Oregon Elevation ToolsOpen Wetness Map on the map →

Water · Select a property, draw a box or polygon, or upload a boundary

Topographic wetness index map for Oregon land

The topographic wetness index maps where the shape of the land tends to keep ground wet: lots of upslope area draining onto flat ground scores high, a steep ridge with nothing above it scores low. It is calculated from the USGS 3DEP lidar model with a 0.62 mi buffer so water from beyond the boundary is counted.

Use it to find fields that stay muddy, sites for wet-tolerant planting, and places to rule out early when you are looking for a septic drain field.

Free to run · pay to download

See the full result on the map free, with no account. Download the wetness index as a GeoTIFF with a pass: US$29 for 24 hours, US$99 for 30 days or US$399 for 12 months, a one-off payment in US dollars that never renews. Every download on the site is included while the pass lasts.

Open Wetness Map on the map →Pass prices and what’s included

Who uses this

  • Farmers. Target drainage tile and grazing on the ground that stays wet.
  • Restoration planners. Match species to wet hollows and dry slopes.
  • Septic designers. Screen for drain field locations before the soil tests.

When to use it

  • Finding the parts of a field likely to stay wet, get muddy or need drainage tile.
  • Choosing planting sites: wet-tolerant species in the blue areas, drought-tolerant on the tan.
  • Screening a property for possible septic drain field locations before the soil tests.

Tools for your job

Wetness Map is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.

For the job: Drainage, flooding and wet ground

Where does the water go, and where will it sit?

  1. 1.Water & Drainage — The drainage channels across an area, and where water ponds once low spots fill.
  2. 2.Wetness Map (this tool) — Which parts of a field the shape of the land keeps wet.
  3. 3.Catchment — All the land that drains to one culvert, draw or low corner.
  4. 4.Landforms — Hollows, valleys and footslopes at a glance: where water gathers.

For the job: Farms, ranches, orchards and timber

Which ground suits which use?

  1. 1.Slope & Aspect — Equipment limits and erosion-prone slopes.
  2. 2.Sunlight — Frost pockets and shaded slopes in winter.
  3. 3.Wetness Map (this tool) — Wet-tolerant planting in the blue, drought-tolerant on the tan.
  4. 4.Landforms — Exposed ridges, sheltered hollows and well-drained spurs.

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.

Step by step: Mount Hood

We map which parts of Mount Hood’s south side tend to stay wet.

1.Zoom to the area and run the analysis. Tan is dry ground, blue is where water collects. The panel shows the index minimum, mean and maximum.

2.Zoom in and the canyon floors and the flatter benches stand out as the wettest ground.

What it showed

  • The index is relative to this area. Use it to rank ground within one property, not to compare two places.
Try it yourself on Mount Hood →

How it works

Water is routed downhill across the USGS 3DEP bare-earth model, with a 0.62 mi buffer loaded around the area so that upslope 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 upslope 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 colors 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 colors stop changing.

Limits and caveats

  • Terrain only. Soil type, water table, ditches and drainage tile are not known to the tool, and it is not a wetland determination.
  • Values are comparable within one run, not between different areas or dates.
  • Where lidar has not been flown, the USGS 3DEP model falls back to its 1/3 arc-second layer, about 33 ft per pixel, and downloads state what share of the area came from it. That coarser model is not fit for site-scale decisions. DOGAMI reports about 99% of Oregon covered by at least one lidar project. The fallback is rare.

Data and attribution

Results come from the USGS 3D Elevation Program (3DEP) bare-earth elevation model: lidar at 3.3 ft per pixel where it has been flown, and the 1/3 arc-second model, about 33 ft per pixel, elsewhere, with elevations above NAVD 88. The tools with a surface option (Sunlight, Viewshed, Sightline, Object Heights) read DOGAMI’s statewide digital surface model of trees and buildings.

USGS 3DEP elevation data and USGS maps are U.S. Government works in the public domain: you may use the results, including commercially. A credit to the USGS 3D Elevation Program is appreciated, and every file you download carries it. DOGAMI lidar products are published by the State of Oregon; credit "DOGAMI / Oregon Lidar Consortium". County taxlot boundaries are the assessor's GIS data, not surveys, and each county publishes its own disclaimer, shown with the parcel. The aerial basemap is from Esri and follows Esri's terms; it is not included in downloads.

Questions

Is it a soil moisture reading or a wetland map?

Neither. It is a relative ranking from terrain shape alone. Soil type, water table and existing drains are not known to the tool, and only the Oregon Department of State Lands and a wetland professional can say what counts as a wetland.

Ready to try it?

Open Wetness Map on the map →

Free to use, no account. The analysis runs in your browser on public-domain USGS 3DEP data. Downloading the results needs a pass: see pricing.