Floodplain Information

Lane County is concerned about flood hazards. The purpose of this section of the county’s Web site is to provide citizens information regarding flood hazard safety as well as information about flood insurance and construction within the floodplain. The information found on these pages is not to be considered a substitute for the language of federal or local floodplain regulations. Specific county flood regulations are located in Lane Code 16.244 (applicable to rural Lane County) and Lane Code 10.271(applicable within the urban growth boundaries of small cities).

If requested, Land Management planning staff will conduct a site visit to review potential flood problems and explain ways to stop flooding or prevent flood damage to your property. You may call the Planning staff at 541-682-3577 to discuss this service.

Overview

Lane County features several large rivers and smaller tributaries and streams that are susceptible to annual flooding events. The flooding of these waterways threatens life and safety and can cause significant property damage. Large rivers include the Willamette (Main Stem, Middle and Coast Forks) the McKenzie (including the South Fork), the Siuslaw (including the North Fork) the Row River and Lake Creek. Smaller streams and tributaries susceptible to frequent flooding include the Mohawk, Long Tom, Fall Creek, Little Fall Creek, Camp Creek, Horse Creek, Coyote Creek, Mosby Creek, Poodle Creek, Siltcoos River and Tenmile River.

Lane County has nearly 140,000 Acres of land in the floodplain. This is equivalent to well over 200 square miles! Over 11,000 individual parcels are partially or entirely located within the floodplain. Statewide, Lane County has more river miles of floodplain than any other county. Ongoing development along these rivers continues to displace natural areas that have historically functioned to store and flood waters.

The Army Corps of Engineers operates 13 multi-purpose water projects (also known as dams) in the Willamette Valley, with nine of those projects situated in Lane County. The primary purpose of these dams is flood control, although they only control flooding on 50% of the tributaries in the Willamette Basin. Reservoirs behind the dams are drained throughout the summer and fall months to create storage capacity for water from heavy winter and spring rains. Therefore, most flooding in Lane County occurs on tributaries that do not feed these reservoirs or along rivers with no flood control devices, such as the Siuslaw. It is important to recognize that even if you live downstream of a dam, flooding is possible. During prolonged and intense flood events reservoirs do fill up. In these situations, the Army Corps must release flood waters from the reservoirs.

Recent Flooding Events

While some type of seasonal flood-related damage occurs nearly every year, the flooding and associated landslide events of February and November 1996 represent the most recent significant flooding. 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 Lane County to rise to 100-year flood levels. Flooding was particularly severe along the Siuslaw and Mohawk Rivers. Damage to Lane County businesses, residences and infrastructure was estimated to be roughly $19 million dollars.

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 statewide, and 20 Oregonians lost their lives. In addition to the '96 and '64 floods, Lane County has experiences several other significant floods since records have been kept. In 1972, flooding along the Siuslaw River caused extensive damage within the community of Mapleton. The floods of 1945, 1942 and 1927 caused severe damage to the City of Eugene and the surrounding areas. Early records indicate that the Southern Willamette Valley flooded often in the mid to and late 1800’s, with major flooding occurring in 1850-51, 1861, 1881 and 1890. While the 1996 events were devastating to the entire region, the floods of 1861, 1890, and 1964 exceeded the 1996 event in terms of velocity and volume of water. All three floods are estimated to have exceed the so-called “100-year flood,” or Base Flood in Lane County, and all within a time frame of about 100 years.

Causes of Flooding in Lane County

Flooding occurs when climate, geology, and hydrology combine to create conditions where river and stream waters flow outside of their usual course and “overspill” beyond their banks. In Lane County, the combination of these factors, augmented by ongoing development, create chronic seasonal flooding conditions. Lane County spans a wide range of climatic and geologic regions from the Pacific coast to the high Cascades. This diversity results in considerable variation in precipitation. The average annual precipitation ranges from less than 40 inches in the Willamette Valley to over 100 inches in the Coast Range and along the west slope of the Cascades. Snowmelt from the Central Cascades provides a continuous water source throughout the year, and can contribute significantly to flooding.

Flooding is most common from October through April , when storms from the Pacific Ocean bring intense rainfall to the area. Larger floods result from heavy rains that continue over the course of several days, augmented by snowmelt at a time when the soil is near saturation from previous rains.

Lane County’s Flood Program

Lane County is a participating member of the National Flood Insurance Program or NFIP. In order to participate in the NFIP, Lane County is required to adopt and enforce floodplain management ordinances aimed at reducing the likelihood of future flood damage to new construction within the regulated floodplain, also known as the Special Flood Hazard Area (SFHA). The county must manage land within SFHA in ways that meet or exceed standards set by the Federal Emergency Management Agency (FEMA). Oversight of the county flood program is the responsibility of the Land Management Division. View more information about county regulations pertaining to development in the SFHA.

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