Turbulent and Advective Momentum Fluxes in Streams

Autor: Noss, Christian; Salzmann, Thomas; Storchenegger, Isidor
In:

WATER RESOURCES RESEARCH

Bandangabe: Vol. 46
Ergaenzung: doi:10.1029/2010WR009297
Jahr: 2010

Einordung:
Institut: Professur Hydrologie und Angewandte Meteorologie

Abstract:
The scope of the present paper is the evaluation of the exchange of momentum in natural streams to explore the contribution that turbulence and secondary currents have on the shear stress distributions within the flow, and hence evaluate the overall hydraulic resistance. Existing methods for the evaluation of shear stresses in rivers are examined with respect to their applicability to complex flow fields, and a new mathematical formulation for analyzing the shear stresses affecting the longitudinal velocity distribution is presented. This new method enables one to estimate the time-averaged principal shear stress and its particular components due to turbulence and secondary currents directly from three-dimensional velocity data. An acoustic Doppler velocimeter (ADV) was used to measure the currents and turbulence at five cross-sections of two field sites over a wide range of discharges. The results of the cross-sectional measurements reflect the nonuniformity of the river bed roughness, cross-sectional form, and planform. Limited applicability was found for methods based on the theory of two-dimensional boundary layer flows. Shear stresses estimated using the new method emphasize the dominance of secondary currents on the total momentum flux. Momentum fluxes caused by secondary currents were an order of magnitude larger than momentum fluxes due to turbulence.

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