Front view of a fiberglass 1-inch Parshall Flume.  Note the defining hourglass shape of the flume.  

The 1-inch Parshall was one of the last three Parshall Flume sizes developed (along with the 2-inch and 3-inch).  Dr. Parshall's original investigations started at the 6-inch size, progressed to the very large flumes.  Later, the smaller 1/2/3-inch Parshall Flumes were developed.