What is a combined flood hazard area?
The combined flood hazard area adopted in Title 33 is land located in the 100-year floodplain, as currently defined by the Federal Emergency Management Agency (FEMA); the City’s Modeled Willamette River 1996 Flood Extent; and the 1996 Flood Inundation Area mapped by Metro. There are slight differences between the combined flood hazard area and the combination of the 100-year floodplain and the Composite February 1996 Flood Inundation Area regulated in Title 24.50 – Flood Hazard Areas.
What is a floodway?
The floodway is the portion of the FEMA 100-year floodplain that is reserved in order to convey the 100-year flood without cumulatively increasing the water surface elevation more than a designated height. The floodway is usually associated with a stream channel or river and may include adjacent land areas.
How do I know if my property is in a combined flood hazard area?
If your property is within a 100-year floodplain, 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 floodplain is determined by FEMA. Copies 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 through the Advanced Gallery or Open Data.
How do these regulations affect proposed land divisions?
Zoning Code Chapter 33.631 applies to land division proposals on sites with any area within the combined flood hazard area. The standards and approval criteria limit the creation of lots on lands subject to flood in order to direct development away from hazardous areas and to preserve the natural function of floodplains.
A project may either meet standards, or if the standards cannot be met, the project must meet the approval criteria in order for the land division to be approved.
Standards:
To meet standards, all lots and most services must be located outside of the combined flood hazard area and the combined flood hazard area must be placed in a tract, which cannot be developed.
Approval Criteria:
- 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 proposed lots must have adequate building areas outside of 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 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 Existing Conditions Map must include the location of the combined flood hazard area and floodway boundaries, including elevations of combined flood hazard area, including the FEMA 100-year floodplain, the Modeled Willamette River 1996 Flood Extent or the 1996 Flood Inundation Area inundation elevations, in addition to theFEMA Floodway boundaries. Elevations must be surveyed relative to the North American Vertical Datum of 1988 (NAVD 1988) or the City of Portland datum. Sites that contain a water body not shown on the FEMA maps must identify the boundaries of the associated 100-year flood hazard areas. See 24.50.050 for details.
- If the proposed lots are within the combined flood hazard area, the Proposed Improvements Map must show the proposed building locations.