Some aspects of turbulent flow structure in large alluvial rivers

This paper reports different aspects of turbulent flow structure using the ship-board time-series velocity data collected by an Acoustic Doppler Current Profiler (ADCP) in the large multi-thread Jamuna River in Bangladesh. The measurements were made during different river stages in various bed-form environments ranging from mega-ripples to dunes. Based on the analysis of the downstream flow velocity obtained from the three subdivisions of the water column, different turbulence parameters such as frequency spectra and intensities were found. Spectral analysis indicates a mixed picture of random turbulent motion and periodicity. The maximum period observed was about 18 min and the minimum was about 11.5 s. Analysis of the frequency of occurrence of all the grouped events shows that about 70% of the turbulence have their origins in the river-bed, the rest are horizontal eddies. It is shown that a 15 min averaging time is required to estimate the higher order moments such as the turbulence intensity. The vert...

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