Snohomish Delta

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Snohomish delta after.jpg

The Snohomish is one of the largest river delta sites in Puget Sound. Recovery of historical wetland area is a target of Salmon Recovery in the Snohomish Watershed. Portions of the Estuary are in the City of Everett but most are in Snohomish County. It is in usual and accustomed harvest areas of the Tulalip Tribes of Washington with portions within the tribal reservation. The lower delta is being modified under a series of large scale restoration projects including Qwuloolt Restoration, Smith Island Restoration, and Blue Heron Mitigation Bank among others. These projects are reestablishing a large area of tidal inundation in the saline mixing zone, and when complete will be the largest estuary restoration by area in Puget Sound. Upstream, freshwater tidal lands are in agricultural production, divided into diking districts such as Marshlands and Ebey Island, and depend on diking and pumping to lower water tables. There is controversy over the loss of agricultural lands as Snohomish County works to increase Snohomish Agricultural Resilience. Sea Level Rise effects may be important to long term planning. The Estuary is a study area of the Snohomish Sustainable Lands Strategy.

map of snohomish estuary public land ownership from salmon recovery plan


For sites with lots of ecosystem management activity, maintaining a chronology with links is a great way to organize information:


Nearshore Strategies Data Report

Cereghino et al 2012 completed a soundwide analysis to identify and describe river delta sites in Puget Sounds as part of a nearshore ecosystem restoration strategy (using remote sensing data c. 2000-2006). The following narrative of this delta site was developed to support distribution and use of analysis results:

The Snohomish Delta in the Whidbey sub-basin historically contained 18,706 acres of vegetated wetland along a 95 km shoreline. The delta receives flow from a 465,216 square kilometer watershed. These characteristics make this system the 2nd largest delta out of 16 systems in Puget Sound.
Simenstad et al 2011 found that this system had lost 90% of its vegetated tidal wetlands, and 37% of its shoreline length. Of the remaining shoreline, 87% shows some evidence of infrastructure development. In the surrounding uplands, 55% of land is estimated to have greater than 10% impervious surface. Across the watershed, 32% of land is estimated to have greater than 10% impervious surface. Based on these paramters, the site was given a degradation score of 54 out of 100, making it the 4th most degraded delta in Puget Sound. It faces a medium risk of future development locally, and a low risk of development across the watershed. Approximately 53 percent of the watershed is currently impounded behind dams.