The Large 60 Degree Trapezoidal Flume

The Large 60º V Trapezoidal flume is one of the original Trapezoidal flumed developed. The flume has good low-end resolution, while the v-shaped cross section allows for larger flow rates to be measured with reasonable head. Solids passage is good with the flume having a flat floor.

Applications

fiberglass large 60 degree v trapezoidal flume

The Large 60º V Trapezoidal flume is versatile and can be used in a number of different applications:

Watershed monitoring
Edge-of-field monitoring
Seepage monitoring
Ditch and furrow flows
Small surface water gauging
Industrial pretreatment monitoring
Furrows, ditches, small canals
Spring discharge

Configurations

large 60 degree v trapezoidal flume in a fiberglass packaged metering manhole The Large 60º V Trapezoidal flume is available in several different configurations:

Plain flume
- Transitions into / out of the flume are formed in the field
End adapters
- Allowing connection to inlet / outlet pipes and flanges
Stage end adapters
- Curved transitions to allow installation in an existing concrete manhole
Metering manholes
- Factory integration into a fiberglass manhole
Wing walls
- To span rectangular channels

Flume Accuracy

Trapezoidal flumes are rated by the U.S. EPA as accurate to within +/-2-5% (+/-2% by Humpherys and Bondurant).

This accuracy is in line with other flume types. In the field, Openchannelflow expects accuracy to be +/-5% with good approach and installation conditions.

Flume Dimensions

Trapezoidal flumes have been described in research publications - and not national publications like the Parshall flume - so no national or organizational standards exist.

Free-Flow Equation

The general free-flow equation for 60º V Trapezoidal flumes is as follow:

general 60 degree V trapezoidal flume free flow equation

For the Large Trapezoidal flume the values are:

Minimum Head (ft)	0.015	Minimum Head (m)	0.0457
Minimum Flow Rate (cfs)	0.0116	Minimum Flow Rate (l/s)	0.3287
Maximum Head (ft)	0.50	Maximum Head (m)	0.1524
Maximum Flow Rate (cfs)	0.2592	Maximum Flow Rate (l/s)	7.341
Equation (cfs, ft)	1.55*H^2.58	Equation (l/s, m)	941.2*H^2.58

Discharge Table

The Large 60º Trapezoidal flume is available for download.

The table provides:

Plan view showing the point of measurement (H_a)
Discharge equations for a variety of units
Flume accuracy
Submergence Transition (S_t)
Source of the table

Materials

galvanized Large 60 Degree V Trapezoidal flumes with staff gauges

Openchannelflow's offers Large 60º Trapezoidal flumes in:

Fiberglass (FRP)
- Light weight
Galvanized steel
- Low cost
Stainless steel
- Corrosion resistance

Fiberglass construction allows the greatest customization.

Submergence Transition

A flume is said to be submerged when the downstream conditions are such that the flow out of a flume is restricted - the indicated flow is greater than the actual flow out of the flume.

For a Trapezoidal flume the primary point of measurement (H_a) is in the first section of the flume - where the walls are parallel and before the flume contracts. The secondary point of measurement (H_b) is in the last section of the flume - again, where the walls are parallel after the flume has expanded.

The Trapezoidal flume has a flat floor, making zero elevation the same for both points of measurement - unlike the Parshall flume.

submergence ratio equation

As downstream conditions restrict the flow out of the flume, the indicated flow and actual flow rates begin to diverge (the indicated flow rate being higher).

At some point the difference between these two flow rates is such that the flow rate needs to be corrected. This point is termed the Submergence Transition (S_t) and for Trapezoidal flumes it occurs at 75-85%.