For Engineers

Nationwide overland flow paths, on current LiDAR.

A free public reference layer of overland flow paths for civil, stormwater and three waters engineers. Built from 2024 LINZ LiDAR (composite L121859). Aligned with TP108, SWCoP v4 and NZS4404. The map most council layers don't show.

How engineers use it

Where the OFP layer fits in your workflow.

  1. Cross-check the council viewer. Open the FloodMap layer alongside your council GIS. Anywhere the council layer is older than the LINZ survey, FloodMap will surface flow paths the council layer misses.
  2. Site-walk preparation. Search the address before driving out. Know where the flow paths cross the property and where the upstream catchment is, before you turn up.
  3. Sense-check upstream catchment area. Every flow path is classified by upstream contributing area (Tier 3 = 25–500 ha, Tier 4 = 2–25 ha, Tier 5 = 0.4–2 ha). Useful for rational-method runoff sanity checks.
  4. Spot the AUP E36 trigger. Tier 5 captures flow paths down to 0.4 ha catchment — well below the 4,000 m² AUP E36 trigger — so you can see the paths that catch out a consent at site visit stage.
Why use it

What the layer gives you.

Newer LiDAR

2024 LINZ composite

Most council overland flow layers are derived from 2016 or older DEMs. FloodMap rebuilds against the latest LINZ composite (L121859) and the layer is reissued as new survey blocks land.

Sub-regulatory detail

Down to 0.4 ha catchment

Tier 5 picks up flow paths smaller than the AUP E36 4,000 m² trigger — the fine paths that catch you out at site visit if your screening tool stops at the major streams.

Defensible methodology

Open and auditable

D8 routing on hydroflattened bare-earth DEM, WhiteboxTools / GRASS pipeline. Full method published at /methodology — no black-box steps.

No friction

Free public access

Search any NZ address on the map. No login, no quota. The layer is published as a public reference because property-level flow visibility is, in our view, public information.

Honest limits

What the OFP layer is not.

The OFP layer is a screening reference, not a regulatory hazard map. It shows where surface water would route across bare earth — culverts, stormwater pipes and constructed drainage are not modelled. It does not include depth, velocity or hazard category. For a site-specific flood assessment with HEC-RAS 2D depth and hazard outputs, that's an engineering job done on commission, not a productised report — see "What's coming" below or contact us via SAE Ltd.

What's coming

The current published layer is overland flow paths only. We are working on:

  • Tier 1 / Tier 2 (large-catchment) coverage where a defensible approach can be applied
  • Tier 6 (property-scale, <0.4 ha) — under development
  • Site-specific HEC-RAS 2D flood assessments (depth, velocity, hazard) — currently delivered as bespoke engineering through SAE Ltd
  • Data exports and council partnerships — register interest via the contact form

Try it on a current job.

Open the map, search any NZ address, see what the layer shows for your site. Free, no login.

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