Salmon habitat restoration efforts on the Cedar River

Todd Bunker, Volunteer writer

Ask around, and you may find that most people do not know the Cedar River is the main source of freshwater for Seattle and surrounding areas in King County. From its beginnings at Chester Morse Lake, it flows from the foothills of the Cascade mountains, through Maple Valley, eventually emptying into Lake Washington. By the time it passes through the city of Renton to its mouth it is mostly tamed – so much so that the Renton City Library spans the river’s channel.

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The upper portion of the watershed is owned by the City of Seattle and is a protected forest area with little to no development outside of recreational trails. The lower portion, managed by King County, flows from the city of Maple Valley to Renton through mixed-use land consisting of sparse housing development until hitting the Renton city limits where housing subdivisions and an 18-hole golf course line its banks. 

Due to the location of the Cascade mountains and the elevation difference from the headwaters to the mouth of the river, much more rain (and snow) falls at the head of the watershed as clouds from the Pacific Ocean release precipitation as they rise and pass over the mountain range.

This makes the water quality of the Cedar River watershed remarkably good. Due to the natural habitat of the upper watershed, which has not been subjected to timber harvest or mining since the early 20th century (many of those operations were destroyed by flooding and not replaced), the level of pollutants is low. Undoubtedly, since the watershed is an important source of fresh water, much caution has been exercised in the recent past in prohibiting development that would contribute pollutants to the water. Some 100 million gallons of water is used every day by approximately two-thirds of the residents of King County. The upper watershed area and reservoir/pipelines are owned by the City of Seattle and is highly regulated due to its importance to the city.

Of the few water qualities that are of concern, the impact on the local salmon population is the most important. Due to climate change, the river has seen an increase in water temperature, and consequently the decline of dissolved oxygen, both of which are detrimental to spawning fish. 

Additionally, traditional stone levee type flood control of the mid-20th century era only served to tightly channel the water in the river, which led to fast moving waters that created more flooding downstream, and severely hampered the ability of the local salmon population during spawning season. These levees also required constant maintenance due to erosion. King County is currently undergoing a restoration of riverbend areas between Maple Valley and Renton, where flood control areas will be restored to natural habitat so that the water, even during high flow volumes, will have buffer areas that slow the river and provide safe areas for salmon and other animals. 

The first of these projects, Rainbow Bend, was completed in 2014, and restored approximately 40 acres of floodplain. A similar project downstream at Riverbend is currently under construction. It included buying out/relocating occupants of an RV park that was prone to flooding and will remove old levees, providing another 52-acre area that will mimic the natural habitat of shifting gravel bars and downed trees to slow the flow of the river during floods. 

Aerial of the Riverbend Breach

https://www.kingcounty.gov/services/environment/animals-and-plants/restoration-projects/projects/riverbend-levee-setback.aspx

Currently there are plans to build an asphalt plant adjacent to the new Cedar Grove Natural Area on the river between Maple Valley and Renton. While mitigation of pollution is being designed into the construction of the plant, there is still a risk involved with the processing of petroleum products so close to restored habitat, and the estimated hundreds of trucks passing in and out of the facility daily present another opportunity to undo the efforts of the recent habitat restoration.

It is not enough to have an upper watershed that remains mostly pristine and provides clean water to a large population. Environmental compromises towards the mouth of the river severely impact and limit the ability of salmon to reach ideal spawning areas upstream, thus disturbing the natural balance of the ecosystem. The health of the Cedar River must be considered not only at the pristine headwaters that provide fresh water for humans, but all the way to the mouth at Lake Washington, where salmon gather and seek their historical spawning grounds. 

An appeal to the permit to allow the asphalt plant is currently underway. For more information and to take action, please visit: https://www.savethecedarriver.org

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