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Flow structure investigation over a pool-rife sequence in a variable width river

Tabarestani Ehsan Shahiri, Afzalimehr Hossein, Pham Quoc Bao

Acta Geophysica

2022

Vol. 70, no 2

713--727

A comprehensive overview of flow characteristics in natural channels with bedforms is a vital issue in river management projects. Pool-rife sequences as common bedforms in the gravel-bed rivers significantly impact flow characteristics and turbulence intensity. The present study was taken by field investigation in the Babolroud River, Iran. A 95 m reach with variable width was chosen in this river and velocity components and shear stress were obtained in different sections. Quadrant analysis was also applied to determine the dominant bursting event in the pool section. The results revealed a phase shift for stream-wise velocity, near-bed velocities, and bed shear stress versus bed profile. In the pool, vertical velocity components were oriented downward near the bed and upward near the water surface, while in the rife section vectors were oriented towards the bed. The findings of quadrant analysis demonstrated the ejections and sweeps as a dominant event close to the bed and water surface, respectively.

The spatial organisation of time-averaged streamwise velocity and its correlation with the surface topography of water-worked gravel beds

Cooper J. R., Tait S. J.

Acta Geophysica

2008

Vol. 56, no. 3

614-641

An examination was made into the spatial pattern of time-averaged streamwise velocity in the near-bed region over two water-worked gravel beds. Laboratory observations revealed that there is considerable spatial variability in velocity. It was organised into streamwise streaks of high-speed fluid which were overlain by spots of low-speed fluid. This spatial pattern was found to be consistently and heavily dependent on relative submergence. The spatial pattern of velocity was shown to have little linear coherence with bed surface topography at the grain-scale. It suggested that for flows above the two beds studied here, bed surface topography at the grain-scale exerted less of an influence on the spatial organisation of time-averaged streamwise velocities than relative submergence.