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Trapezoidal flumes are popular choice when industrial users need to measure pretreatment discharges. 

The flumes provide:

  • Good resistance to submergence
  • Pass solids and sediments well
  • Able to accurately measure low flows
  • Suiteable for sanitary / mixed industrial flow streams
  • Available with end adapters to connect to inline piping
  • Smaller sizes retrofit readily into existing manholes

stainless steel Trapezoidal pretreatment flume

Design Advantages

The trapezoidal shape of the flumes provides sensitivity to the low flow rates (like during a plant shut down), while retaining the ability to handle large, peaking flows (from wash downs, batch dumps, or storm water events). 

The flat floor and outward sloping walls of Trapezoidal flumes mean that sanitary solids pass easily – allowing the flumes to be used on mixed industrial flow streams.  The flat bottom design also mean that heavier sediments that might settle out of the flow stream during low flows tend to wash trough the flume as the flow rate increases….resulting in fewer maintenance issues that other flume types.

Large 60 Degree V Trapezoidal flume monitoring mixed industrial discharge


The installation of the Trapezoidal flume is generally easier than that of other flume types.  Unlike the Parshall flume, there is no need to accommodate a drop through the flume.  As a result, it is unusual to need to make downstream piping changes to accommodate the installation of a Trapezoidal flume. 

The outward sloping walls of the Trapezoidal flume do mean than the flume tends to have a larger (or at least wider) footprint than other types of flumes.  As a result it is not always possible to install a Trapezoidal flume into an existing manhole or vault.

Trapezoidal flume in a fiberglass packaged flow metering manhole

Packaged Metering Manholes

Luckily, many of the popular sizes of Trapezoidal flumes can be included as part of a packaged flow metering manholes.  Here the flume is factory installed into a fiberglass manhole, the result of which is a single, watertight and corrosion resistant monolithic unit.  Any portion of the flume that does not fit inside the manhole barrel is allowed to extend upstream / downstream of the manhole as necessary.  Reinforced watertight covers are laminated to those portions of the flume outside the manhole barrel and the entire unit is then laminated together.

For industrial users, factory integration means single source responsibility and confidence that the flume is properly installed.  Additionally, as the unit is an integrated structure, plant/line downtime is considerably shorter when compared to traditional installation methods; making metering manholes ideal for weekend or holiday shutdown installations.

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