The evolution of a colluvial hollow to a fluvial channel with periodic steps following two transformational disturbances: A wildfire and a historic flood

F. K. Rengers, L. A. McGuire, B. A. Ebel, G. E. Tucker

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The transition of a colluvial hollow to a fluvial channel with discrete steps was observed after two landscape-scale disturbances. The first disturbance, a high-severity wildfire, changed the catchment hydrology to favor overland flow, which incised a colluvial hollow, creating a channel in the same location. This incised channel became armored with cobbles and boulders following repeated post-wildfire overland flow events. Three years after the fire, a record rainstorm produced regional flooding and generated sufficient fluvial erosion and sorting to produce a fluvial channel with periodically spaced steps. An analysis of the step spacing shows that after the flood, newly formed steps retained a similar spacing to the topographic roughness spacing in the original colluvial hollow (prior to channelization). This suggests that despite a distinct change in channel form roughness and bedform morphology, the endogenous roughness periodicity was conserved. Variations in sediment erodibility helped to create the emergent steps as the largest particles (>D84) remained immobile, becoming step features, and downstream soil was easily winnowed away.

Original languageEnglish (US)
Pages (from-to)121-130
Number of pages10
JournalGeomorphology
Volume309
DOIs
StatePublished - May 15 2018

Keywords

  • Colluvial hollow
  • Erosion
  • Steps
  • Wildfire

ASJC Scopus subject areas

  • Earth-Surface Processes

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