Combining elements of both a flume and a weir, the H series of flumes (HS / H / HL) are well adapted to measuring a wide range of flows accurately. As a result, H flumes are frequently used where wide swings in the flow rate are expected – such as edge-of-field and storm water runoff, and industrial applications.

However, because the H flume acts in some capacity as a sharp-crested weir, the H flume has little resistance to the effects of submergence.  This means that particular care must be taken in transitioning effluent away from the flume so that it doesn’t submerge.  Usually this means having the flow freely spill off the end of the flume. 

However, in applications where the flume is used inline with piping, free spilling discharge may not be possible.  Here something else needs to be done.

H Flume Drop Boxes

Drop boxes are molded structures that are attached to the end (or nose as it is sometimes called) of a H series flume.  The box serves to contain the flow and provide a transition out to a pipe stub or flange.  In sizing the drop box it is important to make sure that the box provides sufficient vertical height so that the effluent piping can be set low enough so as not to submerge the flume. 

Additionally, a H flume drop box must be long enough to prevent the discharge cascading off the end of the flume from splashing back – potentially disrupting level measurement in the flume itself.

H Flume drop boxes can be used with H flumes that are free-standing, encased in concrete, or installed in fiberglass metering manholes.