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French and Pilchuck watersheds

The French Creek and Pilchuck River watersheds are part of the Snohomish watershed. They help support important salmonid resources, agricultural uses, and recreational activities. The Pilchuck River is the largest tributary to the Snohomish River. Both watersheds are at the outer boundary of tidal influence in the Snohomish River.

Each water body has unique characteristics and influence. For example, water quality and fish passage in French Creek are significantly affected by the French Slough pump station and numerous changes to the watershed in the floodplain area. There were structural changes on the lower reaches of the Pilchuck River.  The middle and lower sections of the river are also affected by summer irrigation withdrawals and municipal wastewater discharges from the city of Granite Falls.

Water quality issues

Although we think water temperatures and dissolved oxygen (DO) levels are good in the Pilchuck River watershed for most of the year, high water temperatures and low DO values occur during the warm weather months. Lower French Creek experiences similar problems during the summer.

French Creek and the Pilchuck River are considered core summer salmonid habitat. This means their waters are expected to remain cool (below 16°C or 60.8°F) and oxygen rich (DO above 9.5 milligrams per liter) for optimal conditions. Maintaining cooler water temperatures helps increase DO levels in the water, improving habitat for fish and other aquatic life.

What we have done

We originally began a combined temperature/DO total maximum daily load (TMDL) project for the French Creek and Pilchuck River watersheds in 2012. During the initial phases of the project, we worked with the EPA and a scientific consulting firm to design the study. During the summer of 2012, we conducted extensive field studies.

As part of the 2013 data assessment, we determined that we could not use some of the data collected in lower French Creek because stream flows were extremely low. When looking at our Pilchuck River data, we determined that additional flow and groundwater data was needed. We collected that data during the summers of 2014 and 2016.

In fall of 2016, we separated the Pilchuck River Temperature/DO TMDL from the French Creek Temperature/DO TMDL to speed delivery of useful information to salmon recovery specialists working in that watershed.  We also decided to conduct additional modeling and analysis for the Pilchuck River TMDL. This helped ensure that work would provide the broadest and most meaningful implementation actions to benefit salmon recovery. 

A shortage of modeling resources forced us to delay additional work on the French Creek. At this time, we are taking a phased approach to completing our study of French Creek and are now referring to that work as an “Alternative Restoration Plan.”  The resulting product will contain water quality modeling that will show the benefits of various corrective actions such as planting trees and reconfiguring the shape of lower French Creek along with a plan for improving water quality.

Status of the projects

Pilchuck River Temperature/DO TMDL:  We will complete the additional modeling work for the Pilchuck River in summer 2018. We are now drafting the Pilchuck River temperature/DO TMDL and expect to form an advisory group in fall/winter 2018.  Following advisory group meetings, we will gather public comment.

French Creek Temperature/DO Alternative Restoration Plan:  We expect to start modeling for the French Creek Temperature/DO Alternative Restoration Plan in early 2019. When modeling is complete, we will create a local stakeholder advisory group including the French Slough Flood Control District. We plan to explain our analyses and work with the group to develop a plan for improving water quality.

Why this matters

Oxygen dissolved in water is vital for fish and aquatic life to "breathe” to survive. It is more difficult to transfer oxygen from water to blood than it is to transfer oxygen from air to blood. Therefore, it is critical that an adequate amount of oxygen is maintained in the water for this transfer to take place efficiently and to sustain aquatic life. Oxygen is also necessary to help decompose organic matter in the water and bottom sediments as well as for other biological and chemical processes.

Water temperature influences what types of organisms can live in a water body. Cooler water can hold more dissolved oxygen that fish and other aquatic life need to breathe. Warmer water holds less dissolved oxygen. Many fish need cold, clean water to survive.