A Montana Flume is a modification of the standard Parshall Flume where the throat and diverging sections have been removed.  

The resulting flume is shorter, cheaper, and lighter than a standard Parshall Flume yet that still uses the same discharge equations / flow tables under free-flow conditions.

Unlike the the Parshall Flume, the Montana Flume has little resistance to the effects of downstream submergence.  As a result, Montana Flumes should only be used where free-spilling, free-flow discharge is possible under all flow conditions.