Manhole frame and cover elevation documentation is a required component of sewer and storm drain as-built packages in virtually every municipal jurisdiction. City engineers use the data to verify that manholes were set to design grade, that frames were adjusted to finished pavement, and that invert elevations confirm designed pipe slopes before accepting the system. Missing or incomplete manhole elevation data is one of the most common reasons sewer as-built packages are rejected at first submission.
What elevation data is required for manhole frame and cover documentation?
Manhole frame and cover documentation requires: rim elevation (top of frame or cover at finished grade), invert elevation for each pipe connection entering and exiting, manhole depth (rim to lowest invert), horizontal GPS coordinate or station-and-offset, and pipe size, material, and slope for each connection. Rim elevation verifies grade setting and frame adjustment. Invert elevations verify pipe slope and flow direction. Both are required for municipal as-built acceptance.
Most city sewer and storm drain standards specify the minimum data elements required for each manhole in the as-built package. The following table summarizes the typical requirements:
| Data Element | What It Verifies | Measurement Method |
|---|---|---|
| Manhole ID / station | Identifies location in the system and on drawings | From construction plans; confirm against field conditions |
| Rim elevation | Frame set to design grade; frame adjusted to finished pavement | Total station, GPS rover, or digital level to top of frame |
| Invert elevation (each pipe) | Pipe slope; flow direction; compliance with design | Tape or rod from rim to pipe invert; subtract from rim elevation |
| Manhole depth | Rim to lowest invert — used for access and maintenance records | Calculated from rim elevation minus lowest invert elevation |
| Pipe size and material | Specification conformance | Field verification against approved submittals |
| Pipe slope | Minimum slope requirements; flow direction | Calculated from upstream and downstream invert elevations |
| GPS coordinate (X, Y) | Horizontal location for GIS record | GPS rover at center of manhole frame; accuracy ±0.10 ft typical |
Invert elevation is the elevation of the inside bottom of the pipe at the point where it enters or exits the manhole structure. Because city engineers use invert elevations to calculate pipe slope, the measurement must be taken at the right location — not at the pipe centerline or the top of the pipe.
The standard field procedure for measuring invert elevation in an existing manhole:
The timing of manhole elevation documentation matters for accuracy and for protecting the contractor from disputes about whether frames were set correctly before the city's paving contractor covered them.
| Rejection Reason | Prevention |
|---|---|
| Rim elevation missing for one or more manholes | Shoot every manhole on the project — no exceptions, even for manholes outside the immediate work area if they are in the system |
| Invert elevation recorded to top of pipe, not inside bottom | Train field crew to measure to the inside bottom (invert) of the pipe, not to the pipe centerline or top |
| Rim elevation taken before frame adjustment | Document final rim elevation after pavement is in place and final frame adjustment is complete |
| Missing GPS coordinate | Use GPS rover to record location for every manhole, even in areas with control points — city GIS requires it |
| Calculated slope does not match design slope | Calculate slope in the field and flag any discrepancy before backfill; correction after the fact requires excavation |
Log manhole rim elevations, invert measurements, and GPS coordinates in the field. Sitemark compiles the data into the as-built table format most city engineers require — ready to submit at project close.
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