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Velocity structure in gravel rivers

University of British Columbia

This thesis investigates velocity profiles in high gradient rivers with rough beds. Experimental work was carried out in the Hydraulics Laboratory of The Department of Civil Engineering at the University of British Columbia. Velocity measurements were taken in the flume with variable slope (S=0.01 to 0.021) and the size of bed material was D5o=5.0 cm. An Acoustic Doppler Velocity (ADV) probe was used and the turbulent flow structure was examined. Velocities in all three directions were measured and Reynolds stresses have been calculated. Existing methods for determination of velocity profiles are based on the theory that was developed for smooth rigid boundaries and low gradient rivers. These theories lead to a logarithmic velocity profile. However, a limited number of previous studies have shown that the velocity profile in mountain rivers is non4ogarithmic and therefore the mean velocity can be under or overestimated. This study shows that the commonly used logarithmic law does not give the best results. Using a different approach to the existing theory, a new velocity profile equation was developed. In addition, the Froude number, flow rate and Manning's roughness coefficient n were calculated. These parameters show that high energy dissipation is produced by large roughness elements and the flow is slightly subcritical. When additional roughness elements were added to the model, the Froude number decreased and Manning's n increased. The equation developed herein has a reasonable fit with the measured data, but additional work is needed to determine the exact range of applicability. Some existing field measurements agree and some disagree with the present theory, therefore further field measurements with the same measuring equipment need to be made to investigate whether natural streams behave in a similar manner.

Thesis/Dissertation

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2009-02-14

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http://hdl.handle.net/2429/4582

Civil Engineering

University of British Columbia

UBCV

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