Pouring benching around a Palmer-Bowlus Flume in a fiberglass Packaged Metering Manhole.  

Benching is required inside the manhole in the even a downstream blockage occurs.  Should a blockage occur, flow may back up into the manhole and spill over the top of the flume.  Benching also allows the water to be contained and directs it back into the flume once the blockage has cleared.  Finally, benching also give the operator a place to stand in the manhole while they conduct their operations.