Multnomah County, Oregon
A shallow water table limits basements on 30% of Multnomah County's mapped land and the 8th highest of 35 Oregon counties. Shrink-swell clay limits houses without basements on 0%.
36.3% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 29 flood losses here since 2016. 60% of homes were built before 1980, against 50% nationally; the median home dates from 1972.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Multnomah County
| Expansive clay (limits slab homes) | 0.0% |
| High water table (limits basements) | 29.9% |
| Septic fields very limited | 74.2% |
| Clay swell (LEP, by area) | 1.9% |
| High-swell land (LEP 6%+) | 0.0% |
| Urban land, not rated | 13.5% |
| Mapped soil | 297,657 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Zygore | 8% | n/a |
| Cascade | 7% | n/a |
| Goble | 6% | n/a |
| Multnomah | 5% | n/a |
| Sauvie | 5% | n/a |
| Aschoff | 5% | n/a |
How we count · survey areas OR051 (2025-09-09)
What the numbers mean here
On 30% of Multnomah County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 59.50 in, 3.86 in below the 1991-2020 average year of 63.36 in.
USDA rates 74% of the land very limited for septic absorption fields.
Drought
36.3% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 19 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the December 2, 2025 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 36.3% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
29 flood losses since 2016, $158,997 paid. The worst year was 2016, with 6.
| Year | Flood losses |
|---|---|
| 2016 | 6 |
| 2017 | 5 |
| 2018 | 0 |
| 2019 | 2 |
| 2020 | 2 |
| 2021 | 4 |
| 2022 | 4 |
| 2023 | 4 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 63.36 in |
| 12 months to August 2026 | 59.50 in (-3.86) |
| 2025 | 58.84 in (-4.52) |
| Wettest year since 1895 | 1996: 96.98 in |
| Driest year since 1895 | 1944: 40.56 in |
| Days with 1 inch or more, normal at PORTLAND WFO (6 mi away) | 5.3 |
Homes
| Housing units | 371,179 |
| Median year built | 1972 |
| Built before 1980 | 60% |
| Built 2000 or later | 23% |
| Owner-occupied | 53% |
| Median value, owner-occupied | $552,700 |
| Single-family detached | 53% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Clark County, WA | 16 mi | 3% | 22% |
| Clackamas County, OR | 29 mi | 5% | 30% |
| Washington County, OR | 33 mi | 7% | 42% |
| Hood River County, OR | 37 mi | 0% | 5% |
| Skamania County, WA | 40 mi | 4% | 5% |
| Columbia County, OR | 42 mi | 7% | 35% |
| Marion County, OR | 45 mi | 19% | 40% |
| Cowlitz County, WA | 47 mi | 4% | 10% |
Sources: USDA SSURGO (September 9, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status