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Controls on the geometry of potholes in bedrock channels
Author(s) -
Pelletier Jon D.,
Sweeney Kristin E.,
Roering Joshua J.,
Finnegan Noah J.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl062900
Subject(s) - pothole (geology) , bedrock , radius , geology , sediment , geomorphology , geometry , hydrology (agriculture) , soil science , geotechnical engineering , mathematics , computer security , computer science
Potholes (circular depressions carved into bedrock) are the dominant roughness elements in many bedrock channels. Here we show, using data from previous studies and new data from the Smith River, Oregon, that pothole depths increase in proportion to both the mean pothole radius (such that the most common pothole depth‐to‐radius ratio is 2) and the diameter of the largest clasts episodically stored in potholes. We present a theory for these observations based on computational fluid dynamics and sediment transport modeling of vortices in cylindrical cavities of different shapes and sizes. We show that the shear stress at the bottom of a pothole (which controls the rate of pothole growth) is maximized for potholes with a depth‐to‐radius ratio of approximately 1 and decreases nonlinearly with increasing depth‐to‐radius ratio such that potholes with depth‐to‐radius ratios larger than 3 are uncommon. Our model provides a mechanistic explanation for pothole shapes and sizes.