County personnel are available to provide specific flood and flood-related data and make site visits to review flood, drainage and sewer problems and advise and assist on retrofitting techniques. To speak with someone directly about these issues, please call the Clackamas County Planning Division at 503-742-4500.
Clackamas County features several large rivers and smaller tributaries, or streams, that are susceptible to annual flooding events that pose threats to life and safety and cause significant property damage. Large rivers include the Clackamas, Tualatin, Molalla / Pudding, Salmon, Sandy, Willamette and Zig Zag, while streams include Johnson Creek, Abernethy Creek, Beavercreek, Milk Creek, and Cedar Creek.
While some sort of seasonal flood-related damage occurs nearly every year, flooding and channel migration in the Sandy River Basin in January 2011, and flooding and associated landslide events of February and November 1996 represent the most recent significant flooding events. In February 1996, prolonged precipitation accompanied by an early snowmelt, caused by a warm-weather trend known as a "Pineapple Express," caused many rivers and creeks throughout the Willamette River watershed to rise to 100-year flood levels, causing flooding in both rural and urban areas.
Although the floods of 1996 represented a large-scale disaster, they are not unprecedented within the recent past. The Christmas Flood of 1964 caused $157 million in damage, and 20 Oregonians lost their lives. County records dating back to the mid-1800s indicate that the Willamette River has caused significant flooding to the County at least seven times, while flooding from the Clackamas River has dramatically affected the County at least five times.
Flooding occurs when environmental factors create conditions where river and stream waters flow outside of their usual course and "overspill" beyond their banks. In Clackamas County, the combination of these factors, augmented by ongoing development, create chronic seasonal flooding conditions. Riverine flooding and urban flooding are the two types of flooding that primarily affect Clackamas County. Riverine flooding is the overbank flooding of rivers and streams, the natural processes of which add sediment and nutrients to fertile floodplain areas. Urban flooding results from the conversion of land from fields or woodlands to parking lots and roads, through which the land loses its ability to absorb rainfall.
Clackamas County participates in the National Flood Insurance Program (NFIP) that makes available federally backed flood insurance for all structures, whether or not they are located within the floodplain. Membership within NFIP - and the availability to County residents of flood insurance - requires the County to manage its floodplain in ways that meet or exceed standards set by FEMA. Federal financial assistance requires the purchase of flood insurance for buildings located within the SFHA - a requirement that affects nearly all mortgages financed through commercial lending institutions. While the mandatory flood insurance purchase requirement has been in effect for many years, not all lending institutions required flood insurance in the past. Today, however, most institutions are now requiring the flood insurance purchase, and some are reviewing all mortgage loans to determine whether flood insurance is required and should have been required in the past.
Floodplain Development Materials
- County Floodplain Ordinance
- General Land Use Application
- Supplemental Floodplain Development Application
- Elevation Certificate and Instructions
- Variance Policy for Accessory Structures
- Federal Emergency Management Agency (FEMA)
- Clackamas County Code Enforcement
- Clackamas County Department of Water Environment Services (WES)
- Clackamas County Library System (floodplain publications and other information)
- Division of State Lands (DSL)
- Oregon Department of Fish and Wildlife (ODFW)
- Oregon Department of Forestry (ODF)
- National Marine Fisheries Service (NMFS)
- U.S. Army Corps of Engineers
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