5 county-level rules, plus city-specific rules for 3 cities in Multnomah County, Oregon.
Verified from official government sources
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.
Multnomah County erosion control follows DEQ 1200-C NPDES permits for construction sites over 1 acre and local erosion control programs under PCC 10 (Portland) and GRC 6.18 (Gresham). Portland requires Erosion & Sediment Control Plans for all permitted earthwork. Best management practices include silt fences, straw wattles, stabilized construction entrances, and covered stockpiles. Sediment discharge to waterways carries severe penalties.
Multnomah County is inland on the Columbia and Willamette rivers and has no Pacific coastline. Oregon's Coastal Zone Management Program (Statewide Planning Goal 17 and 18) does not apply to Multnomah County. Riverfront development along the Columbia and Willamette is governed by the Willamette Greenway (Goal 15) and the Columbia River Gorge National Scenic Area east of Troutdale. No coastal commission jurisdiction exists.
Multnomah County has extensive flood management responsibilities along the Columbia and Sandy Rivers. The Urban Flood Safety and Water Quality District (est. July 1, 2024) manages 13,000 acres of floodplain including 27 miles of levees. County flood hazard areas require permits and NFIP compliance. Community Rating System discounts flood insurance premiums.
Portland requires grading permits under PCC Title 24 for excavation or fill exceeding 50 cubic yards or slopes over 20%. Portland's Landslide Hazard areas (West Hills) require geotechnical reports. Drainage cannot be redirected onto neighboring properties (ORS 105.170). Retaining walls over 4 feet require engineered plans. Multnomah County Land Use requires grading permits in unincorporated areas on SEC overlay or steep slopes.
3 cities in Multnomah County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
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