Floodplain Proposed Draft proposals and the effects on areas of Portland

Summary of the Floodplain Resilience Plan Proposed Draft and its proposals, including updates to the plan since the Discussion Draft, and how the proposals will affect different geographic areas of Portland.
On this page

The purpose of the Floodplain Resilience Plan is to reduce the impacts of future flooding and degradation of floodplain habitat on endangered and threatened fish species. The plan will update the City’s floodplain regulations to increase environmental protections of floodplains and expand access to mitigation banks as an off-site option to address development impacts. Read more about the Floodplain Resilience Plan

Key updates since the release of the Discussion Draft

The Floodplain Resilience Plan Discussion Draft was released in early November of 2021. Public comments were gathered on the draft through the end of January 2022. The Proposed Draft incorporates changes in response to those comments, as well as additional research and evaluation by project staff, including:

  • Separate building code (Title 24) update process – Several updates to the Building Code Chapter 24.50, Flood Hazard Areas, were included in the Discussion Draft, along with Zoning Code (Title 33) changes. City staff subsequently decided to split the updates to Titles 33 and 24 into separate projects. Addressing this work in a separate project will allow the City to ensure there are off-site mitigation banking options for development that can’t mitigate on site and provide the necessary time for the Bureau of Development Services to better prepare for implementation of the changes. As this separate project progresses, BDS will consider the comments received during the Discussion Draft comment period on the proposed Building Code changes.
  • Incorporated Modeled Willamette River 1996 Flood extent – In collaboration with the U.S. Army Corps of Engineers, City staff completed a new model of a Willamette River flood event similar to the February flood of 1996, which is expected to be more common due to climate change. Areas with a high probability of flooding identified in the model have been incorporated into the “combined flood hazard area,” which also includes the FEMA 100-year floodplain and Metro’s 1996 Flood Inundation Area. This updated combined flood hazard area has been used to refine the boundaries of the environmentally-focused overlay zone currently applied or proposed along the Willamette River and Lower Columbia Slough. In the future, Building Code Chapter 24.50 requirements will also apply to this updated combined flood hazard area. 
  • Apply environmental zoning to undeveloped floodplains – The Discussion Draft proposed the application of environmental regulations to all floodplains along Fanno Creek, Tryon Creek and the Willamette River Central Reach that are not already in an environmentally-focused overlay zone. The River Environmental overlay zone is currently applied to all Willamette River South Reach floodplains. After discussions with Bureau of Development Services staff, we determined that the application of the environmental regulations to developed floodplains (the River Environmental overlay zone landward of the Willamette River riparian buffer area and the Environmental Conservation overlay zone along Fanno and Tryon Creek) would only result in unnecessary development review process and costs without significant benefit. Therefore, this draft proposes to apply the environmental regulations to undeveloped floodplains. Environmental regulations are still proposed for all floodplains in the riparian buffer area (where applicable). The riparian buffer area includes floodplains within 170 ft of the ordinary high-water mark in the Central and South reaches of the Willamette River.  
  • Update requirements in the Willamette River South Reach – The extents of the River Environmental overlay zone and the riparian buffer area have been modified to apply to the updated combined flood hazard area, which includes the new Modeled Willamette River 1996 Flood Extent. In some cases, this resulted in an expansion of the River Environmental overlay zone and/or riparian buffer area and, in others, the extent of these areas was reduced. Additionally, consistent with the previous bullet, the removal of the River Environmental overlay zone is proposed for developed floodplains not in the riparian buffer area.        
  • Remove proposed Environmental Conservation Overlay expansions in Columbia Corridor – The Discussion Draft included some targeted expansion of the Environmental Conservation overlay zone on floodplains along the Columbia River and Columbia Slough not in the Heavy Industrial (IH), General Industrial 2 (IG2) and General Employment 2 (EG2) zones. After further evaluation, these proposed expansions were removed from the Proposed Draft. Instead, they will be included in a package of future Zoning Code updates that will be part of the Economic Opportunities Analysis (EOA). That package will update the City’s inventory of natural resources in the area, consolidate the existing Columbia Corridor resource management plans into a single document, and include changes to the Environmental overlay zones that are consistent with the Floodplain Resilience Plan proposals and the recently completed Ezone Map Correction Project.

Summary of Proposed Draft proposals by area

The Floodplain Resilience Plan Proposed Draft includes different proposals depending on location of the property, including:

Willamette River Central Reach

  • Adopt a new Zoning Code map to identify the Central Reach riparian buffer area and apply the existing riparian buffer area requirements (located in Zoning Code chapter 33.475, River Overlay Zones) to the area shown in the map. Development proposed in the riparian buffer area is required to mitigate all impacts on identified natural resources and demonstrate an improvement in one of two floodplain-related riparian functions. Improvements to floodplain functions are approved through land use review.  
  • Expand the River Environmental overlay zone to encompass the proposed riparian buffer area and any undeveloped floodplain landward of the riparian buffer area.

Willamette River South Reach

  • Update the boundaries of the existing riparian buffer area and River Environmental overlay zone to include the areas identified in the Modeled 1996 Willamette River Flood Extent and FEMA 100-year Floodplain.
  • Remove the River Environmental overlay zone from developed floodplains landward of the riparian buffer area.

South Waterfront

  • Add new standards for tree and vegetation removal and maintenance, similar to those in the River Overlay Zones chapter (33.475).
  • Code clarifications and updates to the Greenway land use review process, including:
    • Restructure the South Waterfront Greenway overlay zone (33.510.253) requirements to address the issue that the current code structure limits the application of the exterior lighting standards only to the Greenway Area (100 ft from top of bank). The original intent was to apply these requirements to all development in the River General overlay zone.  
    • Change the process for South Waterfront Greenway Review from a Type III to a Type II procedure, consistent with the approval process in other environmental overlay zones in the city. A Type II procedure allows for a determination on a proposed development to be made by Bureau of Development Services staff, rather than requiring Design Commission approval.  

Elsewhere in the city (including Fanno Creek, Tryon Creek, Johnson Creek, Columbia River and Columbia Slough)  

  • Expand the Environmental Conservation overlay zone to encompass undeveloped floodplains along Fanno and Tryon creeks.
  • Update 33.430, Environmental Zones, to limit, in some cases, when a tree can be removed through an exemption and establish a requirement that at least three trees are to be planted whenever a tree is removed in the floodplain.