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Nisqually River

Draft Evacuation Maps

Flooding on the Nisqually River is related largely to the amount of water released from LaGrande Dam (in Pierce County near the southeast corner of Thurston County). This, in turn, is related to how much water enters Alder Lake and is released from Alder Dam. Feeder streams such as Ohop, Yelm, and Taxwax creeks also influence flooding, as does high tide in the Nisqually Delta.

The National Weather Service issues a flood warning for the Nisqually River when their forecast model indicates the river will reach a stage of 12 feet or higher at the McKenna gage. Minor flooding (low-lying roads and pasturelands) occurs when the flow rate at La Grande exceeds about 8,000 cfs (cubic feet per second) or a gauge height of about 8.75 feet at the McKenna gauge. Moderate flooding (individual residences are threatened) in Thurston County occurs when the flow rate exceeds about 15,000 cfs or a reading of 10 feet or over at the McKenna gauge. A high tide could flood the banks at Hayko Lane, 6th Avenue, Riverbend Campground and Riverside Manor apartments. Major flooding (widespread threat to communities and major thoroughfares) occurs when the flow rate tops 16,500 cfs or a gage height of 10.5 feet at McKenna.

Recently work was done in the Nisqually Delta to restore the natural estuary habitat. It is unknown exactly how this reclamation will affect the anticipated flooding impact levels shown below.

Gauge at McKenna, River Mile 21.8

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
 
Gage at La Grande, River Mile 40.4

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
​2/8/1996 17.3 50,000 MAJOR FLOOD STAGE
The Nisqually River will cause major flooding from LaGrande downstream through McKenna to the mouth. Deep and swift waters will flood roads, farms and residential areas, including the residential care facility in McKenna. Erosion may cause severe damage. Flooding will occur all along the river including headwaters, tributaries and other streams within and near the Nisqually River Basin.
               16.0​ ​37,000
               14 26,500
1/29/1965 ​13 23,300 MODERATE FLOOD STAGE
The Nisqually River will flood from LaGrande downstream through McKenna to the mouth. Swift waters will flood roads, farms and some residential areas including the residential care facility in McKenna. Erosion will likely damage properties along river banks.
11/30/1995 ​12.48 21,700 ​FLOOD STAGE
The Nisqually River will flood from LaGrande downstream through McKenna to the mouth. Floodwaters will flow over some roads and through farms and residential areas. Erosion may damage some properties. High tidal levels on Puget Sound will cause flooding along the lower reaches, threatening homes along Riverside Drive, Conine Street and Conine Avenue.
​ ​ ​ ​
​​12/26/1980​12.4821,400
​​12/12/1955​12.4821,400
​12.4820,200
​12.4814,700
​12.489,970ACTION STAGE