A 48-inch concrete Parshall Flume measuring flow in an irrigation ditch in Wyoming.  

The flume was cast with reduced sidewalls 2-feet high, instead of the standard 3-feet high.  Its common in irrigation applications to select a flume that is large enough to span the channel but which has reduced sidewalls (so the flume doesn't stick up above the channel banks).  

Normally when a flume's sidewall height is modified, it is usually to make the flume taller to increase the flow capacity. Here it works the other way with the walls going shorter to make it easier to span the channel.

The flume also has a porcelain enameled iron staff gauge mounted at the point of measurement.