Wetness Map

When to use it

• Finding the parts of a paddock likely to stay wet, pug up or need drainage.
• Choosing planting sites: wet-tolerant species in the blue areas, drought-tolerant on the tan.
• Screening a block for soakage field or effluent disposal locations.

How to use it

1. Select a property, draw an area or upload a boundary.
2. Run. Tan is dry ground; deep blue is where water collects.
3. Read the index range in the panel. The gradient bar and the map legend show the same two end values.

How it works

Water is routed downhill across the LiDAR bare-earth model, with a 1 km buffer loaded around the area so that upstream ground outside the boundary is counted. For each cell the tool takes the area draining into it and divides by the local slope. Lots of upstream area on flat ground gives a high value; a steep ridge with nothing above it gives a low one.

The number is the topographic wetness index, a standard hydrology measure. It is a relative ranking, not a moisture reading.

Reading the results

The colours are stretched between the 2nd and 98th percentile of the area, so the deepest blue is the wettest ground in this area, not a fixed threshold.

Minimum, mean and maximum in the panel are the true extremes; the bar shows where the colours stop changing.

Limits and warnings

• Terrain only. Soil type, water table, drains and tile drainage are not known to the tool.
• Values are comparable within one run, not between different areas or dates.
• Where 1 m LiDAR has not been flown the tool falls back to the national 8 m elevation model, and the result says what share came from the fallback. The 8 m model was interpolated from 20 m map contours and is not fit for site-scale decisions.

Data and attribution

Results come from the LINZ national 1 m LiDAR bare-earth elevation model, read in your browser, with the national 8 m model filling any gaps. Tools that use the surface model (Sunlight, Viewshed, Object Heights) read the matching LiDAR surface tiles.

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

Related

Neighbouring tools

• Water & Drainage — Extracts the drainage channels across an area as an ordered stream network, and maps where water would pond once hollows fill, with depth, area and volume.
• Catchment — Maps all the land upstream of a point you click, so you can see where the water arriving at a culvert, a gully or a stream crossing comes from.
• Landforms — Classifies every part of your area into one of ten landforms, such as ridge, spur, slope, hollow and valley, at a scale you choose.