Near-Field Mixing Downstream of a Multiport Diffuser in a Shallow River

Abstract

Near-field mixing downstream of a multiport diffuser in a wide shallow river was studied with a field dye test. Dye concentrations at different depths and lateral locations were measured. The near-field mixing was analyzed in four zones: the free jet zone, the jet surface-impingement zone, the merging zone, and the vertical mixing zone. Analytical models were proposed to derive the three-dimensional concentration field after the jets impinged the water surface. After the impingement, the dye concentration can be predicted well by treating the multiple jets as a simple mathematical summation of individual jets. The vertical mixing zone was dominated by the riverbed friction-induced turbulence, with little effect from the effluent momentum and buoyancy. The results of the field data were also used to validate the applicability of some existing models for multiport diffusers.