The Seismic Signal of Sediment Transport in Rivers

Abstract:

Seismic signals near rivers are partially generated by sediment particles impacting the river bed as they are transported downstream. Predicting river channel evolution depends heavily upon understanding when and at what rate this sediment moves. We present two approaches to using these seismic signals to constrain sediment transport. First, we examine hysteresis in the relationship between 1-45 Hz seismic amplitude and flow depth over the course of individual flood events following the removal of a 13 m dam on the Chijiawan River in northern Taiwan. We compare two floods of similar magnitudes with and without bedload transport, and find that the seismic amplitude generated at a given flow depth changes over a single storm only when sediment transport is active. Along-stream variation in hysteresis for each storm appears to scale qualitatively with total sediment transport along the river, and reveals transport patterns consistent with a migrating sediment pulse that is a predicted consequence of the dam removal. Second, we examine the spectral signals of water turbulence, rain, and bedload sediment transport during flood events on the Erlenbach stream in Switzerland. We perform a general linear least squares inversion of the data and find that the signal generated by rain exhibits a roughly broadband spectrum, while discharge and sediment transport exhibit power primarily in lower frequency bands. Our results indicate that seismic signals near rivers may be used to track sediment transport.