active depth is still scarce. In this paper we present a meta-analysis over active depth data coming from ~130 transport episodes extracted from a series of published field studies. We also incorporate our own field data for the rivers Ebro and Muga (unpublished), both in the Iberian Peninsula. We explore the database searching for the influence of flow strength, grain size, streambed mobility and channel morphology on the vertical extent of the active layer. A multivariate statistical analysis (stepwise multiple regression) confirms that the set of selected variables explains a significant amount of variance in the compiled variables. The analysis shows a positive scaling between active depth and flow strength. We have also identified some links between the active depth and particle travel distances. However, these relations are also largely modulated by other fluvial drivers, such as the grain size of the bed surface and the dominant channel macro-bedforms, with remarkable differences between plane-bed, step-pool and riffle-pool channels.

Original languageEnglish
Pages (from-to)323-343
Number of pages21
JournalEarth Surface Processes and Landforms
Volume46
Issue number2
DOIs
StatePublished - Feb 2021
Externally publishedYes

Keywords

  • active depth
  • active layer
  • bed scour
  • bedload
  • flow strength
  • grain size
  • particle entrainment
  • river morphology

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