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fiberglass open top packaged metering manhole manufactured by Openchannelflow integrating a Parshall flumeOpen Top manholes provide the ultimate in operator access.   The clear, unrestricted opening provides complete access to the manhole interior by the operator.

Open Top manholes typically require a dedicated structure over them (e.g. fiberglass equipment shelter) or fiberglass grating to prevent unauthorized access.

Suitable Locations

Open Top manholes are typically only used in protected locations.  They must be away from any vehicle traffic and are usually away from foot traffic.

If an Open Top manhole is going to be installed near an area frequented by vehicular traffic, bollards or other protection may be needed to protect the manhole.


4', 5', 6', and 8' [1.22, 1.52, 1.83, and 2.44 m] diameter manholes.

Sizing Open Top Manholes

Open Top manholes are usually sized to be above the surrounding surface grade unless protected.  Operator access is easy and natural, with the lip of the manhole provides a convenient handhold to steady the operator as they enter / exit the manhole.

By extending above grade, it is easier to enter / exit an Open Top manhole.  Unfortunately, unless otherwise protected, Open Top manholes are subject to inflow and may be a fall hazard.

Should a manhole be incorrectly sized (and too short), Openchannelflow offers manhole extensions to help bring the top back up to its desired height.


Lacking any sort of cover, hatch, or other barrier to entry, Open Top manholes are extremely easy for operators to enter / exit.