Flow resistance under conditions of intense gravel transport

Water Resources Research



A study of flow resistance was undertaken in a channelized reach of the North Fork Toutle River, downstream of Mount St. Helens, Washington. Hydraulic and sediment transport data were collected in flows with velocities up to 3 m/s and shear stresses up to 7 times the critical value needed for bed load transport. Details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance. The plane gravel bed persists up to stresses ∼3 times critical, at which point, irregular bed forms appear. Bed forms greatly increase flow resistance and cause velocity profiles to become distorted. The latter arises as an effect of flows becoming depth-limited as bed form amplitude increases. At very high rates of bed load transport, an upper stage plane bed appeared. Velocity profiles measured in these flows match the law of the wall closely, with the equivalent roughness being well represented by ks = 3D84 of the bed load. The effects noted here will be important in very large floods or in rivers that are not free to widen, such as those cut into bedrock.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Flow resistance under conditions of intense gravel transport
Series title Water Resources Research
DOI 10.1029/91WR02932
Volume 28
Issue 3
Year Published 1992
Language English
Publisher American Geophysical Union
Contributing office(s) Washington Water Science Center
Description 13 p.
First page 891
Last page 903
Public Comments Part of a Special Section: Problems and Issues in the Validity of Benefit Transfer Methodologies
Country United States
State Washington
Other Geospatial North Fork Toutle River
Online Only (Y/N) N
Additional Online Files (Y/N) N
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