Historic Flood Information

Overview

Centralia features several large rivers and smaller tributaries, or streams, which are susceptible to annual flooding events that pose threats to life and safety and cause significant property damage. Large rivers include the Centralia and Skookumchuck, while streams include China Creek, Scammon Creek, Salzer Creek, and Coffee Creek. The City including its Urban Growth Area (UGA) is approximately 10,143 acres in size with around 2,662 of those acres in the floodplain or 26%.

Recent Flooding Events

City records dating back to the 1970s indicate that the Chehalis and Skookumchuck rivers have caused significant flooding within the City at least nine times in the last 37 years. The floods in 2009, 2007, 1996, 1990, 1986, and 1972 were record-high levels for the Chehalis River at Centralia. Centralia has experienced at least 24 flood events from 1887 to 2009 a 122-year time frame. All of the recent floods would have been estimated to exceed the so-called "100-year flood," or Base Flood.

The flooding in December 2007/2009 and in February 1996 was caused by prolonged precipitation accompanied by snowmelt, caused by a warm-weather trend known as a "Pineapple Express," caused many rivers and creeks throughout the Chehalis River watershed to rise to well over the 100-year flood levels, causing flooding in both rural and urban areas.

Causes of Flooding in Centralia

Flooding in Centralia usually occurs when weather patterns, geology, and hydrology combine to create conditions where river and stream waters flow outside of their usual course and "overspill" beyond their banks. In Centralia, the combination of these factors, augmented by ongoing development, create chronic seasonal flooding conditions. Lewis County spans a wide range of climatic and geologic regions that results in considerable variation in precipitation, the primary factor of which is elevation.

Flooding is most common from October through April, when storms from the Pacific Ocean, 40 miles away, bring intense rainfall to the region. Centralia receives approximately 47 inches of rain on average each year. 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.

Riverine flooding and urban flooding are the two types of flooding that primarily affect Centralia. 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.

Past Flood Events