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Bed load transport and boundary roughness changes as competing causes of hysteresis in the relationship between river discharge and seismic amplitude recorded near a steep mountain stream
Author(s) -
Roth Danica L.,
Finnegan Noah J.,
Brodsky Emily E.,
Rickenmann Dieter,
Turowski Jens M.,
Badoux Alexandre,
Gimbert Florent
Publication year - 2017
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/2016jf004062
Subject(s) - geophone , hysteresis , geology , bed load , sediment transport , amplitude , seismometer , sediment , turbulence , flow (mathematics) , geotechnical engineering , hydrology (agriculture) , seismology , geomorphology , mechanics , physics , quantum mechanics
Abstract Hysteresis in the relationship between bed load transport and river stage is a well‐documented phenomenon with multiple known causes. Consequently, numerous studies have interpreted hysteresis in the relationship between seismic ground motion near rivers and some measure of flow strength (i.e., discharge or stage) as the signature of bed load transport. Here we test this hypothesis in the Erlenbach stream (Swiss Prealps) using a metric to quantitatively compare hysteresis in seismic data with hysteresis recorded by geophones attached beneath steel plates within the streambed, a well‐calibrated proxy for direct sediment transport measurements. We find that while both the geophones and seismometers demonstrate hysteresis, the magnitude and direction of hysteresis are not significantly correlated between these data, indicating that the seismic signal at this site is primarily reflecting hysteresis in processes other than sediment transport. Seismic hysteresis also does not correlate significantly with the magnitude of sediment transport recorded by the geophones, contrary to previous studies' assumptions. We suggest that hydrologic sources and changes in water turbulence, for instance due to evolving boundary conditions at the bed, rather than changes in sediment transport rates, may sometimes contribute to or even dominate the hysteresis observed in seismic amplitudes near steep mountain rivers.