Countywide FEMA Floodplain Maps Effective December 19, 2006

***See Interactive Mapping Tool at bottom of page***

Polk Co SFHA

 

Principal Flood Problems

Flood season in the Willamette River Basin extends from October through April, with most major floods occurring in December and January. Floods in the areas are normally general in extent rather than limited to a few streams. They are caused primarily by heavy rainfall, sometimes augmented by snowmelt at a time when the soil is saturated by prior rainfall or is frozen. The Willamette River remains above bankfull stage for up to 10 days following a major flood, while smaller tributaries recede in 4 or 5 days. Floodwaters may remain standing in the floodplain for several days after streams recede.

Damage from flooding in Polk County is mainly to farmlands, largely in terms of flooded crops and pastures and fields and bank erosion. However, there is some flooding nearly every year; this results in damage to roads and bridges necessitating increased maintenance and repair patrols during flooding.

The largest flood on record on the Willamette River occurred in 1861 with an estimated peak flow of 500,000 cubic feet per second (cfs) at Salem. Many large floods have occurred since then. The December 1964 flood, unregulated, would have been the largest Willamette River flood since 1861. However, operation of seven upstream flood control storage dams reduced its estimated potential 472,000 cfs flow to 309,000 cfs and its flood level by 7 ft. at Salem. default Read more...


Changes since last mapping

No discussion


Community Links:

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-Polk County WebMap...
-Polk County Floodplain Maps...
-Polk County Hazard Mitigation Plan...

 


Download Products

- 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.


Future Mapping

None planned at this time


Snapshots around the County

None at this time


***NEW INTERACTIVE MAP for Special Flood Hazard Area ("100-year" flood)***

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)

Interactive Map


 

Contact for Oregon Risk MAP

The Department of Land Conservation and Development is the lead on the Oregon Risk MAP project. To reach the program coordinator contact:

Stephen Lucker
635 Capitol St. NE, Suite 150
Salem, OR 97301-2540

stephen.lucker@state.or.us