In applications where an existing flume is oversized for the flows that it is experiencing, either due to changes in plant design or process, certain flume types allow for the nesting of smaller flumes inside of larger flumes.  

Nested flume inserts are intended to fit level in the larger flume.  The nesting flume is typically provided with inlet and outlet wing walls so that it fits snuggly into the larger flume.  The connection between the two flumes should be caulked or sealed so that the join is watertight.  Stainless steel fasteners may be used to permanently secure the nesting flume to the larger flume.  Finally, the spaces between the exterior of the nesting flume and the interior of the larger flume may be filled with sand capped by grout (or similar materials) to reinforce the smaller flume and ensure that water does not collect between the two flumes.  

Parshall, Montana, and Cutthroat flumes are the flume types most commonly nested.