Water · Select a property, draw a box or polygon, or upload a boundary
Overland flow path map for any New Zealand property
This overland flow path map shows where surface water runs across any New Zealand property in heavy rain, and how many hectares of land drain through each path, traced from the LINZ LiDAR ground model. A second view shows where water would pond once the hollows fill, with depth, area and volume.
Council flood maps often show only rivers and mapped floodplains, and some were drawn before the latest LiDAR was flown. This map picks up the small paths too, down to 0.1 ha of catchment, names the survey it was traced from, and labels every path in hectares, the number engineers and councils work in. Auckland’s Unitary Plan, for example, treats a path draining more than 4,000 m² (0.4 ha) as an overland flow path.
It is a screening map: it shows where to look and what to ask, not whether a house will flood. The method, sources and limits are set out in full below.
Free to run · pay to download
See the full result on the map free, with no account. Download the flow paths as GeoJSON or KML with a pass: NZ$49 for 7 days or NZ$299 for 12 months, one-off, GST included, not a subscription. Every download on the site is included while the pass lasts.
Who uses this
- Buyers. Check whether water runs across a section or block before going unconditional, and know what to ask the council and an engineer.
- Landowners. Keep a house, shed, driveway or septic field out of the path water takes and the hollows where it sits.
- Engineers and surveyors. Cross-check a council layer against current LiDAR and read off upstream catchment areas for a quick runoff check.
- Drainage and landscape designers. Plan swales, soak holes and culverts on real flow paths, sized from the land draining to them.
- Farmers. See which gullies carry the most water and where paddocks pond.
When to use it
- Checking whether a flow path crosses a house site, building platform or driveway before you buy or design.
- Cross-checking a council flood or overland flow layer against the current LiDAR.
- Locating low spots that will hold water, for drainage design or to keep a building out of them.
- Planning culverts, swales and fence crossings, with the catchment area of each path to size them from.
Which tool for your job
Flow Paths is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.
If you’re working on buying a section or lifestyle block
What is the ground like, and how does it compare with the others on my list?
- 1.Property — Selects the legal parcel so every other tool is clipped to the boundary.
- 2.Property Report — A PDF with contours, slope, aspect, winter sun, drainage, elevation and old aerial photos for that parcel, or several selected together.
- 3.Saved Properties — Up to five places side by side: elevation, slope, winter sun and drainage.
- 4.Flow Paths (this tool) — Where water will run and pond across the block in heavy rain.
- 5.Aerial History — Old aerial photos back to the 1930s in places: past slips, filled gullies and streams that have since gone.
- 6.Elevation Change — Where LiDAR was flown twice: whether the ground has slipped, been filled or been cut since.
If you’re working on drainage, flooding and wet ground
Where does the water go, and where will it sit?
- 1.Flow Paths (this tool) — The overland flow paths across an area, sized by the land draining through them, and where water ponds once hollows fill.
- 2.Wetness Map — Which parts of a paddock the shape of the land keeps wet.
- 3.Catchment — All the land that drains to one culvert, gully or low corner.
- 4.Landforms — Hollows, valleys and footslopes at a glance: where water gathers.
How to use it
- Select a property, draw an area or upload a boundary.
- Run. Switch between the Flow paths and Ponding views in the panel.
- Tap any flow path to see how much land drains through it.
- Export the flow paths as GeoJSON or KML to open in GIS, CAD or Google Earth.
Step by step: Mt Iron, Wānaka
We trace where rain runs off Mt Iron and where it would pond.
What it showed
- Check where the larger flow paths leave the hill before siting a building, a driveway or a septic field.
- Culverts and pipes are not in the terrain, so treat ponding behind embankments as a place to check, not a prediction.
Screenshots from NZ Elevation Tools. Aerial imagery from LINZ Basemaps. Sourced from the LINZ Data Service and licensed by Environment Southland, Otago Regional Council and Queenstown-Lakes District Council for re-use under the Creative Commons Attribution 4.0 International licence.
How it works
Small pits in the LiDAR bare-earth model are filled so water can always find a way downhill. Each cell then passes its water to its steepest neighbour, and the land upstream of every cell is added up. The terrain loaded reaches beyond your boundary, so water arriving from neighbouring land is counted at its true size.
Cells draining at least 0.1 ha are joined into flow paths and grouped by that upstream area: minor flow paths under 0.4 ha, overland flow paths of 0.4 to 10 ha, watercourses of 10 to 100 ha, and streams or rivers above that. On large areas the smallest path drawn rises so the map stays readable, and the panel says where the cut-off sits.
Ponding compares the filled surface with the original ground: wherever the fill raised the ground, water would stand there, and the difference is the depth.
Method, sources and who built it
- Terrain: the LINZ elevation tiles of the national bare-earth elevation model (LiDAR where it has been flown), read in your browser at the finest zoom that fits, about 0.5 m cells for property-sized areas, padded beyond the area you choose so upslope land is included.
- Depression filling: the Priority-Flood algorithm (Barnes, Lehman and Mulla, 2014), with a 1 mm gradient added across filled flats so every cell still drains toward an outlet.
- Flow routing: each cell sends its water to its steepest downhill neighbour of eight (the D8 method of O’Callaghan and Mark, 1984), and upstream area is accumulated for every cell in the padded grid.
- Flow paths: cells draining 0.1 ha or more (a higher, stated cut-off on large areas) are linked into lines and classed by upstream catchment at 0.4, 10 and 100 ha. The 0.4 ha break is the Auckland Unitary Plan’s overland flow path threshold of 4,000 m².
- Ponding: filled surface minus original ground gives standing-water depth once each hollow fills to its spill point. Depths under 15 cm are left out as within the data’s noise.
Not modelled
- Rainfall amount, intensity or return period (AEP), so no flood depth or velocity for a design storm.
- Stormwater pipes, culverts, kerbs and narrow drains.
- Soakage, soil saturation and groundwater.
- Buildings, which bare-earth LiDAR removes.
- River flooding beyond the area loaded, coastal inundation, storm surge and sea-level rise.
References
- Toitū Te Whenua LINZ, New Zealand LiDAR 1 m DEM, via the LINZ Data Service (CC BY 4.0; each survey licensed by the council or agency that commissioned it).
- Barnes, R., Lehman, C. and Mulla, D. (2014). Priority-flood: an optimal depression-filling and watershed-labeling algorithm for digital elevation models. Computers & Geosciences, 62, 117–127.
- O’Callaghan, J. F. and Mark, D. M. (1984). The extraction of drainage networks from digital elevation data. Computer Vision, Graphics, and Image Processing, 28(3), 323–344.
- Auckland Unitary Plan (Operative in part): Chapter J definition of “overland flow path”, and Chapter E36 Natural hazards and flooding.
Built and maintained by MapScaping. The processing chain is published here in full so you can judge whether the result fits your purpose. It is a screening reference, not engineering advice: for consent, design or a purchase decision that turns on flooding, get the council’s hazard information and a site-specific assessment from a chartered professional engineer. Method last checked against the code 2026-11-05.
Reading the results
Thicker, paler lines drain more land. The hectare figure on each line is the area of land upstream of it, the number engineers and councils use to decide whether a path matters.
The panel names the LiDAR survey the paths were traced from and the years it was flown. If a council layer was drawn from an older survey, the two can disagree where the ground has since changed.
Ponding depth, area and volume describe the hollow when full. Real ponds drain into the soil and evaporate, so these are upper bounds.
Limits and warnings
- This is a screening map of where the ground sends water, not a flood hazard map. It does not say how deep or fast water would run in a given storm.
- Culverts, pipes, kerbs and open drains that are narrower than the sampling are not in the terrain, so water is routed over roads and through embankments.
- Bare-earth LiDAR has buildings removed, so paths are drawn straight through existing houses.
- A large river's catchment reaches far beyond any area you can draw, so its hectare figure is a lower bound. Use Catchment to trace one point further upstream.
- Where 1 m LiDAR has not been flown, the LINZ elevation tiles hold the national 8 m elevation model instead. It was interpolated from 20 m map contours and is not fit for site-scale decisions. The on-map result does not say which one it read: Data Here shows whether LiDAR covers a spot.
Compare quotes without ringing around
Flow Paths gives you a fast, indicative answer. When the job needs pricing, designing or signing off, getting quotes usually means calling around and explaining the same site over and over. Instead, run the tool on your site and choose Compare quotes under the result. Describe the job once and we’ll send it to up to 3 local drainage engineers, with an aerial map of the site, a Google Earth file and your results attached, so they can price it properly from the start. They quote you directly. It’s free and there’s no obligation.
Data and attribution
Heights come from the LINZ elevation tiles: LINZ’s national bare-earth elevation model (LiDAR where it has been flown, the 8 m model elsewhere), stored in 0.1 m steps, read in your browser at the finest zoom that fits the area: cells of about 0.5 m on a small area, coarser on a larger one. Over the sea the tiles read 0 m; they hold no seabed.
Elevation and cadastral data is sourced from the LINZ Data Service and licensed for re-use under the Creative Commons Attribution 4.0 International licence. Copyright in each LiDAR survey belongs to the body that commissioned it — a regional or district council, Waka Kotahi, NIWA and around thirty others — rather than to LINZ, which hosts and processes the national dataset. Every file exported from this site names the licensors whose surveys cover the area, and anything you publish from those files carries the same attribution requirement. See https://www.linz.govt.nz/products-services/data/licensing-and-using-data/attributing-elevation-or-aerial-imagery-data
Questions
Is this a flood map?
No. It is a screening map of where the ground sends water and where it can sit, not flood depths for a given storm. For flood hazard, check your council’s flood maps and the LIM. If you need flood levels for a consent, that is a site-specific assessment by a chartered engineer.
What is an overland flow path?
The route surface water takes when rain falls faster than the ground and pipes can take it. Auckland’s Unitary Plan defines one as a low point carrying runoff from more than 4,000 m² of land upstream, not counting streams. Other councils use similar ideas, and many note flow paths on LIMs.
Why doesn’t the council map show this flow path?
Council maps are drawn for planning across a whole district: some only model rivers and large floodplains, and some pre-date the latest LiDAR. This map is traced from the most recent 1 m survey and names it, so you can compare dates. Where the two disagree, ask the council or an engineer which is right. The council’s layer is the one consent decisions use.
How small a flow path does it show?
Anything draining 0.1 ha (1,000 m²) or more on a property-sized area. On large areas the cut-off rises so the map stays readable, and the panel says where it sits. Tap any line to see exactly how much land drains through it.
What does it miss?
Culverts, pipes, kerbs and drains narrower than the sampling are not in the terrain, so water is routed over roads and through embankments. Bare-earth LiDAR also removes buildings. Check the result against what you see on site.
Ready to try it?
Open Flow Paths on the map →Free to use, no account. Runs in your browser on LINZ open data. Downloading the results needs a pass: see prices.
Missing something you need? Suggest a feature or ask about custom work.