A fiberglass Parshall Flume with reduced height sidewalls, end adapters, and pipe stubs.  

The sidewalls of some flumes (Parshall, Montana, Cutthroat, and USGS Portable) can be raised / lowered as needed.  Lowering the sidewalls can ensure that the flume doesn't extend about a vault's walls or channel's banks.  Raising the flume can increase the flow capacity of a flume when standard designs don't meet a site's particular space restrictions / flow requirements.