engleski

Spatial and temporal averaging of velocity profiles in natural watercourses

Introduction of ADCP devices resulted in great progress in hydrometry of open watercourses. Simple use and fast measuring allow collecting of a large number of data on channel geometry, distribution of velocities and the discharge. By conventional method of measuring in the watercourse, using the hydrometric wing, the point velocity is obtained by temporal averaging of the velocity component in the direction of the device. ADCP at the measuring point gives the ¨momentary¨ value of the spatial velocity vector. In both procedures, the discharge is obtained by integrating the product of multiplying of unit area and the corresponding vertical velocity component over the profile. The velocity profile over depth, obtained by the conventional method, has the shape of an exponential function. On the other hand, the velocity profile over depth, taken by ADCP, assumes the shape of a random function, with values that often have the negative sign. Spatial averaging of velocity profiles from several neighboring verticals, results in a smoother shape of the function, which becomes closer to the shape resulting from temporal averaging in a single vertical. This paper analyses spatially and temporally averaged velocity profiles in a number of discharge profiles of the Drava River. The conclusion is that it is possible, by spatial averaging of velocity profiles in neighboring verticals, to get sufficiently precise picture of the profile of temporarily averaged velocities over depth.

Natural watercourses ; turbulent flow ; measurements ; velocity profiles

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