FEMA Floodplain Maps Effective November 6, 2010
***See Interactive Map Tool at bottom of page***
Principal Flood Problems
Flooding in Portland is caused in spring by the Columbia River Basin snowmelt freshet and in winter by intense rainstorms that result in high flows in the Columbia and Willamette Rivers. Flooding also occurs in more localized areas within the city as a result of ponding from seepage through levees during prolonged high-river stages and from winter storm runoff in tributaries such as Johnson Creek.
The annual Columbia River snowmelt freshet occurs in Mayor June and has caused flooding in Portland during high runoff years. The Willamette River floods during the spring freshet primarily as a result of backwater effects from the Columbia River. The June 1894, 1948, and 1956 floods, with recurrence intervals of 80.48, and 18 years, respectively, were snowmelt freshets. At The Dalles, Oregon, the nearest gaging station with a reliable discharge measurement. those flood events had peak discharges of 1,240,000, 1,010,000, and 823,000 cubic feet per second (cfs), respectively. Minor flooding in the Portland area begins when flows at The Dalles reach 450,000 cfs, and major damage begins when flows reach 600.000 cfs. default Read more...
Changes since last mapping
A "KML" is a file that can be downloaded and opened directly in Google Earth, ArcGIS Explorer and other viewing software available on the Internet. The KML below is for the Special Flood Hazard Area (SFHA), also known as the "100-year" flood.
- Download KML:Portland SFHA KML (289.24 kB)
A Flood Insurance Study (FIS) is the publication developed in conjunction with the Flood Insurance Rate Map (FIRM) and discusses the engineering methods used to develop the FIRMs. The study also contains flood profiles for studied flooding sources and can be used to determine Base Flood Elevations for some areas.
- Download County Flood Insurance Study:
None planned at this time
None at this time
Note - For general information only - DO NOT use for regulatory purposes, especially for non-modernized areas: see "description" for source information and disclaimer
(hint: once in Viewer select "Basemap" in upper left corner for imagery background)