The lateral turbulent mixing of a continuous line source of neutral tracer or contaminant in steady uniform open channel flow illustrates several useful concepts of advective diffusion. Flow visualization of the slender plume downstream of the source in a laboratory flume is presented. The self-similar tracer concentration field is obtained by both conductivity measurements and laser-induced fluorescence (L1F) techniques. The dimensionless turbulent diffusivity is determined, and the pedagogical features of the experiment are discussed.
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