Countywide FEMA Floodplain Maps Effective June 17, 2008
New preliminary maps for Sandy River Watershed spring 2016
-See bottom of page for Interactive Map of flood hazards-
Principal Flood Problems
Historically, flooding within Clackamas County normally occurs from October through April. Cyclonic winter storms from the Pacific Ocean sometimes produce intense rainfall on drainage basins of the Pacific Northwest. When these storm fronts move in a downstream direction, greater discharges are produced. If this condition is accompanied by rapid snowmelt and frozen ground in the upper watersheds, large floods can result.
Floods in the study area are normally widespread rather than limited to a few streams. Because of longer travel times between the upstream headwaters and the study area, crests on larger rivers occur several days later than those on some of the smaller tributaries. For example, the Willamette River remains above the bankfull stage for approximately 10 days following a major flood, whereas most tributaries recede to within their banks in 4 or 5 days. The Tualatin River is an exception because there is considerable ponding in the middle and lower reaches. default Read more...
Updates from previous floodplain maps
As part of the countywide update, floodplain boundaries were digitized from the effective FIRM and Floodway panels. USGS topographic maps and aerial photography were used to adjust floodplain and floodway boundaries where appropriate. No new detailed studies were undertaken for this project.
- 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.
- 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 Clackamas Co KML (updated Nov. 2016):
Clackamas Co FIS:
- default Clackamas Co FIS, vol1 (1.24 MB)
- default Clackamas Co FIS, vol2 (5.31 MB)
- default Clackamas Co FIS, vol3 (3.88 MB)
New floodplain mapping for Sandy River Watershed; Public meeting July 12, 2016. Preliminary FIRMs can be downloaded at: https://msc.fema.gov/portal/advanceSearch
Snapshots around the county
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)