Boundary interaction occurs when the flow contacts the surface, bottom, or forms a terminal layer in
a density-stratified ambient environment.
Boundary interaction also determines if mixing is controlled by stable or unstable
discharge source conditions.
Boundary interaction generally provides the transition from near-field (discharge source controlled) to far-field (ambient controlled) mixing processes as illustrated by the image on the right.
However, boundary interaction in the form of dynamic plume attachments to the bottom are considered near-field mixing processes.