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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. F1, 6010, doi:10.1029/2003JF000018, 2003

Turbulent flow over three-dimensional dunes: 2. Fluid and bed stresses

T. B. Maddux

Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA


S. R. McLean

Department of Mechanical and Environmental Engineering, University of California, Santa Barbara, California, USA


J. M. Nelson

U.S. Geological Survey, Denver, Colorado, USA


Abstract

Dunes formed in response to fluid flow exert a total boundary stress on the fluid that is made up of form drag and skin friction, the latter of which is generally considered important for predicting sediment transport and dune evolution. Previous research has used various methods to estimate the total stress and its subcomponents, with recent work suggesting the application of a spatial average to the equations of motion. A complete, three-dimensional (3-D) form of this analysis is derived and applied to recent measurements of turbulent open-channel flow over 3-D dunes. Spatial averages of Reynolds shear stresses over 3-D dunes cannot be used to predict total boundary shear stress. However, estimations of total boundary shear stress from the spatially averaged equations of motion agree with not only the sum of form drag and skin friction but also the direct measurements of average free surface slope. Form-induced stresses from secondary circulations augment the relatively low Reynolds shear stresses over the 3-D dunes. These low turbulence levels have ramifications for sediment transport predictions, in that use of the total boundary shear stress in prediction of sediment transport over 3-D dunes must account for these low turbulence levels so as not to overpredict transport rates.

Received 6 January 2003; accepted 26 August 2003; published 11 December 2003.

Index Terms: 4219 Oceanography: General: Continental shelf processes; 4235 Oceanography: General: Estuarine processes; 4546 Oceanography: Physical: Nearshore processes; 4558 Oceanography: Physical: Sediment transport; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 896379 bytes)

Citation: Maddux, T. B., S. R. McLean, and J. M. Nelson (2003), Turbulent flow over three-dimensional dunes: 2. Fluid and bed stresses, J. Geophys. Res., 108(F1), 6010, doi:10.1029/2003JF000018.