concrete metal composite fiber reinforced polymers or combinations thereof vgs are always positioned in regions of zero or negative streamwise pressure gradients in order to create a stream wise vortex the vgs are placed at locations where 1 they can be effective in creating stream wise vortices that bring higher velocity fluid toward the surface wall e g vgs 3 a or 2 they can be effective to create stream wise vortices that bring river bed materials close to the foundation e g vgs 3 b and 3 c the vgs 3 a are located at least one vortex generator length upstream of where the stream wise pressure gradients become positive the spacing between them must be great enough that they allow the vortex on an adjacent vg to form generally at least u00bd of a vg length they cause higher velocity fluid to move toward the wall and mix and energize the near wall fluid this more energetic fluid will move further along a streamlined surface than otherwise thus producing a smaller less energetic and scouring downstream separation vortex this reduced rear or stern separation has lower downstream velocities and much less downstream scour the vg 3 b is initially buried under the surrounding river bed material in front of the pier nose under intense scouring conditions such as during floods or other high flow speed events this river bed material in front of the nose of the pier is scoured away revealing the vgs 3 b each vg 3 b then generates a stream wise.