Stormwater Management: Gresham vs Portland
How do stormwater management rules compare between Gresham, OR and Portland, OR?
Gresham has fewer restrictions than Portland.
Gresham, OR
Multnomah County
Multnomah County stormwater is regulated under Oregon DEQ MS4 permits. Portland holds a Phase I NPDES permit and administers the Stormwater Management Manual (SWMM) under PCC 17.38. Post-construction runoff controls required for any development creating 500 sq ft or more of new impervious surface (stricter than the state 0.25-acre threshold). Clean River Rewards program incentivizes green infrastructure.
View full Gresham rules →Portland, OR
Multnomah County
Portland's Bureau of Environmental Services (BES) enforces comprehensive stormwater management under City Code Title 17 (Public Improvements) and the Stormwater Management Manual (SWMM). All new development and redevelopment creating 500 square feet or more of impervious surface must manage stormwater on-site. Portland holds an MS4 NPDES permit from Oregon DEQ requiring pollutant reduction in all stormwater discharges.
View full Portland rules →Key Facts Comparison
| Fact | Gresham | Portland |
|---|---|---|
| Portland Code | PCC 17.38; SWMM | - |
| Impervious Trigger | 500 sq ft (PDX) | - |
| State Trigger | 10,890 sq ft | - |
| Regulator | DEQ + Portland BES | - |
| Program | Clean River Rewards | - |
| Governing Code | - | Title 17 (Public Improvements) and SWMM |
| Trigger | - | 500+ sq ft new/replaced impervious surface |
| Utility Fee Basis | - | Impervious area on property |
| Discount Program | - | Clean River Rewards up to 100% off |
| Penalty | - | Up to $10,000/day per violation |
Highlighted rows indicate differences between cities.
Gresham FAQ
Do I need stormwater controls for a new driveway?
In Portland, yes if the new/replaced impervious surface totals 500 sq ft or more. Small residential patches below that may be exempt but check with BDS during permitting.
Can I wash my car in the driveway?
It is discouraged. Soapy water flowing to storm drains violates PCC 17.38.034. Use a commercial car wash or wash on gravel/grass where water infiltrates.
Portland FAQ
When do stormwater management requirements apply?
Requirements apply to any development or redevelopment that creates or replaces 500 square feet or more of impervious surface. The Stormwater Management Manual specifies pollution reduction, flow control, and infiltration standards.
Can I reduce my stormwater utility fee?
Yes. The Clean River Rewards program offers discounts of up to 100% on stormwater charges for properties that manage stormwater on-site using approved facilities like rain gardens, ecoroofs, or permeable pavement.
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