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Drainage schedule QA

Manhole Schedule Gradient Checker

Check drainage runs from manhole coordinates or scheduled plan lengths. Compare coordinate distance with schedule length, calculate bearing and invert gradient, derive ground-to-invert depths, and expose connected-row level differences before work starts.

Manhole Schedule Gradient Checker

Enter or import drainage runs

Use metres throughout. Each row runs from the entered upstream manhole to the downstream manhole.

Saved locally
Check tolerances
%
Flags coordinate versus scheduled plan length differences above this percentage.
mm/m
Compares calculated fall with an optional scheduled 1:n gradient.
mm
Flags invert, cover or coordinate differences where one row ends at the next row's starting reference.
Schedule rows, CSV files and results are processed in this browser. Local saving is device-specific; export a checked CSV for a portable copy.
Drainage-design limitation: This is an independent arithmetic and transcription aid, not hydraulic design, pipe-capacity analysis, clash detection, survey certification, approval or a compliance check. Confirm flow direction, datum, coordinate grid, pipe data, cover requirements, manhole drops and all tolerances against current approved design information.

What the manhole schedule checker calculates

For a run with complete Easting and Northing pairs, the checker calculates horizontal coordinate distance and survey bearing clockwise from grid North. You can also enter the scheduled plan length. When both are available, the result records the chosen source and reports coordinate distance minus scheduled length in metres and percent.

plan distance = √[(E₂ − E₁)² + (N₂ − N₁)²]
fall = upstream invert − downstream invert
gradient (mm/m) = fall ÷ plan length × 1,000
gradient ratio n = plan length ÷ |fall|

A positive fall means the downstream invert is lower in the entered run direction. A negative result is labelled as a rise, not silently converted into a fall. Equal inverts are reported as a level run. The 1:n value always describes the magnitude, while the direction text and signed percentage/mm-per-m values preserve meaning.

Coordinate or scheduled length

Auto uses coordinate plan distance when four valid, distinct coordinates are present; otherwise it uses a positive scheduled plan length. Choose a source explicitly when the project procedure requires one to control. The checked table and CSV always state which length was actually used.

Drainage gradients normally use horizontal plan length. This checker does not use three-dimensional pipe slope length. Coordinates must use the same grid, units and scale. A bearing calculated from inconsistent grids or truncated coordinates can look plausible while still being wrong.

Connected manhole checks

When an earlier row ends at the reference where a later row begins, the checker compares the earlier downstream invert with the later upstream invert. It also compares repeated cover levels and coordinates when those values are present. Differences above the entered connected-level tolerance are flagged.

An invert difference is not automatically an error. Incoming and outgoing pipes may have an intentional manhole drop, backdrop or level arrangement. The purpose of the flag is to make that change visible for comparison with the approved schedule, long section and manhole detail.

Depths and cover terminology

The calculated depth is entered cover/ground level minus invert level. It is a ground-to-invert depth, not cover above pipe crown. Pipe diameter, wall thickness, bedding and actual cover to crown are not inferred. A negative depth is flagged because it means the invert has been entered above the corresponding cover level.

CSV format and local records

An import needs From MH, To MH, Upstream invert and Downstream invert columns. Optional columns are From/To Easting and Northing, Scheduled length, Length basis, Upstream/Downstream cover level, Scheduled gradient and Notes. Use coordinate, scheduled or auto for Length basis. Enter scheduled gradient as the denominator only: enter 80 for 1:80.

Imports and saved schedules remain in local browser storage. Exported CSV adds checked length and source, bearing, fall, gradient formats, depths, variances, connected invert difference and readable issue text. A browser-local record is not a controlled project record unless it is exported, identified and managed through the project procedure.

Checks still required before construction

Confirm schedule revision, pipe direction, manhole identifiers, datum, grid, coordinates, units, inverts, pipe sizes and materials against approved drawings. Review minimum cover, gradients, velocities, capacities, self-cleansing requirements, surcharging, outfall levels, connections and adoptable standards through the responsible design and approval process. Independently verify setting-out information and any critical calculation.

Frequently asked questions

How is gradient calculated from manhole invert levels?

Fall equals upstream invert minus downstream invert. The checker divides horizontal plan length by the magnitude of that fall for the 1:n ratio, and also reports signed percentage and millimetres per metre.

Can I check a manhole schedule without coordinates?

Yes. Enter a positive scheduled plan length and choose scheduled plan length, or leave the length basis on Auto. Without coordinates, bearing and coordinate-versus-schedule length comparison are unavailable.

Does a continuity warning prove that a manhole schedule is wrong?

No. Different incoming and outgoing inverts can represent an intentional manhole drop. The warning makes the difference visible so it can be verified against approved design information.

Is the manhole schedule uploaded?

No. Rows, CSV imports, calculations and local saving stay in the browser. A file leaves the browser only when you deliberately export it.