Benton County, Oregon

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Printed on Aug 29, 2015 @ 7:35 AM

Benton County Emergency Management – Flood Causes & History

Causes and History of Flooding in Benton County

Floods are the #1 natural disaster in the United StatesIn Benton County a combination of factors create seasonal flooding conditions.

Flooding occurs when climate or weather patterns, geology, and hydrology combine to create conditions where river and stream waters flow outside of their main channel and overspill their banks.

Development in the County also causes displacement of acreage that has historically functioned as flood storage.

Benton County's climate consists of mild, wet winters and warm, dry summers, with an average temperature in the Willamette River Valley ranging from 34°F in January to 81°F in July.

Precipitation varies over the County, depending on elevation and location.

Flooding History (recorded in feet)

Floods are the #1 natural disaster in the United States

While the 1996 flood affected and inconvenienced the entire region, thirteen prior flood events far exceeded the velocity and volume of water associated with the floods of 1996: Dec. 1861, Jan. 1881, Feb. 1890, Jan. 1901, Jan. 1903, Feb. 1907, Nov. 1909, Jan. 1923, Feb. 1927, Jan. 1943, Dec. 1945, Jan. 1948, Dec. 1964.

Hwy. 34 during the 1996 floodFlooding most commonly occurs between the months of November and March when storms from the Pacific, only 45 miles away, bring intense and sustained rainfall to the area. This condition often results in simultaneous flooding of all streams.

The Willamette Valley receives approximately 37 inches of rain on average each year.

Larger floods result from heavy rains which continue over the course of several days coupled with snowmelt at a time when the soil is near saturation from previous rains. Frozen topsoil also contributes to the frequency of floods.

The types of flooding that affect Benton County are primarily riverine and urban.

Riverine flooding is the over bank flooding of rivers and streams, the natural process of which adds sediment and nutrients to fertile floodplain areas.

Urban flooding can result from the conversion of land from fields or woodlands to parking lots and roads, decreasing its ability to absorb rainfall.

Historic Flood Image

More Information

For more information on flooding, see:

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