Countywide FEMA Floodplain Maps Effective September 29, 2010
***See Interactive Map Tool at bottom of page***
Principal Flood Problems
In Linn County, the annual flood season extends from October through April, with a majority of the larger flood occurring in December and January. During the winter, storms move inland from the Pacific Ocean, bringing periods of intense rainfall over the Pacific Northwest. Floods are a possibility whenever rainfall is abnormally intense or prolonged.
Floods in Linn County are normally widespread, rather than limited to a few streams in a single basin, and may occur several times during a flood season. They are caused primarily by intense rainfall lasting 2 to 5 days, augmented by snowmelt at a time when the soil is nearly saturated from prior rains. The freezing level may raise to 10,000 feet or higher during the more intense rainstorms, causing rapid melting of accumulated snow in the Cascade Range. When the ground is frozen or saturated, runoff becomes greater and more rapid. The direction of the storm path also influences the rate of runoff. Higher flows are generated when the storm front moves in a downstream direction, producing a buildup of floodwaters.
The greatest known flood on the Willamette River at Albany occurred in December 1861, before there was a stream gaging network for recording flood heights. This flood had an estimated peak discharge of 340,000 cfs and a recurrence interval of 100 years. Discharges and crest elevations for large Willamette River floods at the USGS Albany gage (No. 14174000) from 1941 to 2007 are listed in Table 4. The most recent Willamette River flood occurred in 1997 and had a recurrence interval of about 6 years. The 1964 flood resulted from unusually intense precipitation on a frozen topsoil augmented by snowmelt in the mountains and valleys. Little damage occurred within the North Albany unincorporated area. Further upstream, the City of Harrisburg is located on high ground along the Willamette River, and has suffered only minor damage from past Willamette River flooding. default Read more...
Changes since last mapping
The floodplain boundaries of the detailed study areas were revised with new topographic mapping; Oak Creek, Calapooia River, and Willamette River with contour interval of 2 feet and 5 feet, North Santiam River with contour interval of 2 feet and 5 feet, Cox Creek and Truax Creek with a contour interval of 2 feet, North Lake Creek and Santiam River, and with a contour interval of 5 feet, and Ames Creek with a contour interval of 2 feet.
Approximately 21 miles of the South Santiam River floodplain boundaries, from River Mile 14.57 to River Mile 35.78, were revised using topographic mapping with a contour interval of 2 feet and 5 feet.
The remaining floodplain boundaries were digitized from the effective FIRM and Floodway panels. Where new topographic mapping was available, approximate Zone A areas were refined with a contour interval of 2 feet and 5 feet. Where applicable, the contour data was used to adjust the flood hazard areas to more accurately match the topography. In addition, aerial photography was used to adjust floodplain boundaries where appropriate. See the Flood Insurance Study for references.
-Linn County GIS...
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 (updated Dec. 2016): Linn_SFHA
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 at this time
Snapshots around the County
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)