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The free-spilling discharge required for an H flume to operate under free-flow conditions can make mounting the flume somewhat more challenging that other flume types.


H Flume Mounting

Concrete Channels

HL flume cast into concrete channelConcrete encapsulation is the common method of installing an H flume not used for watershed or edge of flow monitoring.  Here the flume is set in an oversized, roughed in channel and then grouted into place.  To help secure the flume during installation and make sure that it does not float out of place, wire is run through the anchor clips on the outside of the flume back to rebar before the grout pour begins.

H flumes are frequently used to measure very flow rates and it is important that the dimensional accuracy is maintained and that the sidewalls / floor do not distort.  The inside of the H flume must be cribbed and weighted so that the flume does not shift out of place or the sidewalls / floor distort.  Once the installation has been completed, the cribbing is removed.

Earthen Channels

edge-of-field installation with an H flumeMost H flumes are installed to measure edge-of-field or watershed flows.  There earthen channel installation are the common.   An oversized area is excavated, typically bedded on a compactable base, and then backfilled.  To help secure the flume in place, earth anchors or threaded rod is typically run through the anchor clips on the outside of the flume.

Flow bypass can be a concern upstream of the flume and both here and downstream geotextiles / channel armoring should be used.  Downstream scour is a particular concern with H flumes due to the free-spilling discharge.

H flumes are frequently used to measure very flow rates and it is important that the dimensional accuracy is maintained and that the sidewalls / floor do not distort.  The inside of the H flume must be cribbed and weighted so that the flume does not shift out of place or the sidewalls / floor distort.  Once the installation has been completed, the cribbing is removed.


Integrated Enclosures

H flume mounted in an Openchannelflow fiberglass Redstone equipment enclosureAbove grade industrial flows may require that a small monitoring flume be secured.  For those applications, Openchannelflow offers factory integration of a 0.4 to 1.0-foot HS and 0.5 / 0.75-foot H flumes into one of our Redstone Fiberglass Equipment Enclosures.  

Each integration includes:

  • Flume
  • Approach section
  • Outlet drop box
  • Inlet / outlet pipe stubs (or flanges)

The result is a secure, integrated solution that allows for the accurate measurement of flows while maintaining data integrity.

Flow Metering Manholes

For applications where below grade flow monitoring is required, Openchannelflow offers HS and H flumes integrated into our fiberglass Packaged Metering Manholes.


H Flume End Connections

Approach Section

galvanized H flumes with integral approach sectionsInlet end connections for H flumes usually involve an approach section.   An approach section is nothing more than an upstream extension of the rectangular cross-sectional shape of the inlet of an H flume.

Approach sections are recommended to be 3 to 5 times the maximum anticipated head (Hmax).  As a default they are usually sized to be 3 to 5 times the depth of the H flume.

An approach section is also a convenient location to mount other accessories that otherwise would not fit in the H flume itself.

It is to the approach section that inlet pipe stubs, flanges, caulking collars or other connections are usually made.

While approach sections are not mandatory when connecting an H flume to inlet piping, they are strongly recommended as the straight run of the approach section.

H flume approach sections can be factory made or field formed.  The dimensional tolerances for an approach section are not strict as the actual flow measurement occurs in the flume itself. 

Drop Box

outlet drop box on a H flumeFor an H flume to operate correctly it must have free-spilling discharge off the end of the flume.  

To connect the flume to downstream piping, a drop box is offered to collect the flow spilling out of the flume and to direct it into the effluent piping.

Inlet Bulkhead

H flume inlet bulkhead drilled for flanged connectionAn inlet bulkhead is a flat plate attached to either inlet of an H flume or (more usually) an approach section.  The bulkhead provides an area onto which a pipe stub, flange, or caulking collar can be integrated – allowing the H flume to be connected to upstream piping.

While approach sections are not strictly mandatory when using a bulkhead, they are strongly recommended as the straight run of the approach section allows the flow to develop a more uniform velocity profile before it enters the flume.

Staged Manhole Transition

Taking our standard H flume approach section, a curved is molded into the inlet so that the flume can now be directly connected to a manhole wall – eliminating the need to either form a transition or have a pipe connection to the flume.  Staged transitions are available for 0.4 and 0.6-foot HS flume and 0.5 and 0.75-foot H flumes. Contact Openchannelflow for additional details.

Wing Wall Transitions

wing walls on the approach section of a galvanized steel H flumeWing walls are or flat plates that are attached to the inlet of the H flume to direct flow into the flume or approach section from the larger channel that it is installed in.  

Wing walls can be factory attached or shipped loosed for field installation as required.