An 8-Inch fiberglass Palmer-Bowlus Flume measuring industrial discharge in a concrete manhole.  The flume is grouted into the bottom of the manhhole between pipe stubs.  Palmer-Bowlus Flumes are sized to - generally - match the line size that they are monitoring flow in (e.g. a 6-inch Palmer-Bowlus Flume on a 6-inch line).  Infrequently you may need to go up / down one flume size.