Skip to main content
U.S. flag

An official website of the United States government

Acoustic bed velocity and bed load dynamics in a large sand bed river

January 1, 2006

Development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics. Measurement of bed load motion with acoustic Doppler current profiles (ADCPs) has emerged as a promising approach for evaluating bed load transport. However, a better understanding of how ADCP data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications. In this paper, we discuss the response of ADCP bed velocity measurements, defined as the near-bed sediment velocity detected by the instrument's bottom-tracking feature, to changing sediment-transporting conditions in the lower Missouri River. Bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed. The ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer, the bed load layer thickness, and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed. A model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success. Bed velocities become more variable and increase more rapidly with shear stress when the transport stage, defined as the ratio of skin friction to the critical shear stress for particle entrainment, exceeds a threshold of about 17. This transition in bed velocity response appears to be associated with the appearance of longer, flatter bed forms at high transport stages.

Citation Information

Publication Year 2006
Title Acoustic bed velocity and bed load dynamics in a large sand bed river
DOI 10.1029/2005JF000411
Authors D. Gaeuman, R. B. Jacobson
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research F: Earth Surface
Index ID 70028332
Record Source USGS Publications Warehouse
USGS Organization Columbia Environmental Research Center

Related Content