Portland erosion control requirements
If you are disturbing soil anywhere in Portland, the city expects you to keep it on site. The rules are stricter for seven months of the year, and most of the trouble people run into comes from not knowing which season they are in.
Last reviewed October 2026. Rules change, so check the city and state pages linked below before you rely on this.
Shaded months are the wet season, when the two day rule applies.
What are Portland’s rainy season rules?
From October 1 to April 30 the city treats every site with bare soil as a wet weather risk. Three things change.
Sports fields and playgrounds surrounded by vegetative cover or permanent curbing are exempt from the cover requirement.
Source: City of Portland, extra erosion control measures from October
Cover bare soil within two days
Any area stripped by ground disturbing work needs temporary or permanent cover as soon as practicable, and no more than two days after the work that exposed it.
Inspect weekly and write it down
An on site erosion and sediment control manager has to inspect and record it at least once a week.
Inspect after storms
Also within 24 hours of any rainfall over half an inch measured in a 24 hour period.
City deadlines and state deadlines are different
Worth separating these, because people quote one at the other.
- Two days from October 1 to April 30
- Seven days from May 1 to September 30
- Driven purely by the date on the calendar
- No wet or dry season rule at all
- Under five acres: start immediately once an area has been inactive 14 or more days, finish within 14 days of starting
- Five acres and over: finish within seven days of starting
Inside Portland on a site over an acre, both apply. Work to whichever is tighter, which in winter is the city’s two days. The permit defines immediately as no later than the end of the next business day.
Source: Oregon DEQ, 1200-C permit, Schedule A.16
Where work is banned outright
Inside the environmental zones of the Balch Creek and Forest Park subdistricts of the Northwest Hills Plan District, ground disturbing work is prohibited between October 1 and April 30. Not restricted. Prohibited.
If your site is in the west hills, check which plan district you are in before you schedule anything for the winter. This one catches people who assumed they could work with extra controls in place.
What changes on May 1?
The cover requirement stays, the clock gets longer. From May 1 to September 30 you have up to seven days to cover exposed soil rather than two.
Everything else about keeping sediment on site still applies. The dry season is a longer deadline, not a holiday.
Which rules apply to my site?
It depends on how much ground you are disturbing and which jurisdiction you are in. The state permit covers any project disturbing one acre or more, and an Erosion and Sediment Control Plan has to be approved before work starts.
Cities set their own lower tiers. Tualatin separates single family residential, under 1,000 square feet, and 1,000 square feet or more, before you reach the 1200-CN threshold. West Linn asks for the erosion control plan with the building permit under an acre, a standalone permit over an acre, and a DEQ 1200-C on top of that over five acres.
| Area disturbed | What applies |
|---|---|
| Under 1 acre | Local erosion control permit, usually submitted with your building permit |
| 1 to 5 acres | 1200-CN, administered locally |
| 5 acres and over | 1200-C, administered by Oregon DEQ |
Sources: City of Tualatin, City of West Linn, Oregon DEQ.
Does seeding count as cover?
Yes, but with a condition that catches a lot of people in the autumn.
Local standards in the metro say grass seed, whether sprayed or spread by hand, does not provide adequate ground cover protection unless maximum germination is reached by October 1. If the seeding does not take, you have to install something else: straw, yard debris compost or an erosion control blanket.
That is why late September is the wrong time to gamble on seed. If it does not come up, you are buying blankets anyway, on a wet site, in a hurry.
When is the site finished?
For a 1200-C site, DEQ approves termination once there is uniform perennial vegetation, excluding noxious and invasive weeds, giving at least 70 percent cover. Arid and drought stricken areas have an exception, which is not much help here. Farmland restored to its previous use is exempt from the vegetation criteria.
You then file the Notice of Termination within 30 days of meeting the criteria, with photographs of the final stabilization, the status of any open compliance issues, and any unpaid fees settled. You remain responsible under the permit until DEQ approves it.
Source: Oregon DEQ, Schedule A.17 and Condition I.10
Washington County is not the same
Sites in Beaverton, Hillsboro, Tigard, Tualatin and Sherwood follow Clean Water Services design and construction standards rather than Portland’s Title 10. The thresholds and the paperwork differ. Clean Water Services handles erosion control inspection requests on 503-681-4444.
Who do I call with a question about my site?
The City of Portland Erosion Control Hotline, 503-823-0900. That line also takes reports of possible violations.
What does an inspector actually look at?
Whether cover is in place, whether perimeter controls are working, and whether your inspection log is on site and up to date. The log is the one people forget.
Do I need an inspection log in summer?
The weekly documented inspection requirement is tied to the October to April window. Keeping records year round is still the easier habit.
Does a small residential job need any of this?
Usually yes, in some form. Under an acre it typically rides along with your building permit rather than being a separate application.
What if rain is forecast the day after I strip the site?
Cover it the same day. Two days is the outer limit, not a target.
Can I just use plastic sheeting?
It is an accepted temporary measure in city guidance alongside mulch, blankets and temporary grasses. It is not a permanent solution and it moves in wind if it is not weighted properly.
Need cover on a Portland site?
Tell us the site and the deadline and we will match cover to your plan. See what we install.
[TRACKING NUMBER]- Acreage or square footage
- How steep the ground is
- Which permit the site is under
- Your deadline