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Combined Flood Hazard Areas

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Learn more about zoning regulations related to development in combined flood hazard areas.
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What is a combined flood hazard area?

A combined flood hazard area is land that is in the 100-year flood plain, as currently defined by the Federal Emergency Management Agency (FEMA); the Modeled Willamette River 1996 Flood Extent; and the 1996 Flood Inundation Area.

What is a floodway?

A Floodway is the portion of the flood hazard area that is actively flowing during a flood. The floodway is usually associated with a stream channel or river.

How do I know if my property is in a combined flood hazard area?

If your property is within a 100-year flood plain, the Modeled Willamette River 1996 Flood Extent, or the 1996 Flood Inundation Area, your site is in a combined flood hazard area. The 100-year flood plain is determined by FEMA. A copy of the FEMA floodplain maps are available here. The combined flood hazard area is also mapped digitally on the City of Portland GIS system. You may view digital GIS information, including the combined flood hazard area, at PortlandMaps.

How do these regulations affect proposed land divisions?

  • Single dwelling zones: In single dwelling zones all lots must be outside the combined flood hazard area. Or, if it’s not possible to have all lots outside of the combined flood hazard area, all existing and proposed building areas must be outside the combined flood hazard area.
  • All other zones: In multi-dwelling residential and commercial, employment, and industrial zones, each lot must have adequate area outside the combined flood hazard area to accommodate allowed or proposed uses (this criterion does not apply to river-dependent uses). Where the proposed uses and development are river-dependent, lots must be configured so that development on them will minimize obstruction of floodwaters.
  • All zones: Services proposed in the combined flood hazard area must be located and built to minimize or eliminate flood damage to the services, and the floodway must be entirely within a flood hazard tract unless river-dependent land uses and development are proposed on the site.

Submittal requirements – Zoning Code Section 33.730.060.D

When a land division application is submitted to the City, it must include the following information regarding the combined flood hazard areas:

  • The Vicinity Map must show the location of flood hazard areas for the site and the area extending at least 800 feet in each direction from the land division site.
  • The Existing Conditions Map must include the location of the combined flood hazard area and floodway boundaries, including elevations of 100-year floodplains and FEMA Floodway boundaries. Sites that contain a water body not shown on the FEMA maps must identify the location of flood hazard areas.
  • If the proposed lots are within a combined flood hazard area, the Proposed Improvements Map must show the existing and proposed building locations.