Interaction between a bubble plume and the near field in a stratified lake
A steady state bubble-plume model is evaluated using full-scale temperature, salinity, and dissolved oxygen data collected in a Swiss lake. The data revealed a plume-generated near-field environment that differed significantly from the ambient far-field water column properties. A near-field torus of reduced stratification developed around the plume, the extent of which is on the same lateral scale as the horizontal dislocations generated by persistent first-mode seiching. The plume fallback water was found to penetrate much deeper than expected, thereby maintaining reduced vertical gradients in the near-field torus. The plume entrains a portion of the fallback water leading to short-circuiting, which generates a complex plume-lake interaction and reduces far-field downwelling relative to the upward plume flow. As the integral plume model incorporates the entrainment hypothesis, it is highly sensitive to the near-field environmental conditions. After identifying appropriate near-field boundary conditions the plume model predictions agree well with the field observations.