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Chehalis River

​Due to its large drainage area, the Chehalis River tends to rise and fall slowly over a long period of time. The most predictable scenario for the Chehalis occurs when rains fall over all of southwestern Washington and all regional rivers and streams rise.

However, the Chehalis can also experience flooding when there is little or no rain in Thurston or Grays Harbor counties, but heavy rain in Lewis and Pacific counties. This causes flooding to occur later than normal.

A third scenario occurs when heavy rain falls in Grays Harbor County, but not in Thurston or Lewis counties. Feeder streams can fill the Chehalis and cause water to "back up" into Thurston County.

Due to these varying scenarios, we urge floodplain residents to keep an eye on the river and to continue to monitor local media reports even if the rain has stopped and all other local rivers have receded. Minor flooding (low-lying roads and pasturelands) occurs at a gauge height of about 139.53 feet at the gauge near Grand Mound. Moderate flooding (individual residences are threatened) occurs at about 142.53 feet, and major flooding (widespread threat to communities and major thoroughfares) at about 144.03 feet.

Gauge near Grand Mound at Prather Road Bridge - River Mile 59.9

Source: National Weather Service, Advanced Hydrologic Prediction Service (click graph to open site)
Graph above reloads every three minutes

Source: Washington State Department of Ecology, Flow Monitoring Network (click graph to open site)
Graph above reloads every three minutes
 
Gauge at Centralia - River Mile 65

Source: National Weather Service, Advanced Hydrologic Prediction Service (click graph to open site)
Graph above reloads every three minutes

Source: Washington State Department of Ecology, Flow Monitoring Network (click graph to open site)
Graph above reloads every three minutes
 
Gauge Near Doty

Source: National Weather Service, Advanced Hydrologic Prediction Service (click graph to open site)
Graph above reloads every three minutes

Source: Washington State Department of Ecology, Flow Monitoring Network (click graph to open site)
Graph above reloads every three minutes
 
​Historical
Crests
​Feet​CFS
(Cubic Feet per Second)
​Anticipated Impacts
​12/4/2007 ​147.26 ​79,500 ​MAJOR FLOOD STAGE   The Chehalis River inThurston County will cause major flooding, inundating roads andfarm lands in Independence Valley. Deep and swift flood waters willcover SR-12 and James, Independence and Moon Roads. Flooding will occur all along the river including headwaters, tributaries andother streams within and near the Chehalis River Basin. ​ ​ ​ ​ ​ ​ ​
​2/9/1996 147.01​ ​75,500
​1/10/1990 ​146.37 ​65,800
​146.03 ​61,100
​11/25/1986 ​145.65 ​53,500
​12/29/1937 ​145.62 ​53,200
144.03​ ​43,100
144.03​ 38,800​
​142.53 29,600 MODERATE FLOOD STAGE
The Chehalis River in Thurston County will flood several roads in Independence Valley with swift moving water including SR-12 and James Road, Independence Road, Moon Road, and Anderson Road. Flood waters will also cut off access to and from the Chehalis Reservation and inundate nearby farm lands. Some residential structures may be threatened.​
​141.03 22,900 ​FLOODSTAGE The ChehalisRiver in Thurston County will flood several roads in IndependenceValley including James Road, Independence Road and Moon Road. Floodwaters will also cover nearby farm lands.
​139.23​16,600ACTION STAGE  TheC hehalis River in Thurston County will locally spill out of itsbanks into nearby fields and over a few roads.
​Historical
Crests
​Feet​CFS
(Cubic Feet per Second)
​Anticipated Impacts
​12/4/2007 ​178.10 ​71,050 ​MAJOR FLOOD STAGE
The Chehalis River in Lewis County will cause major flooding... inundating residential and commercial areas... farms... and many roads including I-5. Flood waters will be deep and swift in some areas. Flooding will occur all along the river including headwaters... tributaries... and other streams within and near the Chehalis River Basin. A stage of 72 feet corresponds to a Phase III flood, and a stage of 73.4 feet corresponds to a Phase IV flood in the Lewis County flood system.
​2/9/1996 177.63​               
​1/10/1990 ​176.82               
​176.72               
​1/8/2009 ​175.72               
               ​175.32 ​51,100
​11/25/1986 ​175.31                MODERATE FLOOD STAGE
The Chehalis River in Lewis County will flood some residential and commercial areas... with water encroaching upon the first floor of some homes and businesses. Swift flood waters will cover some roads. A stage of 68 feet corresponds to a Phase II flood in the Lewis County flood system.
​171.8234,200
​168.32 22,550 ​FLOOD STAGE
The Chehalis River in Lewis County will cause shallow flooding of farmlands and some roads. A stage of 65 feet corresponds to a Phase I flood in the Lewis County flood warning system.
​166.32 ACTION STAGE
The Chehalis River in Lewis County will spill over its banks into nearby pasture lands around Chehalis and Centralia.
​​​164.32