Water inundation from heavy rains and excessive snowmelt has led to a considerable number of historic flooding events in the twin cities of Centralia and Chehalis.

[18] A large episode of rising waters, given the name the Schoumacher Flood after a man who was stranded for threes days,[19] occurred in 1906 as the Cowlitz River affected the area, again cutting off the city.

[20][14] Factory areas and parts of the Pennsylvania Avenue-West Side Historic District suffered flooding in January 1909 after continuous rain and snowmelt caused the Chehalis to rise 19 feet (5.8 m) above its low water mark; residents could only move about by boat.

[21] A record-setting event followed that November and was due to the excess rise of the Chehalis and Newaukum rivers which led to landslides, the inundation of the Southwest Washington Fairgrounds, and caused significant economic losses to lumber milling in the city.

Again due to heavy rains and the overflow of both rivers, the waters also inundated the fairgrounds where the local rail tracks were covered and a small mudslide occurred.

[13]: 55 [24] A new road between the Twin Cities was covered in 2 feet (0.6 m) of water, mudslides were reported in the area, and electricity had to supplanted by the local steam plant as larger power operators in the region were forced to shut down.

The flood was mentioned in regional newspaper accounts to have broken the record for highest depth but gauges reported that the waters fell 18 inches (46 cm) short of the mark.

The weather pattern that caused the 1948 Columbia River flood was a widespread disaster throughout the region and both the Chehalis and Newaukum crested, leading to closures of roads and the airport.

[52] The Pacific Northwest event, described by the United States Geological Survey (USGS) as one of the 20th century's worst flood disasters, was ushered in by a weather pattern that dropped 6 in (150 mm) of rain during the course of a week in the city.

A minor overflow of the Chehalis in mid-January caused few issues but access to the airport was closed and a small mudslide shut down a portion of the main thoroughfare to Centralia.

[64] Continuing rainfall over the next week led to the Chehalis to overflow its banks again, and the United States Army Corps of Engineers (USACE) was mobilized in advance due to concerns over severe flooding.

[66][67] While no deaths were reported, schools were closed, dozens of people, including a squirrel, were evacuated from the city and the Yard Birds Mall was under two feet of water, recording $500,000 in losses.

[11][68] A severe snowstorm followed days later, and flood disaster declarations were announced at the city, county, state, and federal levels;[70][71][72] official costs were determined to be nominally $400,000.

The dike at the fairgrounds suffered a minor leak but was repaired with help from students from Green Hill School[75] and the venue was spared from major losses due to new pumps that were installed after the 1972 flood.

The inundation caused a spillage of approximately 10,000 US gallons (38,000 L; 8,300 imp gal)[b] of a mixture of creosote, diesel fuel, and chemicals used in the treatment of lumber which spread into the surrounding neighborhoods as well as the Dillenbaugh Creek watershed.

[97] A small overflow of the Chehalis, reaching 3 feet (0.9 m) above flood stage, occurred in early January 1997, creating an influx of waters in low-lying areas, specifically around Washington State Route 6 (SR 6).

[101] Accompanying heavy rainfall in late December 1998, several roads were under a minor amount of water in the city but no waterways reached flood level.

[109] The Red Cross operated a command station in the downtown district and, due to a large number of requests, had to limit the amount of services to 100 people per day.

[11] A year after the event, damages to the Chehalis sewage treatment plant, which included cracked storage basins, unstable soil, and a destroyed pump, were estimated to reach as high as $1.5 million.

[128] At the end of the month, a downpour of 2 inches (51 mm) during a single evening led to an immediate flood warning by the National Weather Service (NWS).

[140] Despite local opposition, a dike at the airport near the interstate was intentionally breached[141] by the Washington State Department of Transportation (WSDOT) the day after the rivers crested.

[13]: 126  Between the Twin Cities, 220 business suffered damages, which included a combined loss of $6.8 million to the local landmark shopping centers, Sunbirds and Yard Birds Mall.

[148] Due to the closure of the highway, approximately $4 million of daily economic losses to the state were estimated and repairs to the freeway in Chehalis were assessed to cost several hundred thousand dollars.

[160][161][162] Similar to the 2007 event, reiterated concerns were brought up regarding the increase in flooding in the valley, specifically the logging practice of clearcutting and the conversion of floodplains for development.

West High School experienced approximately 1 foot (0.30 metres) of flood depth, and the accumulation was due in part to an unnamed creek in the area unable to handle the additional flow of water.

[184] Most of the plans or ideas were considered too costly at the time by the Army Corps of Engineers, including expenditures on check dams and additional dikes that would outweigh the potential return in local economic benefits.

[185] Flood control measures, including levees, dams, and relocations, were repeatedly rejected by various local groups, as well as regional, state, and federal governments and agencies between the 1960s and into the 1980s.

[191] In the same year a $30 million plan was authorized by the state legislature meant to expand the Skoomkumchuck Dam (built 1970) and build levees;[192] it was rejected by the county, as well as the cities of Centralia and Chehalis, due to concerns of future maintenance costs.

[155] Proposals in the 2010s by the Washington State Department of Transportation (WSDOT) centered on protecting I-5, either by widening and raising the highway, or building additional levees or walls.

The efforts were part of a two-phase, $1.2 million project to increase the levee structure's size, providing additional flood protection to the transportation hub and surrounding business district.