Journal
GEOMORPHOLOGY
Volume 309, Issue -, Pages 121-130Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.geomorph.2018.01.003
Keywords
Colluvial hollow; Wildfire; Erosion; Steps
Funding
- National Science Foundation [EAR-1331828, EAR-0952247]
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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 (> D-84) remained immobile, becoming step features, and downstream soil was easily winnowed away. Published by Elsevier B.V.
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