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Magnitude‐frequency distributions of boundary shear stress along a rapidly eroding bedrock river
Author(s) -
Barbour J. R.,
Stark C. P.,
Lin C.W.,
Chen H.,
Horng M.J.,
Ko C.P.,
Yi T.C.,
Tsai T.T.,
Chang W.S.,
Lee S.P.,
Huang C.
Publication year - 2009
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 - 10.1029/2008gl035786
Subject(s) - bedrock , geology , stream power , shear stress , geomorphology , magnitude (astronomy) , alluvium , flood myth , erosion , floodplain , hydrology (agriculture) , storm , stress field , geotechnical engineering , mechanics , oceanography , ecology , philosophy , physics , theology , astronomy , finite element method , biology , thermodynamics
The magnitude‐frequency distribution of boundary shear stress frames erosion rates in bedrock rivers, but empirical constraints are rare, particularly for extreme floods. Here we present measurements of mean stress τ b and its frequency distribution along a fast‐eroding river in Taiwan. We construct rating functions of discharge and hydraulic geometry using high‐resolution satellite images of flood patterns, river stage time‐series, topographic profiles, and post‐flood field surveys. The method allows us to assess the spatiotemporal variation in τ b along the channel. The boundary shear stress PDF p ( τ b ) has a steep power‐law tail, and includes semiannual floods generating τ b ≈ 100–200 Pa and 50‐year, 3000 m 3 s −1 events driving τ b ≥ 300 Pa. All such floods contribute to modification of the coarse alluvial cover and erosion of the bedrock bed. Given the steep tail decay in p ( τ b ), the rapid channel incision probably owes more to the exceptional frequency of moderate shear stresses than to the magnitude of the extremes.