Turbulent velocity fluctuations in natural rivers Bhowmik, N. G., and R. Xia. 1993. Turbulent velocity fluctuations in natural rivers. In Hydraulic Engineering '93, Proceedings of the 1993 Conference, sponsored by the Hydraulics Division/ASCE, San Francisco, California, July 25-30, 1993. Reprinted by the National Biological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, April 1994. LTRMP 94-R005. (NTIS # PB94-178142) ABSTRACT The longitudinal and transverse components of flow velocity, as well as the normal and tangential stresses, must be expected to fluctuate with time and space when flow at a high Reynolds number moves between fixed boundaries. Although these nonperiodic fluctuations are generally secondary in magnitude compared to the mean motion, they have profound effects on properties of the primary mean motion. Scientists from the Illinois State Water Survey are involved in collecting and analyzing detailed velocity data from the Illinois and Mississippi Rivers using 2-D electromagnetic current meters. The goal of the present research is to understand and evaluate the turbulent structure in natural river systems, especially near the channel border areas. The fluctuation characteristics of flow velocity were analyzed systematically. Flow velocities were measured with time at six different lateral locations and at three different vertical elevations. Analysis of the velocity data included the cross- sectional and vertical distributions of longitudinal and transverse velocity components (u, v), the fluctuating velocity components (u', v') and their frequency-distribution curves, turbulent intensities (åx, åy), turbulent shear stress (- u'v'), and turbulent kinetic energy. It appears that velocity, velocity fluctuation, turbulent intensity, turbulent shear stress, and turbulent kinetic energy are all relatively high within the main channel. Moreover, all of these flow parameters decrease in the channel border areas. Thus the main channel area above the riverbed appears to be the most active zone in the river. The study shows that the values of åx, åy, çxy, and average KE are high at elevations of 10 to 20 percent above the bed. KEYWORDS Turbulence, velocity, rivers, Illinois River, turbulent fluctuations, main channel, channel border areas