A fiberglass 36-inch L x 16-inch W Cutthroat Flume being installed at the end of a concrete channel.

The flume has been fitted into the rough opening where it will be cast in place.  The form for one of the inlet wing walls has begun installation.  

Wing walls are used to smoothly direct flows into / out of flumes.  Abrupt transitions into flumes should be avoided unless other flow conditioning devices (typically tranquilizing racks) are between the channel and the flume inlet.  On the outlet side of the flume, wing walls are only necessary if the downstream channel is unarmored or if downsteam turbulence needs to be minimized.