Water Quantity

The amount of water available for humans and wildlife was a high priority concern identified in the Chehalis Watershed Management Plan. The Partnership would like to see all existing and future needs for water withdrawals be met, while assuring adequate water in streams.

As far as we know, there is not enough water to meet the needs of all existing claims to water (water rights) within the Chehalis Basin. Each water right gives the user the right to use a certain volume of water during a given period of time. But when you add all those rights together, the total volume of water claimed is greater than the amount of water that flows in the Chehalis River in the summer months. We don’t know whether everyone with a right is actually using the water, however, since very few water users monitor – or meter- their water use.

The Chehalis Basin Partnership has sponsored several studies to better understand water resources in the basin – both below and above ground.  The Partnership continues to look for ways to measure and manage water quantity in the watershed.

Groundwater Studies


Hydrogeologic Framework and Groundwater/Surface-water Interactions of the Chehalis River Basin. Prepared in cooperation with the US Army Corps of Engineeers, Washington State Department of Ecology and the Chehalis Basin Partnership. 2011.

The purpose of this study is to describe the hydrogeologic framework and groundwater/surface-water interactions of the Chehalis River Basin. The recognition of the interdependence of groundwater and surface-water resources of the Chehalis River Basin became the impetus for this study.

USGS’s website for all USGS studies completed in the Chehalis Basin

Project Summaries:  Data on whether each main tributary is a gaining or losing reach;  Synoptic well inventory from July-Aug 2009; Groundwater geospatial data.

Streamflow Studies

How do forest practices influence stream flow? These authors found that 40- to 50-yr
harvest rotations of Douglas-fir plantations can produce persistent, large summer low flow deficits. This result was true for contemporary forest practices that included clearcutting of the plantation with riparian buffers. The study is part of the Alsea Watershed Study on the Oregon Coastal Range.

What do summer low flows mean for fish? Streamflow management could be improved if it were guided by a better understanding of how flow regimes affect fish communities. This review paper points out that changing stream flows may have positive or negative effects on fish depending on when in the year the flow changes occur and what fish life stage is affected.

Freeman, M. C., and coauthors. 2022. Toward improved understanding of streamflow effects on freshwater fishes. Fisheries

Water Rights Studies
Basin-Wide Water Quantity Assessment
Chehalis Basin Water Quantity Evaluation (2003) Prepared by Tetra Tech.

This report addresses the magnitude and distribution of consumptive water use in the basin. Water use information represents the most significant data gap identified in previous Chehalis Basin Studies. The study provides a “rough-cut” water balance, and a pilot water quantity evaluation in several sub-basins. Click on the title above to access the document. If the above link does not work, please contact the Chehalis Basin Partnership for a copy of the study.

Water Storage
Chehalis Basin Multipurpose Water Storage Assessment (2003) Prepared by Tetra Tech and Triangle Associates.

This survey of multipurpose storage opportunities provides information that can be used for: project development for providing water for instream uses, projects to promote infiltration of rain water on the land, and information for educating the community about water consumption in the Chehalis Basin.

Drought Response and Adaptation
Water Conservation

Chehalis WaterSmart Report. 2023.  Sofia Dreeson, University of Washington Program on the Environment. Produced for the Chehalis Basin Partnership, March, 2023.

This report outlines water conservation measures that could be employed in the City of Chehalis to reduce demand for water during peak use through changes to water pricing, incentives for fixture replacement, and public outreach.

Factsheet: Water Conservation and Salmon draft May 30_2020

Interactive Map tells Story of Streamflow Restoration Plan

Human water use in the basin can affect how much water is in streams because of underground connections through “groundwater.” The Chehalis Basin Partnership identified where future rural growth will be, and how much water associated wells will use. They then developed a Plan to offset the impacts of the new wells on stream flow. Learn more about future water quantity impacts from wells and proposed offset projects here!

Upper Chehalis Watershed: Focus on Water Availability

This watershed is one of the most intensely farmed basins in western Washington, and much of the water has already been spoken for. There is limited water available for new uses in the Upper Chehalis watershed, especially given that river levels need to be maintained to ensure adequate water quality and fish migration. Increased demands from population growth, naturally low summer and early fall streamflow levels, and impacts from climate change add to the challenge of finding new water supplies.

Visit this webpage by the Department of Ecology to get location-specific information about water rights, factors affecting water availability, pending water rights applications and available water supply in the Upper Chehalis Basin.